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II. Development of Herbicide Antidotes

II. Development of Herbicide Antidotes

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HERBICIDE ANTIDOTES



27 1



opment of weed science it was realized that the growth responses of a single plant

species to combined applications of two or more herbicides could not always be

predicted from the responses of the same plant to each chemical applied individually. Depending on the types of interactions of herbicides applied as a

mixture, these responses have been described as synergistic, antagonistic, or

independent (Putnam and Penner, 1974). Two chemical components of a mixture

are said to interact synergistically when they complement the action of each other

such that the total effect of their cooperative action is greater or more prolonged

than the sum of the two components taken independently. Antagonism is a term

used to describe the opposing action of two or more chemicals such that the

action of one is impaired or the total effect of their cooperative action is smaller

than the effect of the most active component alone. Two chemicals are said to

interact independently when the total effect of their cooperative action is equal to

the effect of the most active component of the mixture alone.

Understanding antagonistic herbicides interactions is essential for the development of effective herbicide antidotes. It was the observation of the antagonistic

interaction of two herbicides that was instnunental in the development of the

concept of using chemical antidotes to increase crop tolerance to herbicides. In

1947 Hoffman noticed that 2,4,6-T, an inactive analog of the herbicide 2,4-D,

antagonized the epinastic growth caused by sublethal doses of 2,4-D on tomato

(Hoffman, 1953). Because of the structural similarity existing between 2,4,6-T

and 2,4-D, a competitive inhibition at some common site of action was proposed

as an explanation for the observed antagonism. Hoffman continued his efforts in

che area of biologically important chemical interactions and in 1960 he reported

that the injurious effects of the carbamate herbicide barban on wheat could be

antagonized by 2,4-D (Hoffman et al., 1960). Because barban and 2,4-D are

structurally different, the hypothesis of a competitive inhibition of these two

chemicals at a common site of action was ruled out as an explanation for the

observed antagonism. Instead, because 2,4-D accelerates plant growth and barban slows it down, Hoffman (1962) hypothesized that 2,4-D and barban may act

at the same site with opposite effects. Indeed, 10 years later Beste and Schreiber

(1970, 1972a,b) supported the hypothesis of Hoffman when they showed that

whereas EFTC, another carbamate herbicide, inhibited ribonucleic acid (RNA)

synthesis, 2,4-D enhanced it, even in the presence of EPTC. Efforts by Hoffman

to make practical use of the antagonism of barban by 2,4-D on wheat failed

because 2,4-D or other phenoxyacetic acid herbicides were too toxic to be useful

as seed dressings, and foliar sprays with 2,4-D would also antidote barban effects

on wild oats, a serious weed problem in wheat.

Subsequent screening efforts by Hoffman using other chemicals that caused

2,4-D-like symptoms on tomato but were safe as dressings of grass crop seeds

met with success. In 1962 Hoffman introduced the concept of chemically enhancing crop tolerance to herbicides by introducing the compound s-449 as an

effective chemical antidote against barban injury to wheat (Hoffman, 1962).



272



IUUTON K. HATZIOS



Hoffman continued his efforts and in 1969, 21 years after his initial observation

of the 2,4-D antagonism by 2,4,6-T on tomato, introduced the compound 1,8naphthalic anhydride (NA) as an effective protectant of corn against injury from

the herbicide EPTC (Hoffman, 1969). 1,&Naphthalicanhydride became the first

commercialherbicide antidote and in 1971it was patented by Gulf Oil Chemicals

Company (Hoffman, 1971). At the same time, researchers of Stauffer Chemical

Company discovered that dichloroacetamidederivatives were effective antidotes

of thiocarbamateherbicides on corn, and the compound R-25788 was patented in

1972 as the second commercially developed herbicide antidote (Pallos ef al.,

1972,1977). In 1974 the antidotal properties of oxime ethers were discovered in

Switzerland by researchers at the Ciba-Geigy Corporation. After extensive field

evaluation of these chemicals in the United States, CGA-43089, the most promising of these compounds to protect grain sorghum against injury from the

herbicide metolachlor, was patented in 1978 as the third commercial antidote

(Martin, 1978). A few years later, Monsanto Company introduced MON-4606,a

derivative of 2,4-disubstituted 5-thiazolecarboxylicacid, as a new safening agent

for alachlor injury to grain sorghum (Howe and Lee, 1980). MON-4606 is

presently being developed as the fourth commercial herbicide antidote. Finally,

CGA-92194, a chemical analog of CGA-43089, was introduced by the CibaTABLE III

Major Events in the Development of Herbicidal Antidotes



YtW



Event



1947

1960

1%2



Hoffman observed the antagonistic interaction of 2,4,6-T and 2,4-D on tomato

Hoffman demonstrated that barban injury to wheat could be antagonized by 2,4,-D

Hoffman introduced the concept of a chemical herbicide antidote by introducing the chemical S-449 as an effective antidote of barban injury to wheat

Hoffman introduced 1.8-naphthalic anhydride (NA) as an antidote against EFTC injury to

corn

Pallos er al. discovered R-25788 and other dichloroacetamides as effective chemical antidotes against thiocarbamate injury to corn

1,8-Naphthalic anhydride was patented as the first commercial herbicide antidote (U.S.

Patent No. 3,564,768)

R-25788 was patented as the second commercial herbicide antidote (Belgian Patent No.

782,120; U.S.Patent No. 4,021,224)

Martin discovered the antidotal properties of oxime ethers against chlomacetanilide herbicide injury to grain sorghum

CGA-43089 was patented as the third commercial herbicide antidote (U.S. Patent No.

4,070,289)

Howe and Lee introduced 2,4-disubstituted 5-thiazolecarboxylic acids as effective antidotes

against chlomacetenilide herbicide injury to grain sorghum (US.Patent No. 4,199,506)

The Ciba-Geigy Corporation introduced CGA-92194 as an effective antidote against metolachlor injury to grain sorghum (U.S. Patent No. 4,269.775)



1%9

1970

1971

1972

1974

1978

1980

1982



HERBICIDE ANTIDOTES



273



Geigy Corporation (Dill et al., 1982) as the fifth commercially developed herbicide antidote. CGA-92194 is also a grain sorghum protectant against

metolachlor injury. A brief summary of the major events that played a key role in

the development of herbicide antidotes is given in Table III.

B.



SEARCH FOR



HERBICIDE'

ANTIDOTES



I . Important Considerations

In general, the process of discovering and developing effective herbicide

antidotes resembles very much that of the commercial development of herbicides. Both of these processes are quite lengthy and very expensive, primarily

because of the increased governmental clearance requirements regulating

pesticide registration. The use of random screening techniques has been long

recognized as the preferred approach of the herbicide industry in finding and

evaluating candidate chemicals as herbicides. The selection of candidate chemicals for inclusion in screening tests evaluating herbicidal activity can be based on

three main methods, known as the empirical, imitative, and rational methods

(Saggers, 1976). The empirical method is based on experiment and observation

and includes the synthesis or acquisition of a large number of novel compounds

with unknown biological properties, which are tested for possible activity. Commonly, one compound for each 12,000 or more screened is developed commercially as a herbicide (Krzeminski and Ryan, 1980). However, this method is very

popular in spite of its low ratio of success because of its excellent chances for

exclusive patentability of discovered active compounds. The imitative method is

based on the synthesis of derivatives or analogs of existing compounds with

known biological activity and selectivity. Obviously, this method has a much

higher ratio of success than the empirical method, but its potential for exclusive

patentability of discovered active chemicals is very limited. The third method,

known as the rational method, is based on the selection of compounds that have

been specifically synthesized to interfere with a desired biochemical or physiological plant process. Application of this method in herbicide development has

been very limited.

Random screening techniques based primarily on the empirical and to a lesser

extent on the imitative method of selecting candidate chemicals also have been

instrumental in the commercial development of herbicide antidotes. Herbicide

antidoting, however, is very much dependent on the specific interactions of three

main factors; the crop to be protected, the herbicide to be antidoted, and the

potential antidote. Furthermore, because a desirable screening program for candidate antidotes must be economical, the program has to be selective as to the

crops and herbicides that need to be considered. The primary screening tests for

herbicide antidotes should involve most combinations of important herbicides,



274



W O N K. HATZIOS



possible antidotes, and major crops. On a worldwide basis, the major crops of

importance include corn, wheat, soybeans, rice, grain sorghum, cotton, barley,

oats, rye, sugar beets, potato, and alfalfa. A number of selective herbicides are

already available for controlling problem weeds in these crops and there is no

doubt that new ones will be developed in the future. However, as the weed

complexes affecting any given crop are in continual change and new weed

problems develop as existing problems are solved, the need for alternative herbicides to deal with these new weed problems continues. Alternative herbicides

to control weeds that have developed resistance to triazine herbicides are very

much needed at the present time for weed control programs in corn. Weeds that

bear a very close botanical relationship to a given crop have always been difficult

to control because the existing herbicides that are effective in controlling them

are frequently injurious to the respective crops. The problem is exemplified by

our limited success in the chemical control of wild oats in cultivated oats,

shattercane in cultivated grain sorghum, and wild rice in cultivated rice. Herbicides and crops in this kind of situation need to be seriously considered for

inclusion in screening programs of candidate antidotes. Most of the success in

developing herbicide antidotes has been with antidoting such herbicides on several grass crops (Blair et al., 1976; Pallos and Casida, 1978; Parker, 1983).

Candidate antidotes that are effective in protecting one or more major crops

against one or more important herbicides are identified in the so-called primary

antidote screen. This process includes laboratory and greenhouse multiple

crop-multiple herbicide screening assays and a large number of candidate antidotes. The antidotes that show promise in the primary screen are further evaluated for their practical value under field conditions in the so-called secondary

antidote screen. The most important properties of an antidote that are considered

during this stage are selectivity, optimum rates for antidotal activity, antidote-toherbicide dosage ratios, suitability of active material for practical fomulations,

and reliability of the antidote under field conditions. A herbicide antidote is said

to be selective when it counteracts herbicides only on crop plants and not on

weed species. In practice, the selectivity of herbicide antidotes is primarily the

result of a selective placement, which usually is the coating of crop seeds with

the antidote. Thus, coating of corn and grain sorghum seeds with the herbicide

antidotes NA and CGA-43089 offers sufficient protection to these crops against

injury from the herbicides EFTC and metolachlor, respectively, without protecting any weeds. In some cases, however, the selectivity of a herbicide antidote

could be the result of a very specific crop-herbicide-antidote interaction such as

occurs with corn-EFTC-R-25788. Broadcast application of the antidote

R-25788 offers good protection against EFTC injury only to corn and not to any

other grass or broad-leaved weeds that are present in the field (Stephenson and

Chang, 1978). Eventually, it is the suitability of a candidate antidote for practical

use in the field that determines whether or not this compound will be further

developed commercially. Several of the important considerations for the evalua-



HERBICIDE ANTIDOTES



275



tion and development of candidate antidotes are discussed briefly in the next

section.



2. Screening of Candidate Antidotes

a. Antidotes for Chloroacetanilide and ThiocarbamateHerbicides. The first

empirical screening tests of candidate herbicide antidotes were conducted by

Hoffman (1962, 1978a), who found that with the exception of herbicides that

inhibit photosynthesis at photosystem II, most of the important herbicides could

be antidoted to some extent on some crop. By using multiple crop-multiple

herbicide screening assays, Hoffman showed that the tolerance of all grass crops

to chloroacetanilideor thiocarbamate herbicides could be enhanced chemically to

some extent. In particular, the chloroacetanilide herbicide alachlor could be

antidoted on many grass crops, including rice, grain sorghum, wheat, oats,

barley, and rye, by more antidotes than any other available herbicide (Hoffman,

1978a). The highest ratio of success in Hoffman’s screening assays, however,

was obtained with antidoting the thiocarbamate herbicide EFTC on corn. Hoffman screened over 4000 chemicals as candidate antidotes and observed that 40%

(1600) of these chemicals could antidote EPTC injury to corn to some extent

when applied as seed treatments (Hoffman, 1978a). The great majority of these

chemicals were identified as amides or as ketone, acid, or amhe derivatives.

Further evaluation led to the discovery and commercial development of NA as an

antidote against EPTC injury to corn (Hoffman, 1969, 1971). In early studies

(Giineyli, 1971), it was found that broadcast applications of NA to the soil were

not practically effective because high rates (28 kg/ha) were required for antidoting EPTC injury to corn. Application of NA to the soil offered good protection to

many weeds such as green foxtail (Stephenson and Chang, 1978). Therefore, in

order to be selective NA must be applied as a seed treatment. Treatment of corn

seeds with 5 g NA/kg of seed (0.5%) appears to be the optimum rate for antidotal

activity, although rates as high as 2% have been reported as effective (Blair et

al., 1976).

As shown in Table IV, NA as a seed dressing is a very versatile herbicide

antidote exhibiting limited botanical or chemical specificity; it can offer complete protection to corn, grain sorghum, rice, oats, and wheat against a number

of herbicides such as the thiocarbamates, chloroacetanilides, barban, and perfluidone. In addition, NA is capable of offering partial protection to several grass

crops against injury from a number of herbicides shown in Table IV. In practice,

NA is not effective in protecting broad-leaved crops against herbicide injury.

However, seed treatment with NA has resulted in partial protection against EPTC

injury to field beans (Blair, 1979); DCPA, diphenamid, and trifluralin injury to

tomato (Blumenfeld et al., 1973); and cisanilide injury to cotton (Holm and

Szabo, 1974). In Tables IV-VIII, which summarize the main crop-herbicide



KRITON K. HATZIOS



276



Table N

Eft'icacy of the Antidote NA as a Crop Protectant Pgoiost Herbicide Iqjury

crops protected

Herbicides

counteracted



Complete

protection



Reference



Partial

protection



Reference



ChloroaCetgnilides



Alachlor



Sorghum



Rice



Catizone (1979); Hahn

(1974); Jordan and

Jolliffe (1971); Rains

and Fletchall (1971);

da Silva (1978); Spotanski and Bumside

(1973); Truelove and

Davis (1977); Whitwell and Santelman

(1975)

de Andrade (1981);

Parker and Dean

(1976)



Corn



Sorghum

Kentucky

bluegrass

Timothy

Bertges (1977)



Acetochlor



Corn



Butachlor



Sorghum

Sorghum



Rice

Diethatyl



Corn



H-26910

Metolachlor



Sorghum



Rice



Leavitt and Penner

(1978a)

Eastin (1972)

Bertges (1977)



Leavitt and Penner

(1978a)

Eastin (1972)

Ali and Mercado

(1980)

Parker and Dean

(1976); Wirjahardja

and Parker (1977)

Leavitt and Penner

(1978a)

Leavitt and Penner

(1978a)



Truelove and Davis

(1977)

Parker and Dean (1976)

Bertges (1977)

Kentucky

bluegrass

Bertges (1977)

Timothy



Propachlor



Thiowbamates



m



Corn



Ahle and Cozart

(1972); Burnside et

al. (1971); Chang er

al. (1973b); Giineyli

(1971); Gupta and

Niranwal(l976);

Hoffman (1969);

Jeffery and Connel

(1973); Leavitt and



Jeffery et al. (1971);

Lee et ~ l (1974b);

.

Wicks et ~ l (197lb)

.

Blumenfeld et al.

Sorghum

(1973)

Field beans Blair (1979)

Corn



277



HERBICIDE ANTIDOTES



Table IV Continued

Crops protected

~



Herbicides

counteracted



Butylate



Complete

protection



Corn



Reference



Penner (1978a); Lee

er al. (1974a); Peters

and Dest (1971);

Phatak and Bouw

(1974); Rains and

Fletchall (1971,

1973); Reeder

(1970); Rceth

(1973); Schmer et al.

(1973); Schwartzbeck and Hoffman

(1973); Wicks et al.

(1971a)

Roeth (1973)

Corn



Sorghum



Cycloate

Diallate



Sorghum



Mohate



Rice



Thiobencarb



Rice



Triallate



Jordan and Jolliffe

Oats

(1971)

de Andrade (1981);

Henry (1972); Parker

and Dean (1976);

Price and Merkle

(1977); Smith

(1971); Wirjahardja

and Parker (1977)

Henry (1972); Wyahardja (1979); Wyahardja and Parker

(1977)

Oats

Wheat

Corn



Vernolate

Phenylcarbamates

Barban



Partial

protection



Corn

Oats



Blair (1978)

Ali and Stephenson



Corn



Reference



Burnside et al. (1971);

Jeffery et al. (1971);

Wicks et al.

(1971a,b)

Blumenfeld et al.

(1973)

Chang et al. (1974b)



Chang et al. (1974b)

Blair (1979); Miller

and Nalewaja (1980)

Lee et al. (1974b);

Schmer et al. (1973)



Ali and Stephenson

(1979)



KRITON K. HATZIOS



278



Table N Continued

crops protected

~~~~~



Herbicides

counteracted



Complete

protection



Wheat

Terbutol



Amides

Butam

Cisani1ide



~



Reference



~



Partial

protection



(1979); Chang et al.

(1974b); Thiessen et al.

(1980)

Miller et al. (1978)

Bertges (1977)

Kentucky

bluegrass

Bertges (1977)

Timothy

Corn



Diphenamid



Corn

Cotton

Sorghum

Tomato



Dinitroanilines

Pendimethali



Sorghum



Trifluralin



sorghum



Tomato

Miscellaneous

Buthidazole

Chlorsulfuron



Reference



corn

Corn



Sorghum



Rice

Barley

Wheat

DCPA



Tomato



Diclofop-methyl

Dimefuron



Corn



Dowco 221

Epnmaz



Rice



Corn

Rice



Richardson and Parker

(1977)

Holm and Szabo (1974)

Holm and Szabo (1974)

Holm and Szabo (1974)

Blumenfeld et al.

(1973)

Ali and Mercado

(1980)

Blumenfeld et al.

(1973)

Blumenfeld er al.

(1973)

Hatzios and Penner

(1980)

Hatzios (1983b); Parker

(1981); Parker et al.

(1980); Richardson

er al. (1981)

Hatzios and Mauer

(1983); Parker er al.

(1980)

Parker (1981); Parker

et al. (1980)

Parker et al. (1980)

Parker et al. (1980)

Blumenfeld et al.

(1973)

Parker (1981)

Richardson and Parker

(1977)

Parker and Dean (1976)

Parker and Dean (1976)



279



HERBICIDE ANTIDOTES



Table IV Continued

Crops protected

Herbicides

counteracted



Complete

protection



Reference



Ethofumesate

Flumifop-butyl



Partial

protection

Rice

Corn

Sorghum



Mefluidide

NP 55

Perfluidone



Corn



Corn

Corn

Sorghum



Sethoxydim



Blair and Dean (1976);

Parker (1981)

Parker (1981)



Rice



Corn

Sorghum



Reference

Parker and Dean (1976)

Hatzios (1983b); Parker

(1981)

Hatzios and Mauer

(1983)

Parker (1 98 1)

Parker (1981)

Parker and Dean (1976)



Hatzios (1983b)

Hatzios and Mauer

(1983)



interactions that have been reported for the five commercially developed herbicide antidotes, the term complete protection denotes the protection offered by a

given antidote that has been described in the literature as excellent, good, sufficient, significant, or effective, whereas the term partial protection refers to what

has been described as moderate, limited, marginal, or low protection.

The development of R-25788 and other dichloroacetamide derivatives as effective antidotes against thiocarbamate injury to corn appears to be an example of

the application of the imitative method for selecting candidate antidotes. Support

for this conclusion comes from the fact that chloroacetamides had been introduced as effective herbicides (Hamm and Speziale, 1956) and the potential of

chloroacetanilide compounds as herbicide antidotes had been reported long before the discovery of R-25788 (Hoffman, 1962). In fact, the structural similarity

of the antidote R-25788 to the chloroacetamide herbicide CDAA is remarkable,

and the potantial activity of CDAA as a herbicide antidote against EPTC or other

herbicide injury to corn has been documented (Chang et al., 1973b; Leavitt and

Penner, 1978a; Hatzios and Penner, 1980). Of more than 500 N,N-substituted

amides that showed initial promise as antidotes against thiocarbamate injury to

corn, R-25788 was the most active and best suited for practical application

(Pallos et al., 1977). Early studies with field applications of R-25788 showed

that this compound was equally effective in protecting corn from EPTC whether

applied as a seed treatment at a rate of 0.1% (w/w) or as a tank mixture with

EPTC incorporated into the soil (Pallos et al., 1975). Soil applications of

R-25788 did not' provide any protection to any grass or broad-leaved weeds



280



KRITON K. HATZOS



(Stephenson and Chang, 1978). Thus R-25788 exhibits a high degree of botanical specificity, being particularly effective only as a protectant of corn (Table V).

Apart from its botanical selectivity, R-25788 is also chemically selective, as it

is particularly effective in antidoting thiocarbamate and chloroacetanilide herbicides on corn (Table V). The chemical selectivity of R-25788 may be a result

of the structural similarity between the antidote and the thiocarbamate and chloroacetanilide herbicides (Leavitt and Penner, 1978b). However, R-25788 has

also been r e p r k d to effectively antidote barban and perfluidone on corn (Table

V), and additionally to partially protect some grass crops against injury from a

number of different herbicides (Table V). In practical terms, R-25788, like NA,

is not effective in protecting broad-leaved crops from herbicide injury, but some

preliminary studies showed that R-25788 was partially effective in protecting

field beans against EPTC (Blair, 1979) and tomato against EFTC, cycloate,

diphenamid, and trifluralin (Blumenfeld et al., 1973). Apart from the N,Ndisubstituted dichloroacetamides such as R-25788, other chemicals effective as

thiocarbamate antidotes on grass crops include derivatives of N-dichloroacetyl-l,3-oxazolidine(Spotanski and Burnside, 1973, Leavitt and Penner, 1978a; Godig et al., 1982), phosphorus-containing compounds (Pallos and

Baker, 1977), sulfide derivatives (Ameklev and Baker, 1977), thiobenzoic acid

derivatives (Anonymous, 1977b), substituted azepines, diazepines, azabicycloalkanes and piperazines (Anonymous, 1977a), and the fungicide carboxin (Miller and Nalewaja, 1980). In particular, the N-dichloroacetyl-l,3-oxazolidinederivatives known by the designations R-29148, R-28725 (or AD-2), and AD-67

have shown promising activity for antidoting thiocarbamate herbicides on corn

(Leavitt and Penner, 1978a, Gorog et al., 1982) and chloroacetanilideherbicides

on sorghum (Spotanski and Burnside, 1973).

Although specific details about the screening method of selecting oxime ether

derivatives as candidate antidotes have not been revealed, it is probable that the

antidotal properties of these compounds were discovered by means of empirical

screening. Further evaluation of a large number of oxime ether derivatives led to

the commercial development of CGA-43089 as an antidote against metolachlor

injury to grain sorghum. Table VI summarizes the crop-herbicide interactions

that have been reported for this antidote. As does R-25788, CGA-43089 exhibits

a good degree of botanical and chemical selectivity; it appears to be a specific

antidote counteracting chloroacetanilide injury to grain sorghum (Table VI).

Good protection of grain sorghum was also offered by CGA-43089 against the

herbicides ethofumesate, SD-58525, and SD-91779 (Leek and Penner, 1980;

Hardcastle, 1982). CGA-43089 was also partially effective in protecting corn,

rice, and grain sorghum from a number of herbicides (Table VI). Preliminary

field studies with CGA-43089 showed that preemergence application of the

antidote as a tank mixture with the herbicide improved the tolerance of grain

sorghum to metolachlor, but the 4:l or greater antidote-to-herbicide ratio re-



28 1



HERBICIDE ANTIDOTES



Table V

Efficacy of the Antidote R-25788as a Crop Protectant against Herbicide Injury

Crops protected

Herbicides

counteracted

Thiocarbamates

EPTC



Butylate



Complete

protection



Corn



Corn



Reference



Appleby er al. (1972);

Carringer et al.

(1974); Catizone

(1979); Chang et al.

(1972, 1973a,b);

Dowler (1973); Elliot

and Pumell (1976);

Hammerton (1974);

Heikes and Swink

(1973); Herman et al.

(1974); Jeffery and

Connel (1973); Kennedy and Krueger

(1978); Leavitt and

Penner (1978b); Lee

et al. (1974b); Martin

and Burnside (1982);

Meggitt et al. (1972);

Michieka et al.

(1978); Orr et al.

(1978); Pallos er al.

(1975); Phatak and

Bouw (1974); Purnell

and Bracey (1978);

Rains and Fletchall

(1971, 1973); Sagaral

and Foy (1982);

Schmer er d. (1973);

Smith et d. (1973);

Somody et al. (1 978);

Wiese et al. (1979);

Williams et al.

(1973); Wright et 01.

( 1974)

Chang et d. (1973a);

Heikes and Swink

(1973); Martin and

Burnside (1982);

Meggitt et al. (1972);

Michieka et al.



Partial

protection



Corn

Barley

Sorghum

Field bean

Tomato



Reference



Lee et al. (1974a)

Lee et al. (1974a)

Chang et al. (1972)

Blair (1979)

Blumenfeld er al.

(1973)



(Continued)



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