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9 Tree Fruit Crops in the Eastern United States Potential Role for New Fungicides
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.ch009
Alan L. Jones Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824
Fungicides are essential for the production of high quality deciduous tree fruit crops in the humid eastern United States. On apples, ten to fifteen applications of one to three fungicides are used each season. Although the frequent application of fungicides is costly, dependence upon chemicals for the production of disease-free fruit crops will continue for the foreseeable future. A number of experimental fungicides that have the potential for easing the complexity of disease control on tree fruit crops in the east are currently being evaluated. Most of these fungicides are either ergosterol biosynthesis inhibiting (EBI) compounds or members of the dicarboximide group of fungicides. Research has been con ducted at several experiment stations throughout the eastern United States to determine the effectiveness of these fungicides against the spectrum of diseases in the various regions and to define application rates. In addition, specific studies have been conducted to estab lish the practical mode of action of these compounds for controlling the most important diseases. Activity Against Apple Scab Because the management of apple diseases revolve around control strategies for apple scab (Venturia inaequalis), specific studies have been conducted on the capabilities and limitations of the EBI fungicides to control this disease. The EBI fungicides inhibit the spore infection process at a later stage than earlier fungicides. Fungicides such as captan, metiram and sulfur inhibit spore germina tion while the benzimidazole group of fungicides inhibit appressoria formation but not spore germination. With the EBI fungicides, spores germinate, form appressoria, and penetrate the cuticle of the host before they are killed. This is exemplified in an experiment where an apple leaf was treated with fenarimol 12 hours before inoculation with conidia of Venturia inaequalis and then incubated in a moist chamber for 23 hours after inoculation (Figure 1). Although the spore produced a germ tube, appressorium, and penetrated the cuticle within 24 hours after inoculation, no scab symptoms developed on 0097-6156/86/0304-0135$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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t r e a t e d p l a n t s a f t e r two weeks, w h i l e unsprayed p l a n t s were s e v e r e l y infected. C o n i d i a on p l a n t s t r e a t e d w i t h b i t e r t a n o l and e t a c o n a z o l e r e a c t e d s i m i l a r l y , and no d i s e a s e symptoms were observed a f t e r two weeks. Greenhouse s t u d i e s i n d i c a t e t h a t EBI f u n g i c i d e s p r o v i d e about one t o f o u r days of p r o t e c t i o n compared to f i v e to seven days f o r c o n v e n t i o n a l p r o t e c t a n t s such as c a p t a n , metiram, and mancozeb (20, 23). The degree of p r o t e c t i o n by the EBI f u n g i c i d e s depends on dosage, on the s p e c i f i c f u n g i c i d e u s e d , on the weather c o n d i t i o n s ( p a r t i c u l a r l y r a i n ) , and on the r a t e of p l a n t growth a f t e r the a p p l i c a t i o n . M i x t u r e s o f EBI f u n g i c i d e s w i t h c o n v e n t i o n a l f u n g i c i d e s are c u r r e n t l y b e i n g e v a l u a t e d as a means o f i m p r o v i n g the p r o t e c t i v e a c t i o n and spectrum o f a c t i v i t y o f the EBI f u n g i c i d e s . The EBI f u n g i c i d e s have o u t s t a n d i n g after-infection control a c t i v i t y compared t o c o n v e n t i o n a l f u n g i c i d e s . The l i m i t of a f t e r i n f e c t i o n c o n t r o l f o r a p a r t i c u l a r f u n g i c i d e i s d e f i n e d as the number of hours from the s t a r t o f a wet p e r i o d t h a t a s p r a y can be a p p l i e d and s t i l l p r e v e n t development of v i s i b l e symptoms. Conventional f u n g i c i d e s p e r f o r m b e s t when a p p l i e d i n a n t i c i p a t i o n of i n f e c t i o n periods. T h e i r e f f e c t i v e n e s s i s v e r y l i m i t e d when they are a p p l i e d a f t e r c o n d i t i o n s are f a v o r a b l e f o r i n f e c t i o n . F u n g i c i d e s such as c a p t a n , metiram, and mancozeb are e f f e c t i v e f o r 18 t o 24 hours a f t e r the i n i t i a t i o n o f f a v o r a b l e c o n d i t i o n s f o r i n f e c t i o n w h i l e the EBI f u n g i c i d e s are e f f e c t i v e f o r 72-96 hours (1^,19,20,23). The s p e c i f i c d u r a t i o n of a f t e r - i n f e c t i o n a c t i v i t y i s p r o p o r t i o n a l t o the amount of a c t i v e i n g r e d i e n t t h a t i s a p p l i e d (20) and, i n the s p e c i f i c case of b i t e r t a n o l , i t can be improved by a d j u v a n t a d d i t i o n ( 1 9 ) . When the EBI f u n g i c i d e s are a p p l i e d l a t e r than 72-96 hours a f t e r the b e g i n n i n g of the scab i n f e c t i o n p e r i o d but b e f o r e symptoms are v i s i b l e , c h l o r o t i c s p o t s o r f l e c k s w i t h few or no c o n i d i a are p r o duced i n p l a c e of t y p i c a l s p o r u l a t i n g l e s i o n s ( F i g u r e 2 ) . This i s r e f e r r e d to as presymptom c o n t r o l by S z k o l n i k (23) and i t i s a form o f p o s t - i n f e c t i o n o r c u r a t i v e a c t i o n . Dodine and benomyl are exam p l e s of f u n g i c i d e s w i t h presymptom a c t i v i t y . Presymptom a c t i v i t y becomes more o b v i o u s as the time o f a p p l i c a t i o n i n c r e a s e s beyond the 72-96 hour a f t e r - i n f e c t i o n p e r i o d . In greenhouse t r i a l s , s p r a y s of b i t e r t a n o l , etaconazole, f e n a r i m o l and t r i f o r i n e reduced c o n i d i a l p r o d u c t i o n 85 t o 99% when a p p l i e d f i v e days a f t e r i n o c u l a t i o n ( 2 0 ) . Presymptom a c t i v i t y has a l s o been observed i n f i e l d t r i a l s . If s p r a y s are d e l a y e d l a t e i n t o the i n c u b a t i o n p e r i o d , presymptom c o n t r o l can be i n c r e a s e d by a p p l y i n g a second s p r a y seven days a f t e r the f i r s t a p p l i c a t i o n ( 1 2 ) . There are i n d i c a t i o n s t h a t c h l o r o t i c l e s i o n s w i l l not produce c o n i d i a a f t e r the use of EBI f u n g i c i d e s i s discontinued (6). However, the v i a b i l i t y of the fungus i n t h e s e l e s i o n s i s i n f l u e n c e d by m o i s t u r e , dosage of f u n g i c i d e , t i m i n g , and other f a c t o r s . I n one t r i a l , the scab fungus was i s o l a t e d from c h l o r o t i c l e s i o n s i n leaves (12). Because of t h e i r a f t e r - i n f e c t i o n and a n t i s p o r u l a t i o n a c t i v i t y a g a i n s t s c a b , the EBI f u n g i c i d e s are e s p e c i a l l y s u i t a b l e f o r use i n p r e d i c t i v e d i s e a s e c o n t r o l programs. P r e d i c t i v e d i s e a s e c o n t r o l i s an i m p o r t a n t p a r t o f i n t e g r a t e d p e s t management programs on a p p l e s . A p r e d i c t i v e system means c o n t r o l measures are a p p l i e d a f t e r the onset o f i n f e c t i o n . S m a l l s p e c i a l purpose computers w i t h field
In Fungicide Chemistry; Green, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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.ch009
9. J O N E S
Fungicides on Tree Fruit Crops
F i g u r e 1. A germinated c o n i d i u m o f V e n t u r i a i n a e q u a l i s on a a p p l e l e a f t r e a t e d w i t h f e n a r i m o l 12 hours b e f o r e i n o c u l a t i o n and i n c u b a t e d i n a m o i s t chamber f o r 23 hours a f t e r i n o c u l a t i o n . Bar * 1 m i c r o n .
F i g u r e 2. D e n s e l y s p o r u l a t i n g l e s i o n s o f a p p l e scab on an unsprayed l e a f ( l e f t ) compared w i t h c h l o r o t i c n o n s p o r u l a t i n g l e s i o n s on a l e a f sprayed w i t h e t a c o n a z o l e ( r i g h t ) .
In Fungicide Chemistry; Green, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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s e n s o r s can be u t i l i z e d as an a i d i n i d e n t i f y i n g i n f e c t i o n p e r i o d s and t i m i n g f u n g i c i d e s p r a y s ( 1 1 ) . Because they are l i m i t e d i n p r o t e c t i v e a c t i o n , the most e f f i c i e n t use o f the EBI f u n g i c i d e s i s i n c o n j u n c t i o n w i t h a p r e d i c t i v e system. R e c e n t l y , the v a l u e of a microcomputer t o enhance the e f f i c i e n c y of b i t e r t a n o l , f e n a r i m o l , e t a c o n a z o l e , and t r i f o r i n e was demonstrated under f i e l d c o n d i t i o n s (2). T r i a l s w i t h EBI f u n g i c i d e s used as post-symptom t r e a t m e n t s i n d i c a t e they are l e s s e f f e c t i v e than dodine and benomyl f o r s t o p p i n g the development of e s t a b l i s h e d l e s i o n s . I n greenhouse t r i a l s i n v o l v i n g the removal o f c o n i d i a from s p o r u l a t i n g l e s i o n s and s p r a y i n g the l e s i o n s i m m e d i a t e l y w i t h EBI f u n g i c i d e s , numbers of c o n i d i a were not reduced a f t e r t h r e e days ( 2 3 ) . However, i n f i e l d t r i a l s i n v o l v i n g two s p r a y s of b i t e r t a n o l or e t a c o n a z o l e a p p l i e d s e v e n - d a y s - a p a r t s t a r t i n g about two days a f t e r symptoms were v i s i b l e , immature s p o r e s predominated i n the l e s i o n s seven days l a t e r ( 1 2 ) . The immature s p o r e s were d i f f i c u l t to remove from the l e s i o n s and those t h a t were removed f a i l e d t o g e r m i n a t e . F a i l u r e t o o b t a i n a r e d u c t i o n i n number o f c o n i d i a i n greenhouse t r i a l s , but not i n f i e l d t r i a l s i n v o l v i n g m u l t i p l e s p r a y s , may be r e l a t e d to the d u r a t i o n of time needed to d e p l e t e the r e s e r v e s o f e r g o s t e r o l w i t h i n the fungus. On fruit, post-symptom c o n t r o l was e x h i b i t e d by a " h e a l i n g " of the scab l e s i o n s (12). The p o s t - i n f e c t i o n p r o p e r t i e s of these f u n g i c i d e s suggest they are s y s t e m i c i n a p p l e f o l i a g e . L i m i t e d s t u d i e s w i t h e t a c o n a z o l e and f e n a p a n i l i n d i c a t e t h e r e i s f o l i a r uptake or a t l e a s t a b i n d i n g of the f u n g i c i d e to the c u t i c l e ( 1 3 ) . A d d i t i o n a l r e s e a r c h on the r a t e of uptake and p e r s i s t a n c e o f t h e s e compounds may h e l p t o r e s o l v e the p r a c t i c a l q u e s t i o n of how l o n g s p r a y d e p o s i t s must dry b e f o r e they r e a c h maximum e f f e c t i v e n e s s . F i e l d o b s e r v a t i o n s suggest t h a t a r a i n d u r i n g or i m m e d i a t e l y a f t e r the a p p l i c a t i o n of an EBI fungicide reduces i t s e f f e c t i v e n e s s . The importance of the EBI f u n g i c i d e s i s i n c r e a s i n g because of the w i d e s p r e a d development of r e s i s t a n c e i n the scab fungus to dodine and/or the b e n z i m i d a z o l e f u n g i c i d e s i n the e a s t e r n U n i t e d States (A,8,25). The use of these o l d e r f u n g i c i d e s have been d i s c o n t i n u e d i n some a r e a s , f o r c i n g growers t o use l e s s e f f e c t i v e f u n g i c i d e s and more t o t a l c h e m i c a l per h e c t a r e than was p r e v i o u s l y r e q u i r e d . The p o t e n t i a l f o r development o f r e s i s t a n c e i n the scab fungus t o the EBI f u n g i c i d e s may be of g r e a t e s t c o n c e r n i n the n o r t h e r n s t a t e s . In t h i s r e g i o n the spectrum of d i s e a s e s c o n t r o l l e d by the EBI f u n g i c i d e s i s s u f f i c i e n t t o p e r m i t season l o n g programs. In s o u t h e r n a r e a s , o t h e r f u n g i c i d e s must be mixed w i t h the EBI f u n g i c i d e s and this s h o u l d h e l p d e l a y r e s i s t a n c e problems. A c t i v i t y A g a i n s t Other Apple D i s e a s e s A l a r g e number o f f u n g a l d i s e a s e s i n a d d i t i o n t o scab a f f e c t a p p l e s i n the m i d - A t l a n t i c and s o u t h e r n s t a t e s . In areas w i t h i n these s t a t e s , the f o l l o w i n g d i s e a s e s must be c o n t r o l l e d : cedar a p p l e r u s t (Gymnosporangium j u n i p e r i - v i r g i n i a n a e ) , q u i n c e r u s t (G. c l a v i p e s ) , powdery mildew (Podosphaera l e u c o t r i c h a ) , b l a c k r o t (Physalospora o b t u s a ) , bot or w h i t e r o t ( B o t r y o s p h a e r i a dothidea), b i t t e r rot
In Fungicide Chemistry; Green, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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9.
JONES
Fungicides on Tree Fruit Crops
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( G l o m e r e l l a c i n g u l a t a ) , s o o t y b l o t c h (Gloeodes pomigena), f l y speck ( M i c r o t h y r i e l l a r u b i ) and Brooks s p o t ( M y c o s p h a e r e l l a pomi). The EBI f u n g i c i d e s have shown o u t s t a n d i n g a c t i v i t y a g a i n s t a p p l e powdery mildew everywhere i n t h e e a s t e r n U n i t e d S t a t e s . Mildew c o n t r o l was improved p a r t i c u l a r l y i n the m i d - A t l a n t i c r e g i o n ( 5 , 2 9 ) , where the d i s e a s e i s more severe than i n the n o r t h e a s t e r n and n o r t h central states. The EBI f u n g i c i d e s d i f f e r from o l d e r m i l d e w c i d e s l i k e s u l f u r , d i n o c a p , and benomyl by i n h i b i t i n g s p o r u l a t i o n and m y c e l i a l growth i n e s t a b l i s h e d l e s i o n s ( 5 ) . T h e i r h i g h l e v e l o f c o n t r o l e f f i c i e n c y i s p r o b a b l y due t o a r e d u c t i o n i n b o t h p r i m a r y inoculum and secondary s p r e a d . As w i t h d i n o c a p ( 2 9 ) , the EBI f u n g i c i d e s may be more e f f e c t i v e when a p p l i e d on a 5- t o 7-day i n t e r v a l a t low r a t e s r a t h e r than on a 10- t o 14-day i n t e r v a l a t h i g h r a t e s . S u b s t a n t i a l c o n t r o l o f powdery mildew has a l s o been o b t a i n e d i n greenhouse t r i a l s through vapor a c t i o n w i t h t r i a d i m e f o n and e t a c o n a z o l e ( 2 3 ) . The r o l e o f vapor a c t i o n i n c o n t r o l l i n g mildew i n o r chards remains u n c l e a r . Cedar apple r u s t i s a c r i t i c a l problem where s u s c e p t i b l e a p p l e c u l t i v a r s are grown i n p r o x i m i t y t o cedar t r e e s . The d i s e a s e i s a problem i n p a r t o f New Y o r k s t a t e and most o f the s o u t h e r n and n o r t h central states. Use o f p r o t e c t a n t f u n g i c i d e s has been t h e o n l y method a v a i l a b l e t o c o n t r o l i n f e c t i o n i n a r e a s where e r a d i c a t i o n o f r e d cedar t r e e s i s i m p r a c t i c a l . The EBI f u n g i c i d e s , except p r o c h l o r a z , have shown b e t t e r a c t i v i t y a g a i n s t cedar a p p l e r u s t than s t a n dard p r o t e c t a n t compounds ( 2 7 ) . Dosages needed t o c o n t r o l r u s t a r e g e n e r a l l y lower than those used t o c o n t r o l scab and mildew ( 2 7 ) . The c a p a b i l i t y o f the EBI f u n g i c i d e s t o g i v e p o s t - i n f e c t i o n c o n t r o l o f cedar a p p l e r u s t s h o u l d r e s u l t i n t h e development o f new c o n t r o l s t r a t e g i e s f o r t h i s d i s e a s e (15,22). Although the EBI f u n g i c i d e s a r e o f greatest b e n e f i t f o r the c o n t r o l o f s c a b , r u s t , and powdery mildew e a r l y i n the season, t h e i r b e n e f i t i n t h e c o v e r s p r a y p e r i o d w i l l d i f f e r between p r o d u c t i o n areas. I n the n o r t h e r n U n i t e d S t a t e s where a p p l e scab and powdery mildew are the main d i s e a s e s t o be c o n t r o l l e d , the E B I f u n g i c i d e s w i l l be o f b e n e f i t from the b e g i n n i n g o f t h e growing season u n t i l harvest. However, i n t h e s o u t h e r n , m i d - A t l a n t i c , and s o u t h e a s t e r n s t a t e s , a complex o f summer f r u i t r o t d i s e a s e s i s common. Because the EBI f u n g i c i d e s are weak a g a i n s t t h i s group o f d i s e a s e s , they w i l l need t o be mixed w i t h more e f f e c t i v e f u n g i c i d e s such as mancozeb o r captan ( 2 7 ) . B i t e r t a n o l s h o u l d f i t b e t t e r i n t o mid- t o l a t e - s e a s o n programs than t h e o t h e r E B I f u n g i c i d e s because o f i t s s t r o n g e r a c t i v i t y a g a i n s t s o o t y b l o t c h and f l y speck ( 2 8 ) . New
F u n g i c i d e s f o r Stone F r u i t D i s e a s e C o n t r o l
F u n g i c i d e s are used on stone f r u i t c r o p s i n the e a s t e r n U n i t e d S t a t e s t o c o n t r o l brown r o t blossom b l i g h t and f r u i t r o t ( M o n i l i n i a f r u c t i c o l a ) , cherry l e a f spot (Coccomyces h i e m a l i s ) , powdery mildews (Sphaerotheca ρannosa and Podosphaera o x y a c a n t h a e ) , and scab ( C l a d o sporium c a r p o p h i l i u m ) . I n the n o r t h e a s t e r n s t a t e s about s i x a p p l i c a t i o n s are a p p l i e d per season w h i l e i n the s o u t h e a s t e r n s t a t e s up t o t e n a p p l i c a t i o n s are a p p l i e d .
In Fungicide Chemistry; Green, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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.ch009
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The need f o r new f u n g i c i d e s f o r stone f r u i t s has i n c r e a s e d because of the development o f b e n z i m i d a z o l e - r e s i s t a n t M o n i l i n i a f r u c t i c o l a (8,9,30) and Coccomyces h i e m a l i s (10) i n i m p o r t a n t stone f r u i t p r o d u c t i o n areas of the e a s t e r n U n i t e d S t a t e s . R e s i s t a n c e has been a major problem f o r stone f r u i t growers because a l t e r n a t i v e f u n g i c i d e s are l e s s e f f e c t i v e , more c o s t l y or r e q u i r e more f r e q u e n t a p p l i c a t i o n s than b e n z i m i d a z o l e f u n g i c i d e s . The r e c e n t r e g i s t r a t i o n s of i p r o d i o n e and t r i f o r i n e f o r c o n t r o l of stone f r u i t d i s e a s e s have h e l p e d t o a l l e v i a t e problems caused by b e n z i m i d a z o l e r e s i s t a n c e . Programs f o r the management o f stone f r u i t d i s e a s e s r e v o l v e around the c o n t r o l of brown r o t a t bloom and a t h a r v e s t . Between these two s t a g e s of f r u i t development, the c o n t r o l of c h e r r y l e a f s p o t , powdery mildew, and peach scab i s more i m p o r t a n t than c o n t r o l of brown r o t . The EBI f u n g i c i d e s have shown h i g h a c t i v i t y a g a i n s t a l l these d i s e a s e s except peach scab. Peach scab i s a mid-season problem i n the s o u t h e r n s t a t e s . I n these s t a t e s the EBI f u n g i c i d e s would need t o be supplemented w i t h o t h e r f u n g i c i d e s f o r scab c o n t r o l . In the n o r t h e r n s t a t e s , the EBI f u n g i c i d e s would be of b e n e f i t f o r c o n t r o l l i n g the spectrum of d i s e a s e s t h a t o c c u r from bloom u n t i l harvest. Cherry l e a f spot i s p a r t i c u l a r l y severe i n the Great Lakes s t a t e s of M i c h i g a n , W i s c o n s i n , and New York. Protective fungicides such as c a p t a f o l , c h l o r o t h a l o n i l , c a p t a n , and ferbam p l u s s u l f u r are the main f u n g i c i d e s used i n i t s c o n t r o l . These f u n g i c i d e s l a c k the broad spectrum a c t i v i t y of the EBI f u n g i c i d e s and o f t e n must be supplemented w i t h o t h e r f u n g i c i d e s t o c o n t r o l a l l the d i s e a s e s t h a t are p r e s e n t . A l s o , the c a p a b i l i t y of the EBI f u n g i c i d e s t o g i v e p o s t - i n f e c t i o n c o n t r o l o f l e a f spot s h o u l d be a v a l u a b l e a s s e t i n the c o n t r o l of t h i s d i s e a s e ( 2 1 ) . I f p r o t e c t i v e s p r a y s are missed and l e a f spot i n f e c t i o n o c c u r s , the EBI f u n g i c i d e s c o u l d be used as emergency t r e a t m e n t s i n much the same way t h a t c y c l o h e x i m i d e was used, b e f o r e i t s use was d i s c o n t i n u e d ( 3 ) . A second group of f u n g i c i d e s w i t h p o t e n t i a l f o r use on stone f r u i t s i s the d i c a r b o x i m i d e s . The d i c a r b o x i m i d e f u n g i c i d e s p r o v i d e d e x c e l l e n t c o n t r o l o f brown r o t blossom b l i g h t i n l a b o r a t o r y t e s t s i n M i c h i g a n (7) and b o t h d i c a r b o x i m i d e and EBI f u n g i c i d e s p r o v i d e d e x c e l l e n t c o n t r o l of brown r o t blossom b l i g h t when a p p l i e d 18 o r 24 hours a f t e r i n o c u l a t i o n i n greenhouse t r i a l s i n New Y o r k ( 2 4 ) . Because of t h i s a f t e r - i n f e c t i o n a c t i v i t y , the d i c a r b o x i m i d e and the EBI f u n g i c i d e s s h o u l d be s u b s t i t u t e d f o r d i c h l o n e i n emergency c o n t r o l programs f o r brown r o t blossom b l i g h t . F o r t h i s p u r p o s e , the f u n g i c i d e s are a p p l i e d a f t e r c o n d i t i o n s have been f a v o r a b l e f o r infection. The d i c a r b o x i m i d e s have a narrower spectrum of d i s e a s e c o n t r o l than the EBI f u n g i c i d e s . At t i m e s , they w i l l need t o be supplemented w i t h o t h e r f u n g i c i d e s t o c o n t r o l the e n t i r e spectrum of diseases that i s present. L a b o r a t o r y t e s t s w i t h M. f r u c t i c o l a (26) and f i e l d e x p e r i e n c e w i t h the d i c a r b o x i m i d e s f o r B o t r y t i s c o n t r o l i n s t r a w b e r r y f i e l d s (14) suggest f u n g i c i d e r e s i s t a n c e may be a problem i f the d i c a r b o x imide f u n g i c i d e s are used e x t e n s i v e l y and c o n t i n u o u s l y season a f t e r season. A l t h o u g h many workers c o n s i d e r d i c a r b o x i m i d e resistant s t r a i n s l e s s f i t than w i l d - t y p e s t r a i n s (16,17), the r e s e a r c h sug g e s t s t h a t f i e l d r e s i s t a n c e w i l l develop i f s t e p s are not taken t o
In Fungicide Chemistry; Green, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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a v o i d t h e problem. As p o i n t e d o u t by G i l p a t r i c k ( 4 ) , t h e main b e n e f i t o f h a v i n g a wide v a r i e t y o f f u n g i c i d e s a v a i l a b l e f o r brown r o t c o n t r o l i s t o p r e v e n t t h e development o f r e s i s t a n c e . Another b e n e f i t o f h a v i n g a wide v a r i e t y o f f u n g i c i d e s a v a i l a b l e f o r stone f r u i t s would be t h e p o s s i b i l i t y o f c o n t r o l l i n g a broader range o f diseases.
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A Need f o r Root Rot F u n g i c i d e s P h y t o p h t h o r a crown r o t , caused by P h y t o p h t h o r a cactorum and o t h e r Phytophthora spp., o c c u r s on a p p l e r o o t s t o c k s such as MM104 and MM106 p l a n t e d i n heavy p o o r l y d r a i n e d s o i l s . S o i l drenches w i t h copper sulfate, c a p t a f o l , and mancozeb a r e n o t h i g h l y e f f e c t i v e f o r c o n t r o l l i n g crown r o t , b u t m e t a l a x y l has been e f f e c t i v e i n l i m i t e d t r i a l s (1 ). F o s e t y l - A l i s a l s o a c t i v e against Phytophthora, but i t has n o t y e t been i n v e s t i g a t e d e x t e n s i v e l y f o r use i n t h e e a s t e r n U n i t e d S t a t e s . The p o t e n t i a l v a l u e o f these compounds i s u n c e r t a i n because growers o f t e n f a i l t o t r e a t t r e e s u n t i l t h e i n f e c t i o n has p r o g r e s s e d beyond a stage where t h e t r e e can r e c o v e r . Moreover, through proper r o o t s t o c k and s i t e s e l e c t i o n , crown r o t can be p r e vented. A Need f o r A n t i b i o t i c s S i n c e t h e e r a o f t h e a n t i b i o t i c s , no new compounds have been d e v e l oped f o r t h e c o n t r o l o f d i s e a s e s caused by p h y t o p a t h o g e n i c prokaryotes. Even these a n t i b i o t i c s a r e n o t used i n many areas o f t h e w o r l d because o f governmental r e s t r i c t i o n s t h a t p r e v e n t t h e i r use on a g r i c u l t u r a l crops. Problems w i t h r e s i s t a n c e a r e r e d u c i n g t h e u s e f u l n e s s o f t h e a n t i b i o t i c s even f u r t h e r . Copper compounds, w h i c h a r e g e n e r a l l y l e s s e f f e c t i v e than t h e a n t i b i o t i c s , a r e t h e main compounds a v a i l a b l e t o c o n t r o l b a c t e r i a l i n c i t e d d i s e a s e s . Unfor t u n a t e l y , copper compounds a r e p h y t o t o x i c t o many c r o p s . The need f o r e f f e c t i v e b a c t e r i c i d e s i s g r e a t e r today than a t any time i n h i s t o r y . The r e c o g n i t i o n t h a t mycoplasma-like organisms and x y l e m - l i m i t e d b a c t e r i a cause p l a n t d i s e a s e means t h a t t h e r e a r e a d d i t i o n a l d i s e a s e s t h a t a r e amenable t o c o n t r o l w i t h a n t i b i o t i c - l i k e compounds. X - d i s e a s e , pear d e c l i n e , peach y e l l o w s , phony peach, and plum l e a f s c o r c h a r e a few examples o f d i s e a s e s on deciduous t r e e f r u i t c r o p s caused by p h y t o p a t h o g e n i c p r o k a r y o t e s . H i g h l y e f f e c t i v e c h e m i c a l s a r e a l s o needed t o c o n t r o l b a c t e r i a l d i s e a s e s o f t r e e f r u i t and many o t h e r h i g h v a l u e c r o p s . Current methods f o r c o n t r o l l i n g f i r e b l i g h t , b a c t e r i a l s p o t , and b a c t e r i a l canker a r e n o t adequate. F i r e b l i g h t , f o r example, has spread t o Europe. The r o l e o f Pseudomonas s y r i n g a e pv. s y r i n g a e as an " i c e n u c l e a t o r " has s t i m u l a t e d t h e hunt f o r f r o s t p r o t e c t i o n compounds t h a t c o n t r o l o r compete w i t h these b a c t e r i a . New c h e m i c a l s f o r t h e c o n t r o l o f p h y t o p a t h o g e n i c p r o k a r y o t e s a r e a l s o needed as t o o l s f o r a v o i d i n g r e s i s t a n c e problems. Industry should recognize that the p o t e n t i a l market f o r a new c h e m i c a l cannot be e s t i m a t e d a c c u r a t e l y based on c u r r e n t s a l e s o f a v a i l a b l e compounds ( 1 8 ) .
In Fungicide Chemistry; Green, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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Summary For many years virtually no fungicides with new chemistry were approved for use on tree fruit crops in the United States because of the slow federal registration process. Many experimental fungicides have been evaluated by agricultural experiment stations in several states in the eastern United States during the last ten to fifteen years. At least three of these new fungicides (triforine, triadi mefon, and iprodione) are now registered for use on tree fruit crops, but many additional fungicides are awaiting final federal registra tion. As these new registrations are approved, the potential promise of these fungicides to improve disease pest management on tree fruit crops can finally be realized. Literature Cited 1. Ellis, M.A., Grove, G.G., and Ferree, D.C. 1982. Effects of metalaxyl on Phytophthora cactorum and collar rot of apple. Phytopathology 72:1431-1434. 2. Ellis, M.A., Madden, L.V., and Wilson, L.L. 1984. Evaluation of an electronic apple scab predictor for scheduling fungicides with curative activity. Plant Dis. 68:1055-1057. 3. Eisensmith, S.P., and Jones, A.L. 1981. Infection model for timing fungicide applications to control cherry leaf spot. Plant Dis. 65:955-958. 4. Gilpatrick, J.D. 1983. Management of resistance in plant pathogens. Pages 735-767 In: "Pest Resistance to Pesticides". G.P. Georghiou and T. Saito, eds. Plenum Press, N.Y. 809 pp. 5. Hickey, K.D., and Yoder, K.S. 1981. Field Performance of sterol-inhibiting fungicides against apple powdery mildew in the mid-Atlantic apple growing region. Plant Dis. 65:1002-1006. 6. Hoch, H.C., and Szkolnik, M. 1979. Viability of Venturia inaequalis in chlorotic flecks resulting from fungicide applica tion to infected Malus leaves. Phytopathology 69:456-462. 7. Jones, A.L. 1975. Control of brown rot of cherry with a new hydantoin fungicide and with selected fungicide mixtures. Plant Dis. Rep. 59:127-130. 8. Jones, A.L. 1981. Fungicide resistance: Past experience with benomyl and dodine and future concerns with sterol inhibitors. Plant Dis. 65:990-992. 9. Jones, A.L., and Ehret, G.R. 1976. Isolation and characteriza tion of benomyl-tolerant strains of Monilinia fructicola. Plant Dis. Rep. 60:765-769. 10. Jones, A.L., and Ehret, G.R. 1980. Resistance of Coccomyces hiemalis to benzimidazole fungicides. Plant Dis. 64:767-769. 11. Jones, A.L., Lillevik, S.L., Fisher, P.D., and Stebbins, T.C. 1980. A microcomputer-based instrument to predict primary apple scab infection periods. Plant Dis. 64:69-72. 12. Kelley, R.D., and Jones, A.L. 1981. Evaluation of two triazole fungicides for post-infection control of apple scab. Phytopath ology 71:737-742. 13. Kelley, R.D., and Jones, A.L. 1982. Volatility and systemic properties of etaconazole and fenapanil in apple. Can. J. Plant Pathol. 4:243-246.
In Fungicide Chemistry; Green, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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Maraite, Η., Gills, G., Meunier, S., Weynes, J., and Bal, Ε. 1980. Resistance of Botrytis cinerea Per. ex Pers. to dicarbox imide fungicides in strawberry fields. Parasition 36:90-91. 15. Pearson, R.C. Szkolnik, M., and Meyer, F.W. 1978. Suppression of cedar apple rust pycnia on apple leaves following post -infection applications of fenarimol and triforine. Phytopath ology 68:1805-1809. 16. Ritchie, D.F. 1983. Mycelial growth, peach fruit-rotting capability, and sporulation of strains of Monilinia fructicola resistant to dichloran, iprodione, procymidone, and vinclozolin. Phytopathology 73:44-47. 17. Ritchie, D.F. 1982. Effect of dichloran, iprodione, procymi done, and vinclozolin on the mycelial growth, sporulation, and isolation of resistant strains of Monilinia fructicola. Plant Dis. 66:484-486. 18. Schroth, M.N., and McCain, A.H. 1981. The nature, mode of action, and toxicity of bactericides. In "Handbook of Pest Management in Agriculture" (D. Pimental, ed.) Vol. III, pp. 47-58. CRC, Cleveland, Ohio. 19. Schwabe, W.F.S., and Jones, A.L. 1983. Apple scab control with bitertanol as influenced by adjuvant addition. Plant Dis. 67:1371-1373. 20. Schwabe, W.F.S., Jones, A.L., and Jonker, J.P. 1984. Green house evaluation of the curative and protective action of sterol-inhibiting fungicides against apple scab. Phytopathology 74:249-252. 21. Szkolnik, M. 1974. Unusual post-infection activity of a piperazine derivative fungicide for the control of cherry leaf spot. Plant Dis. Rep. 58:326-329. 22. Szkolnik, M. 1974. Unique post-infection control of cedarapple rust on apple with triforine. Plant Dis. Rep. 58:587-590. 23. Szkolnik, M. 1981. Physical modes of action of sterol-inhibit ing fungicides against apple diseases. Plant Dis. 65:981-985. 24. Szkolnik, M. 1983. Greenhouse evaluations on protective and after-infection activities of fungicides in the control of sweet cherry brown rot blossom blight. Fungicide and Nematicide Tests 38:117. 25. Szkolnik, Μ., and Gilpatrick, J.D. 1969. Apparent resistance of Venturia inaequalis to dodine in New York apple orchards. Plant Dis. Rep. 53:861-864. 26. Sztejnberg, Α., and Jones, A.L. 1978. Tolerance of the brown rot fungus Monilinia fructicola to iprodione, vinclozolin and procymidone fungicides. (Abstr.) Phytopathol. News 12:187. 27. Yoder, K.S., and Hickey, K.D. 1981. Sterol-inhibiting fungi cides for control of certain diseases of apple in the Cumber land-Shenandoah region. Plant Dis. 65:998-1001. 28. Yoder, K.S. 1982. Broad spectrum apple disease control with bitertanol. Plant Dis. 66:580-583. 29. Yoder, K.S., and Hickey, K.D. 1983. Control of apple powdery mildew in the mid-Atlantic region. Plant Dis. 67:245-248. 30. Zehr, E.I. 1982 Control of brown rot in peach orchards. Plant Dis. 66:1101-1105. RECEIVED October 1, 1985
In Fungicide Chemistry; Green, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
