Field Crops News

Fungus Naturally Controls Potato Leafhopper

Natural enemies can be integrated into farming systems at several levels. The most basic level is to understand and utilize the benefits of natural control to your advantage. This requires no specific actions by the producer beyond an appreciation for what Mother Nature is doing. An important example in the Midwest is the impact of the potato leafhopper disease, Zoophthora radicans. This fungus is present throughout the upper Midwest. When a leafhopper becomes infected it will die in 2-3 days. Under the right conditions (cool and moist) the fungus then goes on to produce thousands of spores capable of infecting other leafhoppers. As the disease spreads through the population, leafhopper numbers can drop rapidly. In Michigan, outbreaks of this disease (epizootics) have occurred every year since 1989. Typically they occur in late July or August in conjunction with a cool, wet period. Producers watch for these epizootics in both dry beans and alfalfa, and frequently find no need for further insecticide applications after epizootics occurs.

- Doug Landis, Michigan State University

Alternate Hosts for Aphid Parasite Might Improve Biological Control

The parasitic wasp, Diaeretiella rapae, is distributed worldwide and is known to attack over 30 species of aphids. It has been suggested that increasing the diversity of crop and noncrop plants would increase biological control by allowing reservoirs where the wasp can buildup on aphids and then move to other sites. However, little is known on the ability of this wasp to rapidly shift to different aphid species. Wasps that had been reared for 12 generations on cabbage aphids feeding on cabbageAphis helianthi (a sunflower aphid). The percentage of aphids attacked ranged from 94% for cabbage aphid to 21% for cotton aphid. There was no difference in survival of D. rapae from mummy stage to adult emergence for different aphid host species, but there were significant differences in wasp adult weights and developmental periods (ranging from 12.3 - 19.5 days). These results suggest that a diversified cropping system with several potential aphid hosts would allow D. rapae to maintain itself in an area during periods of low levels of aphid abundance on one crop.

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