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IV. Field Performance of Herbicide Antidotes

IV. Field Performance of Herbicide Antidotes

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Table X

Agricultural Uses, Formulations, and Application Methods of Five Commercial Herbicide Antidotes




Crop protected counteracted

1,8-Naphthalic acid Corn













95% seed




Tank mixture,


with herbicide SUTAN+@


20% seed



2.09 S




Grain sorghum Metolachlor


Grain sorghum Metolachlor 70 WP or 50 SD CONCEP 11"


Grain sorghum Alachlor

80 wp

1% Granular




Seed dressing



0.5% by



0.56 kgha

incorporation 0.25 kgha

0.56 kg/ha

Seed dressing 0.5% by seed


Seed dressing

Seed dressing

Seed dressing



Storage stability

of treated seed Manufacturer

More than 1 year Gulf Oil



More than 1 year Stauffer

0.125% by

More than 1 year

seed weight

0.054.3% by More than 1 year

seed weight

0.06-0.25% by More than 1 year

seed weight









preferable to apply R-25788 preplant incorporated into the soil as a tank mixture

with thiocarbamate herbicides. Under practical conditions, the application of

herbicide antidotes in the field does not involve any extra operation, because the

respective companies that manufacture herbicide antidotes market them either as

prepackaged tank mixtures with the herbicide, as in the case of R-25788, or as

crop seeds dressed with the antidote, as in the case of CGA-43089

and CGA-92194.

To be effective in the field, a herbicide antidote that is used as a prepackaged

tank mixture with a herbicide must have several features in common with the

herbicide. According to Prochnow (1978), the most important of these features

are (1) the antidote should not be more soluble than the herbicide, to avoid

leaching of the antidote from the zone of protection under conditions of heavy

rainfall or irrigation; (2) the antidote should remain in the protection zone as long

as the crop is susceptible to the herbicide; (3) the antidote should not interfere

with the effectiveness of the herbicide on target weeds; and (4) the antidote

should be compatible with other herbicides or insecticides that may be added in

the spray tank or applied to the soil control zone when the herbicide plus antidote

mixture is present. The tank mixtures of R-25788 with the thiocarbamate herbicides EPTC, butylate, and vernolate are marketed by Stauffer under the trade

names Eradicane, Sutan+ , and Vernam+ , respectively. The herbicide-to-antidote ratio is 12:l in Eradicane and Vernam+, and 24:l in S u m + . R-25788 can

also be used as a seed treatment on wheat to protect it from triallate injury.

1,8-Naphthalic acid is applied as a seed dressing to corn, but because its

effectiveness in protecting corn from thiocarbamate herbicide injury is less than

that offered by R-25788 under field conditions (Stephenson and Chang, 1978),

its practical use is not as extensive now as it was earlier. In fact, Sanders (1981)

revealed that NA is no longer made by Gulf Oil Chemicals Company and that

other companies are testing NA for possible licensing from Gulf.

All three grain sorghum protectants against chloroacetanilide herbicide injury

are applied in the field primarily as seed dressings. In addition, MON-4606is

effective as an in-furrow application (Schafer et al., 1980). With seed dressings,

the duration of the safening activity in stored seeds is a factor that needs to be

considered. Tests with all five antidotes have shown that storage for more than 1

year of crop seeds dressed with antidotes does not result in a loss of safening

activity. However, it is recommended that in every planting season, crop seeds

should be used that have been recently treated with antidote. Dressing of crop

seeds with herbicide safeners could be done in two ways (Muller and Nyffeler,

1981): (1) as a sequential treatment after the seed has received the usual

fungicidelinsecticideprotection, or (2) as a “one-shot treatment” together with

the usual fungicide/insecticide seed dressing. It is obvious that, in either method,

if an antidote is to be effective it should be compatible with the fungicides or

insecticides that are also used as seed dressings.





Several environmental factors such as temperature, light, soil moisture, and

soil type have been reported to influence the efficacy of herbicide antidotes in the

field. In addition, the timing of the antidote and herbicide applications as well as

varietal differences are also important. The activities of the antidotes NA and

CGA-43089 against herbicide injury on crops were higher at high than at low

temperatures (Guneyli, 1971; Leek and Penner, 1981). Soil moisture appears to

be very important for the antidotal activity of CGA-43089 under field conditions.

Ketchersid et al. (1981) reported that CGA-43089 was not effective in counteracting metolachlor injury to grain sorghum under extremely wet conditions in

the field, In contrast, Nyffeler et al. (1980) showed that under greenhouse

conditions, the safening effect of CGA-43089 was greater in wet soils, when

crop injury from metolachlor is greater. Variations in the antidotal activity of

CGA-43089 as a result of variations of soil moisture levels also have been

reported by Simkins et al. (1979). Muller and Nyffeler (1981) reported that

temperature and soil moisture changes do not affect the safening activity of

CGA-43089 directly, but rather they influence the response of grain sorghum to

treatments with metolachlor. Soil moisture did not appear to affect the antidotal

activity of NA (Hahn, 1974), R-25788 (Burt and Akinsorotan, 1976), and

MON-4606 (Gingerich ef al., 1981). However, some reports indicated that

R-25788 is more mobile than the herbicide EPTC in wet soils (Buzio and Burt,

1977; Burt and Buzio, 1978). This separation of EPTC and R-25788 following

the application of Eradicanea to wet soils has been proposed as a possible reason

for the sporadic toxicity of this herbicide/antidote mixture on corn (Burt and

Buzio, 1979). The EPTC/R-25788 ratio could be restored to normal upon drying

of the soil (Buzio and Burt, 1977).

Soil type has also been associated with antidote efficacy in the field. For

example, NA was highly effective as a barban antidote in oats grown in light

sandy soils but was much less effective in silty clay soils (Thiessen et al., 1980).

The antidotal activity of NA against barban on wheat was not dependent on

changes in soil fertility (Thiessen et al., 1980). Similarly, in light soils R-25788

was less effective as an EPTC antidote on corn (Crook, 1975). The antidotal

activity of MON-4606, however, was not highly dependent on soil type because

this antidote was equally active on soils with textures ranging from silt loam to

muck (Schafer et al., 1981).

The timing of the antidote application with respect to the herbicide application

can also affect the safening activity; NA was most protective to corn when

applied on the same day or 1 day after treatment with EPTC (Guneyli, 1971).

Protection of corn by NA was not complete if the antidote was applied 2 or more

days after treatment with the herbicide. The influence of critical timing for the



effectiveness of the antidote R-25788 as a protectant of corn against EPTC injury

has been demonstrated in a series of experiments conducted by Donald and

Fawcett (1976). They found that R-25788 was able to prevent EPTC injury to

corn when applied as a soil drench at any time prior to coleoptile emergence. If

the antidote was applied to EFTC-treated corn after coleoptile emergence, various degrees of corn injury were evident. Thus when R-25788 was applied after

the second and third leaves of EPTC-treated corn had bent and failed to uncurl, it

was completely ineffective as an EPTC antidote. If the injured second and third

leaves were removed, the higher order leaves still did not expand, even when the

antidote was supplied (Donald and Fawcett, 1976). In another study, corn was

found to be more susceptible to EPTC plus R-25788 at 4 weeks after planting,

indicating that application of the mixture at earlier dates was effective (Burt and

Buzio, 1979). Timing appeared to be less critical for the effectiveness of

CGA-43089; this antidote, in addition to its effectiveness against preplant-incorporated and preemergence applications of metolachlor, was also effective against

early postemergence applications to grain sorghum seedlings (Leek and Penner,


Finally, intraspecific differential responses of several crop cultivars or genotypes to combinations of herbicides and antidotes have been reported. For

example, the corn cultivar ‘TXS114‘ was highly tolerant to EPTC at 6.7 kg/ha

with or without the antidote R-25788 (Sagaral and Foy, 1982). Furthermore,

although R-25788 was able to protect many of the EPTC-susceptible corn

cultivars examined in the previous study, it did not alleviate EF’TC injury to

‘XL55’and ‘XL379’ corn cultivars. Similarly, although MON-4606 offered

good protection to 12 out of 13 grain sorghum hybrids against alachlor injury, it

was not effective in protecting the ‘G623GBR’ hybrid of sorghum (Schafer et

al., 1980). Also, despite pretreatment with NA, three cultivars of oats did not

recover from postemergence applications of barban (Thiessen et al., 1980). Of

the many grain sorghum hybrids tested, no hybrid was found that had insufficient

tolerance to metolachlor in the presence of CGA-43089 (Davidson ef al., 1978).

In general, the crop tolerance offered by herbicide antidotes against herbicide

injury in the early stages of crop growth persists throughout the life of the crop.

An exception is seen in the work of Wright et al. (1974), who reported that the

protection offered by R-25788 to many corn genotypes against EPTC injury early

in the season was greatly reduced, in many of the genotypes, symptoms of EF’TC

injury appeared later in the season.




In all investigations reported, treatment of crop seeds with the optimum rates

of herbicide antidotes did not result in any adverse phytotoxic effects on crop



growth. However, NA applied alone as a seed dressing to corn at 0.5% by seed

weight has been reported to interfere slightly with corn growth (Giineyli, 1971;

Hickey and Krueger, 1974a). Eastin (1972) reported that the same treatment of

NA (0.5% by seed weight) was injurious to sorghum in the absence of herbicide

treatments. Although NA provided some protection to field beans against injury

from EPTC when applied as seed dressing at 0.5%, it caused marked chlorosis to

the bean foliage (Blair, 1979). Chlorotic effects of bean foliage were also caused

by R-25788 in the absence of EPTC when R-25788 was applied as seed treatment

at 2% by seed weight (Blair, 1979). Reports on adverse effects of R-25788 to

corn or any other grass crop are not available. Adverse effects of CGA-43089 on

the seed viability of sweet and yellow endosperm sorghum have been observed

(Davidson et al., 1978; Dill et al., 1982), and the application of CGA-43089 as a

seed dressing at rates higher than 1.88 gtkg of sorghum seeds was found to be

phytotoxic even to grain sorghum (Davidson et al., 1978). In contrast to

CGA-43089, its chemical analog CGA-92194 is not phytotoxic to grain sorghum

and does not adversely affect the seed viability of sweet or yellow endosjwm

sorghum (Dill et al., 1982). Similarly, MON-4606 has not been found to cause

any adverse effects on the seed viability or growth of grain sorghum (Schafer et

al., 1980, 1981). However, Ketchersid and Merkel (1983) observed measurable

effects of the protectants CGA-92194 and MON-4606 on the growth and respiration of sorghum seedlings during imbibition and early stages of germination.

These effects of CGA-92194 and MON-4606 were less than those caused by

CGA-43089 under similar conditions.


The exact mechanisms by which the currently available herbicide antidotes

protect grass crops against injury from chloroacetanilide and thiocarbamate herbicides are not fully understood. Our limited understanding of the mechanisms of

the phytotoxic action of the chloroacetanilideand thiocarbamate herbicides at the

biochemical or physiological level is partly responsible for this. Shoot absorption

through the emerging coleoptile of grasses has been shown to be more important

than root uptake for both of these herbicidal classes (Gray and Joo, 1978; Ashton

and Crafts, 1981). The meristematic region of grass shoots also appears to be the

site of action of these herbicides and, in general, chloroacetanilideand thiocarbamate herbicides are considered to act as inhibitors of early shoot growth of

germinating grass seedlings (Ashton and Crafts, 1981). Following soil applications of thiocarbamate or chloroacetanilide herbicides, susceptible grass seedlings that emerge from the soil are either greatly stunted or seriously deformed,

but they are not killed. The symptoms of chloroacetanilide and thiocarbamate



herbicide injury to corn or sorghum seedlings involve leaf or shoot deformations

such as leaf twisting or rolling, and at high rates leaves fail to emerge through the

coleoptile (Leavitt and Penner 1978b). These effects of chloroacetanilide and

thiocarbamate herbicides on grass crops are counteracted by the currently available herbicide antidotes.

Advances in our understanding of the modes of action of herbicides antidotes

are also complicated by the fact that some of the studies examining the phytotoxic effects of chloroacetanilideand thiocarbamate herbicides on plants, as well as

their counteraction by herbicide antidotes, have been conducted with broadleaved plants that are not protected against these herbicides under field conditions. Isolated spinach chloroplasts (Wilkinson and Smith, 1975), red beet disks

(Wilkinson and Smith, 1976), and tobacco suspension cultures (Rennenberg et

al., 1982) have all been used as plant systems to study the phytotoxic effects of

thiocarbamate herbicides and their counteraction by the antidotes NA and/or

R-25788. The significance of the results of these studies is difficult to assess

when attempting to explain the protective action of herbicide antidotes on grass


Extensive research on the mode of antidotal action of herbicide safeners has

been conducted primarily with the antidoteR-25788 and to a lesser extent with the

antidotes NA and CGA-43089. The findings of all these studies have resulted in a

plethora of proposed hypotheses about the mechanisms of the antidotal action of

herbicide safeners. Herbicide antidotes could protect grass crops from chloroacetanilide or thiocarbamate herbicide injury by (1) interfering with herbicide

uptake and/or translocation in the protected plant, (2) counteracting herbicide

phytotoxicity through a competitive inhibition at some common site within the

protected plant, (3) stimulatingherbicide degradation by the protected plant, and

(4) combinations of mechanisms (1)-(3). The status of our current knowledge on

the antidotal action of the herbicide safeners NA, R-25788, and CGA-43089 is

discussed briefly in the following sections. Studies on the mode of action of the

antidote MON-4606 are not yet available, whereas the antidotal action of

CGA-92194 probably resembles that of its chemical analog CGA-43089.




Early studies on the mode of antidotal action of NA revealed that its protective

effect against alachlor injury to sorghum was physiological in action and not the

result of a physical deactivation of the herbicide (Hickey and Krueger, 1974a).

Also, it was shown that the counteraction of alachlor effects on sorghum by NA

was more apparent in sorgbum shoots than in sorghum roots (Jordan and Jolliffe,

1971). Subsequent reports proposed that the protective effect of NA against

metolachlor injury to sorghum was partly caused by decreased herbicide uptake

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