Fungicides and Wheat Production Technology - ACS Symposium

8 Fungicides and Wheat Production Technology Advances in the Eastern United States

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.ch008

Herbert Cole, Jr. Department of Plant Pathology, The Pennsylvania State University, University Park, PA 16802

Science, technology, and marketing are linked together in the broad est sense when advances in pesticide chemistry are translated into new production systems for wheat. Science seeks to understand the wheat plant -- technology manipulates it. The level of technology used in the production of wheat is controlled by the value of the crop. When an agricultural producer contemplates various levels of input, the yield X unit price algorithm will dictate the level of technology that can be utilized in producing that crop. In the United States, wheat production has been limited as a sophisticated technological enterprise because of the linkage of U.S. wheat prices to world markets. In Europe, depending on the country, wheat prices are usually far higher than in the U.S. thus allowing a much more sophisticated level of technologic input with regard to pesticides, fertilizers, plant spacing, and permanent tramways for spraying fields. How rapidly U.S. producers emulate European production systems will depend on the U.S. wheat price. In spite of market constraints, eastern U.S. wheat production systems are growing in complexity. No element of wheat production can be considered as an isolated unit existing in a vacuum. What can be implemented from a disease management point of view is influenced by everything else done; the use of fungicides as a technological element in the disease management component of production has become more feasible as other technological inputs are optimized. For example, the use of fungicides for disease control is dependent on successful management of other elements in the system such as new varieties, planting dates, fertilizers, application equipment, row spacing, seed spacing, and seeding rate. Overall, gains in wheat production have resulted because the whole production system has been upgraded. This paper is an examination of the changes in wheat production that are taking place in the eastern U.S., the interaction between the various elements, and where the opportunities exist for further gains. Technological improvements have been occurring for a long time. Although minimum tillage production systems are considered a 0097-6156/86/0304-0127S06.00/0 © 1986 American Chemical Society

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


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r e c e n t i n n o v a t i o n , i n r e a l i t y farmers have been a t t e m p t i n g to p l a n t w i t h o u t p l o w i n g f o r a t l e a s t 84 y e a r s . G r a i n y i e l d i s dependent on the number o f heads per h e c t a r e , the number of k e r n e l s per head and the s i z e and d e n s i t y of those k e r n e l s (9). To maximize y i e l d s , e v e r y element i n the whole production system must be d i r e c t e d towards b a l a n c i n g and o p t i m i z i n g those t h r e e c o n t r i b u t i n g f a c t o r s . In many ways, change i n wheat p r o d u c t i o n i n the l a s t ten y e a r s has been a microcosm of what has t a k e n p l a c e i n the l a s t f o r t y y e a r s of maize p r o d u c t i o n . The changes are s i m i l a r but have been compressed i n time. One of the major a r e a s of p r o g r e s s has been the i n t r o d u c t i o n of p r e c i s i o n p l a n t i n g e q u i p m e n t — p l a n t e r s t h a t a l l o w depth c o n t r o l and p r e c i s e s p a c i n g of k e r n e l s ( 7 ) . U n f o r t u n a t e l y , the g o a l t h a t e v e r y seed and e v e r y p l a n t i s e q u i d i s t a n t from e v e r y o t h e r seed or p l a n t i n the f i e l d has y e t to be r e a c h e d . As row s p a c i n g s are narrowed from 18 cm t o 10 cm, y i e l d s i n c r e a s e even though s e e d i n g r a t e s have been kept constant. Much of the c u r r e n t development e f f o r t i n p l a n t i n g t e c h n o l o g y i s devoted i n some way to a c h i e v i n g the e q u i d i s t a n t seed placement. A i r seeders r e p r e s e n t the newest way of a c c o m p l i s h i n g t h i s g o a l . The concept of a i r s e e d i n g i n v o l v e s b l o w i n g a m i x t u r e of f e r t i l i z e r and seed through a tube t o a c h i s e l shank t h a t i s l i f t i n g the s o i l . The seed i s spread randomly by the a i r s t r e a m beneath the s o i l l i f t e d by the c h i s e l . Depth i s u n i f o r m , s p a c i n g i s random but r e m a r k a b l y equidistant. C u r r e n t l y manufactured s e e d e r s are s u i t a b l e f o r the s o i l s of the h i g h p r a i r i e s , but not f o r the heavy c l a y s or s t o n y loams of the e a s t e r n U.S. For the E a s t the c h a l l e n g e i s to make the system f u n c t i o n w e l l i n h e a v i e r s o i l s and w i t h s m a l l e r s c a l e e q u i p ment. Where the a i r s e e d i n g concept i s not f u n c t i o n a l , row p l a n t i n g remains a v i a b l e o p t i o n . I n t h i s c a s e , a m e c h a n i c a l d e v i c e drops seed through tubes i n t o rows of s i n g l e or double d i s k openers t h a t are f o r c e d downward to p r o p e r p l a n t i n g depth by the weight o f the equipment. Rows p r e c l u d e e q u i d i s t a n t seed s p a c i n g , a l t h o u g h narrow (10 cm) rows would r e p r e s e n t a c o n s i d e r a b l e advance from 18 cm rows. In attempting the u l t i m a t e g o a l , a wheat farmer i n the s t a t e of Washington has developed a c o m b i n a t i o n s e e d e r , f e r t i l i z e r and p e s t i c i d e a p p l i c a t o r t h a t weighs a p p r o x i m a t e l y 25 t o n s . I t places one h e r b i c i d e over the seed row, another h e r b i c i d e between the seed rows, the f e r t i l i z e r beneath the seed, and then f i n a l l y p l a n t s the seed, a l l i n a precise fashion. I n the s m a l l f i e l d s of the e a s t e r n U n i t e d S t a t e s , d i f f e r e n t k i n d s of equipment may be needed. The concept of e q u i d i s t a n t geo m e t r i c seed s p a c i n g r e m a i n s , but lower c o s t , s m a l l e r s c a l e p l a n t e r s are needed t o a c c o m p l i s h t h i s g o a l . I f an a i r seeder cannot be used i n heavy s o i l s , the a l t e r n a t i v e i s t o p l a c e the seed i n v e r y narrow rows u s i n g d i s c or c h i s e l openers to o b t a i n a 10 cm row spacing. U n f o r t u n a t e l y , s o i l s u r f a c e t r a s h and s o i l c l o d s have c r e a t e d p r o b lems i n the s u c c e s s f u l d e s i g n and o p e r a t i o n of narrow row p l a n t e r s . Both s m a l l s c a l e a i r and d r i l l row p l a n t e r s are b e i n g used i n Europe, and are now b e i n g imported i n t o the U n i t e d S t a t e s . I n the e a s t e r n U.S., the g r a i n p l a n t e r has o f t e n been the o l d e s t p i e c e of equipment


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on t h e farm. T h i s i s changing as farmers p e r c e i v e new o p p o r t u n i t i e s i n p r o d u c i n g wheat. Changes i n one p r o d u c t i o n element may i n f l u e n c e many o t h e r elements i n t h e system. F o r example, s t u b b l e mulch f a l l o w i n g e v e r y o t h e r y e a r t o conserve m o i s t u r e f o r n e x t y e a r ' s crop had been a standard p r a c t i c e i n c e r t a i n areas o f the western United States. ( 7 ) . As a g r i c u l t u r i s t s sought t h e u l t i m a t e i n m e c h a n i c a l t i l l a g e and cropped more and more d r y l a n d s , s t u b b l e m u l c h i n g was i g n o r e d and l a r g e b l o c k s o f f i n e l y p r e p a r e d s o i l began t o e x p e r i e n c e wind e r o s i o n s i m i l a r t o t h a t which o c c u r r e d d u r i n g t h e dust bowls o f the 1 9 3 0 s . In a d d i t i o n , p e o p l e i n c i t i e s and towns o f the Dakotas e x p e r i e n c e an annoying s i d e e f f e c t c a l l e d SNUD, a m i x t u r e o f snow and mud. After the snow m e l t s , a l l s u r f a c e s a r e c o v e r e d w i t h t h i s s o i l r e s i d u e . I n the d r y l a n d wheat a r e a o f t h e U.S., t h e management o f s o i l s t o p r e v e n t wind e r o s i o n has become a major c o n c e r n . C h e m i c a l t e c h n o l o g y i s p r o v i d i n g a l a r g e share o f t h e s o l u t i o n . I n Nebraska, t h e s o l u t i o n i s c a l l e d " e c o f a l l o w ; i n o t h e r a r e a s o f t h e U.S. i t i s c a l l e d c h e m i c a l f a l l o w . R e g a r d l e s s o f name, t h e system i n v o l v e s the use o f h e r b i c i d e s , r a t h e r than m e c h a n i c a l c u l t i v a t i o n , t o p r o v i d e m o i s t u r e r e t e n t i o n and t h e c o n t r o l o f v e g e t a t i o n i n t h e i n t e r v e n i n g f a l l o w y e a r . T h i s a l l o w s c o n s e r v a t i o n o f the s o i l beneath an i n t a c t p l a n t r e s i d u e and almost c o m p l e t e l y e l i m i n a t e s s o i l l o s s due t o wind erosion. However, i n a c h i e v i n g t h e s o i l and m o i s t u r e r e t e n t i o n g o a l , another feed-back l o o p t o a m e c h a n i c a l t e c h n o l o g y problem was c r e a t e d . How does one p l a n t e f f i c i e n t l y i n a s o i l s u r f a c e c o n s i s t i n g o f v e g e t a t i v e crop debris? Those o f us i n a g r i c u l t u r a l s c i e n c e and technology i n the " i n t e l l e c t u a l c e n t e r s " o f the w o r l d , both corporate and u n i v e r s i t y , l i k e t o t h i n k t h a t p r o g r e s s o c c u r s s o l e l y because o f our g r e a t i d e a s . T h i s i s sometimes t r u e , b u t i n o t h e r i n s t a n c e s we must r e l y on o t h e r s . We observe and u t i l i z e unique i d e a s c r e a t e d by a g r i c u l t u r a l p r o d u c e r s throughout t h e w o r l d who see s o l u t i o n s t o t h o r n y problems a s a r e s u l t o f t h e i r v e r y c l o s e a s s o c i a t i o n w i t h t h e land. The concept o f n o - t i l l o r minimum t i l l a g e p l a n t i n g o f wheat has been t r i e d i n v a r i o u s p l a c e s throughout t h e w o r l d by farmers w i t h equipment o f t h e i r own c r e a t i o n . I n one known i n s t a n c e , a farmer d e c i d e d t h a t he would p l a n t wheat w i t h h i s " n o - t i l l " c o r n p l a n t e r by r u n n i n g i t a c r o s s the f i e l d o f f s e t each time so t h a t 15-18 cm row spacing r e s u l t e d . These k i n d s o f attempts by a g r i c u l t u r a l p r o d u c e r s throughout the w o r l d u l t i m a t e l y l e d t o the development o f t h e commer c i a l minimum t i l l a g e o r " n o - t i l l a g e " d r i l l p l a n t e r . These p l a n t e r s h e l p e d s o l v e an e n v i r o n m e n t a l problem through p r e c i s e p l a n t i n g i n t o s o i l c o v e r e d by r e s i d u a l s u r f a c e d e b r i s . Subsequent t e c h n o l o g i e s a l l o w e d c o n c u r r e n t p r e c i s e placement o f t h e h e r b i c i d e and f e r t i l i z e r a l l i n a s i n g l e pass over the f i e l d . The day when t h e farmer used h i s c o r n p l a n t e r was o v e r . P r o d u c e r s thought they had found a t o t a l s o l u t i o n , b u t i t became apparent t h a t they had then c r e a t e d a n o t h e r problem. F o r example, wheat p l a n t r e s i d u e s c o n t a i n f o l i a r pathogens such a s S e p t o r i a t r i t i c i ( 8 ) . The f o l l o w i n g season, s p o r e s a r e produced by these f u n g i and a r e blown t o a d j a c e n t f i e l d s o f wheat where severe i n f e c t i o n may r e s u l t . Mechanical t i l l a g e destroys the crop r e s i d u e ; c h e m i c a l f a l l o w does n o t . So i n s o l v i n g one problem, another was


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created. I n the e a s t e r n and midwest U.S., the immediate n o - t i l l a g e p l a n t i n g of wheat i n t o c o r n s t u b b l e , c u t f o r e n s i l a g e , i s the p l a n t p a t h o l o g i s t ' s c o n c e p t u a l dream o f how one i n o c u l a t e s a f i e l d w i t h G i b b e r e l l a zeae t o produce head scab ( 8 ) . A s i n g l e p e r i t h e c i a - c o n t a i n i n g c o r n s t a l k , every 30 cm i n 76 cm row s p a c i n g s , w i l l p r o v i d e enough inoculum the n e x t s p r i n g t o almost c e r t a i n l y ensure head scab of the wheat. Throughout the U n i t e d S t a t e s , the use of minimum t i l l a g e and c h e m i c a l f a l l o w systems has r e s u l t e d i n c o n s e r v a t i o n of s o i l and energy, but has c r e a t e d a new s e t o f d i s e a s e problems t h a t were f o r m e r l y managed by m e c h a n i c a l t i l l a g e and c u l t u r a l p r a c t i c e s . For example, e s t i m a t e d y i e l d r e d u c t i o n s o f up t o 40% have o c c u r r e d i n P e n n s y l v a n i a when p r o d u c e r s p l a n t e d wheat f o l l o w i n g wheat w i t h the p r e v i o u s crop r e s i d u e l e f t on the s o i l s u r f a c e . Major problems r e s u l t e d from S e p t o r i a d i s e a s e s ( S e p t o r i a nodorum and Septoria t r i t i c i ) , t a k e - a l l (Gaeumannomyces g r a m i n i s v a r . t r i t i c i ) , head scab ( G i b b e r e l l a zeae) and v a r i o u s o t h e r f o l i a r , crown and r o o t d i s e a s e s . A t t e m p t s t o grow c o n t i n u o u s wheat under minimum t i l l a g e c o n d i t i o n s have been d i s c o n t i n u e d by P e n n s y l v a n i a farmers because of these diseases. S i m i l a r f a i l u r e s have been e x p e r i e n c e d i n o t h e r a r e a s of the e a s t e r n and mid-western U.S. The i n t r o d u c t i o n o f new nitrogen responsive varieties has g r e a t l y i n c r e a s e d the y i e l d p o t e n t i a l of wheat i n the a r e a s o f the U.S. where r a i n f a l l i s not a l i m i t i n g f a c t o r . O l d e r v a r i e t i e s m e r e l y grew t a l l e r and lodged when a d d i t i o n a l n i t r o g e n f e r t i l i z e r was a p p l i e d . Newer v a r i e t i e s r e l e a s e d i n the 1978-83 p e r i o d have g r e a t e r stem s t r e n g t h and respond t o a d d i t i o n a l n i t r o g e n by p r o d u c i n g g r e a t e r number o f t i l l e r s per h e c t a r e w i t h l a r g e r heads. I n t h i s manner, the b a s i s f o r i n c r e a s e d g r a i n p r o d u c t i o n has been e s t a b l i s h e d ( 4 ) . U n f o r t u n a t e l y , the powdery mildew s u s c e p t i b i l i t y o f most wheat v a r i e t i e s g r e a t l y i n c r e a s e s as n i t r o g e n f e r t i l i t y l e v e l s i n c r e a s e . I n seasons and l o c a t i o n s o f h i g h h u m i d i t y , many o f the g a i n s due t o i n c r e a s e d f e r t i l i t y are n u l l i f i e d by powdery mildew l o s s e s . Powdery mildew has l o n g been r e c o g n i z e d as a wheat d i s e a s e , but o n l y w i t h the advent o f h i g h n i t r o g e n f e r t i l i t y d i d i t become a major y i e l d l i m i t i n g f a c t o r i n wheat p r o d u c t i o n . F u n g i c i d e s f o r powdery mildew c o n t r o l have e v o l v e d s l o w l y . S u l f u r was the f i r s t product and i t has been a v a i l a b l e s i n c e the e a r l y 1900's, but i t has n e v e r been e f f e c t i v e enough f o r commercial use. Then came e t h i r i m o l , (5 B u t y l 2-ethylamino-4-hydroxy-6-methyl p y r i m i d i n e ) , a compound proven t o p r o v i d e e f f e c t i v e powdery mildew c o n t r o l i n Europe, but be o n l y m a r g i n a l l y e f f e c t i v e i n the U.S., and was n e v e r r e g i s t e r e d f o r commercial use. Triadimefon (l-(4-chlorophenoxy)-3,3-dimethyl-l( l H - l , 2 , - 4 , - t r i a z o l - l - y l ) - 2 - b u t a n o n e ) was the f i r s t EPA r e g i s t e r e d c o m m e r c i a l l y e f f e c t i v e powdery mildew f u n g i c i d e . The use o f t r i a d i mefon on h i g h f e r t i l i t y r e s p o n s i v e , powdery mildew s u s c e p t i b l e v a r i e t i e s has r e s u l t e d i n y i e l d i n c r e a s e s of 10-30 p e r c e n t i n absence o f o t h e r f o l i a r pathogens. I t i s u n f o r t u n a t e , but not s u r p r i s i n g , t h a t a f u n g i c i d e e f f e c t i v e o n l y a g a i n s t powdery mildew, such as e t h i r i m o l , a l l o w s o t h e r pathogens not s e n s i t i v e t o the f u n g i c i d e t o invade the u n a f f e c t e d foliage. For example, where powdery mildew had been the p r i m a r y p r o b l e m , S e p t o r i a t r i t i c i and P u c e i n i a r e c o n d i t a now invaded the



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f o l i a g e from w h i c h powdery mildew had been e l i m i n a t e d ( 3 ) . Thus, t e c h n o l o g i c a l i n n o v a t i o n s o l v e d one problem, but a g a i n c r e a t e d a new problem. I t became apparent t h a t an a d d i t i o n a l f u n g i c i d e must be added t o the s p r a y tank t o c o n t r o l S e p t o r i a l e a f b l o t c h . An a p p l i c a t i o n method a l s o had t o be developed. One p o s s i b l e s o l u t i o n was a e r i a l s p r a y i n g ; t h e o t h e r was t h e development o f ways t o ground s p r a y i n mid-season w i t h o u t e x c e s s i v e p l a n t damage. By d e v e l o p i n g narrow wheel t r u c k o r t r a c t o r mounted s p r a y e r s , s m a l l e r f i e l d s c o u l d be s p r a y e d from the ground w i t h v e r y l i t t l e damage. The wheel t r a c k s r e p r e s e n t e d an a c c e p t a b l e l e v e l o f y i e l d l o s s ( 1 - 2 % ) . A d d i t i o n a l new s y s t e m i c fungicides are being introduced for wheat d i s e a s e c o n t r o l . One m a t e r i a l CGA 64250 ( T i l t ) , ( l - ( 2 - ( 2 , 4 - d i chlorophenyl)4-propyl-l,3,-dioxolan-2-yl methyl)-H-l,2,4-triazole), i s e f f e c t i v e f o r c o n t r o l o f powdery mildew, r u s t , and S e p t o r i a l e a f blotch. However a t t h i s p o i n t i n t i m e , i t i s not c e r t a i n whether U.S. EPA r e g i s t r a t i o n w i l l a l l o w a s h o r t enough i n t e r v a l between t r e a t m e n t and h a r v e s t f o r e f f e c t i v e d i s e a s e c o n t r o l by t h i s compound. F o l i a r s p r a y s r e q u i r e a p p l i c a t i o n d u r i n g the growing season. An a l t e r n a t i v e would be seed treatment w i t h a l o n g - t e r m s y s t e m i c f u n g i c i d e t h a t c o u l d be a p p l i e d a t p l a n t i n g . Such a m a t e r i a l i s c u r r e n t l y being tested. Triadimenol (Baytan),(3-(4-Chlorophenoxy)-a-(l,1-dimet h y l e t h y l ) - l H - l , 2 , 4 - t r i a z o l e - l - e t h a n o l ) , when a p p l i e d a s a seed t r e a t m e n t , w i l l p r o v i d e c o n t r o l o f powdery mildew on wheat i n t o mid-season. I n most y e a r s , t h i s would p r e c l u d e the need f o r f o l i a r s p r a y s f o r powdery mildew c o n t r o l , but does not p r o v i d e a s o l u t i o n f o r c o n t r o l o f S e p t o r i a l e a f b l o t c h or l a t e season l e a f r u s t . The new s y s t e m i c f u n g i c i d e s o f f e r a g r e a t p o t e n t i a l b e n e f i t ; however, the mechanisms o f f u n g i c i d a l a c t i o n o f these p r o d u c t s tend t o be narrow, o f t e n based on i n a c t i v a t i o n o f a s i n g l e enzyme system. W i t h wide usage o f these f u n g i c i d e s , pathogen r e s i s t a n c e may become a major problem. The n a t u r a l m u t a t i o n r a t e o f t h e f u n g a l pathogen combined w i t h almost u n i v e r s a l exposure t o the f u n g i c i d e p r o v i d e s a b a s i s f o r s e l e c t i o n o f r e s i s t a n t s t r a i n s o f the pathogen. I f these s t r a i n s a r e f i t t o s u r v i v e and compete i n t h e h o s t / p a t h o g e n eco system, t h e f u n g i c i d e w i l l have a v e r y s h o r t l i f e e x p e c t a n c y . Benomyl was h a i l e d a s the s o l u t i o n t o many p l a n t d i s e a s e s . However, r e s i s t a n c e has o c c u r r e d i n C e r c o s p o r a , E r y s i p h e , B o t r y t i s , S c l e r o t i n i a , V e n t u r i a , and o t h e r f u n g a l genera. F o r t u n a t e l y , r e s i s t a n c e t o t r i a d i m e f o n has not y e t appeared i n wheat pathogens i n a r e a s o f the w o r l d where the f u n g i c i d e has been i n w i d e s p r e a d use f o r a t l e a s t t e n years. This i s a hopeful s i g n . Triadimenol i s c l o s e l y r e l a t e d t o t r i d i m e f o n but h a s not y e t been used e x t e n s i v e l y and one c a n o n l y s p e c u l a t e r e g a r d i n g f u t u r e r e s i s t a n c e problems. I n a d i s e a s e c o n t r o l experiment i n 1979 (H. C o l e , unpublished), t r i a d i m e f o n was a p p l i e d t o f o u r wheat v a r i e t i e s ('Red Coat', 'Hart', 'S-76', and 'Dancer') grown under b o t h a h i g h f e r t i l i t y regime c o n d u c i v e t o maximum g r a i n y i e l d s , and the s t a n d a r d moderate f e r t i l i t y regime. I n the case o f 'Red C o a t ' , a powdery mildew r e s i s t a n t v a r i e t y , the h i g h f e r t i l i t y r e s u l t e d i n v e r y l i t t l e y i e l d g a i n (3555 kg/ha v s 3230 k g / h a ) ; y i e l d r e s p o n s i v e n e s s t o f e r t i l i t y was n o t p r e s e n t i n the v a r i e t y . On the o t h e r hand, 'Hart' and 'S-76' r e sponded d r a m a t i c a l l y to h i g h f e r t i l i t y . The use o f t r i a d i m e f o n under s t a n d a r d f e r t i l i t y r e s u l t e d i n a 20% y i e l d i n c r e a s e , whereas t h e


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i n c r e a s e was almost 70% under h i g h f e r t i l i t y p l u s f u n g i c i d e . H i g h f e r t i l i t y alone r e s u l t e d i n no y i e l d i n c r e a s e due t o the e x t r e m e l y severe powdery mildew l e v e l s t h a t were e x p e r i e n c e d . The maximum y i e l d s o b t a i n e d from the f u n g i c i d e p l u s h i g h f e r t i l i t y treatment p l o t s were 6370 kg/ha f o r H a r t and 6150 kg/ha f o r 'S-76'. The v a r i e t y ' D a n c e r , w h i c h i s e x t r e m e l y s u s c e p t i b l e t o powdery mildew, produced a poor y i e l d (2340 kg/ha) a t moderate f e r t i l i t y i n the absence of powdery mildew c o n t r o l , and w i t h the use of t r i a d i m e f o n produced a moderate g r a i n y i e l d of 3430 kg/ha. The c o m b i n a t i o n of h i g h f e r t i l i t y p l u s t r i a d i m e f o n on 'Dancer' r e s u l t e d i n o n l y a s l i g h t y i e l d i n c r e a s e (7%) because the y i e l d r e s p o n s i v e n e s s t o f e r t i l i t y was not p r e s e n t i n t h i s v a r i e t y . These r e s u l t s and many o t h e r s c l e a r l y i n d i c a t e t h a t y i e l d p o t e n t i a l and f e r t i l i z e r r e s p o n s i v e n e s s must be p r e s e n t i n a v a r i e t y i n o r d e r f o r the use o f f u n g i c i d e s t o r e s u l t i n dramatic y i e l d i n c r e a s e s . We have a l s o examined the i n t e r a c t i o n s between f u m i g a t i o n , t o c o n t r o l r o o t pathogens, and f u n g i c i d e s p r a y s , t o c o n t r o l f o l i a r pathogens. T h i s c o m b i n a t i o n c r e a t e d even g r e a t e r c o m p l e x i t i e s . The s o i l f u m i g a t i o n treatment c o n s i s t e d of 400 kg a i / h a of m e t h y l bromide a p p l i e d t h r e e weeks p r i o r t o p l a n t i n g w i n t e r wheats. The foliar spray was a c o m b i n a t i o n o f t r i a d i m e f o n (140 g a i / h a ) and mancozeb (1 kg a i / h a ) a p p l i e d a t Feekes' growth s t a g e s 7 and 10 ( 5 ) . The e x p e r i m e n t a l d e s i g n was f a c t o r i a l so t h a t b o t h f u m i g a t i o n and foliar f u n g i c i d e a p p l i c a t i o n c o u l d be c o n s i d e r e d alone as w e l l as t o g e t h e r . Depending on v a r i e t y , t h e r e were some i n s t a n c e s where y i e l d i n c r e a s e s r e s u l t e d from f o l i a r s p r a y s a l o n e and f u m i g a t i o n a l o n e . In other i n s t a n c e s , the c o m b i n a t i o n treatment resulted i n additive yield i n c r e a s e s and i n o t h e r i n s t a n c e s s y n e r g i s t i c i n c r e a s e s g r e a t e r than additive. We do not u n d e r s t a n d the i n t e r r e l a t i o n s h i p s among p a t h o gens, e s p e c i a l l y r o o t and crown r o t pathogens v e r s u s the f o l i a r pathogens. We are c e r t a i n t h a t t h e r e i s an i n t e r a c t i o n and t h a t i t must be c o n s i d e r e d i n development of wheat p r o d u c t i o n t e c h n o l o g i e s . The one t h i n g t h a t I have l e a r n e d o v e r the y e a r s i n e x a m i n a t i o n o f d a t a i s my own tendency t o expect c e r t a i n k i n d s o f r e s u l t s . If they are not o b t a i n e d , I t r y t o e x p l a i n t h i s by b l a m i n g the e x p e r i ment and b l a m i n g e v e r y t h i n g but the f a c t t h a t I may r e a l l y be l o o k i n g a t a unique b i o l o g i c a l paradox t h a t needs t o be u n d e r s t o o d r a t h e r than q u a r r e l e d w i t h . I t has been s a i d t h a t the d i f f e r e n c e between " g e n i u s " and the " r e s t o f u s " i s t h a t " g e n i u s " sees r e l a t i o n s h i p s between seemingly u n r e l a t e d o b s e r v a t i o n s when the " r e s t o f u s " cannot see these r e l a t i o n s h i p s . F u n g i c i d e s cannot be developed and t e s t e d i n i s o l a t i o n from the o t h e r t e c h n o l o g i c a l elements i n a wheat p r o d u c t i o n system. Where r e s e a r c h e r s have d i s c o v e r e d an e f f e c t i v e new f u n g i c i d e and then sprayed i t on t e s t p l o t s w i t h o u t r e g a r d t o the whole system, they have f a i l e d m i s e r a b l y . A c h e m i c a l company s e v e r a l y e a r s ago a t t e m p t ed t o do t h a t w i t h a product t h a t had been e f f e c t i v e i n Europe. They sprayed wheat from F l o r i d a t o New Y o r k , spent s e v e r a l m i l l i o n d o l l a r s , and went home t o t a l l y d i s e n c h a n t e d . They i g n o r e d the f a c t t h a t f u n g i c i d e s are a p a r t o f a complex system t h a t i n v o l v e s more than m e r e l y s p r a y i n g a c h e m i c a l on a c r o p . f

f


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The one element t h a t has not been d i s c u s s e d i s t h a t c u r r e n t l y p o p u l a r term " b i o t e c h n o l o g y " . To most p e o p l e , the word means gene s p l i c i n g and g e n e t i c e n g i n e e r i n g by c h e m i c a l o r a r t i f i c i a l means. T h i s i s u n f o r t u n a t e s i n c e b i o t e c h n o l o g y i n the h o l i s t i c sense i n v o l v e s a l l m a n i p u l a t i o n o f b i o l o g i c a l systems, i n c l u d i n g c l a s s i c plant breeding. The term i s not a s r e s t r i c t i v e as i t s c u r r e n t usage would i m p l y . There has been a g r e a t d e a l o f e f f o r t by u n i v e r s i t y r e s e a r c h e r s , as w e l l as by p r i v a t e seed companies, t o develop wheat v a r i e t i e s t h a t w i l l maximize g r a i n y i e l d s . H y b r i d wheats have been a l o n g - t i m e g o a l b u t t o date have a c h i e v e d o n l y l i m i t e d commercial success. The l a r g e degree o f s e l f - p o l l i n a t i o n and t h e absence o f e a s i l y m a n i p u l a t e d male s t e r i l i t y f a c t o r s have made h y b r i d i z a t i o n a difficult commercial p r o c e s s (.1*2) · Gameticidal chemicals a r e c u r r e n t l y r e c e i v i n g r e s e a r c h emphasis. However, the v a s t m a j o r i t y o f a v a i l a b l e v a r i e t i e s have been developed by c l a s s i c p l a n t b r e e d i n g t e c h n i q u e s w i t h major emphasis devoted t o s t r a w s t r e n g t h , d i s e a s e r e s i s t a n c e , f e r t i l i z e r r e s p o n s i v e n e s s , and y i e l d ( 6 ) . Long l a s t i n g r e s i s t a n c e would be t h e i d e a l s o l u t i o n t o many plant diseases. U n f o r t u n a t e l y , t h e narrow g e n e t i c b a s i s o f t h e r e s i s t a n c e , o f t e n a s i n g l e dominant gene, has r e s u l t e d i n new r a c e s of the pathogen w h i c h bypass the r e s i s t a n c e gene a f t e r s e v e r a l y e a r s of w i d e s p r e a d u s e o f the new v a r i e t y . I n some i n s t a n c e s , such as w i t h ' T y l e r , a new s o f t r e d w i n t e r wheat v a r i e t y , the b e n e f i t s o f powdery mildew r e s i s t a n c e may be t o t a l l y o f f s e t by l e a f r u s t suscep tibility. A l t h o u g h t h e r e has been a measurable l o n g - t e r m b e n e f i t from b r e e d i n g f o r d i s e a s e r e s i s t a n c e , p r o g r e s s t o date h a s n o t e l i m i n a t e d the need f o r use o f f u n g i c i d e s . G e n e t i c e n g i n e e r i n g and gene s p l i c i n g may u l t i m a t e l y b e n e f i t wheat p r o d u c t i o n but no p r o g r e s s has y e t o c c u r r e d . "Super wheat" has not y e t appeared and a l l t h i n g s c o n s i d e r e d , w i l l p r o b a b l y n e v e r come about. From the p r e c e d i n g d i s c u s s i o n , i t i s apparent t h a t we cannot c o n s i d e r any t e c h n o l o g i c a l p r a c t i c e i n a vacuum. Wheat p r o d u c t i o n i s a system composed of many i n t e r a c t i n g elements i n w h i c h every element i n f l u e n c e s o t h e r elements. One c o u l d draw the analogy t h a t i t i s the same a s p r e s s i n g an i n d e n t a t i o n i n t h e s i d e o f a p l a s t i c bag o f w a t e r — a push i n one p l a c e w i l l guarantee t h a t t h e r e w i l l be an e q u a l volume pushed o u t somewhere e l s e . Where i t w i l l appear i s n o t r e a d i l y determined but the f a c t t h a t i t w i l l appear i s a s s u r e d . The same i s t r u e i n a t t e m p t i n g t o understand the i n t e r r e l a t i o n s h i p s i n technology. The major c h a l l e n g e t h a t we f a c e today i s t o r e c o g n i z e and d e a l w i t h the i s s u e s o f t e c h n o l o g i c a l change i n a h o l i s t i c sense. U n f o r t u n a t e l y , we much p r e f e r t o z e r o i n on one's own s p e c i f i c i n t e r e s t , pursue r e s e a r c h i n t h a t d i r e c t i o n and not worry about t h e s i d e e f f e c t s o r r a m i f i c a t i o n s . We s h o u l d be encouraging people t o examine systems o f crop p r o d u c t i o n , and t o examine t e c h n o l o g i e s as they i n t e r a c t r a t h e r than a s i n d i v i d u a l elements. I b e l i e v e t h a t new u s e f u l t e c h n o l o g i e s w i l l be developed and i n c o r p o r a t e d i n t o the wheat p r o d u c t i o n systems and t h a t f u n g i c i d e s w i l l p l a y an i n c r e a s i n g r o l e i n t h i s development. The o b j e c t i v e f o r a l l of u s s h o u l d be t o ensure t h a t we make r e a l p r o g r e s s , e s p e c i a l l y i n p r o f i t a b i l i t y and y i e l d i n c r e a s e , so t h a t wheat producers do more than j u s t spend more money i n production costs without a t l e a s t a s l i g h t gain i n p r o f i t . 1


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1.

Ausemus, E.R.; F.H. McNeal; J.W. Schmidt. 1967. Genetics and Inheritance. Pages 225-259 In "Wheat and Wheat Improvement"; Quisenbery, K.S. and L . P . Reitz, Eds.; Agronomy Monograph No. 13 Amer. Soc. Agron. Madison, Wisconsin. 2. Briggle, L.W. 1963. Heterosis in Wheat -- A Review. Crop S c i . 3: 407-412. 3. James, W.C. and C.S. Shih. 1973. Relationship between Inci dence and Severity of Powdery Mildew and Leaf Rust on Winter Wheat. Phytopathology 63:183-187. 4. Laloux, R., A. Falisse, and J . Poelaert. 1980. Nutrition and Fertilization of Wheat. Pages 19-24 In "Wheat Documenta."; Technical Monograph, Ciba Geigy L&D, Basle, Switzerland. 5. Large, E.C. 1954. Growth Stages in Cereals. Plant Pathology 3:128-129. 6. Poehlman, J.M. 1959. "Breeding Field Crops" Chapter 6. Henry Holt and Co., Inc., New York. 7. Schlehuber, A.M. and B.B. Tucker. 1967. Culture of Wheat, Pages 117-176 In "Wheat and Wheat Improvement"; K.S. Quisenberry and L . P . Reitz, Eds., Agronomy Monograph, No. 13, Amer. Soc. Agron., Madison, Wisconsin. 8. Wiese, M.V. 1977. "Compendium of Wheat Diseases"; The Ameri can Phytopathological Society, St. Paul, Minn. 9. Willey, R.W. and S.B. Heath. 1964. The Quantitative Relation ship between Plant Population and Yield. Adv. Agron. 21: 281-320. RECEIVED October 1, 1985


Fungicides and Wheat Production Technology - ACS Symposium

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