Integration of brassica cover crop, biocontrol agent and fungicide for management of sheath blight of rice in AR

摘要

An experiment was established in a field of Stuttgart silt loam soil at the University of Arkansas's Rice Research and Extension Center, Stuttgart, AR. Plots consisted of six 17-ft rows, and spaced 7.5-in. between rows. The experiment was conducted asa split plot design with four replications. Whole plots consisted of two spring cover crop treatments: 1) mustard (brassica) 'Caliente 199' and 2) fallow. Subplots were five treatments: 1) Bacillus subtilis strain MBI600 at 108 cfu/ml, 2) combination ofB. subtilis strain MBI-600 with Quadris (azoxystrobin) at 4.5 fl oz/A, 3) Quadris at 4.5 fl oz/A, 4) Quadris at 9.0 fl oz/A, and 5) unsprayed control. B. subtilis strain MBI600 is plant growth-promoting rhizobacteria (PGPR) that have demonstrated to have growth promoting effects on rice and other crops. Mustard 'Caliente 199' is a biofumigant cover crop containing high levels of glucosinolates toxic to many plant pathogens including R. solani. Mustard was seeded at 5 lb/A on 30 Apr and was plowed downon 15 Jun. All plots were inoculated with the sheath blight pathogen by manually broadcasting 1200 ml/plot of rice grain and rice hull mixture (1:2 vol/vol) containing R. solani prior to planting of brassica. Seeds of rice were treated with the Bacillusstrains at 108 cfu/ml prior to planting. Rice was drill seeded at 80 lb/A on 20 Jun. Plots received 200 lb N/A of urea fertilizer (46-0-0, N-P-K) prior to permanent flood. Permanent flood was established on 16 Jul. Control of weeds and harmful insects aswell as irrigation followed local recommendations. On 30 Aug, plots were sprayed with the Bacillus strain MBI-600 at 108 cfu/ml and with Quadris at 4.5 or 9.0 fl oz/A using a CO2 pressurized sprayer equipped with a boom of three TeeJet 8002 nozzles spaced 16-in. apart and delivered at 32 gal/A. The Bacillus strain was grown in Nutrient's broth medium on a shaker (120 rpm) at room temperature for 2 days. On 6 Oct, sheath blight severity was rated on a scale of 0 to 9, where 0 represents no disease symptoms and 9 represents most severe symptoms (plants collapsed). Rice was harvested using a plot combine on 21 Oct. Grain yield and moisture were determined and rice yields were adjusted to 12% moisture content. Total rainfall for the rice growing season was 10.1-in. within the historical120-year average 13.4-in.