Herbicide evaluation for weed control in kenaf (Hibiscus cannabinus L.)

Abstract

Kenaf (Hibiscus cannabinus L.) was introduced in 2005 as a fibre crop on a commercial scale in the KwaZulu-Natal Province of South Africa. No herbicides have yet been registered for use in this crop. The purpose of this study was to determine the tolerance of kenaf to a total of five pre-emergence and four post-emergence herbicides under semi- and fully controlled conditions. The herbicides were chosen based on their potential safety for use in Hibiscus spp. as well as on the weed spectra they are registered for in other crops. Several additional factors were also taken into consideration, such as: temperature, soil depth and timing of herbicide application. Four pot trials were conducted to determine the separate and combined effects of herbicide, temperature, planting depth and application timing. During the first trial the effects of five pre-emergence herbicides and four post-emergence herbicides were researched. The pre-emergence herbicides were: S-dimethenamid, imazethapyr, fluometuron/prometryn, pendimethalin, S- metolachlor and the post-emergence herbicides were: bentazone, 2,4-DB, monosodium methanearsonate and pyrithiobac sodium. The trials were conducted under either semi-controlled conditions in a glasshouse or in growth cabinets under fully controlled conditions at the Hatfield Experimental Farm of the University of Pretoria. All experiments were conducted with a Hutton soil with 22% clay. Each trial lasted about 40 days to allow for maximum phytotoxicity damage manifestation on the kenaf seedlings. Measurements that were taken included plant height, herbicide damage, weed control efficiency, fresh plant weight, dried plant weight, and dried root weight. The data were subjected to analysis of variance (ANOVA) to determine the statistical likelihood of damage to plants from the herbicides. In Trial 2, 3 and 4 the interaction effects of herbicide and plant depth, herbicide and temperature, and herbicide and application timing were researched respectively. Neither planting depth nor application timing affected the kenaf seedlings negatively, but low temperature in combination with the application of herbicides during germination of seed and seedling emergence had serious deleterious effects on the young kenaf seedlings. Based on the findings the majority of the herbicides can be included in further field trials on Hibiscus cannabinus L. with the exception of S-dimethenamid and fluometuron/prometryn which caused substantial injury to the kenaf seedlings. Copyright