Effects of nozzle types, adjuvants and spray volumes on the spray application quality and control of Asian Soybean Rust

摘要

The soybean crop became the biggest area of agricultural culture in Brazil. That biggest area most of time is in quite big farms with a continuous soybean plantation, making plants highly exposed to pests and disease losses. The disease that mainly worries farmers since mid-2001 is the Asian Soybean Rust (ASR), caused by Phakopsora pachyrhizi Sydow, whose main control form is based on fungicides. The objective of this research was to evaluate the effects of three commercial adjuvants (Nimbus, LI 700,Veget Oil) in a mixture with the fungicide (azoxystrobin + cyproconazole) applied with three models of flat fan spray nozzles (TT, TTJ, DLAD - all 11002) and two spray volumes (150,200 L ha1) in the control of ASR. The experiments were performed with amedium cycle soybean cultivar, that was harvested 124 days after germination. Parameters evaluated were: spray coverage and deposition on the upper, middle and bottom leaf layers of the soybean plants; severity of ASR in three leaf layer heights of the plant from the first symptoms of the disease and the crop yield. The data were subjected to the F test and means compared by Tukey's test. Spray nozzle models influence leaf coverage of soybean, especially in the upper and middle leaf layers, and a greater coverage of the most exposed culture leaf layers is not necessarily related to the smaller droplet size. The composition of the spraying liquids and the volume of application influence the spraying liquid deposition on hard to reach leaf layers, such as the lower third of the soybean crop. The ASR severity can be related to the amount of deposits in the lower leaf layers of the crop and to the coverage for medium and higher leaf layers. The treatments were viable and necessary regardless of the adjuvants, nozzles and volumes tested, with significant variations in relation to the control without application in the mass of 1000 grains and in the productivity.