Formulation and Application Technology for Microbial Weed Control

Chapter 16

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Formulation and Application Technology for Microbial Weed Control Donald J . Daigle and William J . Connick, Jr. Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, New Orleans, LA 70179 Fungal weed pathogens (mycoherbicides) are d i f f i c u l t to formulate into effective products because, as l i v i n g organisms, their v i a b i l i t y must be preserved throughout processing and storage. Furthermore, the pathogens, as packaged in a f i n a l product, must be able to control weeds after application under natural environmental conditions of moisture and temperature. This overview of formulation and application technology for microbial weed control describes the current developmental status of experimental and commercial products. A b r i e f review of combinations of mycoherbicides with chemical pesticides and beneficial insects i s included. There are two s t r a t e g i e s commonly employed f o r the b i o l o g i c a l c o n t r o l o f weeds. One i s the c l a s s i c a l i n which the m i c r o b i a l h e r b i c i d e , a f t e r r e l e a s e , i s capable o f s e l f - d i s s e m i n a t i o n and epidemic i n i t i a t i o n . The other strategy, inundative b i o l o g i c a l c o n t r o l , r e q u i r e s i n s t a n t i n t r o d u c t i o n o f l a r g e populations o f a p l a n t pathogen, and i t s a p p l i c a t i o n follows the same patterns as chemical h e r b i c i d e s (.43) . The inundative strategy a l s o c a l l s f o r formulation o f a d e l i v e r y system f o r the microorganism, since t h i s type o f strategy i s not dependent on the m i c r o b i a l h e r b i c i d e spreading r a p i d l y on i t s own. Formulation i s a mixing o f the a c t i v e i n g r e d i e n t with appropriate adjuvants and c a r r i e r . Today, the formulation o f chemical h e r b i c i d e s may be considered a science, whereas the formulation o f m i c r o b i a l h e r b i c i d e s remains more o f an a r t . A major d i f f e r e n c e between the two types o f h e r b i c i d e s i s that the l i f e and v i r u l e n c e o f the b i o l o g i c a l c o n t r o l organism must be maintained. To t h i s end, the d i f f e r e n t a d d i t i v e s and d i l u e n t s o f the formulation must be t e s t e d , s i n g l y This chapter not subject to U.S. copyright Published 1990 American Chemical Society

In Microbes and Microbial Products as Herbicides; Hoagland, Robert E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.


16.

DAIGLE &CONNICK

MknMalWeedControl

289

and i n various combinations/ t o insure the v i a b i l i t y of the mycoherbicide. These adjuvants and d i l u e n t s should a l s o increase the e f f i c i e n c y of a p p l i c a t i o n , and p a r t i c u l a r l y , the e f f i c a c y of the c o n t r o l agent. Formulation a l s o may i n v o l v e i n t e g r a t i n g the pathogens i n t o a weed management system. Researchers have found both b e n e f i c i a l and detrimental i n t e r a c t i o n s between commonly used i n s e c t i c i d e s , h e r b i c i d e s , and weed pathogens (44., j45) . In such a system the problems of a p p l i c a t i o n are magnified. A p p l i c a t i o n can i n c l u d e new or conventional a g r i c u l t u r a l equipment and v a r i a b l e s such as when, where, and how the formulation i s applied. Of course, the researcher makes compromises i n t h i s complex matrix i n an e f f o r t f o r maximum e f f i c i e n c y at minimum c o s t . This chapter discusses m i c r o b i a l weed c o n t r o l agents and t h e i r experimental and commercial formulations. Because most m i c r o b i a l h e r b i c i d e s have a narrow host s p e c i f i c i t y , they are most l i k e l y t o be used i n an i n t e g r a t e d pest management s t r a t e g y with chemical h e r b i c i d e s , i n s e c t i c i d e s , p l a n t growth r e g u l a t o r s , and i n s e c t b i o c o n t r o l agents. A l l of these research i n v e s t i g a t i o n s are presented with emphasis on f i e l d s t u d i e s , except f o r those agents i n t h e i r developmental stage. Water and Surfactant-Based Formulations Water has been the c a r r i e r of choice, e s p e c i a l l y since i t i s inexpensive, easy t o handle, and necessary f o r maintaining the l i f e of the weed pathogens. The most elementary d e l i v e r y system i s a simple mixture of the m i c r o b i a l agent and water. Such a system i s u s u a l l y the f i r s t used by the researcher i n t e s t i n g the b i o c o n t r o l p o t e n t i a l of the organism. Sometimes, t h i s s i m p l i s t i c approach i s bypassed i n favor of a c o n i d i a l suspension which contains a s u r f a c t a n t . Surfactants perform two f u n c t i o n s : they help t o disperse the spores or other fungal propagules i n the tank mix and they serve as wetting agents t o minimize runoff and the r e s u l t i n g l o s s of a c t i v e i n g r e d i e n t from the t a r g e t weed. Table I l i s t s research on water and s u r f a c t a n t based mycoherbicides that has progressed t o the greenhouse stage. In s i x of the eight i n v e s t i g a t i o n s , a s u r f a c t a n t was used. The e f f i c a c y of Protomvces gravidus was h i g h l y dependent upon the s t r i c t environmental c o n d i t i o n of a minimum of 48 hours of dew (2). These studies and others have shown that o l d e r p l a n t s r e q u i r e more spores/ml and/or longer dew periods f o r c o n t r o l . The i n v e s t i g a t i o n s l i s t e d i n Table I are based on the minimum spores/ml and minimum dew p e r i o d to k i l l at l e a s t 80% of the t a r g e t weed at the four (or fewer) t r u e - l e a f stage (young s e e d l i n g s ) .



Protomvces q r a v i d u ? Davis (ascospores)

Giant ragweed Ambrosia t r i f i d a (L.)

(Sw.) DC.

Common p u r s l a n e P o r t u l a c a o l e r a c e a (L.)

Spurred anoda Anoda c r i s t a t a (L.) S c h l e c h t .

A b u t i l o n t h e o p h r a s t i Medik.

Velvetleaf

Prickly sida Sida s p i n o s a (L.)

F l o r i d a beggarweed Desmodium tortuosum

D i chot omophtho r a p o r t u l a c a e M e h r l i c h and F i t z ex M.B. E l l i s

A l t e r n a r i a macrospora Zimm. Fusarium l a t e r i t i u m Nees ex F r .

Fusarium l a t e r i t i u m (Nees) emend. Snyder and Hans.

Colletotrichum truncatum (Schw.) Andrus and Moore (condia)

Horse p u r s l a n e Gibbaqo trianthemae Trianthema p o r t u l a c a s t r u m (L.) Simmons ( c o n i d i a )

Colletotrichum coccodes (Wallr.) Hughes (conidia)

M i c r o b i a l Agent

Eastern b l a c k nightshade Splanum ptveanthum Dun.

Weed

Tween 20

Tween 80

Tween 20 (0.05%)

Tween 80 (0.02%)

Tween 20 (0.02%)

Tween 80 (0.05%)

Surfactant (cone.)

5 χ 10

1 χ 10

1 χ 10

1 χ 10

1 χ 10

1 χ 10

e

3

3

1 χ 10'

1 χ 10

spores/ ml

Table I . Water and S u r f a c t a n t - B a s e d Formulations


18

16

18

14

16

48

16

Dew (hrs)

4

3

2

Ref.

I t . DAIGLE Jk CONNICK


Miscellaneous

Microbial WmdControl

291

Adjuvant-Based Formulations

C e r t a i n adjuvants may s t i m u l a t e the m i c r o b i a l agent to e i t h e r germinate or i n f e c t the t a r g e t weed more effectively. Table II l i s t s adjuvants/ one of which, sucrose (.12), was reported to enhance disease development. For another adjuvant/ g e l a t i n , the f u n c t i o n was not given/ but g e l a t i n could increase the v i s c o s i t y of the formulation to reduce r u n o f f or f u n c t i o n as a humectant to improve spore s u r v i v a l . In those i n v e s t i g a t i o n s with g e l a t i n , only greenhouse r e s u l t s were reported. With the a d d i t i o n of Sorbo (64% s o r b i t o l , Atkemix Inc./ Brandford/ Ontario) i n the suspension/ the number of v i a b l e spores of C o l l e t o t r i c h u m coccodes recovered from i n o c u l a t e d leaves increased 2 0 - f o l d . Also/ three 9-hour dew periods on consecutive n i g h t s were as e f f e c t i v e f o r disease i n c u b a t i o n as one 18-hour dew p e r i o d (10). The length of the dew p e r i o d u s u a l l y c o r r e l a t e s with success or f a i l u r e i n a m a j o r i t y of the work referenced i n t h i s review. Recently/ i t has been reported that i n v e r t ( w a t e r - i n - o i l ) emulsion c a r r i e r s composed of p a r a f f i n wax, mineral ( p a r a f f i n ) oil, soybean oil, and l e c i t h i n r e t a r d e d water evaporation (13). Thus, the pathogen has water a v a i l a b l e over a longer p e r i o d of time f o r germination and i n f e c t i o n of the t a r g e t weed. I n i t i a l l y / the spores were a p p l i e d i n an aqueous c a r r i e r followed by an overspray of an i n v e r t emulsion a p p l i e d with s p e c i a l i z e d a i r - a s s i s t atomizing nozzles (14.) . Greenhouse r e s u l t s using A l t e r n a r i a c a s s i a e against s i c k l e p o d were s u c c e s s f u l (88% m o r t a l i t y ) / but the volumes sprayed were too high f o r p r a c t i c a l i t y (JL3) . Further research with a onestep a p p l i c a t i o n of A. c a s s i a e i n i n v e r t emulsions showed that the q u a n t i t y of p a r a f f i n wax and d r o p l e t deposit s i z e determined the r a t e of water evaporation (Daigle/ D. J . ; Connick/ W. J . , J r . ; Quimby/ P. C, J r . ; Evans/ J . P.; T r a s k - M o r r e l l / B.; Fulgham, F. E., USDA/ ARS/ New Orleans/ LA, and S t o n e v i l l e / MS/ unpublished r e s u l t s ) . Therefore, i n v e r t emulsions c o u l d be both a s u c c e s s f u l d e l i v e r y system and water source f o r A. c a s s i a e . However, the lack of s u f f i c i e n t m o r t a l i t y at reasonable a p p l i c a t i o n r a t e s i n d i c a t e s that the i n v e r t emulsion c a r r i e r needs other adjuvants or a more v i r u l e n t pathogen s t r a i n f o r commercial success. Another approach i s to combine chemical and microbial herbicides. I t was reported that the a d d i t i o n of s u b l e t h a l r a t e s of the h e r b i c i d e s , l i n u r o n [Ν'-(3,4-dichlorophenyl)-N-methoxy-N-methylurea], imazaquin {2-[4,5-dihydro-4-methyl-4(1-methylethyl)-5o x o - l H - i m i d a z o l - 2 - y l ] - 3 - q u i n o l i n e c a r b o x y l i c acid}, and l a c t o f e n {( + )2-ethoxy-l-methyl-2-oxoethyl-5-[2-chloro4-(trifluoromethyl)phenoxyl]-2-nitrobenzoate} to an



Sicklepod Cassia obtusifolia

(L.)

(L.)

Schlecht.

(L.)

F i e l d bindweed Convolvulus arvensis

Spurred anoda Anoda c r i s t a t a

Medik.

Velvetleaf Abutilon theophrasti

Weed

Table

Microbial

Agent

Miscellaneous

Hughes

Alternaria J u r a i r and

cassiae Khan

A l t e r n a r i a macrosoora Zimm. (conidia)

(0.1%)

(0.75%)

2.5

5

p a r a f f i n wax 5 mineral oil soybean oil corn syrup lecithin (soybean oil)

Nonoxynol 9 (0.02% v/v) sucrose (5% w / v )

gelatin

gelatin Sorbo

1

χ

χ

χ

χ

3

10°

10

10*

10

spores/ml

Formulations

Adjuvants

Adjuvant-Based

Phomopsis convolvus Ormeno (conidia)

Colletotrichum coccodes (Wallr.)

II.


0-16

0-24

12-24

24

Dew (hrs)

13 14 15

12

11

9 10

Ref.


16. DAIGLE & CONNICK

Microbial Weed Control

293

invert emulsion containing A . cassiae significantly i n c r e a s e d weed c o n t r o l w i t h o u t dew ( 1 5 ) . With center p i v o t i r r i g a t i o n simulator equipment, p e a n u t a n d o t h e r v e g e t a b l e o i l s were s u p e r i o r t o p a r a f f i n i c o i l s f o r applying A . cassiae spores at rates of 0.4-8 g s p o r e s / h a t o s i c k l e p o d (Phatak, S. C , Univ. o f G e o r g i a , T i f t o n , GA, p e r s o n a l c o m m u n i c a t i o n ) . Good infection occurred at rates of 0.8-1.6 L / h a of the o i l / s p o r e m i x t u r e even w i t h o u t dew. Sicklepod control was b e s t when s p o r e s w e r e a p p l i e d i n o i l , c o m p a r e d w i t h w e t t a b l e powder o r c o n i d i a l s u s p e n s i o n . Formulations

Based

upon

Solid

Carriers

Although water has been used as a c a r r i e r o f P h y t o p h t h o r a p a l m i v o r a (Smith) Leonean, a s o i l - b o r n e fungus, i n the control of stranglervine (Morrenia odorata L . ) (36-38). t h e p o t e n t i a l o f any m i c r o b i a l a g e n t may b e l i m i t e d o n l y b y f o r m u l a t i o n a n d / o r application techniques. With s o i l - b o r n e pathogens, researchers are given the further option of using s o l i d s as c a r r i e r s (Table III). Initially, s o l i d c a r r i e r s were s i m p l e substrates on w h i c h t h e p a t h o g e n g e r m i n a t e d , grew m y c e l i a , a n d sporulated. One c a r r i e r was v e r m i c u l i t e w h i c h was m i x e d w i t h m y c e l i a o f A l t e r n a r i a m a c r o s p o r a Zimm. (24.) . A f t e r s p o r u l a t i o n a n d a i r d r y i n g , t h i s m i x t u r e was a p p l i e d , both preemergence and postemergence, to s p u r r e d anoda (Anoda c r i s t a t a S c h l e c h t ) a n d g a v e 75 t o 95% c o n t r o l o f s e e d l i n g s . However, a t l e a s t two 1 8 h o u r dew p e r i o d s a t 25 C w e r e n e e d e d f o r t h i s l e v e l o f control. The f u n g i c i d e s , PCNB (pentachloronitrobenzene) a n d ETMT [5-ethoxyl-3(trichloromethyl)-1,2,4-thiadiazole], d i d not significantly affect s p u r r e d anoda c o n t r o l w i t h A . macrospora. F i e l d r e s u l t s showed no d i f f e r e n c e between the a p p l i c a t i o n o f A ^ macrospora as a f o l i a r spray o f spores, o r as a g r a n u l a r f o r m u l a t i o n a p p l i e d t o t h e soil (25). F o r many b i o c o n t r o l a p p l i c a t i o n s , a s o l i d m a t r i x that could entrap or encapsulate microorganisms is advantageous. The u s e o f a c h e m i c a l r e a c t i o n between sodium a l g i n a t e (NaAlg) a n d c a l c i u m i o n s t o make g r a n u l e s c o n t a i n i n g any o f a wide v a r i e t y o f m y c o h e r b i c i d e s w a s i n t r o d u c e d i n 1 9 8 3 (4j>) .

2 NaAlg + C a *

->

Ca(Alg) i + 2 N a

+

2

The a l g i n a t e p r o c e s s f o r m y c o h e r b i c i d e f o r m u l a t i o n , w h i c h e v o l v e d from c o n t r o l l e d - r e l e a s e h e r b i c i d e work (47), i s c a r r i e d out i n an aqueous system a t ambient temperature and i s g e n t l e enough f o r use w i t h l i v i n g organisms (48). Uniform size, application using conventional equipment, biodégradation i n the



Spurred anoda Anoda c r i s t a t a S c h l e c h t .

Gliocladium virens M i l l e r , Giddens & F o s t e r

Redroot pigweed Amaranthus r e t r o f l e x u s (L.) η

A l t e r n a r i a macrospora Zimm.

η

S c l e r o t i n i a sclerotiorum (Lib.) de Bary

n

Canada t h i s t l e Cirsium arvense (L.) Scot).

Prickly sida Sida spinosa (L.)

Fusarium l a t e r i t i u m Ness ex F r .

Velvetleaf Abutilon theophrasti

Medik.

π

Fusarium s o l a n i A P P . & Wr. f. sp. c u c u r b i t a e Snvd. & Hans η

M i c r o b i a l Agent

17

16

Ref

kernels

21

20

20

vermiculite

long-grain

rice

24 25

23

peat moss contg. 22 sucrose and ammonium n i t r a t e

wheat

η

a l g i n a t e - k a o l i n granules

a l g i n a t e - k a o l i n granules 18 w/wo 2% w/v soy f l o u r , 19 ground oatmeal/ cornmeal, or carboxymethyl c e l l u l o s e

a l g i n a t e - k a o l i n granules contg. 2% w/v s o y f l o u r

cornmeal/sand

Carrier

Formulations Based upon S o l i d C a r r i e r s

η

II

Texas gourd C u c u r b i t a texana (A.) Grav

Weed

Table I I I .


16. DAIGLE Λ CONNICK

MhvMul Wmd Control

295

environment, a n d s u s t a i n e d a c t i v i t y a r e some p o s i t i v e attributes of alginate granules. Also, alginate g r a n u l e s c o n t a i n i n g k a o l i n (as f i l l e r ) a n d m y c o h e r b i c i d e c a n be p r e p a r e d and s t o r e d f o r up t o 8 months b e f o r e u s e (46). A granular inoculation of Fusarium solani App. & Wr. f . s p . c u c u r b i t a e Synd & H a n s . , p r o d u c e d on a c o r n m e a l / s a n d medium, e f f e c t i v e l y controlled (99% maximum) C u c u r b i t a texana A . Gray (Texas gourd) seedlings (Ij6) . However, a l i q u i d inoculum (2x10 spores/ml) s p r a y e d t o r u n o f f a c h i e v e d t h e same r e s u l t s . Recently, a series of papers u t i l i z i n g the alginate process w i t h t h i s mycoherbicide t o c o n t r o l Texas gourd have been p u b l i s h e d (17-19) . The a d d i t i o n o f n u t r i t i o n a l amendments ( a t 2% w / v ) s u c h a s g r o u n d oatmeal, cornmeal, or soy f l o u r s i g n i f i c a n t l y increased c o n i d i a l p r o d u c t i o n on t h e s u r f a c e o f t h e g r a n u l e s and resulted i n higher s o i l population than granular treatments w i t h o u t amendments o r g r a n u l e s containing carboxymethyl c e l l u l o s e (JL8) . G r a n u l e s amended w i t h soy f l o u r o r ground oatmeal a l s o p r o v i d e d greater control for a longer period than d i d remedial applications (19). These amended g r a n u l e s were applied up t o 6 weeks p r e e m e r g e n c e a n d g a v e g r e a t e r t h a n 80% weed c o n t r o l (18.) .


g

Alginate granules containing Fusarium l a t e r i t i u m Ness ex F r . were as e f f e c t i v e as f o l i a r a p p l i c a t i o n s o f the fungus i n c o n t r o l l i n g e i t h e r v e l v e t l e a f (Abutilon theophrasti Medik.) or p r i c k l y s i d a (Sida spinsosa L . ) i n greenhouse studies (20). The c o n i d i a l suspensions (1.5x10 spores/ml) t h a t were s p r a y e d c o n t a i n e d Tween 80 ( 0 . 0 5 % v / v ) s u r f a c t a n t . In f i e l d t e s t s , granules were s l i g h t l y more e f f e c t i v e against v e l v e t l e a f and slightly less effective against p r i c k l y sida than the c o n i d i a l spray treatment. Throughly colonized (infected) seeds are a commonly u s e d c a r r i e r f o r b i o c o n t r o l microorganisms. For example, inoculum consisting of S c l e r o t i n i a s c l e r o t i o r u m - i n f e s t e d wheat k e r n e l s a n d s c l e r o t i a were hand-broadcast at five different locations to control Canada t h i s t l e rcirsium arvense (L.) Scop.] (21). The m e a n p e r c e n t a g e o f d e a d s h o o t s r a n g e d f r o m 20% t o 80% w h i c h showed a dependence upon l o c a t i o n a n d d a t a collection times. However, at a l l five s i t e s , the percentage o f d e a d s h o o t s was s i g n i f i c a n t l y h i g h e r i n the treated than i n the control plots. G l i o c l a d i u m v i r e n s grown on an a u t o c l a v e d longgrained rice (Orvza sativa) medium p r o d u c e d a phytotoxin, v i r i d i o l , that caused necrosis of germinating cotton (Gossvpium h i r s u t u m L . ) and r e d r o o t pigweed (Amaranthus r e t r o f l e x u s L . ) seed i n the laboratory (.23) . However, a d r i e d and ground p r e p a r a t i o n o f G . v i r e n s c u l t u r e d on r i c e a n d worked into pigweed-infested s o i l above p l a n t e d c o t t o n seed produced v i r i d i o l i n s u f f i c i e n t quantity and duration



296

MICROBES AND MICROBIAL PRODUCTS AS HERBICIDES

to prevent emergence of pigweed without apparent harm to emerging c o t t o n s e e d l i n g s . Sucrose and ammonium n i t r a t e on peat moss, a simple, more economical s u b s t r a t e , has r e c e n t l y r e p l a c e d the r i c e g r a i n (22). Peat moss, because of i t s a c i d i c nature, enhances the s t a b i l i t y of v i r i d i o l . Disadvantages of t h i s system i n c l u d e h i g h a p p l i c a t i o n r a t e s and l o s s of p e r s i s t e n c e . V i r i d i o l p r o d u c t i o n peaks at f i v e or s i x days a f t e r a p p l i c a t i o n and f a l l s t o undetectable l e v e l s by the end of two weeks. Because v i r i d i o l p r o d u c t i o n by £. v i r e n s r e q u i r e s a h i g h - n u t r i e n t s u b s t r a t e , a f o r m u l a t i o n such as a l g i n a t e granules w i t h a p p r o p r i a t e amendments might produce and r e l e a s e v i r i d i o l more s l o w l y and f o r a longer p e r i o d of time. Commercial Mycoherbicide

Products

Cooperation among u n i v e r s i t i e s , government, and i n d u s t r y was e s s e n t i a l i n the c o m m e r c i a l i z a t i o n of the mycoherbicides presented i n Table IV. The f o r m u l a t i o n technology of these m i c r o b i a l agents c o n s t i t u t e s p r o p r i e t a r y i n f o r m a t i o n , but t h e r e are p u b l i s h e d r e p o r t s of the u t i l i z a t i o n of these organisms i n i n t e g r a t e d pest management systems (31-36). C o l l e g o (Ecogen Inc., Langhorn, PA) i s a twocomponent product (,26) . One component i s a watersuspendable d r i e d spore p r e p a r a t i o n of the fungus C o l l e t o t r i c h u m g l o e o s p o r i o i d e s (Penz) Sacc. f . sp. aeschvnomene (CGA). The other i s a r e h y d r a t i n g agent (a sugar) used f o r w e t t i n g the spores t o improve germination. The d r i e d spore component i s packaged by the number of v i a b l e spores r a t h e r than by weight. Each package c o n t a i n s a minimum of 7.57x10 v i a b l e spores. I n i t i a l experiments w i t h C. g l o e o s p o r i o i d e s showed t h a t c o n i d i a l suspensions sprayed u n t i l r u n o f f gave good c o n t r o l of northern j o i n t v e t c h (Aeschvnomene v i r g i n i c a L., B.S.P.) (27). However, t h i s b i o c o n t r o l approach was slower than chemical h e r b i c i d e c o n t r o l by 2,4,5-T [ ( 2 , 4 , 5 - t r i c h l o r o p h e n o x y ) a c e t i c a c i d ] because the i n c u b a t i o n p e r i o d of the fungus was 4 t o 7 days, and the fungus d i d not k i l l the weeds f o r up t o 5 weeks a f t e r treatment. Higher r a t e s of inoculum a p p l i c a t i o n and humidity (warm, moist, cloudy weather and/or f l o o d i n g of the r i c e f i e l d s ) i n c r e a s e d i t s e f f e c t i v e n e s s (28-29). One of the commercial disadvantages of b i o l o g i c a l c o n t r o l i s the h o s t - s p e c i f i c i t y of the pathogen, i . e . , only one weed i s c o n t r o l l e d per a p p l i c a t i o n . The fungus, C o l l e t o t r i c h u m g l o e o s p o r i o i d e s (Penz) Sacc. f . sp. i u s s i a e a (CGJ) was found t o be h i g h l y s p e c i f i c f o r p a r a s i t i s m of winged waterprimrose (Ludwigia decurrens Walt. ) , a weed endemic i n r i c e growing regions (30.) CGJ was p h y s i o l o g i c a l l y d i s t i n c t from CGA as i n d i c a t e d by cross i n o c u l a t i o n of t h e i r r e s p e c t i v e t a r g e t weeds.



(L.)

* Nearing commercialization E x p e r i m e n t a l p r o d u c t - no l o n g e r

Sicklepod Cassia obtusifolia

available

Alternaria J u r a i r and

Butl.

cassiae Khan

rodmanii

Cercospora Conway

(Mart.)

Waterhyacinth Eichhornia crassipes Solms

Phvtophthora palmivora (Butl.) (chlamydospores)

Colletotrichum gloeosporioides (Penz.) Sacc. f. sp. aeschvnomene

Agent

Colletotrichum gloeosporioides f. sp. malvae

(Lindl.)

(L.)

Microbial

Round-leaved mallow Malva p u s i l l a (Sm.)

Stranglervine Morrenia odorata

Northern jointvetch Aeschvnomene v i r g i n i c a B.S.P.

Weed

Table IV. Commercial M i c r o b i a l Agents

a

b

Name

40-42

39

36-38

26-35

Ref

MYD 7 5 1 M (oil)* a n d MYX 1 0 4 (spores)

ABG-5003

BioMal

DeVine

Collego

Commercial



298


A s p o r e s u s p e n s i o n m i x t u r e c o n t a i n i n g 2x10 spores/ml CGA a n d 1x10 s p o r e s / m l C G J a p p l i e d a t 94 L / h a c o m p l e t e l y c o n t r o l l e d b o t h weeds, g r e a t l y enhancing t h e u t i l i t y o f t h i s c o n t r o l method. To i n c r e a s e t h e m a r k e t a b i l i t y o f C o l l e g o , i t s c o m p a t i b i l i t y with chemical p e s t i c i d e s has been investigated. M i x t u r e s o f CGA w i t h p r o p a n i l [N-(3,4dichlorophenyl)propanamide], molinate [S-ethyl hexahydro-lH-azepine-l-carbothioate], 2,4,5-T, and benomyl [methyl 1-(butylcarbamoyl)-2benzimidazolecarbamate] were d e t r i m e n t a l t o C G A ' s efficacy (31). I f , however, p r o p a n i l , 2 , 4 , 5 - T , fentin hydroxide (triphenyltin hydroxide), pencycuron {N-[(4chlorophenyl)methyl]-N-cyclopentyl-N'-phenylurea}, each at 0.56 k g a i / h a , a n d SN-84364 [3'-isopropoxy-2(trifluoromethyl) benzanilide] (at 0.40 kg a i / h a ) were a p p l i e d a f t e r CGA t r e a t m e n t , disease and development w e r e n o t i n h i b i t e d (32.) . The h e r b i c i d e s , acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid) (0.56 kg a i / h a ) and bentazon [3-(1-methylethyl)(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] (0.56 t o 1.1 k g a i / h a ) , or the insecticides, malathion [diethyl(dimethoxyphosphinothioylthio)succinate] (0.56 kg a i / h a ) and carbofuran (2,3-dihydro-2,2-dimethyl-7benzofuranyl methylcarbamate), (0.56 kg a i / h a ) c o u l d be a p p l i e d w i t h CGA f r o m a s i n g l e t a n k m i x t u r e (33-34). Because a c i f l u o r f e n a p p l i e d postemergence effectively c o n t r o l s hemp s e s b a n i a rsesbania exaltata ( R a f . ) R y d b . e x A . W. H i l l ] i n s o y b e a n s (Glycine max). the combined a p p l i c a t i o n o f t h e h e r b i c i d e and CGA, respectively, c o n t r o l s hemp s e s b a n i a a n d n o r t h e r n jointvetch (35). The use o f a low-volume (21.5 L / h a ) c o n t r o l l e d d r o p l e t a p p l i c a t o r (CDA) (spinning-disc) with such a combination produced mixed r e s u l t s . If u n f a v o r a b l y d r y e n v i r o n m e n t s e x i s t e d when t h e CGA was u s e d , i n f e c t i o n was r e d u c e d r e s u l t i n g i n u n s a t i s f a c t o r y weed c o n t r o l . B e n o m y l (33) a n d p r o p i c o n a z o l {2[[2(2,4-dichlorophenyl)-4-propyl-l,3-dioxalan-2yl]methyl]-1H-1,2,4-triazole} (32) a p p l i e d sequentially 7 a n d 14 d a y s a f t e r C G A s u p p r e s s e d t h e g r o w t h a n d development of the pathogen. DeVine (Abbott L a b o r a t o r i e s , N o r t h C h i c a g o , IL) has as i t s a c t i v e i n g r e d i e n t t h e l i v e chlamydospores o f Phytophthora palmivora (Butler) Butler. The commercial formulation i s stable under r e f r i g e r a t i o n f o r only s i x weeks a n d must b e a p p l i e d t o wet s o i l . The v i a b i l i t y o f D e V i n e may b e r e d u c e d b y t h e f u n g i c i d e s Aliett [aluminum t r i s ( e t h y l phosphonate)] and Ridomil [methyl N-(2-methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate]. If f u n g i c i d e s a r e t o be used, a p p l i c a t i o n s h o u l d o c c u r 4 5 60 d a y s p r i o r t o o r a f t e r t h e D e V i n e t r e a t m e n t (36-38) . H e r b i c i d e s such as d i u r o n [Ν'-(3,4-dichlorophenyl)-N,Ndimethylurea], glyphosate [N-(phosphonomethyl)glycine], and paraquat (1,1'-dimethyl-4,4'-bipyridinium ion) also i n h i b i t e d the efficacy of DeVine. The pathogen,



16. DAIGLE A CONNICK


299

however, c o u l d be a p p l i e d t h r e e weeks a f t e r s p r a y i n g glyphosate Q l ) · The product, BioMal (PhilomBios, Saskatoon, Sask., Canada), which c o n t a i n s the mycoherbicide, C o l l e t o t r i c h u m g l o e o s p o r i o i d e s f . sp. malvae, i s n e a r i n g c o m m e r c i a l i z a t i o n ( G a n t o t t i , Β. V., PhilomBios, Saskatoon, Sask., Canada, p e r s o n a l communication). The fungus i s a pathogen o f round-leaved mallow (Malva p u s i l l a Sm.), a common p r a i r i e weed i n Canada t h a t has become a problem i n c u l t i v a t e d crops. An i n i t i a l f o r m u l a t i o n of BioMal, u s i n g standard technology such as a s i l i c a g e l c a r r i e r , has proven very e f f e c t i v e i n the f i e l d . The wettable powder f o r m u l a t i o n of t h i s h y d r o p h i l i c fungus d i s p e r s e s e a s i l y i n water and i s a p p l i e d as a spray. However, f o r e f f e c t i v e weed c o n t r o l , an overnight dew p e r i o d i s e s s e n t i a l (.39) . In s p i t e of t h e e f f o r t s of s e v e r a l r e s e a r c h groups over a 10-20 year p e r i o d , t h e r e are no m i c r o b i a l agents now i n commercial use f o r a q u a t i c weed c o n t r o l . Abbott L a b o r a t o r i e s had developed an experimental wettable powder f o r m u l a t i o n f o r Cercospora rodmanii Conway, a pathogen used t o c o n t r o l waterhyacinth r E i c h h o r n i a c r a s s i o e s (Mart.) Solms] (4£) . The f o r m u l a t i o n contained 4.54x10 propagules p e r pound and t h e spray mixture c a l l e d f o r T r i t o n X-100 t o be added by the user. One of the environmental o b s t a c l e s t o the e f f i c a c y of t h i s pathogen was temperature. I t must be a p p l i e d when daytime temperatures are above 16°C and lower than 32°C. A l s o , when t h e host growth was r a p i d , long-term b i o c o n t r o l w i t h a s i n g l e a p p l i c a t i o n was not obtained (41.) . An approach now under e v a l u a t i o n i s t h e use o f combinations of £. rodmanii and i n s e c t b i o c o n t r o l agents, o r t h e pathogen p l u s s u b l e t h a l r a t e s of chemical h e r b i c i d e s (Charudattan, R., Univ. of F l o r i d a , G a i n e s v i l l e , FL, unpublished r e s u l t s ) . Experimental r e s u l t s confirmed t h a t n e i t h e r t h e pathogens nor t h e arthropods, m o t t l e d waterhyacinth w e e v i l , Neochetina e i c h o r n i a e Warner; chevroned waterhyacinth w e e v i l , N. b r u c h i Hustache (both C o l e o o t e r a , C u r c u l i o n i d a e ) ; the moth, Sameodes a l b i g u t t a l i s (Warren) ( L e p t i d o p t e r a , P v r a l i d a e ) ; a mite, Orthogalumna t e r e b r a n t i s Wallwork (Acarina, Galumnidae); and t h e moth, Arzama densa Walker (Leoidoptera, Noctuidae), alone completely c o n t r o l l e d waterhyacinth (£0) . By combining t h e pathogen w i t h the arthropods, 99% c o n t r o l was achieved i n 7 months. L i m i t e d experiments w i t h s u b l e t h a l r a t e s of glyphosate, t h i d i a z u r o n [l-phenyl-3-(1,2,3t h i a d i a z o l - 5 - y l ) u r e a ] , ethephon (2c h l o r o e t h y l p h o s p h o r i c a c i d ) , 2,4-D [(2,4d i c h l o r o p h e n o x y ) a c e t i c a c i d ] , and diquat (1,1'e t h y l e n e - 2 , 2 ' - d i p y r i d y l i u m i o n ) , i n combination w i t h the pathogen d i d not enhance c o n t r o l o f w a t e r h y a c i n t h . An experimental f o r m u l a t i o n of A. c a s s i a e t o c o n t r o l s i c k l e p o d i n soybeans and peanuts (Arachis



300


hvpogea) has been d e v e l o p e d by t h e Mycogen Corporation (San D i e g o , C A ) . It i s a two-component product consisting of: (a) a n e m u l s i f i a b l e p a r a f f i n i e oil ( d e s i g n a t e d MYD 7 5 1 M ) , a n d (b) s p o r e s o f A . cassiae (MYX 1 0 4 , 100% a i ) . To p r e p a r e t h e s p r a y m i x t u r e , the o i l c o m p o n e n t i s f i r s t e m u l s i f i e d i n w a t e r a t a 1% (v/v) c o n c e n t r a t i o n and t h e n t h e s p o r e s a r e a d d e d a n d d i s p e r s e d by s t i r r i n g . This formulation i s a p p l i e d at a r a t e o f about 0.4 l b s p o r e s / h a t o s i c k l e p o d i n t h e cotyledon to 2 - l e a f stage of development (Bannon, J. S . , Mycogen C o r p . , R u s t o n , LA, p e r s o n a l c o m m u n i c a t i o n ) . Integrated

Weed Management

System with

Microorganisms

In r e c e n t y e a r s , one p r i o r i t y i n a g r i c u l t u r a l research t o r e d u c e t h e amount o f h e r b i c i d e a p p l i e d . To do t h i s , r e s e a r c h e r s have d e v e l o p e d an i n t e g r a t e d weed m a n a g e m e n t s y s t e m (IWMS) (.49) . Some e x a m p l e s o f this approach have a l r e a d y been d i s c u s s e d . IWMS u t i l i z e s the d i f f e r e n t combinations and i n t e r a c t i o n s between . b e n e f i c i a l insects, chemical herbicides, microorganisms, and p l a n t growth r e g u l a t o r s t o control a b r o a d s p e c t r u m o f weeds b e c a u s e no s i n g l e a g e n t gives optimum r e s u l t s . The r u s t f u n g u s , P u c c i n i a c a n a l i c u l a t a (Schw.) Lagerh., d i d not give complete b i o l o g i c a l c o n t r o l of yellow nutsedge (Cyprus e s c u l e n t u s L.) even under the best c o n d i t i o n s f o r i n f e c t i o n and d i s s e m i n a t i o n (50). U r e d i n i o s p o r e s u s p e n s i o n s c o n t a i n i n g T r i t o n Β 1956 ( 0 . 1 % v / v ) g a v e o n l y 60% c o n t r o l (53). However, application of the chemical herbicide, paraquat, after t h e r u s t e p i p h y t o t i c w a s d e v e l o p e d g a v e 99% c o n t r o l c o m p a r e d t o 10% w i t h p a r a q u a t a l o n e . Preliminary results indicated that a beneficial interaction o c c u r r e d when a s e q u e n t i a l a p p l i c a t i o n o f r u s t followed imazaquin (51-53). E n h a n c e d c o n t r o l was a l s o observed a f t e r u s i n g a mixture of the Maryland r u s t s t r a i n and bentazon (54). Both i n s e c t - m i c r o o r g a n i s m and chemical treatmentmicroorganism i n t e r a c t i o n s have r e c e n t l y been s t u d i e d i n the c o n t r o l of v e l v e t l e a f by r e d u c t i o n of seed viability (55-57). Niesthea lousianica Sailer, a n a t i v e s c e n t l e s s p l a n t bug, has been found t o reduce production of v i a b l e v e l v e t l e a f seed d i r e c t l y through f e e d i n g and promoting i n f e c t i o n of seed w i t h detrimental microorganisms. Three main f u n g a l genera ( A l t e r n a r i a , C l a d o s p o r i u m , and Fusarium) and t h r e e b a c t e r i a l genera (Pseudomonas, E s w i n i a , and F l o r o b a c t e r i u m ) were c o n s i s t e n t l y i s o l a t e d f r o m nonviable seed. S e l e c t i o n of t h e most effective m i c r o o r g a n i s m f o r s e e d d e t e r i o r a t i o n may i m p r o v e t h i s approach. Chemical treatment of the s o i l with e t h e p h o n , AC94377 [1-(3-chlorophthalimido)cyclohexane carboximide], butylate (S-ethyl d i isobutylthiocarbamate), or carbofuran plus Fusarium sp.



16.

DAIGLE & CONNICK


301

r e s u l t e d i n nonviable seed h e a v i l y i n f e c t e d with mycelia (52) . Ethephon or carbofuran i n combination with Fusarium sp. a l s o r e s u l t e d i n a reduction i n emergence. The pathogen was d e l i v e r e d on a shredded wheat medium. Another promising IWMS strategy t o c o n t r o l v e l v e t l e a f i n v o l v e s the spray a p p l i c a t i o n of tank-mix combinations of the p l a n t pathogenic fungus C o l l e t o t r i c h u m coccodes (Wallr.) Hughes and the p l a n t growth r e g u l a t o r t h i d i a z u r o n (N-phenyl-N'-1,2,3thiadiazol-5-yl-urea) ( 5 8 - 5 9 ) . The t h i d i a z u r o n causes severe s t r e s s i n v e l v e t l e a f by i n h i b i t i n g stem elongation, l e a f development, and flowering, and the C o l l e t o t r i c h u m causes l e a f n e c r o s i s and a b s c i s s i o n . Use of t h i s combination i n f i e l d t r i a l s l e d t o s i g n i f i c a n t v e l v e t l e a f c o n t r o l and increased soybean yield. Epilogue Researchers have taken d i f f e r e n t approaches i n t h e i r e f f o r t s t o improve germination of mycoherbicides and/or i n f e c t i o n of t a r g e t weeds. One approach has c a l l e d f o r d i r e c t p r o v i s i o n of water i n c a r r i e r s formulated t o r e t a r d water evaporation. Except i n those few cases where high humidity or dew i s n a t u r a l l y present ( i n flooded r i c e f i e l d s , over ponds c o n t a i n i n g water hyacinths, or i n wet s o i l ) , p r e d i c t i o n of a dew f a l l i s u s u a l l y not adequate f o r r e l i a b l e r e s u l t s . Preliminary i n v e s t i g a t i o n of water-holding formulations have shown promise, but weed m o r t a l i t y has not been s u f f i c i e n t or consistent. A second approach, the use of humectanttype adjuvants, e.g., a sugar, has been s u c c e s s f u l i n the formulation of C o l l e g o . Sugars have a l s o been used s u c c e s s f u l l y i n s o l i d c a r r i e r formulations t o promote growth of the pathogen (22). A v i a b l e concept that has not been s u f f i c i e n t l y e x p l o i t e d i s the use of adjuvants that i n t e r a c t with the p l a n t and/or m i c r o b i a l agent t o promote the e f f i c a c y of the i n f e c t i o n process. Because each disease and host b i o l o g y combination i s unique (see Chap. 11, 12), the formulator's challenge i s formidable. M i c r o b i a l i n t e r a c t i o n on p l a n t surfaces should a l s o be considered i n the development of formulations f o r b i o l o g i c a l weed c o n t r o l . Researchers i n i n t e g r a t e d weed management s t u d i e s have proposed that a v a r i a t i o n of the concept i s p o s s i b l e now with the a d d i t i o n of chemical h e r b i c i d e s and/or i n s e c t s . The a d d i t i o n a l s t r e s s (chemical and p h y s i c a l i n j u r y ) i n f l i c t e d by these agents makes some m i c r o b i a l agents more efficacious. The promise of widespread use of m i c r o b i a l agents as h e r b i c i d e s may f i r s t be r e a l i z e d through i n t e g r a t e d weed management systems that broaden the spectrum of weeds c o n t r o l l e d by one a p p l i c a t i o n .


302


Literature Cited 1. 2.


3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.

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1990


Formulation and Application Technology for Microbial Weed Control

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