Fungicide Chemistry

10 Fungicides for Disease Control in Grapes Advances in Development

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on November 5, 2015 | http://pubs.acs.org Publication Date: April 22, 1986 | doi: 10.1021/bk-1986-0304.ch010

Roger C. Pearson Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456

The grape is the most widely planted fruit crop in the world. Spain, Italy, Russia and France, each with over one million hectares of grapes, easily outrank the United States (US) which has 323,000 hectares. As of 1981, the worldwide planting of grapes totaled over ten million hectares (Table I) (1). The US ranks sixth among the wine producing countries (Table II) and first among the raisin producing countries. In 1982, the commodity value of grapes for fresh and processing uses in the US was $1.34 billion, second only to potatoes for all fruits and vegetables (4). Table I.

The World's Vineyards in 1981.

Country Hectares (1,000) Spain 1,650 Italy 1,360 U.S.S.R. 1,353 France 1,154 Turkey 801 Portugal 360 Argentina 324 U.S.A. 323 Romania 307 Other countries 2,441 TOTAL 10,073 Adapted from Ref. 1. Currently, there is a worldwide wine glut which is the result of several factors, among them bumper crops of 1982 and 1983 coupled with a steady decline in consumption in the major European wine producing countries (Table II) (16). Due to the current strength of the US dollar, American wine is placed in a noncompetitive position in the world market. For example, a Bank of America study (14) showed that in 1979, when the dollar was weak, US wine exports grew almost 120% while imports declined 2%. In 1982, when the dollar was strong, imports grew 6% while exports dropped 11%. 0097-6156/86/0304-0145$06.00/0 © 1986 American Chemical Society

In Fungicide Chemistry; Green, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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Table I I .

Wine Consumption and P r o d u c t i o n i n V a r i o u s C o u n t r i e s .


Per Country France Italy Spain U.S.S.R. Argentina U.S.A. West Germany Portugal South A f r i c a Romania Yugoslavia Hungary Chile Greece Austria Bulgaria Australia Denmark Netherlands U.K.

C a p i t a Consumption ( L i t e r s ) 1982 1970 86 109 111 83 62 57 11 14 92 74 8 5 16 25 78 77 10 11 29 23 28 27 30 38 44 55 40 44 38 35 22 19 9 19 16 6 5 13 3 7

P r o d u c t i o n , 1982 (1,000 h e c t o l i t e r s ) 79.2 72.6 37.3 34.6 25.0 19.5 15.4 10.0 8.9 8.7 8.6 6.8 6.1 5.5 4.9 4.9 4.0

Adapted from Ref. 16.

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The wine g l u t i s a l s o p a r t i a l l y t o blame f o r the c u r r e n t huge r a i s i n s u r p l u s i n the US. As young p l a n t i n g s o f wine v a r i e t a l s have come i n t o b e a r i n g i n C a l i f o r n i a and wine s a l e s have slumped, w i n e r i e s have reduced p u r c h a s e s o f Thompson S e e d l e s s g r a p e s , f o r c i n g many o f the Thompson S e e d l e s s growers t o make r a i s i n s . F u r t h e r m o r e , the e n t r y o f Greece, P o r t u g a l and S p a i n i n t o the European Economic Community has eroded the p r i m a r y e x p o r t market f o r C a l i f o r n i a r a i s i n s , t h a t o f n o r t h e r n Europe. D e s p i t e the c u r r e n t b l e a k p i c t u r e f o r the wine i n d u s t r y , the r o m a n t i c a p p e a l o f grapes and wine making c o n t i n u e s t o l u r e p e o p l e i n t o the b u s i n e s s . F o r example from 1974 t o 1983, bonded w i n e r i e s i n the US i n c r e a s e d from 510 t o 1,114. S i n c e 1980, 292 new w i n e r i e s have been l i c e n s e d ( 1 5 ) . C u r r e n t l y t h e r e a r e bonded w i n e r i e s i n 41 s t a t e s ; the l a t e s t t o be added was i n the s t a t e o f Maine. A l t h o u g h the s h o r t - r a n g e o u t l o o k f o r the wine i n d u s t r y i s b l e a k , the l o n g - t e r m o u t l o o k i s b r i g h t a c c o r d i n g t o C a l i f o r n i a ' s Bank o f America ( 1 4 ) , w h i c h p r e d i c t s t h a t wine consumption w i l l c o n t i n u e t o expand i n the US a t an average a n n u a l r a t e o f 6%. Americans w i l l choose t o d r i n k more wine as the economy i m p r o v e s , the p o p u l a t i o n i n the 25- t o 45-year age group i n c r e a s e s , s t a t e s r e l a x r e g u l a t i o n o f a l c o h o l s a l e s , and as m a r k e t i n g campaigns persuade consumers t o d r i n k more wine. C u r r e n t l y , 10% o f the US p o p u l a t i o n consumes 66% o f a l l the wine u t i l i z e d i n the US. The bank p r e d i c t e d t h a t by 1990, wine p r o d u c t i o n w i l l need t o r i s e t o a l l o w f o r a p r o j e c t e d 45% i n c r e a s e i n sales. One b r i g h t s p o t i n the grape i n d u s t r y i s the t a b l e grape market. The per c a p i t a consumption o f t a b l e grapes i n the US i n c r e a s e d from 0.8 kg i n 1972 t o 2.6 kg i n 1982, r e s u l t i n g i n an a n n u a l i n c r e a s e o f



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20% p e r year ( 4 ) . The p e r c a p i t a consumption o f f r e s h f r u i t p l a c e s grapes f o u r t h b e h i n d bananas, a p p l e s , and oranges. Apparently, i n c r e a s e d consumer emphasis on n a t u r a l , n u t r i t i o n a l , and low c a l o r i e foods has had a f a v o r a b l e impact on t h e t a b l e grape market. In t h e US grape i n d u s t r y , C a l i f o r n i a i s f a r ahead o f o t h e r s t a t e s w i t h 92% o f the acreage and 93% o f t h e p r o d u c t i o n as o f 1982. S a l e s o f wine made i n s t a t e s o t h e r than C a l i f o r n i a account f o r l e s s than 10% o f t h e US wine s a l e s . F u r t h e r m o r e , C a l i f o r n i a produces almost 100% o f t h e r a i s i n s and n e a r l y t h a t amount o f t h e t a b l e grapes grown i n t h e US. New York S t a t e , f o r example, has a p p r o x i m a t e l y 17,000 h e c t a r e s o f grapes and i s a d i s t a n t second t o C a l i f o r n i a . The p o s i t i o n o f the US grape i n d u s t r y , p a r t i c u l a r l y i t s c u r r e n t economic d e p r e s s i o n , s h o u l d be kept i n p e r s p e c t i v e when r e c e n t d e v e l opments i n f u n g i c i d e s and t h e i r impact on t h e i n d u s t r y a r e d i s c u s s e d . F i r s t , i t would be u s e f u l t o r e v i e w t h e major f u n g a l d i s e a s e s o f grapes i n t h e US. These i n c l u d e f o u r f u n g a l d i s e a s e s i n e a s t e r n v i n e y a r d s , two o f w h i c h a l s o occur i n C a l i f o r n i a v i n e y a r d s . Powdery mildew ( U n c i n u l a n e c a t o r (Schw.) B u r r ) , o r Oidium as i t i s c a l l e d i n Europe, i s perhaps t h e most common f u n g a l d i s e a s e o f grapes w o r l d w i d e . T h i s fungus a t t a c k s a l l green p a r t s o f the v i n e , but i s most obvious on l e a v e s and f r u i t where i t appears as a w h i t e to g r a y i s h - w h i t e dusty c o v e r i n g . When l e a v e s become i n f e c t e d w h i l e u n f o l d i n g o r expanding, t h e i r development i s i n t e r r u p t e d and they become c u r l e d and d i s t o r t e d . When b e r r i e s a r e i n f e c t e d a t an e a r l y stage i n t h e i r development, they e i t h e r a b o r t o r t h e e p i d e r m i s o f t h e b e r r y s t o p s growing and, as the p u l p c o n t i n u e s t o expand, the b e r r y cracks. Diseased f r u i t account f o r c o n s i d e r a b l e crop l o s s and c r a c k e d f r u i t a r e s u s c e p t i b l e t o r o t organisms. Wine made from i n f e c t e d f r u i t has an o b j e c t i o n a b l e o f f - f l a v o r . S i n c e t h e fungus develops under a wide range o f h u m i d i t y and temperature c o n d i t i o n s and i s n o t f a v o r e d by r a i n f a l l , d i s t i n c t i n f e c t i o n p e r i o d s a r e d i f f i c u l t to identify. Downy mildew, caused by Plasmopara v i t i c o l a (Berk. & C u r t . ) B e r l . & de T o n i , o c c u r s o n l y i n c l i m a t e s t h a t a r e wet d u r i n g t h e growing season and t h e r e f o r e n o t i n C a l i f o r n i a . The fungus c a n i n f e c t a l l green p a r t s o f t h e v i n e t h a t have f u n c t i o n a l stomata. I n f e c t i o n s on l e a v e s f i r s t appear on t h e upper s u r f a c e s as o i l y s p o t s t h a t q u i c k l y develop i n t o y e l l o w i s h l e s i o n s , t h e u n d e r s i d e s o f w h i c h are covered w i t h w h i t e s p o r a n g i a t h a t spread the d i s e a s e . When young s h o o t s , p e t i o l e s , o r t e n d r i l s become i n f e c t e d , they become d i s t o r t e d and c u r l e d . Major crop l o s s can occur when f r u i t become d i s e a s e d . I n f e c t i o n p e r i o d s a r e i d e n t i f i e d on t h e b a s i s o f temperature and d u r a t i o n o f l e a f wetness. B l a c k r o t , caused by G u i g n a r d i a b i d w e l l i i ( E l l i s ) V i a l a and Ravaz, i s f a v o r e d by warm humid weather. R a i n f a l l i s n e c e s s a r y f o r d i s e a s e b u i l d u p and s p r e a d , e l i m i n a t i n g o c c u r r e n c e i n C a l i f o r n i a . B l a c k r o t i s c h a r a c t e r i z e d by brown c i r c u l a r l e s i o n s w h i c h may c o a l e s c e t o d e s t r o y l a r g e areas o f d i s e a s e d l e a v e s o r g i r d l e i n f e c t e d shoots. F r u i t i n f e c t i o n i s p a r t i c u l a r l y d e s t r u c t i v e and can r e s u l t i n complete crop l o s s . The fungus s u r v i v e s from one season t o t h e next i n mummified f r u i t . I n f e c t i o n p e r i o d s can be i d e n t i f i e d based on the o c c u r r e n c e o f r a i n f a l l and the r e l a t i o n s h i p between tempera t u r e and l e a f wetness d u r a t i o n .

American Chemical Society Library 1155 16th St., N.W. In Fungicide Chemistry; Green, M., et al.; Washington, D.C. 20036 ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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B o t r y t i s bunch r o t , caused by B o t r y t i s c i n e r e a P e r s . , o c c u r s throughout the v i t i c u l t u r a l w o r l d . D e s p i t e i t s d e s t r u c t i v e c a p a b i l i t i e s , B. c i n e r e a , a f f e c t i o n a t e l y c a l l e d the "noble r o t organism, i s the p r i z e d i n g r e d i e n t i n the A u s l e s e , B e e r e n a u s l e s e , and Trockenbeere n a u s l e s e wines o f Germany and the Sauternes wine o f F r a n c e . The fungus e n t e r s f r u i t through m e c h a n i c a l o r o t h e r i n j u r i e s , such as c r a c k i n g caused by powdery mildew, o r d i r e c t l y through the e p i d e r m i s of r i p e n i n g b e r r i e s . M o i s t u r e i n the form o f f o g o r dew and tempera t u r e s o f 15-25C are i d e a l f o r d i s e a s e development. The new f u n g i c i d e s b e i n g developed f o r use on grapes i n the US fall i n t o three categories: ergosterol biosynthesis inhibitors a c y l a l a n i n e s , and d i c a r b o x i m i d e s .


1 1

Ergosterol Biosynthesis Inhibitors

(EBI)

The EBI compounds have many i n t e r e s t i n g and unique c h a r a c t e r i s t i c s t h a t a l l o w much more f l e x i b i l i t y i n c o n t r o l programs than e v e r before. Some of these unique c h a r a c t e r i s t i c s are b e n e f i c i a l , but o t h e r s may be d e t r i m e n t a l (Table I I I ) .

Table I I I .

Impact o f New

F u n g i c i d e s on Grower Management P r a c t i c e s

Characteristics Effectiveness L o c a l systemic a c t i v i t y Vapor a c t i v i t y Lengthened s p r a y i n t e r v a l s Low r a t e s per h e c t a r e A f t e r - i n f e c t i o n , presymptom uses Cost o f program Narrow spectrum Potential for fungicide resistance Growth r e g u l a t o r e f f e c t s Nontarget e f f e c t s Flexibility I n t e g r a t e d P e s t Management programs

Beneficial X X X X X X X

Detrimental

X X X X X X X

X X X X

Effectiveness. S e v e r a l EBI compounds are h i g h l y powdery mildew and b l a c k r o t o f g r a p e s .

effective

against

L o c a l Systemic A c t i v i t y . The a c t i v e i n g r e d i e n t ( s ) e n t e r s the p l a n t t i s s u e and moves i n the xylem, where i t i s not s u b j e c t e d t o weather i n g from r a i n f a l l . T h i s i s a g r e a t b e n e f i t t o growers i n the e a s t e r n US where summer r a i n f a l l i s common, and t o C a l i f o r n i a growers where o c c a s i o n a l u n s e a s o n a l r a i n s may o c c u r . Problems a r i s e when growers assume these compounds a r e f u l l y s y s t e m i c and move i n the xylem and phloem, (as does the h e r b i c i d e g l y p h o s a t e ) . Growers must u n d e r s t a n d t h a t l o c a l s y s t e m i c a c t i v i t y w i l l not r e c t i f y poor s p r a y coverage. Furthermore, t h i s a c t i v i t y i n r e l a t i o n to p r o t e c t i o n of b e r r i e s i s unclear.



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Vapor A c t i v i t y . The vapor a c t i v i t y o f some EBI compounds i s s u f f i c i e n t t o c o n t r o l powdery mildew i n the greenhouse ( 1 3 ) . Grapevine c a n o p i e s develop a p a r t i a l l y e n c l o s e d environment and p r o v i d e a l o g i c a l model system i n t h e t r a n s i t i o n from greenhouse t o f i e l d experiments. D u r i n g the 1984 growing s e a s o n , p i e c e s o f c h e e s e c l o t h , p r e v i o u s l y soaked i n e t a c o n a z o l e (Vangard), CGA 71818 (Topas) o r t r i a d i m e f o n ( B a y l e t o n ) , were wrapped around the t r e l l i s w i r e i n s i d e the g r a p e v i n e canopy. E t a c o n a z o l e , CGA 71818 and t r i a d i m e f o n used i n t h i s way r e s u l t e d i n 55%, 87% and 71% c o n t r o l o f powdery mildew on cv. Delaware grape c l u s t e r s , r e s p e c t i v e l y ( P e a r s o n , unpublished data). C o n t r o l was l e s s s a t i s f a c t o r y on c u l t i v a r s (such as c v . R o s e t t e ) w i t h u p r i g h t , open growth h a b i t s . The advantages o f t h i s e x p e r i m e n t a l c o n t r o l method a r e : 1) o n l y one treatment per season may be needed, 2) improved c o n t r o l o f powdery mildew on c l u s t e r s i n s i d e the canopy may be o b t a i n e d , and 3) no r e s i d u e s are p r e s e n t on f r u i t at harvest. Lengthened Spray I n t e r v a l s . B a y l e t o n a p p l i e d on a 3-4 week schedule i n C a l i f o r n i a f o r c o n t r o l o f powdery mildew and 2-3 week schedule i n the e a s t e r n US r e s u l t e d i n s a v i n g s on f u e l , l a b o r , and equipment compared t o the s t a n d a r d s u l f u r a p p l i c a t i o n schedule o f 7-10 days (Table I V ) .

Table IV. Comparison of S u l f u r and B a y l e t o n Powdery Mildew C o n t r o l Programs i n the E a s t e r n U n i t e d S t a t e s and C a l i f o r n i a

Amount

product/hectare

Application interval

(days)

Number of a p p l i c a t i o n s / s e a s o n

Sulfur Calif. E a s t . US 4.5 k g 11.2 k g (WP) (dust) 7-10 7-10 8-12

6-8

B a y l e t o n 50W Calif. E a s t . US 280-420 140-210 gm gm 21-30 14-21 3-6

2-3

Low Rates per H e c t a r e . B a y l e t o n 50WP a p p l i e d a t 140-420 gm p e r h e c t a r e r e s u l t s i n no s p r a y e r n o z z l e p l u g g i n g , l i t t l e v i s i b l e r e s i d u e on t a b l e g r a p e s , s m a l l e r s t o r a g e space r e q u i r e m e n t s f o r the p r o d u c t , and l i g h t e r l o a d s f o r a i r a p p l i c a t o r s ; however, the grower must a l s o be c a r e f u l i n measuring the p r o p e r amount o f f u n g i c i d e because excess p r o d u c t can be e x p e n s i v e i n terms o f p h y t o t o x i c i t y and c o s t o f mate rial. F u r t h e r m o r e , the use o f B a y l e t o n , measured i n grams per hec t a r e , r e s u l t s i n p o t e n t i a l l y l e s s p o l l u t i o n o f the environment than when t r a d i t i o n a l f u n g i c i d e s , measured i n k i l o g r a m s per h e c t a r e , a r e used. A f t e r - i n f e c t i o n , Presymptom Uses. Because o f t h e a f t e r - i n f e c t i o n c o n t r o l c a p a b i l i t i e s of the EBI compounds, the e a s t e r n grower can f o r the f i r s t time c o n t r o l b l a c k r o t 72-96 h o u r s a f t e r i n f e c t i o n h a s t a k e n p l a c e . T h i s approach t o c o n t r o l l i n g b l a c k r o t can mean sub s t a n t i a l s a v i n g s i n the number o f a p p l i c a t i o n s , e s p e c i a l l y d u r i n g d r y o r m o d e r a t e l y d r y y e a r s . U n f o r t u n a t e l y , t h e r e are s e v e r a l drawbacks to t h i s approach. G e n e r a l l y , growers are not accustomed t o m o n i t o r -



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i n g r a i n events and temperature p r e c i s e l y enough t o determine i n f e c tion periods. A l s o , i t r e q u i r e s purchase and maintenance o f r e l a t i v e l y expensive weather i n s t r u m e n t s o r an i n - f i e l d microprocessorbased d i s e a s e p r e d i c t i o n system s i m i l a r t o t h e R e u t e r - S t o k e s a p p l e scab p r e d i c t o r . The EBI compounds do n o t appear t o be as good p r o t e c t a n t s as c o n v e n t i o n a l f u n g i c i d e s used f o r c o n t r o l o f b l a c k r o t . T h e r e f o r e , a tank mix o f B a y l e t o n and a c o n v e n t i o n a l f u n g i c i d e ( e . g . ferbam o r mancozeb) i s recommended. T h i s combination may be used as f o l l o w s : the grower w a i t s f o r an i n f e c t i o n p e r i o d , a p p l i e s t h e tank mix w i t h i n 72-96 hours o f i t s s t a r t and t h e n , assumes p r o t e c t i o n f o r 7-10 days. F o l l o w i n g the 7-10 day p e r i o d , t h e grower w a i t s f o r t h e next i n f e c t i o n p e r i o d , a t w h i c h time a n o t h e r spray i s a p p l i e d . On a 2-week spray s c h e d u l e , t h e grower would assume 10 days p r o t e c t i o n and 4 days a f t e r - i n f e c t i o n c o n t r o l w i t h t h e subsequent s p r a y . I n a wet y e a r , the a f t e r - i n f e c t i o n program may n o t save s p r a y s and the grower r i s k s not b e i n g a b l e t o g e t i n t o the v i n e y a r d i n time o r b e i n g a b l e t o cover h i s e n t i r e acreage w i t h i n t h e 72-96 hour l i m i t f o r a f t e r infection control. F u r t h e r m o r e , t h e spray a p p l i c a t i o n must be done c a r e f u l l y t o ensure complete coverage o f a l l i n f e c t i o n s i t e s , a v e r y d i f f i c u l t task w i t h present technology. Another problem w i t h t h i s approach i n v o l v e s e d u c a t i o n o f t h e grower r e g a r d i n g the terms a f t e r i n f e c t i o n and pre-symptom c o n t r o l . Some growers might w a i t u n t i l they see l e s i o n s b e f o r e they b e g i n s p r a y i n g . T h i s approach would n o t o n l y r e s u l t i n f a i l u r e t o c o n t r o l t h e d i s e a s e , b u t would i n c r e a s e t h e s i z e o f t h e f u n g a l p o p u l a t i o n t h a t i s exposed t o t h e c h e m i c a l , p o s s i b l y i n c r e a s i n g t h e chances o f s e l e c t i o n f o r r e s i s t a n t s t r a i n s o f the fungus. Cost o f F u n g i c i d e Program. As n o t e d above, t h e extended spray i n t e r v a l s f o r powdery mildew c o n t r o l can mean reduced a p p l i c a t i o n c o s t s f o r t h e season. I n 1983, many C a l i f o r n i a growers were on a s e a s o n l o n g B a y l e t o n program, b u t i n l i g h t o f 1984 economic c o n d i t i o n s many growers r e t u r n e d t o s u l f u r d u s t i n g s o r used B a y l e t o n and s u l f u r alternately. S i n c e most s m a l l growers i n C a l i f o r n i a own s u l f u r d u s t i n g machines, b u t few own v i n e y a r d s p r a y e r s , B a y l e t o n must be a p p l i e d by custom a p p l i c a t o r s , t h e r e b y a d d i n g c o n s i d e r a b l e expense t o each a p p l i c a t i o n . Narrow Spectrum. Most c o n v e n t i o n a l f u n g i c i d e s used on grapes p r o t e c t a g a i n s t a t l e a s t two d i s e a s e s , and o c c a s i o n a l l y a g a i n s t t h r e e o r f o u r diseases. However, t h e EBI compounds a r e g e n e r a l l y l i m i t e d t o c o n t r o l o f powdery mildew and b l a c k r o t . Because o f t h i s narrow spectrum o f a c t i v i t y , t h e EBI compounds must be tank-mixed w i t h conventional fungicides f o r c o n t r o l of other diseases, e s p e c i a l l y downy mildew i n t h e e a s t e r n U.S. Furthermore, s i n c e conventional f u n g i c i d e s r e q u i r e s h o r t spray i n t e r v a l s (7-10 days) t o be e f f e c t i v e , growers a r e n o t a b l e t o take f u l l advantage o f t h e extended i n t e r v a l c a p a b i l i t i e s (14-21 days) o f t h e EBI compounds. They would s p r a y on a 7-10 day s c h e d u l e , and add B a y l e t o n t o every o t h e r s p r a y . P o t e n t i a l f o r Resistance. R e s i s t a n c e appears t o be the major p o t e n t i a l o b s t a c l e t o o p t i m a l use o f many o f the new f u n g i c i d e s . I t i s c l e a r from t h e e x p e r i e n c e s w i t h t r i a z o l e r e s i s t a n c e i n powdery mildew



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of b a r l e y (3) and c u c u r b i t s (10) t h a t r e s i s t a n c e must a l s o be con s i d e r e d a p o s s i b i l i t y w i t h t h e grape powdery mildew fungus. There f o r e , s t r a t e g i e s f o r d e l a y i n g r e s i s t a n c e must be implemented from t h e o u t s e t o f t h e i r commercial usage. A l t h o u g h t h e b e s t approach t o a v o i d i n g r e s i s t a n c e s t i l l e l u d e s r e s e a r c h e r s , growers i n New Y o r k , where B a y l e t o n has been used c o m m e r c i a l l y s i n c e 1980, a r e warned n o t to use t h i s m a t e r i a l on an e x c l u s i v e , s e a s o n - l o n g program. We recommend t h a t they a l t e r n a t e o t h e r m i l d e w c i d e s w i t h B a y l e t o n o r use tank m i x t u r e s a t f u l l r a t e s . F u r t h e r m o r e , i t i s n o t recommended t h a t they u s e these f u n g i c i d e s a l o n e under h i g h d i s e a s e p r e s s u r e a s eradicants. U n f o r t u n a t e l y , t h e t h r e a t o f r e s i s t a n c e may c o u n t e r b a l a n c e t h e d e s i r a b l e a t t r i b u t e s o f t h e EBI compounds, n o t a b l y t h e i r extended i n t e r v a l e f f i c a c y and e r a d i c a n t a c t i v i t y . Growth R e g u l a t o r E f f e c t s . Some o f the EBI compounds have i n t e r e s t i n g p l a n t growth r e g u l a t o r (PGR) e f f e c t s when used a t e x c e s s i v e r a t e s , a p p a r e n t l y due t o an i n h i b i t i o n o f g i b b e r e l l i c a c i d s y n t h e s i s (12) r e s u l t i n g i n s h o r t e n e d i n t e r n o d e s and s m a l l , t h i c k , d a r k green l e a v e s ( F i g u r e 1 ) . A common problem i n g r a p e v i n e canopy management i s adequate l i g h t p e n e t r a t i o n t o t h e b a s a l nodes o f c u r r e n t season's shoots which w i l l p r o v i d e n e x t y e a r ' s c r o p . There i s a d i r e c t r e l a t i o n s h i p between y i e l d from these b a s a l nodes and l i g h t exposure d u r i n g t h e i r f o r m a t i o n t h e p r e v i o u s y e a r . T h i s i s n o t o n l y a problem i n l o w l i g h t a r e a s such a s New Y o r k , b u t a l s o i n h i g h l i g h t a r e a s such as C a l i f o r n i a where l a r g e canopies shade t h e f r u i t i n g wood. Perhaps t h e PGR e f f e c t s o f EBI compounds on grape c o u l d be b e n e f i c i a l i n t h a t s h o r t e r i n t e r n o d e s and s t i f f e r shoots w i t h more u p r i g h t growth h a b i t would a l l o w b e t t e r l e a f exposure t o s u n l i g h t and i n crease node f r u i t f u l n e s s . T h i s growth h a b i t combined w i t h s m a l l e r l e a v e s would a l s o a l l o w b e t t e r a i r c i r c u l a t i o n , b e t t e r spray p e n e t r a t i o n and s h o r t e r w e t t i n g p e r i o d s r e s u l t i n g i n l e s s d i s e a s e d e v e l o p ment. U n f o r t u n a t e l y , t h e PGR e f f e c t s might a l s o r e s u l t i n more compact c l u s t e r s w i t h an i n c r e a s e d p o t e n t i a l f o r bunch r o t problems. N o n t a r g e t E f f e c t s . The s h i f t from s u l f u r d u s t i n g t o B a y l e t o n s p r a y ing i n C a l i f o r n i a appears t o be a s s o c i a t e d w i t h an i n c r e a s e i n p r e d a t o r y m i t e p o p u l a t i o n s , w h i c h were uncommon i n v i n e y a r d s on s u l f u r programs ( p e r s o n a l communication). On t h e o t h e r hand, p e s t i f e r o u s Erineum m i t e s and t h r i p s appear t o i n c r e a s e where s u l f u r usage has been reduced, a l t h o u g h a c l e a r cause and e f f e c t r e l a t i o n s h i p has not been e s t a b l i s h e d . Flexibility. The i n t r o d u c t i o n o f B a y l e t o n f o r c o n t r o l o f powdery mildew i n C a l i f o r n i a v i n e y a r d s has g i v e n growers f l e x i b i l i t y i n t h e i r management programs t h a t s u l f u r d u s t i n g d i d n o t a l l o w . When growers use B a y l e t o n , they need n o t program t h e i r i r r i g a t i o n s c h e d u l e s a s c a r e f u l l y as they d i d when weekly s u l f u r a p p l i c a t i o n s were r e q u i r e d . Many C a l i f o r n i a grape growers a l s o have stone f r u i t s t h a t a r e h a r v e s t e d i n May. A l t h o u g h May i s a c r i t i c a l time f o r powdery mildew development i n v i n e y a r d s , extended spray i n t e r v a l s u s i n g B a y l e t o n g i v e t h e grower more time t o devote t o t h e May h a r v e s t o f t r e e f r u i t . S u l f u r i s p h y t o t o x i c a t temperatures above 32C r e q u i r i n g t h a t growers keep a c l o s e watch on t h e weather a t t h e time s u l f u r i s a p p l i e d ;



FUNGICIDE CHEMISTRY

F i g u r e 1. P l a n t growth r e g u l a t o r e f f e c t s o f an EBI compound; note s t u n t e d s h o o t s w i t h s m a l l , cupped, dark green l e a v e s .


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however, injury.

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153


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I n t e g r a t e d P e s t Management (IPM) Programs. The a f t e r - i n f e c t i o n a c t i v i t y o f the EBI compounds a g a i n s t b l a c k r o t o f grape g i v e s growers a c h e m i c a l t o o l analogous t o those now a v a i l a b l e t o e n t o m o l o g i s t s who, based upon counts of i n s e c t or m i t e p o p u l a t i o n s , can recommend s p r a y s when needed. P r e v i o u s l y , without s i m i l a r chemical tools, plant p a t h o l o g i s t s have had t o r e l y on p r o t e c t a n t f u n g i c i d e s t h a t d i d not p e r m i t f u l l b e n e f i t o f IPM m o n i t o r i n g programs. By c a r e f u l m o n i t o r i n g o f i n f e c t i o n p e r i o d s i t may now be p o s s i b l e t o save sprays when not needed o r t o a p p l y more s p r a y s under severe d i s e a s e p r e s s u r e , p r e v e n t i n g crop l o s s . Acylalanines Three a c y l a l a n i n e compounds, m e t a l a x y l ( R i d o m i l ) , cyprofuram ( V i n i c u r ) and b e n a l a x y l ( G a l b e n ) , have been t e s t e d e x t e n s i v e l y f o r c o n t r o l of grape downy mildew i n New Y o r k . None o f these compounds a r e c u r r e n t l y r e g i s t e r e d i n the US. They are narrow spectrum, but h i g h l y e f f e c t i v e compared t o s t a n d a r d p r o t e c t a n t s such as c a p t a n , f o l p e t o r mancozeb. They have l o c a l s y s t e m i c a c t i v i t y and p o s s e s s p r o t e c t a n t and a n t i s p o r u l a n t , as w e l l as a f t e r - i n f e c t i o n a c t i v i t y . Similar to the EBI compounds, the a f t e r - i n f e c t i o n c a p a b i l i t i e s and t h e i r a c t i v i t y o v e r extended i n t e r v a l s (14-21 days) make t h e a c y l a l a n i n e s d e s i r a b l e t o o l s f o r IPM programs. U n f o r t u n a t e l y , r e s i s t a n c e t o m e t a l a x y l by the grape downy mildew fungus r e s u l t e d i n crop l o s s i n France d u r i n g 1980 and 1981 ( 2 ) . R e s i s t a n c e developed i n s p i t e o f the f a c t t h a t R i d o m i l had been s o l d to grape growers a s a package mix w i t h f o l p e t . S i n c e a c t i v i t y over extended i n t e r v a l s i s one o f the d e s i r a b l e c h a r a c t e r i s t i c s o f R i d o m i l , i t was used a s a package mix on a 14-day s c h e d u l e . The a c t i v i t y of f o l p e t , e s p e c i a l l y under h i g h d i s e a s e p r e s s u r e , l a s t s o n l y 7-10 days. T h e r e f o r e , R i d o m i l remained u n a i d e d d u r i n g the l a t t e r h a l f o f the 2-week i n t e r v a l . A l l o f the a c y l a l a n i n e s are b e i n g developed as package mixes ( e i t h e r w i t h f o l p e t o r mancozeb) f o r use on grapes i n the US. I f s p r a y i n t e r v a l s s h o r t e r than 14 days are recommended, i t i s u n l i k e l y growers w i l l be w i l l i n g t o pay f o r the added c o s t o f the a c y l a l a n i n e when they can get good commercial c o n t r o l o f downy mildew w i t h s t a n d a r d p r o t e c t a n t f u n g i c i d e s a p p l i e d alone on a 7-10 day schedule. An a d d i t i o n a l problem w i t h most package mixes i s the low amount of s t a n d a r d p r o t e c t a n t f u n g i c i d e added t o the mix. Not o n l y are the r a t e s b o r d e r l i n e t o c o n t r o l downy mildew i f r e s i s t a n c e d e v e l o p s , but they are inadequate f o r b r o a d e r d i s e a s e c o n t r o l . For example, b l a c k r o t c o n t r o l w i t h R i d o m i l MZ58 r e q u i r e s t h a t a d d i t i o n a l mancozeb o r a n o t h e r p r o t e c t a n t , such as ferbam, be added t o the t a n k mix. Fur thermore, a 14-day schedule t o c o n t r o l b l a c k r o t e a r l y i n the growing season may be inadequate and a grower would need t o supplement t h e R i d o m i l MZ58 program w i t h a d d i t i o n a l b l a c k r o t s p r a y s . An a f t e r - i n f e c t i o n approach to c o n t r o l l i n g downy mildew c o u l d be d e v e l o p e d , p r o v i d i n g growers m o n i t o r downy mildew i n f e c t i o n p e r i o d s u s i n g the same i n s t r u m e n t a t i o n d i s c u s s e d under b l a c k r o t . A c y l a l a n i n e tank-mixed w i t h f o l p e t o r mancozeb would be a p p l i e d a f t e r a


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154

downy mildew i n f e c t i o n p e r i o d was i d e n t i f i e d . No f u r t h e r s p r a y s would be a p p l i e d f o r 14 days (assume adequate p r o t e c t i o n ) a f t e r w h i c h a s p r a y would be a p p l i e d f o l l o w i n g the next i n f e c t i o n p e r i o d . I n d r y seasons, t h i s approach would undoubtedly reduce the number o f s p r a y s , but perhaps not i n wet seasons. U n f o r t u n a t e l y , t h i s program i s v u l n e r a b l e t o the s e l e c t i o n o f a c y l a l a n i n e r e s i s t a n t s t r a i n s i f growers become c a r e l e s s and w a i t u n t i l they see s p o r u l a t i n g l e s i o n s .


Dicarboximides The t h i r d group of new f u n g i c i d e s t o be t e s t e d on grapes i n the US i s the d i c a r b o x i m i d e group. V i n c l o z o l i n ( R o n i l a n ) and i p r o d i o n e (Rovr a l ) are the members of t h i s group t h a t have been e x t e n s i v e l y t e s t e d f o r c o n t r o l o f B o t r y t i s bunch r o t . Our e x p e r i e n c e w i t h b e n z i m i d a z o l e r e s i s t a n c e i n the powdery mildew fungus (8) and B o t r y t i s (7) » i n a d d i t i o n t o r e p o r t s from Europe ( 5 , 11) and Canada (6) c o n c e r n i n g r e s i s t a n c e t o the d i c a r b o x i mides by B o t r y t i s , has i n f l u e n c e d our recommendations r e g a r d i n g the use o f d i c a r b o x i m i d e s on grapes i n New York. Our c u r r e n t recommenda t i o n i s t o a p p l y two s p r a y s : 1) when the f i r s t b e r r i e s r e a c h 5% sugar and 2) two weeks a f t e r the f i r s t a p p l i c a t i o n . S e v e r a l y e a r s of t e s t i n g i n New Y o r k (9) i n d i c a t e d t h a t a d d i t i o n a l a p p l i c a t i o n s o f the d i c a r b o x i m i d e s a t bloom and b u n c h - c l o s i n g d i d not improve c o n t r o l of B o t r y t i s bunch r o t a t h a r v e s t . The r a t i o n a l e f o r t h i s program i s t o keep the c o s t o f these e x p e n s i v e a p p l i c a t i o n s as low as p o s s i b l e and to reduce the s e l e c t i o n p r e s s u r e a g a i n s t the p o p u l a t i o n by a p p l y i n g as few s p r a y s as p o s s i b l e ( h o p e f u l l y d e l a y i n g the development of r e s i s t a n t s t r a i n s ) , y e t u s i n g them a t the most o p t i m a l t i m e . Summary The s h o r t - t e r m o u t l o o k f o r grape growers i s r a t h e r dim. Current economic p r e s s u r e s are f o r c i n g grape growers a c r o s s the n a t i o n t o c u t corners. Perhaps the most s h o r t s i g h t e d c o s t c u t t i n g s t e p i s the r e d u c t i o n i n use of f u n g i c i d e s . I n New Y o r k d u r i n g 1984, f o r exam ple, many growers reduced the number of s p r a y s by 50%, and some a p p l i e d o n l y one o r two s p r a y s . I n C a l i f o r n i a , many growers who were on f u l l B a y l e t o n s c h e d u l e s i n 1983 went back t o s u l f u r o r used o n l y one o r two B a y l e t o n s p r a y s i n 1984. Reduced s p r a y i n p u t s mean an even g r e a t e r t e m p t a t i o n by growers to w a i t u n t i l they see d i s e a s e and then t o use the new f u n g i c i d e s as e r a d i c a n t s under heavy d i s e a s e p r e s s u r e . We must be concerned about t h i s type of usage because o f the t h r e a t of r e s i s t a n c e . O b v i o u s l y f o r the s h o r t term, growers w i l l c o n t i n u e t o reduce i n p u t s i n an e f f o r t to survive economically. The c h a l l e n g e t o e x t e n s i o n and r e s e a r c h p l a n t p a t h o l o g i s t s i s t o develop f u n g i c i d e use s t r a t e g i e s t h a t a v o i d r e s i s t a n c e y e t are r e s p o n s i v e t o g r o w e r s economic con straints. O b v i o u s l y , the c h a l l e n g e t o the c h e m i c a l i n d u s t r y i s t o develop new f u n g i c i d e s w i t h a l l the g r e a t a t t r i b u t e s of the EBI compounds, but w i t h o u t the t h r e a t o f r e s i s t a n c e . 1


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Literature Cited 1. 2.


3.

4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

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Fungicide Chemistry

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