Importation of Perennial Wall Rocket Leaves (Diplotaxis tenuifolia (L.)) 

from the United Kingdom into the continental United States

A Pathway-Initiated Risk Assessment 

September 2008 

Revision 002 

Agency Contact: 

United States Department of Agriculture 

Animal and Plant Health Inspection Service 

Plant Protection and Quarantine 

Center for Plant Health Science and Technology 

Plant Epidemiology and Risk Analysis Laboratory 

1730 Varsity Dr., Suite 300 

Raleigh, North Carolina 27606 USA
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 ii

Executive Summary 

In this document we assessed the risks associated with the movement of fresh leaves of perennial 

wall rocket, Diplotaxis tenuifolia (L.), into the continental United States. It was prepared by risk 

analysts at the USDA Animal and Plant Health Inspection Service. 

We listed pests that affect perennial wall rocket throughout the world if populations of that pest 

were reported in the United Kingdom. The table listing the pests should not be interpreted to 

infer that a direct association of a given pest on perennial wall rocket within the UK was reported 

in the scientific literature, or that all pests known to affect perennial wall rocket in the world are 

listed. 

Quarantine pests likely to follow the pathway selected for further analyses include: 

Chromatomyia horticola and Liriomyza strigata. We qualitatively analyzed these quarantine 

pests using the methodology described in the USDA-APHIS Pathway-Initiated Commodity Risk 

Assessment Guidelines 5.02. Accordingly, we examined the biology of each pest within the 

context of the Consequences of Introduction and the Likelihood of Introduction, and estimated 

the baseline Pest Risk Potential. Both C. horticola and L. strigata were rated to have a Medium

pest risk potential. Based on this assessment, port-of-entry inspections may be insufficient to 

safeguard U.S. agriculture and phytosanitary measures should be implemented in order to reduce 

phytosanitary risk. 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 iii

Table of Contents 

Executive Summary........................................................................................................................ ii 

Table of Contents...........................................................................................................................iii 

1. Introduction................................................................................................................................. 1 

2. Risk Assessment ......................................................................................................................... 1 

2.1. Initiating Event: Proposed Action...............................................................................1 

2.2. Assessment of Weed Potential of Perennial Wall Rocket ..........................................2 

2.3. Previous Risk Assessments, Decision History, and Pest Interceptions ......................2 

2.4. Pest Categorization .....................................................................................................3 

2.5. Quarantine Pests Likely to Follow the Pathway.........................................................8 

2.6. Consequences of Introduction.....................................................................................8 

2.7. Likelihood of Introduction..........................................................................................11 

2.8. Conclusion: Pest Risk Potential and Phytosanitary Measures....................................13 

3. Authors and Reviewers............................................................................................................. 14 

4. References................................................................................................................................. 15 

Appendix A: Risk Management Options for the importation of leaves of perennial wall rocket, 

Diplotaxis tenuifolia (L.), from the United Kingdom................................................................... 19 

A1. Introduction.................................................................................................................19 

A2. Mitigation Options ......................................................................................................19 

A3. Summary .....................................................................................................................22 

A4. Literature Cited ...........................................................................................................23 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 1

1. Introduction 

This pest risk assessment was conducted and reviewed by staff at the Pest Epidemiology and 

Risk Analysis Laboratory (PERAL) of the United States Department of Agriculture (USDA). We 

examined the unmitigated risks associated with the leaves of fresh Diplotaxis tenuifolia (L.) 

imported from the United Kingdom, given that standard industry post-harvest practices for leafy 

vegetables (e.g. lettuce, celery, greens, etc) will be used. In packinghouses, standard practices 

include trimming, washing, and sorting (Cantwell and Kasmire, 2001). Field-packing does not 

guarantee appropriate washing and sorting; therefore, for the purposes of this risk assessment, we 

assume only packinghouse handling occurs (Cantwell and Kasmire, 2001). Should the UK wish 

export to the United States additional plant parts besides the leaves of D. tenuifolia (e.g., stems), 

or if it is determined that the above post-harvest practices are not occurring, this analysis may 

need to be amended. 

Diplotaxis tenuifolia has several common names including perennial wall rocket, narrow-leaved 

wall-mustard, wild rocket and wild arugula. For the purposes of this risk assessment, D. 

tenuifolia will be referred to as “perennial wall rocket” as per the import request from the UK. 

Perennial wall rocket is a drought-tolerant, evergreen sub-shrub in the family Brassicaceae 

[=Cruciferae]. It has edible leaves that are similar in flavor to Eruca sativa (arugula) but 

stronger. Perennial wall rocket can be added to mixed salads, but is generally considered too 

strong to be used in quantity on its own. 

This risk assessment is qualitative, with risk being expressed in terms of high, medium or low 

rather than probabilities or frequencies. The details of the methodology and rating criteria can be 

found in the Pathway-Initiated Pest Risk Assessments: Guidelines for Qualitative Assessments, 

Version 5.02 (PPQ, 2000). 

Regional and international plant protection organizations such as the North American Plant 

Protection Organization (NAPPO) and the International Plant Protection Convention (IPPC) 

provide standards for conducting pest risk analyses (IPPC, 2007: ISPM #11; NAPPO, 2004). The 

methods used to initiate, conduct, and report this assessment, as well as the use of biological and 

phytosanitary terms are based on these standards. The IPPC standards describe three stages of 

pest risk analysis: Stage 1, Initiation; Stage 2, Risk Assessment; and Stage 3, Risk Management. 

This document satisfies the requirements of IPPC Stages 1 and 2. 

2. Risk Assessment 

2.1. Initiating Event: Proposed Action 

This commodity-based, pathway-initiated assessment is written in response to a request for 

USDA authorization to allow imports of a particular commodity presenting a potential plant pest 

risk. In this case, the importation into the United States of leaves of wall rocket, D. tenuifolia 

(L.), from the United Kingdom is a potential pathway for introduction of exotic plant pests. Title 

7, Part 319, Section 56 of the United States Code of Federal Regulations (7 CFR §319.56) 

provides regulatory authority for the importation of fruits and vegetables into the United States. 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 2

2.2. Assessment of Weed Potential of Perennial Wall Rocket 

The initial step in conducting a commodity-based risk assessment, after receiving a request for 

its importation, is to analyze its potential to become a weed. We presented the results of the weed 

screening for D. tenuifolia below (Table 1). Perennial wall rocket is considered a weed in many 

parts of the world, including the United States. However, because it is already widely distributed 

throughout the continental United States, and because we believe the risk of weediness 

associated with importing perennial wall rocket for consumption is Low, this screening did not 

prompt a pest-initiated pest risk assessment. 

Table 1. Assessment of the Weediness Potential

Commodity: Leaves of Diplotaxis tenuifolia (L.) species (Brassicaceae) 

Phase 1: Diplotaxis tenuifolia is apparently distributed in the following United States: 

Alabama, Arizona, California, Connecticut, Delaware, Florida, Idaho, Illinois, Indiana, 

Massachusetts, Maine, Maryland, Michigan, New Mexico, New Jersey, New York, Ohio, 

Oregon, Pennsylvania, Texas, and Virginia. It does not appear to be widespread in any state. 

Phase 2: Is the species listed in: 

 Yes Geographical Atlas of World Weeds Holm et al., 1979 

 No World’s Worst Weeds Holm et al., 1997; Holm et al., 1977 

 No Report of the Technical Committee to Evaluate Noxious Weeds for 

Federal Noxious Weed Act Gunn and Ritchie, 1982 

 No Economically Important Foreign Weeds Reed, 1977 

 Yes Weed Science Society of America list WSSA, 1989 

 Yes Are there any references indicating weediness? e.g., AGRICOLA, CAB, 

Biological Abstracts, AGRIS; search on “species name” combined with 

“weed.” 

Phase 3: Although this species is listed as a weed, it is widely distributed through out the 

United States and is not considered a quarantine weed.

2.3. Previous Risk Assessments, Decision History, and Pest Interceptions 

No decision history exists for this commodity, nor have any previous risk assessments been 

done. Currently 7 CFR §319.56 prohibits the entry of fresh perennial wall rocket from the United 

Kingdom into the United States. No other country currently exports wall rocket into the United 

States. 

APHIS maintains a database of plant pests intercepted at U.S. ports of entry (PestID, 2007). We 

found no pest interceptions at any U.S. ports of entry on/with/in Diplotaxis from anywhere in the 

world. 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 3

2.4. Pest Categorization 

Below we list the pests associated with perennial wall rocket (in any country) that also occur in 

the United Kingdom (Table 2). In this list we identify the following: (1) the presence or absence 

of these pests in the United States, (2) the generally affected plant part or parts, (3) the 

quarantine status of the pest with respect to the United States, (4) whether the pest is likely to 

follow the pathway and enter the United States on commercially exported perennial wall rocket, 

and (5) pertinent citations for either the distribution or the biology of the pest. We eliminated 

many organisms from further consideration as sources of phytosanitary risk on perennial wall 

rocket from the United Kingdom because they do not meet the definition of a quarantine pest.

Table 2. Pests associated with perennial wall rocket, Diplotaxis tenuifolia (L.), and also present in the 

United Kingdom 

Pest Geographic 

distribution 

Host association 

reference 

Quarantine pest Plant part 

association 

Follow 

pathway

ARTHROPODA

Acari: Tetranychidae 

Bryobia praetiosa Koch UK (CABI, 2007); 

US (PestID, 2007) 

Laffi, 2001 No N/A N/A 

Tetranychus urticae 

Kock 

UK, US (Bolland et 

al., 1998) 

Bolland et al., 

19981

No N/A N/A 

Collembola: Sminthuridae 

Sminthurus viridis L. UK (CABI, 2007; 

CABI, 1973); US 

(Alaska) (CABI, 

1973)

Raimo et al., 

2005 

Yes Leaves

(CABI, 2007)

No2

INSECTA 

Coleoptera: Chrysomelidae

Phyllotreta sp. UK, US 

(Konstantinov and 

Vandenberg, 2001) 

Ciampolini et al., 

2001; 

Konstantinov 

and Vandenberg, 

2001 

No N/A N/A 

Diptera: Agromyzidae

Chromatomyia horticola 

(Goureau,) 

[=Phytomyza horticola 

Goureau] 

UK (CABI, 2007) Spencer, 19903 Yes Leaves Yes 

 

1

 Based on its association with Diplotaxis viminea. 2 Sminthurus spp. are tiny hexapods likely to be removed from leaves with even minimal washing and not likely to remain in 

the pathway through harvest and processing. 3

 Based on association with genus Diplotaxis. 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 4

Pest Geographic 

distribution 

Host association 

reference 

Quarantine pest Plant part 

association 

Follow 

pathway

Liriomyza strigata

(Meigen)

UK (Pitkin et al., 

2008) 

Pitkin et al., 

2008; Spencer, 

1973; Spencer, 

19904

Yes Leaves Yes 

Phytomyza rufipes

Meigen 

UK (CABI, 2007; 

Spencer, 1973), US 

(Spencer, 1973) 

Spencer, 1973; 

Spencer, 19904

No N/A N/A 

Diptera: Cecidomyiidae

Dasineura brassicae 

(Winnertz) 

UK (CABI, 2007) Stelter, 1992 Yes Fruits, Seeds 

(CABI, 2007)

No 

Diptera: Drosophilidae 

Scaptomyza flava 

(Fallen) [=Scaptomyza 

apicalis Hardy] 

UK (Pitkin et al., 

2008); US (Fisher et 

al, 2000) 

Pitkin et al., 

2008 

No N/A N/A 

Hemiptera: Aphididae

Lipaphis erysimi 

Kaltenbach 

UK (CABI, 2007); 

US (CABI, 2007) 

Singh et al., 

2004 

No N/A N/A 

Hemiptera: Pentatomidae 

Eurydema oleracea (L.) 

[=Strachia oleracea] 

UK (Douglas and 

Scott, 1865) 

CABI, 2007; 

Arkhipov, 1985; 

Schaefer and 

Panizzi, 20005

Yes Leaves, 

seeds, 

flowers, 

stems 

(Schaefer and 

Panizzi, 

2000) 

No6

Lepidoptera: Crambidae 

 Hellula undalis

(Fabricius)

UK (Kimber, 2008), 

US (HI) 

Robinson et al., 

20084

Yes Leaves, 

stems 

No7

Lepidoptera: Geometridae

Eupithecia pulchellata 

Stephens 

UK (Scoble, 1999) Zhang, 19948 Yes Leaves, 

Stems 

No9

 

4

 Based on association with genus Diplotaxis. 5 Eurydema spp. are pests of all crucifers (Schaefer and Panizzi, 2000) and E. oleracea in particular feeds on a wide range of 

cruciferous crops (Arkhipov, 1985; CABI, 2006). 6 Eurydema spp. are large, very conspicuous, highly mobile, external feeders. Thus, they are very unlikely to remain on the 

commodity through harvest and processing. 7

 This pest may follow the pathway on commodities such as cabbage, because larvae can tunnel into the main stem in 

seedlings and feed on leaves and by tunneling into leaf petioles (Kessing and Mau, 2007). Wall rocket differs greatly from 

cabbage in structure, however, and the pest is highly unlikely to be hidden inside the loose leaves, especially if post 

harvest washing practices are followed. 8

 The host range is not well defined, but according to Zhang (1994) this pest feeds on various Cruciferae (=Brassicaceae). 9

 Adults are highly mobile external feeders, not likely to remain in the pathway through harvest and processing. Larvae and 

eggs are likely to be removed from leaves with even minimal washing. 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 5

Pest Geographic 

distribution 

Host association 

reference 

Quarantine pest Plant part 

association 

Follow 

pathway

Lepidoptera: Lyonetiidae

Bedellia ipomoeae 

Bradley 

UK (CABI, 2007) 

US (Zhang, 1994) 

Zhang, 1994 No N/A N/A 

Lepidoptera: Pieridae

Pieris brassicae 

Linnaeus

UK (CABI, 2007) PPQ, 1984 Yes Leaves No10

Pieris rapae Linnaeus UK, US (Zhang, 

1994) 

Zhang, 199411 No N/A N/A 

Pontia daplidice 

Linnaeus 

UK12 (Zhang, 1994; 

Eeles, 2007) 

CABI, 2007; 

Zhang, 1994; 

Eeles, 200713 

Yes Leaves, 

Stems 

No11

Lepidoptera: Pyralidae

Evergestis extimalis

Scopoli

UK (Fitter and Peat, 

1994; Robinson et 

al., 2008) 

Robinson et al., 

2008 

Yes Fruit, Seed 

(Fitter and 

Peat, 1994)

No 

Evergestis forficalis 

Linnaeus 

UK (Zhang, 1994; 

CABI, 2007) 

Mazzei et al., 

2007; Zhang, 

199414 

Yes Leaves, 

Stems 

No15

FUNGI & CHROMISTANS 16

Albugo candida 

(Pers.:Fr.) Kuntze 

[Oomycetes: 

Peronosporales] 

UK (Anonymous, 

2003), US (Farr et 

al., 2007) 

Anonymous, 

2003; Farr et al., 

2007 

No N/A N/A 

Erysiphe cruciferarum

Opiz ex L. Junell 

[Ascomycetes: 

Erysiphales] 

UK (Anonymous, 

2003; Braun, 1995b) 

US (Farr et al., 

2007) 

Braun, 1995b; 

Farr et al., 2007 

No N/A N/A 

 

10 Larvae are occasionally found within some host vegetables, and pupae are sometimes attached to fresh or dried vegetables 

or crating. For example, it has been intercepted at U.S. ports of entry from France, Greece, Italy, Portugal, Scotland, and 

Spain; but only on Brassica oleracea (cabbage, broccoli, cauliflower, etc.) or as a hitchhiking pest on containers and tiles. 

Given the loose-leaf structure of Diplotaxis spp., if all postharvest practices and visual inspection are in place, the 

likelihood of introduction should be negligible. 11 Based on its association with Diplotaxis virgata. 12 Rare migrant to UK, but occasionally seen in large numbers. 

13 The host range is not well defined, but this pest is associated with various Cruciferae (CABI, 2006; Zhang, 1994; Eeles, 

2007) 14 Mazzei (2007) list this species on Diplotaxis; Zhang (1994) lists it at a pest of “Brassica and wild Cruciferae.” 15 Adults are highly mobile external feeders, not likely to remain in the pathway through harvest and processing. Although 

larvae feed in the heart or amongst young spun leaves of some crucifers, because wall rocket’s leaves are loose (unlike 

cabbage, for example), it is likely that larvae and eggs would be removed from leaves with even minimal washing. 16 Taxonomy according to Farr et al., 2007; Kirk, 2004. 
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Rev. 002 October 07, 2008 6

Pest Geographic 

distribution 

Host association 

reference 

Quarantine pest Plant part 

association 

Follow 

pathway

Fusarium oxysporum 

Schlechtendah 

[Ascomycetes: 

Hypocreales] 

US, UK (CABI, 

2007) 

Garibaldi et al., 

2003 

No N/A N/A 

Peronospora parasitica 

(Pers.:Fr.) Fr. 

[Oomycetes: 

Peronosporales] 

UK (Anonymous, 

2003); US (Farr et 

al., 2007) 

Farr et al., 2007; 

Garibaldi et al., 

2004 

No N/A N/A 

Plasmodiophora 

brassicae Woronin 

[Plasmodiophoromycetes

: Plasmodiophorales] 

UK (Anonymous, 

2003); US (Farr et 

al., 2007) 

Farr et al., 2007 No N/A N/A 

Pseudocercosporella 

capsellae (Ellis & 

Everh.) Deighton 

[Ascomycetes: 

Mycosphaerellales] 

UK, US (Farr et al., 

2007) 

Braun, 1995a17 No N/A N/A 

Sclerotinia sclerotiorum 

(Lib) de Bary 

[Ascomycetes: 

Helotiales] 

UK (Farr et al., 

2007); US (Farr et 

al., 2007) 

Farr et al., 2007; 

Garibaldi et al., 

2005 

No N/A N/A 

Thanatephorous

cucumeris (A.B. 

Frank) Donk 

Anamorph: 

Rhizoctonia solani

J.G. Kuhn 

[Basidiomycetes: 

Ceratobasidiales] 

UK, US (CABI, 

2007) 

Nicoletti et al., 

2004 

No N/A N/A 

BACTERIA18

Xanthomonas campestris 

pv. campestris 

(Pammel) Dowson 

[Xanthomonadaceae] 

UK, US (CABI, 

2007) 

Raio and 

Giorgini, 2005 

No N/A N/A 

VIRUSES

Pepino mosaic 

potexvirus [PepMV] 

UK (restricted 

distribution) (Jones, 

2005), US (CABI, 

2007) 

Córdoba et al., 

200419

No N/A N/A 

 

17 Host association was made with members of the same genus, Diplotaxis erucifolius and D. muralis (Braun et al., 1995b). 

This pathogen also attacks many other genera in the Brassicaceae family (Farr et al., 2007). 18 Taxonomy according to Euzeby, 2007. 

19 Host association was made with the member of the same genus, D. erucoides (Córdoba et al., 2004). 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 7

Pest Geographic 

distribution 

Host association 

reference 

Quarantine pest Plant part 

association 

Follow 

pathway

Turnip mosaic virus 

[Potyviridae] TuMV 

UK, US (Brunt et 

al., 1996 onwards; 

ICTVdB 

Management, 2006; 

CABI, 2007) 

Rimmer et al., 

2007; CABI, 

200720

No N/A N/A 

Turnip yellow mosaic 

tymovirus TYMV 

UK (Rimmer et al., 

2007) 

Brunt et al., 1996 

onwards 21

Yes Whole Plant 

(Brunt et al., 

1996 

onwards) 

No22

 

20 A specific reference for TuMV occurring on Diplotaxis was not found, however the host range for this virus is very broad, 

encompassing hundreds of species and numerous plant families (Rimmer et al, 2007; CABI, 2006). It is possible 

Diplotaxis tenuifolia is also susceptible; therefore it was included on this list. 21 Association of TYMV with D. tenuifolia was based on experimental conditions, not found naturally infected in the field 

(Brunt et al., 1996 onwards). Host range is largely limited to Brassicaceae (Rimmer et al., 2007). 22 TYMV is primarily transmitted by certain beetles in the Chysomelidae and Curculionidae families or by mechanical means 

(Rimmer et al., 2007). Phyllotreta sp. is the only beetle identified in this pest list for U.K. wall rocket. Species of 

Phyllotreta are vectors of TYMV (Rimmer et al., 2007), but due to the external feeding nature of the beetle and processing 

of the commodity, they are unlikely to follow the pathway and therefore would not be present to vector the virus to live 

hosts in the United States. Within the United States it is also unlikely that D. tenuifolia salad greens, imported for 

consumption, will be exposed to the vectors necessary for transmission or be discarded in close proximity to live 

Brassicaceae host plants. Therefore, we considered that the pathogen would not follow the pathway. 
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Rev. 002 October 07, 2008 8

Other organisms included on the pest list (Table 2), but not chosen for further scrutiny, may be 

potentially detrimental to agriculture in the United States. The following are reasons for not 

subjecting them to further analysis: they are well established and widespread in the United 

States; they are mainly associated with plant parts not included with the commodity; they may be 

associated with the commodity, but are not expected to remain with the commodity during 

processing; or, they have been intercepted on rare occasions, as biological contaminants, at the 

ports of entry during commodity inspections and would not be expected to be frequently found in 

commercial shipments. 

2.5. Quarantine Pests Likely to Follow the Pathway 

In our review of the literature, we identified 30 pests that may be associated with perennial wall 

rocket in the United Kingdom (Table 2). Most of the other pests were not considered quarantine 

pests of the continental United States. Furthermore, of the quarantine pests, we found only two 

that were likely to stay with the commodity through harvest, processing, and shipping. Such 

pests are said to “follow the pathway” and we analyzed them in the next section. These were the 

leafminers (Diptera: Agromyzidae) Chromatomyia horticola Goureau, and Liriomyza strigata

(Meigen). 

We did not further consider quarantine pests not expected to follow the pathway. Should any of 

these pests be intercepted in shipments of the commodity, however, quarantine action may be 

taken at the port of entry and additional risk analyses may be conducted. 

2.6. Consequences of Introduction 

In this section we assessed the undesirable consequences that may occur from the introduction of 

quarantine pests. For each quarantine pest, we rated the potential consequences of introduction in 

five areas called “Risk Elements.” The Risk Elements include: Climate/Host Interaction, Host 

Range, Dispersal Potential, Economic Impact, and Environmental Impact. These elements reflect 

the biology, host range and climatic/geographic distribution of each pest and are supported by 

biological information on each of the analyzed pests summarized in this section. For each risk 

element, we assigned pests a rating of Low (1 point), Medium (2 points) or High (3 points). The 

ratings were determined using the criteria in the Risk Assessment Guidelines, Version 5.02 (PPQ, 

2000) (see for more details). 

The major sources of uncertainty present in this risk assessment are similar to those in other risk 

assessments. They include the use of a developing or evolving process (Orr et al., 1993; PPQ, 

2000), the approach used to combine risk elements (Bier, 1999; Morgan and Henrion, 1990), and 

the evaluation of risk by comparisons to lists of factors within the guidelines (Kaplan, 1992; Orr

et al., 1993). To address this last source of uncertainty, the lists of factors were interpreted as 

illustrative and not exhaustive. This implies that additional biological information, even if not 

explicitly part of the criteria, can be used when it is relevant to a rating. Other sources of 

uncertainty are the quality of the biological information and the amount of information available 

on the regional flora and fauna. Inherent biological variation within a population of organisms 

introduces uncertainty as well (Morgan and Henrion, 1990). 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 9

For each pest, we summed the five Risk Elements to give a Cumulative Risk Rating. These risk 

ratings are qualitative estimates of the severity of the impact each pest would have, in terms of 

economic and environmental consequences, should each pest establish and spread in the 

continental United States. The Cumulative Risk Ratings for each pest are summarized below 

(Table 3). 

Chromatomyia horticola Goureau (Diptera: Agromyzidae) Risk Rating

Risk Element #1: Climate/Host Interaction 

Chromatomyia horticola is found throughout tropical, subtropical, and temperate 

Asia, Europe, and Africa (CABI, 2007). Based on this distribution we estimated 

that C. horticola could become established in Plant Hardiness Zones 5-10 in the 

United States (PERAL, 2008). One or more of its potential hosts occurs in these 

zones (NRCS, 2007). 

High 

(3) 

Risk Element #2: Host Range 

Chromatomyia horticola is a highly polyphagous species that feeds on crops in 

many different families including: Alliaceae, Anacardiaceae, Asteraceae, 

Brassicaceae, Caryophyllaceae, Chenopodiaceae, Cucurbitaceae, Fabaceae, 

Ranunculaceae, and Umbelliferae (CABI, 2007). Some of the major crops 

attacked include onions (Allium spp.), Brassica spp., lettuce (Lactuca sativa), 

beans (Phaseolus spp.), and peas (Pisum spp.) (CABI, 2007; Spencer, 1973). 

High 

(3) 

Risk Element #3: Dispersal Potential 

Chromatomyia horticola has a relatively high biotic potential. Females lay as 

many as 50 eggs per day, and may lay more than 300 in their lifetime (CABI, 

2007). Depending on the region, C. horticola generally has three or four 

generations per year. 

In general, leaf miners have minimal natural dispersal potential. Larvae remain 

inside the leaf where the egg they hatched from was laid, until they pupate. 

Adults do not disperse long distances on their own. They can be transported 

through wind currents, but because windborne transfer requires that suitable plant 

hosts be available at the destination during the relatively short lifespan of the fly, 

this is probably not a common method of dispersal (CABI, 2007). Movement of 

economic crop hosts, if containing early stages of the pest, may effectively 

transfer the species to new areas. Despite the large-scale movement of plants of 

European and Asian origin into these regions, the species has not become 

established in the Americas or Australasia (CABI, 2007). 

Medium 

(2) 

Risk Element #4: Economic Impact 

Chromatomyia horticola is a very serious pest almost everywhere it is established 

(CABI, 2007). Infestations on seedlings are especially serious as the plants 

quickly stop developing, and either wilt or die. Infestations on older plants can be 

less serious, but still cause yield reductions (CABI, 2007). 

In northern Europe, C. horticola often seriously damages glasshouse crops of 

tomatoes and lettuce. In the Mediterranean, it damages both glasshouse and field 

crops, especially Cicer, Brassica and Pisum species, and similarly in Japan to 

High 

(3) 
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Rev. 002 October 07, 2008 10

Chromatomyia horticola Goureau (Diptera: Agromyzidae) Risk Rating

Allium, Cucurbita, Mentha and Vicia species (CABI, 2007). The pest can transfer 

plant pathogens during leaf visiting by the females, or even by males feeding at 

the leaf punctures made by the female (CABI, 2007). 

Introduction of the pest could cause loss of regional and domestic markets since 

the fly is not present in Western Hemisphere. 

Risk Element #5: Environmental Impact 

Chromatomyia horticola poses a potential threat to plants in the United States 

listed as Threatened or Endangered, such as Allium munzii (CA), Cucurbita 

okeechobeensis ssp. Okeechobeensis (FL), Helianthus eggertii (AL, KY, TN), H. 

paradoxus (NM, TX), H. schweinitzii (NC, SC) (USFWS, 2007). Chemical 

control programs are unlikely to be initiated against this pest, since those already 

in place for the control of other pestiferous leaf miners, such as Liriomyza sativae 

Blanchard or L. trifolii (Burgess), are likely to be equally effective against C. 

horticola. However, C. horticola could be the target of biological control 

programs, as for other introduced Agromyzidae (e.g., Hawaii; (Culliney and 

Nagamine, 2000)).

High 

(3)

Liriomyza strigata (Meigen) (Diptera: Agromyzidae) Risk Rating

Risk Element #1: Climate/Host Interaction 

The complete geographic distribution of L. strigata is unknown. It is found in the 

Palaearctic region, throughout Western Europe, but the eastern limit of its range 

is unknown (Spencer, 1973). Based on its known distribution, we assume it can 

survive in at least four Plant Hardiness Zones of the United States, and perhaps 

more (PERAL, 2008). One or more of its potential hosts occurs in these zones 

(NRCS, 2007). 

High 

(3) 

Risk Element #2: Host Range 

Liriomyza strigata is a highly polyphagous species that feeds on over 180 genera 

in 31 different families (Spencer, 1973). Main vegetable crops attacked include 

Beta vulgaris (Chenopodiaceae), Lactuca spp. (Compositae), and Pisum sativum 

L. (Fabaceae) (Spencer, 1973). 

High 

(3) 

Risk Element #3: Dispersal Potential 

Species of Liriomyza have a relatively high biotic potential. Lifetime fecundity 

varies greatly by species, but ranges between 100 and more than 600 eggs per 

female (Parrella, 1987). 

In general, leaf miners have minimal natural dispersal potential. Larvae remain 

inside the leaf where the egg they hatched from was laid, until they pupate. 

Adults do not disperse long distances on their own. They can be transported 

through wind currents, but because windborne transfer requires that suitable plant 

hosts be available at the destination during the relatively short lifespan of the fly, 

this is probably not a common method of dispersal (CABI, 2007). Movement of 

economic crop hosts, if containing early stages of the pest, may effectively 

Medium 

(2)
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 11

Liriomyza strigata (Meigen) (Diptera: Agromyzidae) Risk Rating

transfer the species to new areas. However, despite having a large host range, 

including many crops, this species has a relatively restricted global distribution. 

Risk Element #4: Economic Impact 

According to Spencer (1973), large populations of L. strigata are rarely found in 

a single plant; therefore, larval damage to mature plants is generally negligible, 

and young plants are not normally attacked. Chemical control programs are 

unlikely to be initiated against this pest, since those already in place for the 

control of other species of Liriomyza are likely to be equally effective against it; 

therefore, the presence of this species is unlikely to significantly increase 

production costs. Introduction of the pest could cause loss of regional and 

domestic markets since it is apparently not present in the Western Hemisphere, 

Africa, Asia, or the Pacific (CABI, 2007). 

Medium 

(2) 

Risk Element #5: Environmental Impact 

Liriomyza strigata is highly polyphagous (Spencer, 1973) and could potentially 

attack plants listed as Threatened or Endangered in 50 CFR §17.12 (e.g., 

Campanula robinsiae, endangered in FL; Helianthus paradoxus threatened in TX 

and NM; H. schweinitzii endangered in NC and SC) (USFWS, 2007). Chemical 

control programs are unlikely to be initiated against this pest, since those already 

in place for the control of other pestiferous leaf miners, such as Liriomyza sativae 

Blanchard or L. trifolii (Burgess), are likely to be equally effective against L. 

strigata. However, this pest could be the target of biological control programs, as 

has occurred with other introduced Agromyzidae (e.g., Hawaii; (Culliney and 

Nagamine, 2000)).

High 

(3)

Table 3. Risk ratings for Consequences of Introduction. 

Pest Climate/ Host 

Interaction 

Host 

Range 

Dispersal 

Potential 

Economic 

Impact 

Environ. 

Impact 

Cumulative 

Rating 

Chromatomyia 

horticola 

High (3) High (3) Medium (2) High (3) High (3) High (14) 

Liriomyza 

strigata 

High (3) High (3) Medium (2) Medium (2) High (3) High (13) 

a

 Low risk = 5-8 points =, 9-12 points = medium risk, and 13-15 points = high risk. T 

2.7. Likelihood of Introduction 

Likelihood of introduction is a function of two risk elements: 1) the quantity of the commodity 

imported annually and 2) pest opportunity, which consists of five criteria that describe the 

potential for pest survival along the pathway. Details of these two Risk Elements and their rating 

criteria are provided in PPQ (2000). We summarized the ratings and cumulative scores for 

Likelihood of Introduction below (Table 4). 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 12

2.7.1 Quantity Imported Annually 

The quantity expected to be imported annually is reported by the exporting country in the import 

request document. We converted this amount into standard units of 40-foot-long shipping 

containers. In this case, the UK has indicated that the volume of wall rocket shipped to the 

United States is expected to be between 100-150,000 kg annually, which is less than 10 

containers per year. Therefore, we rated this risk element Low for both pests. 

2.7.2. Survive Post-Harvest Treatment 

This risk element evaluates the efficacy of standard post-harvest treatments in terms of the likely 

mortality of pests exposed to the treatments. In the absence of further information, we assumed 

minimal post-harvest treatments, including washing and culling, will be used in processing 

perennial wall rocket in the UK. Because damage is usually obvious, we think the leaf miners are 

likely to be culled during this process. Therefore, we rated both pests Low for this risk element. 

2.7.3. Survive Shipment 

According to information provided by the United Kingdom, perennial wall rocket would be air 

freighted directly from London to Orlando or Miami, Florida. Immediately before flight, each 

consignment would be vacuum-cooled and insulated. Chromatomyia horticola and L. strigata

are both cold tolerant pests, and we assume that more than 10 percent would survive shipment 

under these conditions. Therefore, we rated the risk of shipment survival as High for both pests. 

2.7.4. Not Detected at Port-of-Entry 

Chromatomyia horticola and L. strigata are leaf miners that produce visible and obvious signs of 

infestation (see Figs. 1 and 2) and port inspectors are capable of readily identifying both pests. 

Therefore, we rated the likelihood of these pests escaping detection at ports of entry as Low. 

Figure 1. Leaf mines of C. horticola on Pisum sp. (source: Crop Protection Compendium, 2007 

Edition. CAB International, Wallingford, UK, 2007) 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 13

Figure 2. Leaf mines of Liromyza strigata on Sonchus (The Leaf and Stem Mines of British flies 

and other pests, http://www.ukflymines.co.uk/Flies/Liriomyza_strigata.html) 

2.7.5. Imported or Moved Subsequently to an Area with an Environment Suitable for Survival 

Perennial wall rocket from the UK is likely to be sold in every state. We assume that demand 

will be proportional to the size of the consumer population in potential markets, and that any 

infestations would be distributed equally among consignments. 

Based on what is known about the current geographical distributions of C. horticola and L. 

strigata, these pests would likely survive in much of the United States, or at least Plant Hardiness 

Zones 6-10. States within these zones contain more than 89 percent of the U.S. population 

(PERAL, 2008). Moreover, this region includes several of the most populous states (e.g., Illinois, 

New York, Ohio, Pennsylvania) to which a significant percentage of perennial wall rocket 

imports would likely be diverted. Thus, we estimated a High risk associated with the likelihood 

that both pests will be moved to suitable habitat in the United States. 

2.7.6. Come into Contact with Host Material Suitable for Reproduction 

Because C. horticola and L. strigata have very broad host ranges, and host plants are distributed 

throughout the United States (NRCS, 2007), suitable host material should be widely available for 

both pests. However, in this case perennial wall rocket will only be imported for consumption. 

Both pests have a limited capacity for natural dispersal and remain on their host plants except as 

adults, and adults are poor flyers with relatively short life spans. In order for both C. horticola 

and L. strigata to become established via perennial wall rocket imported for consumption, 

infested leaves would have to be placed outdoors in proximity to host material. Since this is not 

likely to occur, we considered both pests to have a Low risk of coming into contact with host 

material via this pathway. 

2.8. Conclusion: Pest Risk Potential and Phytosanitary Measures 

We summed the values for the Consequences and the Likelihood of Introduction to yield Pest 

Risk Potential values (PPQ, 2000) (Table 5). This is an estimate of the relative risk associated 

with the importation of perennial wall rocket from the United Kingdom. We used the following 

scale to interpret these totals: low risk = 11-18 points, medium = 19-26 points, and high = 27-33 

points. 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 14

Pests with a Pest Risk Potential value of Low do not require specific mitigation measures, 

whereas a value within the Medium range indicates that specific phytosanitary measures may be 

necessary. The PPQ Guidelines state that a High Pest Risk Potential means that specific 

phytosanitary measures are strongly recommended, and that port-of-entry inspection is not 

considered sufficient to provide phytosanitary security. 

Possible pest mitigation options are outlined in the appendix, but the choice of appropriate 

phytosanitary measures to mitigate risks is undertaken as part of Risk Management and is 

beyond the scope of this document. 

Table 4. Risk Ratings for Likelihood of Introduction 

Pest Quantity 

Imported 

Survive 

PostHarvest 

Treatment 

Survive 

Shipment 

Not 

Detected 

at Portof-Entry 

Moved 

to 

Suitable 

Habitat 

Contact 

with 

Host 

Material 

Cumulative 

Rating a 

Chromatomyia 

horticola 

Low (1) Low (1) High (3) Low (1) High (3) Low (1) Medium (10)

Liriomyza 

strigata

Low (1) Low (1) High (3) Low (1) High (3) Low (1) Medium (10)

a

 Low risk = 6-9 points, Medium = 10-14 points, and High = 15-18 points 

Table 5. Pest Risk Potentials 

Pest species Consequences of 

Introduction 

Likelihood of 

Introduction 

Pest Risk Potential 

Chromatomyia horticola High (14) Medium (10) Medium (24) 

Liriomyza strigata High (13) Medium (10) Medium (23) 

3. Authors and Reviewers 

Plant Epidemiology and Risk Analysis Laboratory 

Center for Plant Health Science and Technology (CPHST) 

Authors: Alison Neeley, Entomologist 

Heather Hartzog, Plant Pathologist 

Reviewers: Robert Schall, Plant Pathologist

Marina Zlotina, Entomologist 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 15

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Appendix A: Risk Management Options for the importation of leaves of perennial 

wall rocket, Diplotaxis tenuifolia (L.), from the United Kingdom 

A1. Introduction 

In this PRA we identified only two quarantine pests that could be introduced into the United 

States via the importation of perennial wall rocket from the United Kingdom: Chromatomyia 

horticola and Liriomyza strigata. Both are Dipteran leaf miners in the family Agromyzidae and 

both had Medium pest risk potentials. 

According to PPQ (2000), pests with Medium pest risk potential may require specific 

phytosanitary measures. This section presents possible risk mitigation strategies that PPQ risk 

managers may wish to consider when deciding if and what risk management measures should be 

undertaken. The actual choice of risk mitigation measures is not addressed in this document but 

details are published in the Federal Register as quarantine notices. 

The proposed importation of fresh perennial wall rocket from the United Kingdom, if approved, 

would be regulated by amendment to existing fruits and vegetables regulations (7 CFR § 

319.56). The appropriate level of protection may be achieved through the application of a single 

phytosanitary measure, such as inspection or a quarantine treatment, or a combination of 

measures. 

The Plant Protection Act (7 U.S.C. § 7701-7786, 2000) defines ‘systems approach’ as “...a 

defined set of phytosanitary procedures, at least two of which have an independent effect in 

mitigating pest risk associated with the movement of commodities.” Similarly, the FAO Standard 

for Integrated Measures for Pest Risk Management proposed that a systems approach be defined 

as, “The integration of different pest risk management measures, at least two of which act 

independently, and which cumulatively achieve the desired level of phytosanitary protection” 

(IPPC, 2007: ISPM #14). Systems approaches are employed by an importing country as an 

alternative to the use of single measures that achieve an appropriate level of phytosanitary 

protection when a single phytosanitary measure is nonexistent, infeasible or undesirable. 

Combining specific mitigation measures to provide overlapping or sequential safeguards is 

distinctly different from applying single mitigation methodologies such as fumigation or 

inspection. Specific measures may be selected from a range of pre-harvest and post-harvest 

measures (e.g., surveys, inspections, sanitation, chemical treatments, etc.) and include mitigation 

measures to compensate for uncertainty. PPQ uses systems approaches for the importation of 

many commodities including Unshu oranges from Japan (7 CFR § 319.28), tomatoes from Spain, 

France, Morocco, and Western Sahara (7 CFR § 319.56 28), and peppers from Israel (7 CFR § 

319.56 24). These programs have performed successfully for many years. 

A2. Mitigation Options 

A2.1. Establishment of Pest Free Areas 

A pest free area (PFA) is defined as “an area in which a specific pest does not occur as 

demonstrated by scientific evidence and in which, where appropriate, this condition is being 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 20

officially maintained” (IPPC, 2007: ISPM #s 4 and 5). As a sole mitigation measure, the 

establishment of pest free areas or pest free places of production may be completely effective in 

satisfying an importing country’s appropriate level of phytosanitary protection (IPPC, 2007: 

ISPM #s 4 and 10). This option has been successful in practice, eliminating the need for postharvest commodity treatments to achieve probit-9-level security (e.g., TDOA, 2003). 

Establishment and maintenance of pest free areas or production sites are to be in compliance 

with international standards [e.g., IPPC, 2007: ISPM #s 4, 5 and 10; NAPPO, 2004). 

A2.2. Establishment of Areas of Low Pest Prevalence 

According to the IPPC (2007: ISPM #22), an area of low pest prevalence may comprise all of a 

country, part of a country, or parts of several countries, in which a particular pest species occurs 

at low population densities and which is or are subject to effective surveillance and control or 

eradication measures (IPPC, 2007: ISPM #10). Procedures for the establishment and 

maintenance of areas of low pest prevalence are to comply with international standards (e.g., 

IPPC, 2007: ISPM #22; NAPPO, 2003). For example, elements of an operational plan for 

establishment and maintenance of such areas might include a geographic description to delimit 

the area; specification of an upper limit to pest densities; means to document and verify all 

necessary procedures and maintain records; specification of phytosanitary procedures (e.g., 

survey, pest control); and movement controls to prevent pest entry or re-entry into the area. The 

international standards recommend that the exporting country consult with the importing country 

in the early stages of implementation to ensure that importing country requirements are met. In 

particular, target or threshold population densities defining an area of low pest prevalence are to 

be established in consultation with the importing country. 

Any protocol for establishing and maintaining a pest free area or area of low pest prevalence is 

also to include a pest-reporting procedure and emergency action plan to address target pest 

detections in the pest free or low-prevalence zones (IPPC, 2007: ISPM #s 10 and 22; NAPPO, 

2003, 2004). Combined with inspection, effective IPM programs achieving low pest prevalence 

may be a possible mitigation option for both leaf miners but should be verified by conducting 

an official survey or lot freedom based on inspection of shipping lot. 

A2.3. Control/Suppression Programs 

A control program may be used to suppress or eliminate pests from fields or prevent infestation. 

Generally, such programs should not be used as stand-alone mitigation options, but may be used 

in combination with other measures as part of a systems approach. Successful control programs 

typically include monitoring, cultural, biological and chemical components (Dreistadt, 1994). 

The components of the control program must be clearly defined for use in a systems approach 

(IPPC, 2007: ISPM #14). 

In controlling Agromyzid leaf miners, chemical treatment of seedlings can be very effective in 

preventing the initial laying of eggs (CABI, 2007). However, only using insecticides to control 

leaf miners is not generally an effective long-term strategy. When insecticides are used heavily, 

resistant strains of flies become dominant and the non-selectivity of the insecticides also kills off 

natural predators and parasites. Prolonged application can result in explosive populations of the 

pest (CABI, 2007). 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 21

In greenhouses, the introduction of Hymenoptera parasites can be extremely effective, especially 

during the first period of leaf mine development. Irradiated (and hence sterile) males are also a 

very effective method of reducing egg-laying. Limited success has also been obtained by 

exposing yellow sticky traps close above the growing plants, as the males tend to fly low 

between plants and in general are more mobile than the females (CABI, 2007). 

A2.4. Phytosanitary Certification Inspections 

These may provide an acceptable level of protection when used as part of a systems approach. 

The crop should be sampled and inspected periodically during the growing season and after 

harvest. Survey results must be negative for issuance of a certificate. Statistical procedures are 

available to verify the confidence in declaring an area pest-free based on negative survey results 

(e.g., Venette et al., 2004; Barclay & Hargrove, 2005). 

Yellow sticky traps and water pan traps are very effective in monitoring Dipteran leaf miners 

(CABI, 2007) and are by far the simplest and most inexpensive method of monitoring (Rosen, 

1990). Additionally, plants can be carefully examined for presences of damage and visible pest 

stages. Sampling plans can be developed to give precision on estimates of pest population levels. 

A2.5. Packinghouse procedures 

Washing the commodity and removing obviously infected or infested material may reduce the 

likelihood of introducing quarantine pests into the United States with a shipment. Packinghouse 

operations should include at least the following (Cantwell and Kasmire, 2001): trimming; 

cleaning with chlorinated water (concentrations could vary from 50 to 200 ppm active chlorine); 

sorting and grading to eliminate defective products (including any leaves damaged by pests). 

A2.6. Quarantine treatments 

Quarantine treatments normally provide probit-9 security by killing 99.9968 percent or more of 

the target organisms. 

Irradiation at 400 gy : Recently, APHIS published a final rule establishing “a minimum generic 

dose of 400 Gy for all plant pests of the class Insecta other than pupae and adults of the order 

Lepidoptera” for “all regulated articles (i.e., fruits, vegetables, cut flowers, and foliage)” (Shea, 

2006). Irradiation is not appropriate for all commodities, however, and more research may be 

needed to determine the tolerance of wall rocket is to irradiation. If irradiation is used, measures 

should be implemented to ensure the phytosanitary security of the consignments after treatment 

to prevent re-infestation. Irradiation may not kill all internal insects; the endpoint of treatment 

may be inactivation, sterilization, or preventing maturation of larvae. Therefore, the presence of 

live larvae in a treated consignment would not necessarily result in its rejection, provided 

appropriate safeguarding measures had been used (IPPC, 2007: ISPM #18). 

Fumigation – Methyl bromide fumigation (T101-n-2) is currently approved as a quarantine 

treatment for leaf miners on herbs and leafy vegetables (PPQ, 2006). However, perennial wall 

rocket is not specifically listed, and therefore, not currently approved, but because several close 

relatives are listed, it is likely only minimal research would be needed to add wall rocket. Hence, 

methyl bromide fumigation would be expected to provide probit-9 security against both pests.
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Rev. 002 October 07, 2008 22

A2.7. Pre-shipment programs

Inspection, treatment, or other risk mitigation measures performed in the field and packinghouse 

should be under the direct supervision of qualified APHIS and DEFRA personnel, and in 

accordance with specified phytosanitary procedures. Such programs require all aspects of the 

application of any required phytosanitary measures to be monitored, and also aim to identify 

shortcomings or opportunities for program improvements (IPPC, 2007: ISPM #14). Provision 

should be made for the formal recognition of approved areas, sites, or producers, as well as the 

specification of conditions for revoking approvals or refusing certification for export to the 

United States. 

A2.8. Point-of-entry sampling and inspection

If a preclearance program is not implemented, then inspection at port of entry is necessary. Upon 

arrival in the United States, consignments should be inspected, with particular attention given to 

paperwork and seals on vehicles, to ascertain that the chain of custody has remained intact. Portof-entry inspection may provide an acceptable level of protection against obvious pests when 

used as part of a systems approach. A random sample from each consignment should be 

inspected to detect a pest infestation rate of 10 percent or greater (PPQ, 2007). 

Leaves should be carefully examined as outlined in the APHIS Fruit and Vegetable Manual 

(PPQ, 2008): Inspectors should look for leaf miner larvae and signs of larvae such as frass and 

holes in the leaves. When examining leaves, inspectors should also look for discolored paths 

under the leaf surface and the presence of mines inside the leaf. Using a probe or knife, 

inspectors should extract the leaf miner larvae by pricking the leaf surface at the end of a path 

and looking for small larvae. 

A3. Summary 

Options for risk mitigation are summarized below (Table A1). 

This document does not purport to establish specific work plans or to evaluate the quality of a 

specific program or systems approach. It identifies risks and provides information regarding 

known mitigative measures. The specification and implementation of measures, as would be 

described in an operational work plan, is beyond the scope of this document. 

Table A1. Summary of risk mitigation options for Chromatomyia horticola and Liriomyza 

strigata on perennial wall rocket from the UK 

Measure(s) Pests Efficacy 

Pest-free areas or areas 

of low pest prevalence 

Both When conducted in compliance 

with international standards (e.g., 

IPPC, 2007: ISPM #s 4 and 10; 

NAPPO, 2004) this method meets 

requirements for appropriate level 

of protection 

Suppression /Control 

program 

Both pests of concern could 

be managed, at least in part, 

Research required on effectiveness 

of methods proposed. 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 23

Measure(s) Pests Efficacy 

with a control program, 

whether cultural, chemical, 

or mechanical means, but 

the program should include 

monitoring and inspection to 

verify effectiveness. Control 

must be used in combination 

with other measures. 

Phytosanitary 

Certification Inspection 

and Monitoring 

Both, but must be used in 

combination with other 

measures. 

A phytosanitary certificate guides 

inspection efforts in UK and alerts 

U.S. inspectors to pests of concern 

with this commodity. 

Packinghouse 

procedures, including 

washing and visual 

culling 

Both, but must be used in 

combination with other 

measures. 

Research required on efficacy. 

Point-of-entry sampling 

and inspection following 

guidelines in PPQ fruit 

and vegetables manual 

Both, but must be used in 

combination with other 

measures. 

Sample size must be adequate to 

detect infestation 

Irradiation, generic dose 

400 Gy, combined with 

low pest prevalence 

Both Approved by APHIS; research may 

be needed to determine tolerance of 

wall rocket to irradiation 

Methyl bromide 

fumigation T101-n-2 

Both, but must be used in 

combination with other 

measures. 

Approved by APHIS to treat leaf 

miners, on leafy vegetables. 

Research required to demonstrate 

efficacy on perennial wall rocket.

Port-of-entry sampling 

and inspection combined 

with packinghouse 

procedures 

Both Given the medium pest risk 

potentials of both pests and the 

obvious damage they cause on 

leaves, a combination of packing 

house procedures and port-of-entry 

sampling and inspection may 

effectively mitigate risk. 

A4. Literature Cited 

7 CFR § 319.28. U.S. Code of Federal Regulations, Title 7, Part 319.28 (7 CFR § 319.28 – 

Unshu oranges from Japan). 

7 CFR § 319.56 28. U.S. Code of Federal Regulations, Title 7, 319.56 28– Tomatoes from Spain, 

France, Morocco, and Western Sahara. 

7 CFR § 319.56 24. U.S. Code of Federal Regulations, Title 7, Part 319.56 24– Peppers from 

Israel. 

7 U.S.C. § 7701-7786. 2000. Plant Protection Act, Title 7 United States Code § 7701-7786. 
Perennial wall rocket from the U.K. 

Rev. 002 October 07, 2008 24

Barclay, H. J., and J. W. Hargrove. 2005. Probability models to facilitate a declaration of pestfree status, with special reference to tsetse (Diptera: Glossinidae). Bull. Entomol. Res. 

95(1):1-11. 

CABI. 2007. Crop Protection Compendium. CD-ROM. CAB International (CABI), Wallingford, 

UK. 

Cantwell, M. I., and R. F. Kasmire. 2001. Postharvest Handling Systems: Flower, Leafy, and 

Stem Vegetables. in A. A. Kader, (ed.). Postharvest Technology of Horticultural Crops. 

University of California, Oakland, CA. 

Dreistadt, S.H. 1994. Pests of Landscape Trees and Shrubs: An Integrated Pest Management 

Guide. University of California, Davis, California. 

IPPC. 2007. International Standards For Phytosanitary Measures, 1 to 29 (2007 edition). Food 

and Agriculture Organization of the United Nations, Secretariat of the International Plant 

Protection Convention (IPPC), Rome, Italy. 376 pp. 

NAPPO. 2003. Guidelines for the establishment, maintenance and verification of areas of low 

pest prevalence for insects. NAPPO Regional Standards for Phytosanitary Measures No. 

20. Ottawa: Secretariat of the North American Plant Protection Organization (NAPPO). 

NAPPO. 2004. Guidelines for the establishment, maintenance and verification of fruit fly pest 

free areas in North America. NAPPO Regional Standards for Phytosanitary Measures No. 

17. Ottawa: Secretariat of the North American Plant Protection Organization (NAPPO). 

Rosen, D. 1990. Armoured Scale Insects: Their Biology, Natural Enemies and Control, Volume 

4B. Elsevier, Amsterdam, Netherlands.

Shea, K. 2006. Treatments for Fruits and Vegetables. Rules and Regulations. Final Rule. Federal 

Register: January 27, 2006. (FR Doc. 06-746) 71(18):4451-4464. 

TDOA. 2003. Texas Rio Grande Valley Mexican Fruit Fly, Anastrepha ludens, (Loew) [sic] 

Protocol—2003/2004. Unpublished report. Texas Department of Agriculture (TDOA). 

PPQ. 2000. Guidelines for Pathway-Initiated Pest Risk Assessments, Version 5.02. United States 

Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection 

and Quarantine (PPQ). http://www.aphis.usda.gov/ppq/pra/commodity/cpraguide.pdf.

PPQ. 2006. Treatment Manual (05/2008-25). United States Department of Agriculture, Animal 

and Plant Health Inspection Service, Plant Protection and Quarantine (PPQ). 782 pp. 

PPQ. 2007. Agricultural Quarantine Inspection Monitoring (AQIM) Handbook (10/2007-05). 

United States Department of Agriculture, Animal and Plant Health Inspection Service, 

Plant Protection and Quarantine (PPQ). 196 pp. 

PPQ. 2008. Fresh Fruits and Vegetables Import Manual (06/2008-35). United States Department 

of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and 

Quarantine (PPQ). 616 pp. 

Venette, R. C. and E. E. Davis. 2004. Chili thrips/yellow thrips, Scirtothrips dorsalis Hood 

(Thysanoptera: Thripidae) Mini Pest Risk Assessment. Univ. of Minnesota, St. Paul, MN. 

31 pp.