Effectsofconcentration,dropletdensityofpropiconazoleandkresoxim-methylontheefficacyagainstwheatpowderymildew

The effects of concentration, droplet density of propiconazole and kresoxim-methyl on the control efficacy against wheat powdery mildew were investigated using a combination of indoor bioassay and field experiments. In this study, a new concept, inhibited medium density (EN₅₀) was defined as the density of droplet that achieve 50% inhibition rate. The results showed that: 1) In terms of the indoor propiconazole spraying tests, with the spraying concentration increased from 0.01 g/L to 1.0 g/L, the corresponding EN₅₀ value decreased from 18.7 cm^–2 to 5.1 cm^–2, the EN₉₀ value decreased from 755.8 cm^–2 to 92.8 cm^–2, and the biocide radius increased from 0.92 mm to 1.77 mm. With regards to indoor kresoxim-methyl spraying tests, when the spraying concentration increased from 0.01 g/L to 1.0 g/L, the corresponding EN₅₀ value decreased from 227.1 cm^–2 to 1.0 cm^–2, the EN₉₀ value decreased from 596.1 cm^–2 to 26.9 cm^–2, and the biocide radius increased from 0.27 mm to 4.00 mm. 2) The field spraying test of propiconazole and kresoxim-methyl against wheat powdery mildew were conducted using MG-1S UAV(unmanned aerial vehicle) and knapsack sprayer. When tested with the spray volume of 15.0 L/hm² for UAV at the concentration of 5.0 g/L, the droplet density on flag and 2^nd top leaf was 29.7 cm^–2 and 9.5 cm^–2, respectively. After 3 d, 5 d and 7 d, the control efficacy was 41.9%, 80.7%, 90.2% for propiconazole, respectively, and 30.8%, 67.9%, 84.5% for kresoxim-methyl, respectively. When tested with the spray volume of 450.0 L/hm² for knapsack sprayer at the concentration of 0.17 g/L, the droplet density on flag and 2^nd top leaf was 287.9 cm^–2 and 204.2 cm^–2, respectively. After 3 d, 5 d and 7 d, the control efficacy was 42.1%, 85.3%, 94.3% for propiconazole, respectively, and 28.5%, 80.1%, 90.5% for kresoxim-methyl, respectively. Therefore, droplet density of a certain concentration is enough to achieve good efficient spraying of fungicides. And it is not necessary to wet all the leaves. Using UAV low volume spray, 10-30 cm^–2 droplets can achieve the ideal control efficacy.