Bionomics of patterned herbicide application for wildlife habitat enhancement

Abstract

Outcomes of net-present value analyses were projected for patterned applications of herbicide sprays and pellets to mixed brush in south Texas. Picloram + 2,4,5-T (1:1) were applied but 1987 costs of triclopyr + picloram sprays, currently registered and considered the biological equivalent treatment, were used for analyses. Projected internal rates of return (IRR) ranged from 7.3 to 8.5% when 60 to 65% of the landscape was sprayed in a variable-rate pattern (VRP) at 0, 0.6, and 1.1 kg/ha; sprayed in strips with the higher dosage alternating with untreated strips; or completely sprayed with 1.1 kg/ha. Investment capital requirements were reduced when the VRP or strips were used by 49% and 35%, respectively, compared to complete treatment of the landscape with herbicide sprays. Treatment of 80% of landscapes at 2 locations with tebuthiuron in VRPs generated IRRs roughly equivalent to those from 2.2 kg ai/ha of tebuthiuron pellets applied in strips. Complete treatment of management units with 2.2 kg/ha of the pellets generated more additional beef and higher IRRs than did treatment with either pattern, but required from 50% to 75% greater investments of capital. Economic response also differed among sites of differing forage production capabilities and between otherwise similar sites because of variation in botanical composition of the brush stands. For example, IRRs at the locations, respectively, were 6.3 and 1.3% when 2.2 kg/ha of tebuthiuron were applied to sites with deep soils (drainages), 3.1 and <0% following treatment of uplands, and were negative following application to shallow ridges. Sites with a greater proportion of the woody cover contributed by tebuthiuron-susceptible species such as whitebrush yielded greater IRRs from the investment than did sites with heavy cover of honey mesquite (tebuthiuron tolerant).