Shattercane control

Grower complaints of poor shattercane control with EPTC became numerous by 1977. Loss of efficacy was initially attributed to misapplication, inadequate incorporation, and adverse environmental conditions. However, the continuing widespread reports of unsatisfactory control with EPTC suggested other unknown factors must be involved. Field and greenhouse studies were initiated in 1978 to identify the reasons for poor field performance (1-3). Interestingly the problem appeared to be associated with repeated annual application. Though the extent of EPTC failure was unknown at the time, a 1983-8A survey revealed that 60% and 45% of corn growers in south central Nebraska who used butylate [S-ethyl bis(2-methylpropyl)carbamothioate] or EPTC were dissatisfied with their weed control (4). This was probably representative of the situation in 1978. 

Table I. Shattercane control in corn at Saronville, NE, in 1979. All herbicides were applied preplant and incorporated immediatelyt...

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. 

Shattercane Control and EPTC Persistence on a Silty Clay Loam Soil near Scranton, KS, 1984... 

Herbicide History Shattercane Control 30 DAT 1 EPTC recovery DAT 3 5 7 14... 

Studies comparing the effect of different rates of R251005 (formerly SC-0058) [S-ethyl-N,N-bis(3-chloroallvl) carbamothioate] in combination with 3.4 kg ai/ha EPTC indicate increased shattercane control at 21 DAT control as the rate of R251005 increased from 0.6 to 1.1 kg/ha. Increasing the rate from 1.1 to 2.2 kg ai/ha produced a numerical increase in shattercane control but the increase was not statistically significant (Table IX). 

There was no additional increase in shattercane control above 1.1 kg/ha in another test (Table X). Other, unpublished trials indicate that 2.2 kg ai/ha may provide a numerical increase in control but the results are generally not statistically significant. 

Because the repeated annual use of EPTC + dietholate resulted in reduced control of wild proso millet, woolly cupgrass, and shattercane and because conflicting results were obtained with giant foxtail, alternate extenders were evaluated which could increase the performance of EPTC and provide consistent weed control with repeated annual use. Several extenders were provided for evaluation by Stauffer Chemical Company in 1984 and 1985. A review of the efficacy of these extenders is contained in Harvey et.al (4). 

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