NOMINATING PARTY: The United States of America

FILE NAME: USA CUN12 SOIL SWEET POTATO SLIPS OPEN FIELD 

BRIEF DESCRIPTIVE TITLE OF NOMINATION: 

Methyl Bromide Critical Use Nomination for Preplant Soil Use for Sweet Potato Slips Grown in 

Open Fields (Submitted in 2010 for 2012 Use Season) 

CROP NAME: Sweet Potato Slips Open Fields

QUANTITY OF METHYL BROMIDE REQUESTED: 

TABLE 1. QUANTITY OF METHYL BROMIDE REQUESTED IN EACH YEAR OF NOMINATION

YEAR NOMINATION AMOUNT 

2012 8,709kg 

NOMINATING PARTY CONTACT DETAILS:

Contact Person: John Thompson 

Title: Division Director 

Address: Office of Environmental Policy 

 U.S. Department of State 

 2201 C Street, N.W. Room 2658 

 Washington, D.C. 20520 

 U.S.A. 

Telephone: (202) 647-9799 

Fax: (202) 647-5947 

E-mail: thompsonje2@state.gov

Following the requirements of Decision IX/6 paragraph (a)(1) The United States of America has determined that the 

specific use detailed in this Critical Use Nomination is critical because the lack of availability of methyl bromide for 

this use would result in a significant market disruption. ■ Yes  No 

 

Signature Name Date 

Title: 

 (Details on this page are requested under Decision Ex. I/4(7), for posting on the Ozone Secretariat website under 

Decision Ex. I/4(8).) 

This form is to be used by holders of single-year exemptions to reapply for a subsequent year’s exemption (for 

example, a Party holding a single-year exemption for 2005 and/or 2006 seeking further exemptions for 2007). It 

does not replace the format for requesting a critical-use exemption for the first time. 

In assessing nominations submitted in this format, TEAP and MBTOC will also refer to the original nomination on 

which the Party’s first-year exemption was approved, as well as any supplementary information provided by the 

Party in relation to that original nomination. As this earlier information is retained by MBTOC, a Party need not 

re-submit that earlier information. 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 1 of 15
CONTACT OR EXPERT(S) FOR FURTHER TECHNICAL DETAILS: 

Contact/Expert Person: Jack E. Housenger 

Title: Director 

Address: Biological and Economic Analysis Division 

 Office of Pesticide Programs 

 U.S. Environmental Protection Agency 

 1200 Pennsylvania Avenue, N.W. Mailcode 7503P 

 Washington, D.C. 20460 

 U.S.A. 

Telephone: (703) 308-8200 

Fax: (703) 308-7042 

E-mail: jack.housenger@epa.gov 

 

LIST OF DOCUMENTS SENT TO THE OZONE SECRETARIAT IN OFFICIAL NOMINATION PACKAGE: 

1. PAPER DOCUMENTS: 

Title of paper documents and appendices 

No. of pages Date sent to Ozone 

Secretariat 

USA CUN12 SOIL SWEET POATO SLIPS Open Field 11 

2. ELECTRONIC COPIES OF ALL PAPER DOCUMENTS: 

*Title of each electronic file (for naming convention see notes above) 

No. of 

kilobytes 

Date sent to Ozone 

Secretariat 

USA CUN12 SOIL SWEET POTATO SLIPS Open Field 

* Identical to paper documents 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 2 of 15
METHYL BROMIDE CRITICAL USE RENOMINATION FOR 

PREPLANT SOIL USE (OPEN FIELD OR PROTECTED ENVIRONMENT) 

SWEET POTATO SLIPS 

1. SUMMARY OF THE NEED FOR METHYL BROMIDE AS A CRITICAL USE: 

Sweet potato production in California has two distinct production components: transplant 

production and field production. This cultural requirement is similar to many other crops, e.g. 

strawberries, vineyards, and orchards, but for sweet potatoes the production of transplants and 

harvested roots is done by the same grower. Transplant and field production both utilize 

fumigation when possible, however, greater weed and disease control is required in the 

transplant nursery. This requirement is currently being met by using methyl bromide flat 

fumigation with plastic tarp. Field production utilizes low rate (12 to 15 gallons per acre) of 1,3-

dichloropropene without tarping to control nematodes. Field production of sweet potatoes in 

California is concentrated in a relatively small geographic area in the central part of the state, and 

because of this exceeds the current use allotment of 1,3-dichlropropene allowed within a 

township (640 acres). Growers cannot use 1,3-dichrlopropene in January and the township cap 

restrictions on 1,3-dichlropropene require an application factor of 1.9 in December, and the cap 

being exceeded in November (Cal DPR, 2002). Thus the choice of fumigants available to 

growers for the transplant production is limited by state regulations, 1,3-dichlropropene is 

essentially unavailable for use in the fall when fumigation occurs. Thus, growers use methyl 

bromide + chloropicrin combinations for the transplant production (nursery) areas. 

This request is for the sweet potato transplant production area only, where plant production of 

sweet potato slips occurs. These areas are usually fumigated from November through January. 

Transplants are grown between February – May, and the cuttings (slips) from the transplant 

production area are transplanted between late April and early June. The majority of sweet 

potato roots are harvested in September and October. The total area Sweet potatoes are 

transplanted from plant propagules, called slips that are transplanted between late April and early 

June. The majority of sweet potato roots are harvested in September and October. 

The USG has reviewed all factors affecting transition rates in this sector. Based on this 

assessment the transition rate has been greatly increased for most portions of this sector. For the 

area covered in this nomination, the USG believes that the narrative discussion included in this 

document is technically valid. The USG has nominated amounts of methyl bromide based only 

on those sub-sectors that cannot transition away from methyl bromide at the accelerated rate.

2. SUMMARISE WHY KEY ALTERNATIVES ARE NOT FEASIBLE: 

This request is only for those growers who cannot use 1,3-dichloropropene due to regulatory 

constraints. Fumigation with 1, 3-dichloropropene is prohibited in California during December 

and January. The soil where sweet potato “slips” (transplants) is typically fumigated from 

November through January in order to meet a market window. In addition, those growers who 

fumigate in November do not have 1, 3-dichloropropene available because the township cap has 

been exceeded by other crops that fumigate earlier in the year (see Trout 2005). The 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 3 of 15
combination of 1, 3-dichlropropeme plus chloropicrin is highly rated for control of nematodes, 

certain diseases and some weed species. This is based upon years of grower experiences on 

other crops using the respective ingredients alone and in combinations. Prior to the delabeling of 

1, 3-dichloropropene by Cal DPR in the early 1990’s, tarped 1,3-dichloropropene + chloropicrin 

was the main fumigation choice for the sweet potato nursery area. This combination would also 

be the preferred drop-in replacement for methyl bromide if it were no longer available and 1,3-

dichloropropene restrictions were not in place. Research results from the first year of a three 

year study are described in part 7 below. 

California growers produce their transplants (slips) for propagation in open fields and initially 

cover plants with clear plastic row covers supported by hoops. Prior to being used for transplant 

production, fields are either fallowed or planted to rye or sweet potatoes the previous season. 

The transplants (slips) must be watered during establishment and the low rainfall amounts and 

public water restrictions that exist in the production areas make it imperative that fields are 

situated near private irrigation wells, which significantly limits the land available for growing 

transplants. 

Growers of sweet potato slips face a difficult situation with the township caps because all of the 

fumigated areas fall within just four townships in Merced County. Merced county has already 

exceeded a 2x cap allowance, so growers have already reverted to the lower 1,3 -dichloropropene 

use limit. Additional evidence that the 1,3 -dichloropropene cap will be exceeded in 2012 is that 

in 2002, the California Department of Pesticide Regulation (CDPR) gave a special allowance to 

one of the Merced county townships, where sweet potato was the primary fumigant use, to 

exceed their cap by 16,500 adjusted pounds. Similar allowances have been given several times 

since 2002. 

Iodomethane is not registered in California, where these sweet potato slips are grown. 

There are over 5,000 hectares (> 12,500 acres) acres in sweet potato production, 53 ha (131acres) 

of plant beds of which are fumigated with methyl bromide, and 1987 ha (4908 acres), open field 

treated with 1,3-D. When the banked allowance is expended this will leave 2,227 acres (or 44%) 

that cannot use 1,3 -dichloropropene that otherwise would have. In 2003, for example, the cap 

(without any bank) only allowed for 316,554 pounds of 1,3-dichloropropene while there was 

demand for 583,807 pounds. 

The USG has reviewed all factors affecting transition rates in this sector. Based on this 

assessment the transition rate has been greatly increased for most portions of this sector. For the 

area covered in this nomination, the USG believes that the narrative discussion included in this 

document is technically valid. The USG has nominated amounts of methyl bromide based only 

on those sub-sectors that cannot transition away from methyl bromide at the accelerated rate. 

3. IS THE USE COVERED BY A CERTIFICATION STANDARD?

Methyl bromide is not used to meet a certification standard for sweet potato slip production. 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 4 of 15
4. IF PART OF THE CROP AREA IS TREATED WITH METHYL BROMIDE, 

INDICATE THE REASON WHY METHYL BROMIDE IS NOT USED IN THE OTHER 

AREA, AND IDENTIFY WHAT ALTERNATIVE STRATEGIES ARE USED TO 

CONTROL THE TARGET PATHOGENS AND WEEDS WITHOUT METHYL 

BROMIDE THERE. 

Organic sweet potato growers do not use methyl bromide, or any other fumigants, in their 

transplant beds. It has been observed that fewer and less vigorous transplants result. Since data 

are not available to address these options, the extent of these differences cannot be quantified. In 

addition, in order to produce their crops, organic producers of sweet potatoes must use 

significant amounts of hand weeding. Current costs are not available. 

5. WOULD IT BE FEASIBLE TO EXPAND THE USE OF THESE METHODS TO 

COVER AT LEAST PART OF THE CROP THAT HAS REQUESTED USE OF 

METHYL BROMIDE? WHAT CHANGES WOULD BE NECESSARY TO ENABLE 

THIS? 

The 1, 3- dichloropropene township cap limitation effectively limits the amount of 1, 3- 

dichloropropene that can be used on a sliding scale. This scale is a function of amount, method 

of fumigation, and time of year. To the extent that 1, 3- dichloropropene or a 1, 3- 

dichloropropene plus chloropicrin mixture can be used, it is being used. California growers 

prefer to use 1, 3- dichloropropene when possible (where the key pests are controlled and where 

the township caps are not binding) as it is less costly than mixtures using methyl bromide. The 

US nomination is for growers who will be denied the use of 1, 3- dichloropropene alone or in 

combination with chloropicrin as a result of 1, 3- dichloropropene township caps and regulations. 

Solarization is undergoing evaluation, however, it is not likely that solarization can completely 

replace fumigation. Solarization can only take place during the same time period as cropping 

(the non-cropping season is not warm enough to allow soils to reach the temperatures necessary 

to kill key pests to the required soil depths. 

The USG has reviewed all factors affecting transition rates in this sector. Based on this 

assessment the transition rate has been greatly increased for most portions of this sector. For the 

area covered in this nomination, the USG believes that the narrative discussion included in this 

document is technically valid. The USG has nominated amounts of methyl bromide based only 

on those sub-sectors that cannot transition away from methyl bromide at the accelerated rate.

6. SUMMARY OF RECENT RESEARCH: 

Scott Stoddard presented data from the first year of a three year study at the Methyl Bromide 

Alternatives Outreach conference (Stoddard, 2008). In his email (Oct. 28, 2008) Scott Stoddard 

indicated that the first year is complete; the second year has begun by implementing the 

fumigation treatments with data collection in 2009. He plans on continuing the project for three 

years with a completion in the fall of 2010. In his summary of the first years research the only 

alternatives that would provide adequate pest control and crop safety also contain 1,3-

dichloropropene (Telone) whose label restrictions and townships caps are already a constraint on 

its use. There were no significant differences between treatments for Pythium sp. control 

(number of colony forming units) or root rotting. The methyl bromide: chloropicrin treatment 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 5 of 15
had the fewest weeds. Weed control was improved when napropamide or Valor were added. 

1,3-dichloropropene plus metam sodium and Valor caused some phytotoxicity but did not lead to 

significant yield reduction. We have also presented additional interim data on the second year of 

the three year study. 

TABLE 2. SWEET POTATO SLIP RESEARCH IN CALIFORNIA – YEAR 1 OF 3 YEAR STUDY 

MAIN PLOTS SPLIT PLOTS

1. Methyl Bromide + Chloropicrin (53:47) at 350 

lbs/acre tarped. 

1. Untreated 

2. Chloropicrin at 150 lbs/acre, tarped 2. Devrinol (napropamide) 4 lbs/acre 

3. PicChlor 60 (60% Chloropicrin & 40% 1,3-D ) 

at 45 gal/acre, tarped 

3. Valor (flumioxazin)at 2 oz/acre 

4. Solarization 4. Botran (dichloran) at 3.5 lbs/1000 sq ft 

5. Telone (1, 3- dichloropropene) 20 gal/acre + 

Vapam (metam sodium) 75 gal/acre 

5. Mertec (thiabendazole) at 30 oz/1000 sq ft 

6. Untreated control 

Source: Stoddard, 2008 MBAO. 

Treatments Application Dates 

Solarization June 26, 2007 

MeBr:Pic, Chloropicrin, & PicChlor August 20, 2007 

Telone & Vapam November 12, 2007 

Botran & Mertec February 28, 2008 at planting 

Devrinol & Valor March 7, 2008 

Film – Std LDPE 1.5 mil 

TABLE 3. SWEET POTATO SLIP PLANT PRODUCTION IN 2008

SLIP TREATMENT PLANTS PER 4 SQUARE FEET

1. MeBr + Chloropicrin 160 bc 

2. Chloropicrin 155 b 

3. PicChlor 120 cd 

4. Solarization 110 d 

5. Telone & Vapam 160 b 

6. Untreated control 230 a 

 Source: Stoddard, 2008 MBAO. 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 6 of 15
FIGURE 1. SWEET POTATO SLIPS (PLANTS PER 4 SQUARE FEET) 

 Source: Stoddard, 2008 MBAO. 

TABLE 4. SWEET POTATO CROP PRODUCTION FROM TREATED SLIPS IN 2008

SLIP TREATMENT LBS/ACRE OF ROOTS

1. MeBr + Pic 65,000 c 

2. Chloropicrin 72,000 ab 

3. PicChlor 67,000 bc 

4. Solarization 69,000 bc 

5. Telone & Vapam 78,000 a 

6. Untreated control 57,000 d 

Source: Stoddard, 2008 MBAO. 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 7 of 15
FIGURE 2. SWEET POTATO ROOT YIELD (POUNDS PER ACRE) 

 Source: Stoddard, 2008 MBAO. 

TABLE 5. SUMMARY OF SWEET POTATO SLIP TRIAL TO DATE

TREATMENT WEED 

CONTROL

PLANT 

PRODUCTION

FUMIGATION 

COST

HAND 

WEEDING

REGULATION 

ISSUES

1. MeBr:chloropicrin A A $ 2100 100 Phase out 

2. Chloropicrin BC A $ 1900 400 VOC 

3. PicChlor A B $ 2100 100 VOC, Caps 

4. Solarization C C $ 1200 600 --- 

5. Telone + Vapam AB A $ 500 100 VOC, Caps 

6. Untreated control C A 0 600 --- 

 Source: Stoddard, 2008 MBAO. 

2008 -2009 Methyl bromide fumigation alternatives for sweetpotato hotbeds in California. 

Project Period: June 2008 – December 2009 (2nd fumigation cycle/year) 

A cooperative research project between UC Cooperative Extension and USDA-ARS 

Report Preparer: Scott Stoddard, UC Cooperative Extension 

 2145 Wardrobe Ave 

 Merced, CA 95341 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 8 of 15
MeBr, Pic alone, Pic Chlor 60, and solarization treatments (main plots) were installed on July 15, 

2008, using the services of Tri Cal, Inc. Plastic tarp used was 1.25 mil, standard PE plastic with 

UV inhibitors. Plots were 140 ft long by 25 ft wide, and were replicated three times using a 

randomized split-block design. Soil temperature probes were installed on the same day. Plastic 

and probes were removed on September 16, 2008. On December 11, 2008, the Telone + Vapam 

treatment were applied by Tri Cal using “rotovate and roll” equipment. Because of crop 

phytotoxicity concerns from year one with this treatment, rates were reduced to 15 gpa Telone 

and 40 gpa Vapam. 

On March 9, 2009, the grower cooperator installed hotbeds into the treated areas. Hotbeds were 

8 ft wide by 85 ft long, and centered within each fumigated treatment area. Split plot treatments 

were imposed with the application of fungicides (Botran and Mertect) to the sweetpotato roots 

prior tocovering with soil. On March 16, 2009, pre-emergent herbicides Devrinol and Valor 

were also applied as separate split plot treatments to each bed within the main plot fumigation 

area. All fungicide and herbicide treatments were made using a hand boom attached to a 

backpack sprayer. 

On April 9 and 17, 2009, weeds were evaluated in each split plot. On April 9, visible weeds per 

plot (100 sq ft) were counted and classified: on April 17th hand weeding times were measure for 

the plots. Hand weeding was conducted by using grower cooperator labor. 

On May 7, 2009, a field day was held to view and discuss the treatments in the trial. About 15 

people attended. Nematode and disease sampling also took place on this day. For both, the 

upper 6 inches of soil beneath the sweetpotato roots was sampled using a standard soil probe. 

Inoculum density of Pythium spp. was determined by soil dilution plating onto a semiselective 

agar (corn meal agar amended with pimaricin and antibiotics). All the colonies of Pythium on 

the plates were enumerated. Each assay was done in triplicate. 

Plant stand counts were made on May 15 by randomly tossing a 2 x 2 ft square into the center of 

each split plot and cutting at the soil line all sprouts within this area. 50 plant cutting from this 

selection were also transplanted in a production field on May 19, 2009. The purpose of the field 

transplanting is to determine whether fumigation choice has an impact on the yield potential of 

the harvested root (for example, weak diseased plants would result in reduced yields as 

compared to healthy vigorous plants). 

Results 

Soil temperature data at 1, 3, 6, and 12 inches under bard ground (UTC) and the solarization 

treatment from July 15 to September 15, 2008, are shown in Figures 1 and 2. The clear plastic 

tarp used in this trial significant increased soil temps at all depths. At one inch, temps exceeded 

125 oF with plastic, 109 oF without. 

Nematodes were sampled by taking a 500 cc soil sample from each of the main plot (MeBR + 

Pic, Pic alone, Pic Chlor 60, Telone + Pic, Solarization, UTC) treatments in February before the 

beds were installed and again at plant harvest in May. No root knot nematodes (Meloidogyne 

incognita) or other plant parasitic nematodes were found at either sampling event (Table 1). 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 9 of 15
The soil analysis for potential root rotting pathogens showed no significant differences among 

treatments. Pythium populations were extremely low in all plots (in general, Pythium 

populations in most soils in the San Joaquin Valley average between 20 and 50 dfu/g). 

Weed pressure was not that high in this area, probably because it had been previously fumigated 

with MeBr. However, there were significant differences between the main plot treatments, with 

greatest number of weeds in the untreated *UTC) and solarization treatments. These treatments 

also required the most hand weeding time, averaging 25 and 20 seconds per man per 100 ft2. 

Significant differences were also noted between the split plot treatments for weed control. 

Application of either herbicide significantly reduced weed pressure as compared to not treating, 

with Valor having the greatest efficacy on the weeds present at this location (puncture vine, 

malva, pigweed, mustard, barnyard grass). However, Valor caused some noticeable crop 

phytotoxicity with a corresponding reduction in plant production. Even with this, plant 

production was excellent in 2009, with 240 to 280 plants per 4 ft2 (much better than 2008 

production). No crop phytotoxicity was seen between the fumigation treatments. 

Table 6. Nematode, Pythium, weed counts, and plant production from the 2nd year of the trial (2009). 

Nematodes 

(RKN/100g) 

Nonparasitic Pythium Weeds 

#/plot 

Crop 

Phyto 

Weed 

Time 

Plant 

counts 

Treatment 11 – Feb 7-May 7-May Cfu/g 

soil 

9-Apr 9-Apr Sec/ man/ 

plot 

#/4 sq 

ft 

1 UTC 0 0 200 3.2 47.4 1.2 25 235 

2 MeBr + Pic, 350 

lbs/A 

0 0 94 2.1 4.4 1.2 8 268 

3 PicChlor 60, 45 gpa 0 0 111 2.5 13.4 0.6 16 254 

4 Vapam 40 gpa + 

Telone 12 gpa 

0 0 134 0.5 5.6 1.6 9 306 

5 Pic only, 150 lb/A 0 0 135 3.0 16.4 1.6 14 258 

6 Flat solarization 0 0 190 1.8 22.4 2.0 20 264 

P value Ns Ns ns 0.75 ns 0.001 0.25 ns 0.07 0.79 ns 

LSD 0.05 --- 15.1 --- 12 --- 

CV 147.3 68.4 102 65.6 16.3 

1 UTC 32.2 0 Not weeded 278 

2 Devrinol (napropamide) 4 lb/A 11.9 0.6 15 281 

3 Valor (flumioxazin) 1.5 oz/A 0.7 4.3 6 242 

4 Botran (dichloran) 3.5 lbs/1000 sq 

ft/10 gals

27.3 0.4 20 268 

5 Mertect (thiabendazole) 

30 fl oz/1000 sq ft/10 gals

33.4 0.6 25 274 

6 Devrinol + Valor tank mix 4.0 2.2 9 244 

P value 0.001 0.001 0.001 0.02 

LSD 0.05 8.3 0.9 6.6 28.7 

CV 68.4 102 65.6 16.3 

P value, 

Main Plot x Split plot 

Interaction 

ND ND ND ND 0.001 0.91 ns 0.65 ns 0.47 ns 

Footnote: Nematodes and Pythium were determined within main plot treatments only. 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 10 of 15
Weed counts are a combination of broadleaf, grass, and yellow Nutsedge. Broadleaf spp include puncture vine, 

malva, pigweed, and mustard. 

7. ECONOMIC FEASIBILITY OF ALTERNATIVES 

Please note that in this study net revenue is calculated as gross revenue minus operating costs. 

This is a good measure as to the direct losses of income that may be suffered by the users. It 

should be noted that net revenue does not represent net income to the users. Net income, which 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 11 of 15
indicates profitability of an operation for an enterprise, is gross revenue minus the sum of 

operating and fixed costs. Net income is smaller than the net revenue measured in this study, 

often substantially so. We did not include fixed costs because they are difficult to measure and 

verify. 

The economic reviewers analyzed crop budgets for pre-plant sectors to determine the likely 

economic impact if methyl bromide were unavailable. Various measures were used to quantify 

the impacts, including the following: 

(1) Loss per Hectare. For crops, this measure is closely tied to income. It is relatively easy to 

measure, but may be difficult to interpret in isolation. 

(2) Loss per Kilogram of Methyl Bromide. This measure indicates the value of methyl 

bromide to crop production. 

(3) Loss as a Percentage of Gross Revenue. This measure has the advantage that gross 

revenues are usually easy to measure, at least over some unit, e.g., a hectare of land or a storage 

operation. However, high value commodities or crops may provide high revenues but may also 

entail high costs. Losses of even a small percentage of gross revenues could have important 

impacts on the profitability of the activity. 

(4) Loss as a Percentage of Net Operating Revenue. We define net cash revenues as gross 

revenues minus operating costs. This is a very good indicator as to the direct losses of income 

that may be suffered by the owners or operators of an enterprise. However, operating costs can 

often be difficult to measure and verify. 

(5) Operating Profit Margin. We define operating profit margin to be net operating revenue 

divided by gross revenue per hectare. This measure would provide the best indication of the 

total impact of the loss of methyl bromide to an enterprise. Again, operating costs may be 

difficult to measure and fixed costs even more difficult, therefore fixed costs were not included 

in the analysis. 

These measures represent different ways to assess the economic feasibility of methyl bromide 

alternatives for methyl bromide users, who are sweet potato slip producers in this case. Because 

producers (suppliers) represent an integral part of any definition of a market, we interpret the 

threshold of significant market disruption to be met if there is a significant impact on commodity 

suppliers using methyl bromide. The economic measures provide the basis for making that 

determination. 

Slips are produced for the sole purpose of transplanting into the open fields by growers and they 

are not sold commercially. Therefore, slip production is an input process to sweet potato 

production, with its associated costs. Thus, the yield loss of the final product, sweet potato, is 

the relevant yield loss that may result from the use of alternative to methyl bromide. Methyl 

bromide is used to fumigate hot beds for slip production. One acre of hot beds typically 

produces enough slips for transplanting into about 60 field acres to produce sweet potato. 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 12 of 15
For hot bed fumigation, there are four alternatives to methyl bromide (Tables 4 and 5). Of these, 

Telone + Vapam (1,3-D + Metam-sodium) cannot be used because of the township caps, and 

solarization only partially controls pathogens. Thus, chloropicrin is analyzed as the next best 

alternative to methyl bromide. Table 6 indicates that use of chloropicrin results in an 11% 

increase in production over methyl bromide. Hand weeding costs are greater with chloropicrin 

(Table 7), but overall, production increase outweighs the cost increases and results in positive 

economic impacts as shown in Table 7. 

TABLE 7. CALIFORNIA SWEET POTATO SLIPS - ECONOMIC IMPACTS OF METHYL BROMIDE 

ALTERNATIVES 

CALIFORNIA SWEET POTATO SLIPS METHYL BROMIDE CHLOROPICRIN

YIELD LOSS (%) 0 -11 

 YIELD PER HECTARE (CWT/HECTARE) 737 818 

* PRICE PER UNIT (U.S.$) 28 28 

= GROSS REVENUE PER HECTARE (U.S.$) 20,632 22,902 

- OPERATING COSTS PER HECTARE (U.S.$) 14,200 15,060 

= NET OPERATING REVENUE PER HECTARE (U.S.$) 6,432 7,841 

1. LOSS PER HECTARE (U.S.$) 0 -1,410 

2. LOSS PER KILOGRAM OF METHYL BROMIDE (U.S.$) 0 -6 

3. LOSS AS A PERCENTAGE OF GROSS REVENUE (%) 0 -7 

4. LOSS AS A PERCENTAGE OF NET OPERATING REVENUE (%) 0 -22 

Source: Sweet potato Research Progress Report 2005. 

Table 7 summarizes economic impacts of using chloropicrin. Yield increases by 11% with a 

gain of $1,410/hectare with the use of chloropicrin. This gain is 7% and 22% of the gross 

revenue and net operating revenue, respectively. 

USA CUN12 SOIL Sweet Potato Slips Open Field Page 13 of 15
8. RESULTANT CHANGES TO REQUESTED EXEMPTION QUANTITIES 

TABLE 8: NOMINATION AMOUNT. 2012 Methyl Bromide Usage Newer Numerical 

 Sweet Potato 

Council of 

California 

 Sector Total / 

Average 

Quantity Requested for 2011: Amount (kgs) 14,515 14,515 

Quantity Recommended by 

MBTOC/TEAP for 2011 : Amount (kgs) 11,612 11,612 

Amount (kgs) 11,612 11,612 

Area (ha) 81 81 

Rate 143 179 

Transition from 2011 

Baseline Adjusted Value

Percentage 

(%) -25% -25%

Amount (kgs) 8,709 8,709 

Area (ha) 58 58 

Rate 150 150 

Quantity Approved by Parties 

for 2011:

Quantity Required for 

2012 Nomination:

SECTOR

SWEET POTATO SLIPS

USA CUN12 SOIL Sweet Potato Slips Open Field Page 14 of 15
USA CUN12 SOIL Sweet Potato Slips Open Field Page 15 of 15

CITATIONS 

CDFA (California Department of Food and Agriculture). 2002. Recommended permit 

conditions for using 1,3-dichloropropene fumigants. September 12, 2002. Available 

online at http://www.cdpr.ca.gov/docs/enfcmpli/penfltrs/penf2002/2002atch/attach37.pdf 

CDFA (California Department of Food and Agriculture). 2005. Notice of Proposed and Final 

Decisions and Directors Findings . December 2005. Available online at 

http://www.cdpr.ca.gov/docs/nod/2005-50.htm 

Stoddard, C.S. 2005. Sweetpotato Research Progress Report 2005. UCCE Merced County. 

Provided by C.S. Stoddard. 

Stoddard, C.S. 2008. Research Progress Report: Fumigation and cover crop trial on sweet 

potatoes. University of California Cooperative Extension Service, Merced County. 

Stoddard, C.S. 2008. MeBr Alternatives for Sweet Potato Hotbeds in California. Available 

online at: http://www.mbao.org/2008/027Stoddard.pdf 

Trout, T. 2005. Impact of township caps on telone use in California. Annual International 

Research Conference on Methyl Bromide Alternatives and Emissions Reductions, 2005. 

http://www.mbao.org/2005/05Proceedings/127TroutT%20mb-pest-use-telone-rpt05-

mbao.pdf