SOLARIZATION EFFECTS ON WEED POPULATIONS IN WARM CLIMATES

Soil solarization is one possible alternative for methyl bromide fumigation. In several experiments in two areas of the southern United States, we observed the effects of solarization on weed populations. Clear polyethylene over raised beds (15-18 cm high) was used in all experiments, and moisture was provided during solarization by drip irrigation or subsurface seep irrigation. In sandy soil in southeast Florida, 1.2 ha blocks were solarized for 10 weeks. Control blocks were fumigated with 98 % methyl bromide: 2 % chloropicrin at 202 kgha^-1. During growth of a cucumber (Cucumis sativus) crop following the initial pepper (Capsicum annuum) crop, mean percent weed cover in solarized blocks (59.5%) was higher than the 14.8% in controls. In a sandy loam soil in the more arid climate of central Texas, beds were solarized from 22 July to 19 Aug., 1998. Broccoli (Brassica oleracea var. botrytis ) was planted into plots. Mean dry weight of weeds collected from solarized plots 6 weeks after solarization (9.5 g) was higher than that from non-solarized plots (2.8 g). On 14 July, 1999, during growth of a subsequent tomato (Lycopersicon esculentum) crop, weed coverage in solarized plots (7.8 %) was still higher than that from non-solarized plots (34.9%). On an organic farm in the same area of Texas, plots were solarized from 13 July through 26 Aug., before transplanting broccoli into plots. Although weed dry weights from non-solarized plots 6 weeks later were 2.2 times those from solarized plots, differences were not significant. In these experiments, solarization often lowered weed populations, even a year after solarization. Solarization can be an important weed management tool for warm-climate vegetable growers who cannot or choose not to use fumigation or other chemical weed control.