Field studies with EPTC

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. 

In 1977, Rahman, et. al (2) noted that EPTC provided less than expected weed control at the Manutuke Research Station, near Gisborne, N.Z. They concluded that weed control with EPTC may decrease when used repeatedly on the same field. Further greenhouse studies linked the lack of weed control to increased microbial activity in the soil (3). 

Mussa and Russell (52), however, studied the influence of trifluralin on R, aolani f. sp. phassoli and P. vulgaris, and found that growth was stimulated in culture and virulence increased on the host plant. Altman (1) also reported that lesion size and root rot symptoms increased on several Pinto bean varieties planted in soil infested with the pathogen and pretreated with field rates of trifluralin or EPTC. 

Soils. Characteristics of the three surface (0 to 15 cm sample depth) soils used in this study are given in Table I. The Brookston soil was collected from a field located near Canal Winchester, Ohio that had previously been treated with Eradicane for 1, 2, 3, and 4 consecutive years or had remained untreated. The Plano and Dothan soils were collected from sites in Wisconsin and South Carolina, respectively, which had histories of EPTC and butylate (s-ethyl-N,W-diisobutyl carbamothioate) use. 

Six-vear Herbicide Rotation Study. Mean wild proso millet control obtained in a study conducted from 1984 to 1989 is summnrized in Table IV. Since the field had been treated with 6.7 kg/ha EPTC in 1983, enhanced EPTC biodegradation presumably was present from the beginning of the study. When applied with cyanazine annually over the six-year period, EPTC and EPTC plus dietholate provided only 46 and 64% millet control, respectively. Laboratory studies confirmed that this poor millet control was due to enhanced biodegradation of the active ingredient (Harvey, R. G. Weed Sci.. in press). Every other year and every third year applications of EPTC plus cyanazine and EPTC with dietholate plus cyanazine provided 83 and 86, and 88 and 91% millet control, respectively. Rotating EPTC plus cyanazine or EPTC plus dietholate plus cyanazine treatments with applications of cycloate plus cyanazine, or alachlor plus cyanazine reduced the... 

---