Carbamothioate herbicides

Cross-Adaptation. To determine if other carbamothioate herbicides would degrade more rapidly in soils exhibiting enhanced EPTC degradation, the degradation of EPTC, and two similar carbamothioates, butylate and vernolate (S-propyl dipropylcarbamothioate), were monitored for 44 days following applications to non-history and EPTC-history Kennebec soil (13). 

The degree to which carbamothioate herbicides cause microbial adaptation depends on specific herbicide structure (lj), 21 22). Vernolate and EPTC have similar structures and soil exposure to either herbicide fully affected the degradation of the other. 

Enhanced Biodegradation of Carbamothioate Herbicides in South Carolina... 

Enhanced biodegradation of pesticides has received considerable attention in recent years since it was first described by Audus (1) for the herbicide 2,4-D. Diphenamid, a soil applied herbicide, is also subject to enhanced biodegradation by soil microorganisms (2.31. Fungicides (4.51 and insecticides (6-91 are also subject to enhanced degradation by soil microorganisms. The carbamothioate herbicides are readily degraded by microbes (10.Ill and especially after repeated applications (12-191. ... 

Table III. Performance of carbamothioate herbicides in a butvlate-historv soil near Dobson. NC ...

Table VI. Cross-adaptation for carbamothioate herbicides in butvlate- or vernolate-history soils ...

Based on field and laboratory data, enhanced biodegradation of carbamothioate herbicides was confirmed under South Carolina conditions. A good correlation was observed between enhanced biodegradation and performance failure. Laboratory analyses of "problem" soils could be used to predict potential problems or weak efficacy under field situations. However, lack of soil... 

Systems Allowing Continued Use of Carbamothioate Herbicides Despite Enhanced... 

Continuous use of cycloate plus cyanazine over the six-year period provided an average of 89% millet control even though cycloate is a carbamothioate herbicide (Table IV). Previous studies have shown little potential for enhanced biodegradation of cycloate (8). Alachlor plus cyanazine or pendimethalin plus cyanazine treatments, often considered as alternatives to EPTC for millet control, did not provide better millet control than combinations of cyanazine plus EPTC or EPTC plus dietholate when the latter treatments were used no more frequently than every other year. 

Data presented do not directly address enhanced biodegradation of carbamothioate herbicides other than EPTC. However, research indicates that both dietholate and SC-0058 reduce enhanced butylate biodegradation problems (Harvey, R. G. Weed Sci.. in press). 

Cultural Practices and Chemicals That Affect the Persistence of Carbamothioate Herbicides... 

EPTC was repositioned in the marketplace as an annual grass herbicide in 1985, a rotational statement was added to prevent the repeated annual use of EPTC, and shattercane control claims were removed from the label. EPTC was targeted specifically for foxtail (Setaria spp.) and annual broadleaf weed control in the north where cool and wet soils prevail in the spring. EPTC has been a very successful product, provided excellent weed control, and increased in market share every year since its reintroduction as an annual grass and broadleaf herbicide. The other commercial carbamothioate herbicides, EPTC + dietholate and butylate, were positioned as difficult to control weed and southern corn belt herbicides, respectively. No rotational statements have been added to the EPTC + dietholate and butylate labels. 

This paper reviews the results of previously unpublished trials conducted by Stauffer Chemical Company and ICI Americas Inc. on the effects of cultural and chemical practices on the activity of carbamothioate herbicides in soils. The inter-relationship of these factors in the expression of enhanced biodegradation and the commercial significance and management of enhanced biodegradation in the cases of the carbamothioate herbicides EPTC, EPTC + dietholate, and butylate is demonstrated. 

Other factors besides enhanced biodegradation which influence carbamothioate herbicide persistence include environmental conditions, application efficiency, soil incorporation, crop and chemical rotation, herbicide combinations, and chemical extenders (4-6,12-13,17,20). Lack of commercially acceptable weed control may be attributed to misapplication, poor soil preparation and incorporation, and high weed populations, as well as enhanced biodegradation. 

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