Field Crops News

Influence of Conservation Tillage on Natural Enemies


Numerous studies have documented that predatory soil-inhabiting insects (especially ground beetles) and spiders increase in number as tillage is decreased in a cropping system. Four times more corn plants were destroyed by black cutworms when predators were removed than when they were present in no-tillage plots in Ohio. Common predators in this study included ground beetles, rove beetles, daddy long-legs, wolf spiders and ants.

Many of these ground dwelling predators are generalist feeders. Ground beetles are known to feed on insects and other invertebrates, plant tissue (including weed seeds), and fungi. Although these predators can be important controls of pest insects, their year round survival depends on other food sources, often nonpest species (small insects, mites, slugs, other invertebrates, and fungi) involved in breaking down crop and plant residues.

Although less well studied, some mite and springtail species are predaceous on small insects, insect eggs and nematodes. Tillage may influence these species too. Studies in North Carolina indicate that a predatory mite which feeds on southern corn rootworm eggs was more abundant in no-tillage peanut systems compared with conventional tillage systems. Data from Ohio suggest that similar mites may be important mortality factors for corn rootworm eggs.

Above-ground insect predators and parasites may also be increased by conservation tillage, but the results are less clear cut. In some studies, increased numbers of predatory insects were thought to be associated with increased levels of crop residue and higher densities of certain weeds in conservation tillage systems. A study in Illinois showed that a wasp parasitoid of the black cutworm lived longer, attacked more cutworms and reproduced more successfully when provided with flowering weed species (wild parsnip, wild mustard, chickweed, shepherd's purse, and smartweed) typically found in minimum tillage corn fields.

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