Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/30/2001
Publication Date: N/A
Citation: Interpretive Summary: While a great deal of emphasis is placed on development of pest control materials, little effort has been made to evaluate how to apply these materials to obtain efficacious control of diseases and other pest management problems. When applying fungicides, growers traditionally rely on more drift prone, high-pressure nozzles to ensure good spray coverage and canopy penetration. This study was designed to evaluate how different application techniques would influence the management of foliar and fruit diseases of tomatoes and to assess differences in spray deposition characteristics of each technique within tomato canopies. A wide range of techniques was used including low-drift, air injection nozzles, low- and high-pressure nozzles and air-assist sprayers. There were relatively small differences in the amount of material each technique deposited within the canopies. Even though the air injection nozzle reduced off-target drift, it did not increase canopy deposits. There were no differences in the amount of material deposited in the canopies by low- and high-pressure nozzles. Air-assist sprayers produced higher deposits within the canopy. There were greater differences in spray coverage between treatments than in the amount of material found on the leaves. Smaller droplet and higher volume techniques produced higher spray coverage. The air-assist treatments were the only techniques that produced significant coverage on the undersides of leaves. There were no differences in disease control observed in these experiments. These results should encourage spray applicators to adopt application techniques that better target areas of plant canopies that are more susceptible to damage or infection by certain pests.
Technical Abstract: Among spray applicators, it is popular to use high-pressure atomization to provide the best canopy penetration and coverage. However, small droplets produced by these nozzles often lack sufficient energy to deposit deep in a canopy and are susceptible to wind movement. The objective of this research was to monitor the affect of different application techniques on management of foliar and fruit disease on tomatoes and to assess spray deposit characteristics within the canopy. Protectant fungicides were applied on a calendar schedule. Spray deposit characteristics on tomato leaves were evaluated using imaging technology and colorimetry techniques. Differences in spray deposit characteristics between drift reduction, flat fan and hollow cone nozzles all using the same carrier volume were relatively small. Higher application rates produced higher leaf surface spray coverage. Air-assisted spray delivery produced significantly higher spray coverage on underside leaf surfaces and on leaves deeper in the canopy. Air-assisted delivery also deposited more chemical tracer within the canopies. There were no significant differences in foliar infection observed in treatments made with either full or half-rate applications of chlorothalonil. No significant differences in the yield of marketable fruit between treatments were measured. These experiments demonstrate how growers can improve placement of and use of pesticides, particularly how to better target areas of plant canopies that are more susceptible to infection. Additional studies are required to better define the influence of spray deposit characteristics on the effectiveness of pest management and crop production materials.