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Application of entomopathogenic fungi by inundative releases has been attempted for control of a wide range of insect pests, with generally poor results. This is largely because entomopathogens are often treated as direct substitutes for chemical insecticides and applied without an adequate knowledge of their interactions with the local environment. Humidity of greater than 90% RH has long been regarded as the a critical condition for germination and infection by the spores. With both temperature and humidity controlled, greenhouse crops offer an excellent potential for pest control using entomopathogens. The long-term maintenance of >90% RH, however, is not standard practice in greenhouse production. This study explored the possibility of improving the efficacy of the fungi by temporarily changing greenhouse humidity without adversely affecting crop growth. The study included laboratory and greenhouse trials. In laboratory trials, four humidity levels of 75%, 80%, 89%, and 97.5% RH were evaluated over a 48-h period. Three commercial products of Beauveria bassiana were evaluated (Naturalis-O, Botanigard 22 WP, and Botanigard ES). Greenhouse pests of green peach aphid, melon aphid, western flower thrips, whitefly, and two-spotted spider mite were used as target insects. The infection rate of B. bassiana was found to increase when the sprayed adult insects were exposed to higher humidity levels with the maximum infection obtained at 97.5% RH. Percent infection and difference between humidity levels, however, were formulation- and host-dependent. The highest overall control efficacy was obtained by using Botanigard ES. Botanigard ES was highly effective to adult green peach aphid, melon aphid, and greenhouse whitefly at high humidities. Effects of B. bassiana against biological control agents for greenhouse vegetable crops were also evaluated. Greenhouse trials were conducted in two adjacent greenhouse compartment with high and low humidity conditions for 48 h, respectively, for selected pest insects to valid laboratory results.
This study investigated greenhouse and plant surface microclimate for cucumber crops (Cucumis sativus) under high pressure overhead fogging. Overhead fogging maintained greenhouse humidity above its set point and avoided excessively low humidity conditions on sunny days. Fogging caused minimal to moderate changes in greenhouse air temperature in the fall depending on whether or not the leaves were sunlit or shaded. The temperature of sunlit leaves decreased by 1 to 1.5 °C (1.8 to 2.7 °F) under occasional fogging in the morning and by 3 °C (5.4 °F) under extensive fogging during noon hours. The temperature of fogged shaded leaves did not significantly change (<1 °C) when compared to nonfogged shaded leaves. Leaf wetness duration (LWD) was extended when overhead fogging was used. The length of extended daytime wetness duration (LWDday) from 0800 to 1700 HR in the fogged greenhouse depended primarily on global radiation at the leaf level. A simulation model was developed to predict LWDday using daily integrated global radiation (Rsum) as the input.
Overhead fogging or misting is an essential technique applied in modern greenhouses for cooling and humidifying. This technique can be used to promote yield and quality of greenhouse crops either by providing favorable environment for the plant growth or by increasing the efficiency of greenhouse pest and disease control. In this study, the effect of high-pressure overhead misting on greenhouse climate and leaf surface microclimate conditions for cucumber crops in a glass greenhouse was investigated. It was found that the temperature of the greenhouse air was lowered by 5-6 °C and relative humidity was increased by 20% to 30% during misting. The temperature of sunlit leaves was slightly reduced in the morning (2-3 °C), and leaf wetness duration was significantly extended by misting. Leaf wetness duration under misting was predominately influenced by light intensity at the leaf level and was modelled as a function of misting period and average radiation intensity. Results of this study can be used to improve the predictions of pest and disease breakout and the efficiency of their control measures. The empirical model developed in this study can be integrated with leaf surface microclimate models to correctly predict surface moisture conditions and evaporative cooling from water films at the leaf surface.
Greenhouse crop production technology is advancing rapidly, and the management of greenhouse crops has become increasingly difficult. Computerized environment and fertigation control of greenhouse crops grown in soilless media offer opportunities for unparalleled manipulation of crop growing conditions. However, the optimization of crop growing conditions for maximum productivity must be practiced with an eye on environmental regulations; worker health concerns; consumer demands for safe food; and ultimately on energy, water, fertilizer, and pesticide use economy. Managing the complex greenhouse cropping system requires a multidisciplinary approach that integrates pest and disease protection strategies with routine cultural practices and environmental and fertigation regimes into a common decision-making process or Integrated Crop Management strategy. This poster describes an Expert System for greenhouse cucumber management based on a general model of Integrated Crop Management for greenhouse crops.