Relationship between the Spray Droplet Density of Two Protectant Fungicides and the Germination of Mycosphaerella fijiensis Ascospores on Banana Leaf Surfaces
✍ Scribed by Washington, John R.
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 229 KB
- Volume
- 50
- Category
- Article
- ISSN
- 1526-498X
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✦ Synopsis
The e †ect of fungicide spray droplet density (droplet cm~2), droplet size, and proximity of the spray droplet deposit to fungal spores was investigated with Mycosphaerella Ðjiensis ascospores on the banana (Musa AAA) leaf surface for two contact fungicides : chlorothalonil and mancozeb. When droplet size was maintained at a volume median diameter (VMD) of 250 km while total spray volume per hectare changed, M. Ðjiensis ascospore germination on the leaf surface fell below 1% for both fungicides at a droplet deposit density of 30 droplet cm~2. At a droplet deposit density of 50 droplet cm~2, no ascospores germinated in either fungicide treatment. When both droplet size and droplet cm~2 varied while spray volume was Ðxed at 20 litre ha~1, ascospore germination reached 0% at 10 droplet cm~2 (VMD \ 602 km) for both fungicides. At lower droplet densities (2È5 droplet cm~2 VMD \ 989 km and 804 km respectively), ascospore germination on the mancozeb-treated leaves was signiÐcantly lower than on the chlorothalonil-treated leaves. The zone of inhibition surrounding a fungicide droplet deposit (VMD \ 250 km) on the leaf surface was estimated to extend 1É02 mm beyond the visible edge of the spray droplet deposit for chlorothalonil and 1É29 mm for mancozeb. The efficacy of fungicide spray droplet deposit densities which are lower than currently recommended for lowvolume, aerial applications of protectant fungicides was conÐrmed in an analysis of leaf samples recovered after commercial applications in a banana plantation. Calibrating agricultural spray aircraft to deliver fungicide spray droplets with a mean droplet deposit density of 30 droplet cm~2 and a VMD between 300 and 400 km will probably reduce spray drift, increase deposition efficiency on crop foliage, and enhance disease control compared to aircraft calibrated to spray Ðner droplets.