BACKGROUND: In order to improve the biological control agent (BCA) efficacy, stress factors threatening the viability of microorganisms during spray application need to be determined. The effect of spray mixture temperature and exposure time on Trichoderma harzianum T 22 and Bacillus amyloliquefaciens QST713 viability were tested. Concurrently the combined effect of mechanical and thermal stress effect on BCA viability were tested at two initial spray mixture temperatures (14 and 25 °C) by simulating a spray application using airblast sprayers featured by different tank capacity and a spray liquid circuit (without and with hydraulic agitation system). To assess the BCA microorganism viability, spray mixture samples were collected at time intervals along trials and plated to count the colony forming units (CFU).
RESULTS: The critical temperature threshold that inhibited BCA viability was 35 °C with 30 min of exposure. The sprayer type, the initial temperature of the spray mixture and the temperature increment during the trials significantly decreased the number of CFU recovered. When simulating a spray application, the spray mixture temperature increase rate was determined mainly by the residual amount of spray mixture in the tank. Even if the tank capacity does not substantially affect the final temperature reached by the spray mixture, the higher residual spray mixture in bigger tanks can expose the BCAs for a longer time to critical temperatures.
CONCLUSIONS: Experimental trials allowed us to identify the effect of factors affecting the viability of tested BCAs, providing information about the actual chance to guarantee the biological efficacy of BCA treatments. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Plot size, sample sufficiency, and number of repetitions are factors that affect the experimental errors or residuals and the expression of true differences among treatments. The objective of this study was to determine, using statistical models, the appropriate sample size for application technology experiments in coffee crops through the evaluation of foliar spray deposition and soil runoff in the ground-based application of pesticides. In the first stage, we determined the quantity of leaves per set and the volume of the solution for washing the leaves and extracting the tracer. We analyzed the variability between the coefficients of variation (CVs) of the amount of tracer extracted in two droplet classes (fine and coarse), for the different parts of the plants, and for the different quantities of leaves per set that were organized into intervals of five leaves (1-5, 6-10, 11-15, and 16-20). Less variability was found in the intervals with 10 leaves per set and using 100 mL of extraction solution. In the second stage, a field experiment was conducted using an entirely randomized design with 20 plots: 10 sprayed with fine droplets and 10 with coarse droplets. In each plot, 10 sets (samples) with 10 leaves each were collected from the upper and lower canopy of the coffee trees. Moreover, 10 Petri dishes were placed per plot and collected after application. Based on the results of the spray deposition (mass of tracer extracted per cm2 of leaf), we determined the optimal sample size using the maximum curvature and maximum curvature of the coefficient of variation methods. Higher variabilities were related to the targets that are more difficult to reach. Thus, this study determined an optimal sample size between five and eight sets of leaves for spray deposition, and four to five Petri dishes for soil runoff.