Herbicidal control of pricklypear cactus in western Texas

Abstract

The recommended practice for pricklypear (Opuntia spp.) control in western Texas has been aerial spraying with a 1:1 mixture of 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) at 0.56 kg/ha in late spring-early summer. This practice did not consistently control pricklypear. Experiments were conducted at 2 locations to determine if efficacy of the herbicide mixture could be improved by increasing the rate or by spraying at night. The herbicide mixture was applied at 0.56 and 1.12 kg/ha to dense pricklypear stands in morning and near midnight in December, June, August, and October. The high rate killed more Lindheimer pricklypear (O. lindheimeri) and Edwards pricklypear (O. edwardsii) growing on clay loam soils compared to the low rate during most seasons. The higher rate did not increase control of hybrid pricklypear growing on clay soils sufficiently to justify the added treatment cost or to satisfy the management objectives of most ranchers. Night treatments killed significantly more pricklypear than daytime treatments only during late spring-early summer. The pricklypear species and hybrids were most susceptible to herbicide applications in late summer and early autumn and least susceptible to those in late spring-early summer. The efficacy of early winter treatments was intermediate.