United States I Department of

Agriculture

a

@3 Forest Service I Research Note

Southern Forest

Experiment Station

SO-288

January, 1983

Control of Fusiform Rust in Slash Pine with Bayleton

(Triadimefon) Seed Treatment

Robert C. Hare and Glenn A. Snow

SUMMARY

The Bayleton@ seed treatment protects pine seedlings against fusiform rust for at least 4 weeks after

sowing. If nurserymen use treated seed, no more

than three foliar sprays are needed during the season. These can be timed to give maximum protection

during the most hazardous period and adequate

protection for the remainder of the infection season.

Additional keywords: Systemic fungicide, Cronarfium quercuum f. sp. fusiforme

INTRODUCTION

Bayletonl is a systemic fungicide used in many

southern pine tree nurseries for protective and

curative control of fusiform rust caused by Cronarfium quercuum (Berk.) Miyabe ex Shirai f. sp.

fusiforme (Kelley 1980, Mexal, et al. 1979, Snow,

et al. 1979). It is registered as a foliar spray for

pines in the southeastern states and has given excellent results with as few as three or four applications.

‘Bayleton is registered trademark of Farbenfabriken Bayer

Gmbh, Leverkusen, West Germany.

The use of trade, firm, or corporation names in this pub%

cation is for the information and convenience of the reader.

Such use does not constitute an official endorsement or

approval by the U.S. Department of Agriculture of any product

or service to the exclusion of others which may be suitable.

This publication reports research involving fungicides. All

uses of fungicides must be registered by appropriate State and

Federal agencies before they can be recommended. Use fungicides only when needed and handle them with care. If fungicides are handled, applied, or disposed of improperly, they

may injure humans, domestic animals, desirable plants, pollinating insects, fish, or other wildlife, and may contaminate

water supplies. Follow the directions and heed all precautions

on the container label.

The effectiveness of Bayleton against the fusiform

rust fungus was first observed in seed treatment

tests with loblolly pine (Pinus faeda L.) (Mexal and

Snow 1978). Seedlings grown from seed soaked in

800 mg. triadimefon/liter water were protected until

seed coat shed. Subsequent field trials showed that

seed treatment reduced galling from natural infection, and tended toward better rust control when it

was used along with spraying (Snow, et al. 1979). In

the same field tests, however, four or five foliar

sprays of Bayleton provided good rust control with

or without the seed treatment. Foliar sprays were

then recommended to nurserymen and the chemical

was registered for foliar application.

Nontheless, there are still advantages of seed

treatment with Bayleton that deserve consideration

by nurserymen. The most important is the additional

protection provided during the period between seed

germination and the first foliar spray. Rust hazard is

very high at this time because the trees are very

susceptible, inoculum levels are high, and weather

is most often favorable for infection. Another potential advantage of seed treatment would be a reduction in number of sprays resulting in use of less

pesticide. Also, timing of sprays when pine seed are

germinating would be less critical.

Use of Bayleton as a seed treatment on an operational basis in nurseries depends largely on the

length of time that seedlings are protected after

seed germination. Mexal and Snow (1978), obtained

protection up to 18 days after the seeds were sown.

Longer periods were not tested. Rowan (1982) has

more recently observed rust control with seed

treated 64 days before inoculation. The maximum

time, however, that the Bayleton seed treatment is

effective has not been determined.

Southern Forest Experiment Stationm-102lO U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, E. Oklahoma, Tennessee, E. Texas, Puerto Rico, U.S. Virgin Islands

1
The experiments described herein were carried

out in 1979, 1980, and 1981 to determine the number

of weeks after seed treatment that Bayleton would

protect slash pine (P. elliottii Engelm. var. elliottii)

seedings against galling.

MATERIALS AND METHODS

Bulk slash pine seed from south Mississippi were

treated by soaking in water alone or in water containing 800 mg a.i. Bayleton per liter. After 24 hours,

the water was decanted through a screen and the

seeds were germinated without drying on moist

vermiculite in closed dishes under lights at 25” C.

Germinated seeds were planted in a 1:l (v/v) peatvermiculite mixture in plastic Leach@ containers.

In the 1979 and 1980 experiments, the inoculated

seedlings were grown in the greenhouse for the

duration of the experiment. The 1981 seedlings

were grown outside in full sun because such plants

were expected to be physiologically more similar to

nursery seedlings than seedlings grown indoors.

Typically, about 60 percent of the seeds germinated

within a week after sowing and shed their coats a

week later.

To determine the duration of fungicide effectiveness, seedlings were inoculated weekly from 2 to 9

weeks after sowing. The 1980 inoculations were

carried out at the USDA Forest Service Resistance

Screening Center near Asheville, North Carolina

(Anonymous 1980) with the concentrated basidiospore spray (CBS) system. The 1979 and 1981

inoculations were done at Gulfport, Mississippi,

using the forced air method of Snow and Kais (1972).

Plots consisted of 30 seedlings in 1979 and 20

seedlings each in 1980 and 1981; each plot was

replicated four times in a randomized complete

block design. Seedlings were tallied for the presence of galls at 6-8 months, and analyses of variance were carried out on the basis of percentage

of seedlings galled per plot to determine whether

treatment effects were significant at the 0.05 level.

If so, Duncan’s multiple range test was used to

determine significant differences between individual treatments.

RESULTS AND DISCUSSION

Bayleton seed treatment at 800 mg/liter provided

significant rust control in all 3 years (table 1). In

1979, when inoculated 6 weeks after sowing, 23

percent of the seedlings from treated seed were

galled compared with 80 percent from untreated

seed. In 1980, however, Bayleton gave significant

control for only 2 weeks after sowing. Control

seedlings for the first two inoculations had very few

galls in 1980, whereas in 1981 the first two inoculations gave high infection of controls and Bayleton

significantly controlled rust at 3 and 4 weeks. Failure

to obtain high control infection at 2 and 3 weeks in

1980 may be a weakness in the CBS system related

to the small target area of very small plants. Infection of germinants at all ages has been very

consistent with the forced air system.

Age was a significant factor in fusiform rust

resistance of control seedlings grown in full sun in

1981. Gall frequency dropped from 96 percent at

3 weeks to only 26 percent at 9 weeks (table 1).

This age effect was not apparent in the greenhousegrown experiment of 1980, where there was no

change over time. We suspect the difference between the control seedlings in 1980 and 1981 was

due to the relative succulence of the tissue. Greenhouse conditions promote succulent, susceptible

tissue growth, whereas plants grown in pots in full

sun harden rapidly and become resistant. Nurserygrown seedlings would likely behave similarly and

develop some natural resistance after a few weeks.

This result supports the opinions of many nurserymen who have long recognized that fungicidal

protection is needed most when~the pine seeds are

germinating and in the weeks immediately following. But our finding should not be interpreted to

mean that sprays are not needed later. Other factors

can promote succulence and susceptibility of nursery seedlings such as fertilization (Rowan 1977),

irrigation, and cool, rainy weather.

CONCLUSIONS

The results of these experiments and those reported previously (Mexal and Snow 1978, Rowan

1982, Snow, et al. 1979) indicate that Bayleton seed

treatment effectively controls fusiform rust for at

least 4 weeks after the seeds the sown. Therefore,

no more than three foliar sprays should be needed

to protect seedlings in nursery beds sown with

treated seed (fig. 1). Without seed treatment, the

first Bayleton spray in the nursery must be relied on

to arrest incipient infections. The eradicative effect

of Bayleton spray has been tested and the maximum

time after inoculation that it has been shown to

prevent gall development is 14 days (Rowan 1982).

Therefore, if germination occurs over a period

longer than 14 days, additional sprays may be necesRobert C. Hare is Principal Plant Physiologist and Glenn A. Snow is Principal Plant Pathologist, Southern Forest Experiment Station,

Forest, Service-USDA, Gulfport, MS 39503.

2
sary during this period. Without Bayleton seed treat- their area in planning their rust control program.

ment, timing of these first sprays is critical and the Pesticide Use Policy.-The authors believe the

decision to spray or not to spray may be difficult to present label for Bayleton as a foliar spray for pines

make. With Bayleton seed treatment protection permits its use as a seed treatment. Environmental

through the period during germination is assured Protection‘ Agency policy states that it is not a misand timing of the first spray is less critical. The use to employ any method of application that is not

proposed spray schedule we present is for a nursery prohibited by the labeling, provided the concenin south Mississippi. The critical infection period tration used is at or below that recommended on the

could be earlier or later at other locations and this label. This policy is subject to different interpretacould require an adjustment in the spray schedule. tions and nurserymen are advised to consult their

Nurserymen are therefore advised to seek assist- appropriate state agencies before they treat pine

ante from a forest pathologist who is familiar with seed with Bayleton.

Table 1 .-Percent of slash pine seedlings with fusiform rust galls. Seedlings were grown

from seed soaked in water or 800 mg/L Bayleton and inocol&ed at different

times after sowing

Inoculation schedule-weeks after sowing seed

Year Treatment 2 3 4 5 6 7 a 9

1979

1980

1981

. . . . . . . . . percent galled . . . . . .

Control ,... .._ .._. 80

Bayleton _... 23”

Control 25 22 62 48 57 63

Bayleton 5” 21 51 39 45 66

Control 96a’ 80ab 75b 75b 4lc 28c 26c

Bayleton .._. 61” 51’ 84 55 30 42 31

1 Means followed by a common letter are not significantly different (P=O.O5).

l Significantly different from control (P~0.05).

5EED COAT SHE

7 14 21 7 14 21

, APRIL M,AY IiII

7 14 21

JUNE

SPRAY ‘3

I

\ /

CRITICAL WFECTION PERIOD

Figure 1.-A proposed spray schedule based on April 1 sowing. The seed treatment provides

protection during the critical infection period up to at least a week’after the first seed

coats have been shed, and the first foliar spray has been applied, about May 1. The

second spray is applied 2 weeks later to cover the last of the critical period, and the lash

spray is delayed until the middle of June. The oritical infection period is the approximate time that seedlings are most susceptible, inoculum is most prevalent on oaks, and

weather is most often favorable for pine infection in south Mississippf. The dates for

this period could be earlier or later at other locations.

3
LITERATURE CITED

Anonymous. The resistance screening center,

screening for fusiform rust resistance as a service

for tree improvement programs. USDA For. Serv.

Gen. Rep. ,SA-CR 16, 1960. Folder.

Kelley, W. D. Evaluation of systemic fungicides for

control of Cronartium guercuum f. sp. fusiforme

on loblolly pine seedlings. Plant Disease 64:

773-775; 1960.

Mexal, J. G.; Snow, G. A. Seed treatment with systemic fungicides for the control of fusiform rust

in loblolly pine. Res. Note SO-236. U.S. Department of Agriculture, Forest Service, Southern

Forest Experiment Station; 1976. 4 p.

Mexal, J. G.; Snow, G. A.; Morris, W. G. Fusiform

rust control with systemic fungicides. In: Proceedings, 1976 South. Nursery Conf., U.S. Department of Agriculture, Forest Service Tee. Pub.

SA-TP6; 1979: 149-l 54.

Rowan, S. J. Fertilization and inoculum density’

effect susceptibility to fusiform rust and gall development in slash and loblolly pine seedlings.

Plant Dis. Rep. 61(7): 609-612; 1977.

Rowan, S. J. Influence of method and rate of application of Bayleton on fusiform rust on slash pine

seedlings. Tree Planters’ Notes 33(l): 15-17; 1962.

Snow. G. A.; Kais, A. G. Techniques for inoculating

pine seedlings with Cronartium fusiforme. In: Biology of Rust Resistance in Forest Trees. U.S.

Department of Agriculture Misc. Pub. 1221; 1972:

325-326.

Snow, G. A.; Rowan, S. J.; Jones, J. P.; Kelley,

W. D.; Mexal, J. G. Using Bayleton (triadimefon)

to control fusiform rust in pine tree nurseries. Res.

Note SO-253. U.S. Department of Agriculture,

Forest Service, Southern Forest Experiment Station; 1979: 5 p.

*U.S. GOVERNMENT PRINTING OFFICE: 1~@jg-O85/E-16