Sweet pepper-Leveillula taurica microclimate relations were studied under controlled conditions and in commercial greenhouses. Conidial germination occurred at 10 to 37 degrees C and was optimal at 20 degrees C. Conidial viability declined as temperatures increased to 40 degrees C for 6 h. Leaf colonization was optimal at 15 to 25 degrees C. Severe leaf infections occurred at 15 to 20 degrees C and conidiation was suppressed at 20 to 25 degrees C. Highest germination rates were observed at 75 to 85% relative humidity (RH). Severity of leaf coverage by symptoms was high for plants which were subjected to longer periods of temperatures between 10 to 15 degrees C and daytime RH between 85 to 95%, and positively correlated with nighttime RH. Disease severity was negatively correlated with lengthy periods of temperatures >25 degrees C, day and night average temperatures, and average daytime RH. Conversely, leaf shedding was relatively high under conditions characterized by long periods of temperatures >20 degrees C and <13 degrees C, and positively correlated with average daytime temperatures and periods of RH <75%. Increasing nighttime temperatures by heating and daytime temperatures by closing the greenhouse side walls reduced disease in two commercial greenhouse experiments. A midseason shift from a cooler greenhouse climate to warm daytime climate halted epidemic development. Flower number and yield were reduced in infected crops.
The effects of several spray and climate treatments on Leveillula taurica were tested under controlled and commercial greenhouse conditions either alone or combined with a climate treatment. Ampelomyces quisqualis AQ10 inhibited the germination of conidia on leaves, but not on glass.
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