Management of Mesquite (Prosopis juliflora) Swartz: Using An Integrated Approach

Abstract

Mesquite {Prosopis juliflora (Swartz) DC}, a fabaceae, native to South America was first introduced into Sudan in 1917. Since then the plant, reintroduced several times from different sources, was deliberately distributed into several ecological zones to curb desert encroachment, provide fuel wood and fodder for animals. However, the plant has spread, become a weed of national importance and a threat to agriculture, pastoralism and biodiversity. The present investigation was undertaken at the College of Agricultural Studies, Sudan University of Science and Technology to study i) herbicidal efficacy of Garlone Super®, a ready-made mix of triclopyr and aminopyralid on mesquite, ii) allelopathic potentials of mesquites organs using lettuce (Lactuca sativa L.) and alfalfa (Medicago sativa L.) as test plants, iii) toxic effects of mesquite leaves collected from Garlone Super® treated trees, iv) accumulation under natural conditions of allelochemicals from mesquite in soils, and v) activity and persistence of toxins from mesquite in soils. Garlone Super® formulated as soluble liquid (SL, a.i = 270g/ L) at several rates (0.8 – 6.67 % v/v), in a diesel carrier was applied as basal treatments to mesquite trees. The product at all rates effected complete mortality (100 % yellowing and drying of leaves) of the treated trees. Mesquite trees treated with Garlone Super® at 1.67 % v/v in diesel and cut at 15 days intervals over a 6 months period showed no regeneration, untreated and diesel treated trees showed complete regeneration within 15 and 30 days after treatments (DAT), respectively Garlone Super® applied as aqueous spray was slow acting. The rapidity of kill increased with increasing proportion of diesel in the herbicide carrier. Garlone Super® applied in water as a sole carrier affected 88.33 % mortality 30 DAT. Trees treated with the herbicide in diesel as sole carrier or in diesel : water carrier displayed 98.25 % mortality. All mesquite organs studied including leaves, stems, bark and pods, retarded growth of alfalfa and lettuce seedlings. Of all the parameters measured seed germination was the least affected. Seedlings growth, as indicated by radicle and hypocotyl length was affected negatively by toxins from mesquite. Of the mesquite organs pods were the most toxic followed in descending order by bark, leaves collected from under mesquite, stems and fresh leaves. Mesquite leaves collected from Garlone Super® treated trees were more toxic to lettuce than those collected from untreated trees, while those collected from diesel treated trees were the least toxic as they inhibited radicle length by 39 % and hypocotyl length by 2 %. Toxins from mesquite are soil acting. Furthermore, persistence of the toxins in soil was temporally controlled. The activity of powder from treated leaves progressively declined with time. They were most active as toxins when assayed immediately after treatment and most of the activity (> 90 %) was lost 45 DAT. Based on the above results it could be concluded that Garlone Super® could be deployed as part of an integrated management strategy comprising of chemical control and replacement by suitable plant species. Dissipation of toxins from mesquite in soil could be enhanced by pre-irrigation and/or ploughing whichever relevant.