Toxicant distribution plays a key role in determining toxicant efficacy. However, this role is difficult to study because the variables are confounded with one another. The sprayer can change the numbers, sizes, and velocities of droplets. Changing application volume alters these variables (usually to a lesser extent), and also alters spray retention, dose acquired per contact with a deposit, and penetration. To try and understand the role of these two components (equipment versus concentration) we tested three greenhouse sprayers.
The DRAMM coldfogger (DRAMM), Electrostatics Spraying Systems EPS-5 sprayer (ESS), and a CO2 powered "conventional" sprayer were used in a factorial completely randomized design at three application volumes for control of thistle aphid and green peach aphid infesting potted chrysanthemums in a greenhouse. This design was used to separate the effects on efficacy from changing equipment versus the effects of changing application volume.
Plants treated with the conventional sprayer retained more toxicant than plants treated with either of the other two sprayers. However, as a general rule the plants so treated had more aphids than plants treated with the other sprayers. Plants treated at high application volumes had less toxicant than plants treated with lower application volumes. However, plants treated at high application volumes had fewer aphids.
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