The Eradication of Acacia hockii from Ugandan Rangeland using Stump Treatment with Picloram and Notes on Effects on Productivity

Abstract

Acacia hockii is a thorny bush or tree which can seriously interfere with grazing cattle when populations exceed 1200 per hectare, as is common in Uganda. Experimental use of picloram applications to cut stumps revealed 100% kills with 0.4 g picloram a.e. or 0.1 g picloram + 0.4 g 2,4-D a.e. per stump at certain seasons of the year. The cost of treatment was U.Shs0.16* for pure picloram and U.Shs0.05 for the picloram-2,4-D mixture per stump. At all seasons picloram was more effective and cheaper than a 2,4,5-T-2,4-D mixture in dieseline applied at the rate of 1 g a.e. per stump.

There was a marked seasonal effect with greatest susceptibility being associated with the end of the dry seasons. Preburning the area in which the treated bushes were growing increased their susceptibility but burning immediately after treatment had no effect. It is suggested that the physiological state for shoot extension growth develops during the dry season and susceptibility to arboricide is linked to this. Preburning induces immediate shoot extension growth and also increases susceptibility.

Field trials of approximately 100 ha each on six commercial ranches revealed that clearing costs are approximately U.Shs65.00 (US$9.00) per 1000 bushes or U.Shs 100.00 (US$13.00) per hectare. Clearing A. hockii has to be combined with clearing the weed grass Cymbopogon afronardus and the effects on cattle growth rates and cash returns are discussed.