Field Crops News

Nematodes Applied Through Sprinkler Irrigation Control Larval Corn Rootworms


Research conducted in Nebraska during 1989 and 1990 evaluated the insect-parasitic nematode, Steinernema carpocapsae (All strain) for its potential to control larval corn rootworms in field corn. Nematodes were injected into a center-pivot overhead irrigation system and applied with 0.9 inches of water at 0.5 and 1.0 billion nematodes per acre. Nematodes were applied when second stage corn rootworm larvae were first observed (mid- to late June). Nematodes were compared with planting time applications of Counter 15G and Lorsban 4E applied through the irrigation system in mid - to late June.

Based on root injury ratings, in 1989 nematodes were as effective as Lorsban 4E, and more effective than Counter 15G in reducing injury from rootworm larvae. In 1990, nematodes were as effective as Counter 15G or Lorsban 4E. Soil bioassays indicated that nematodes were commonly recovered 1-3 days after treatment and at low levels up to 28 days after treatment in 1989, but no longer than 7 days after treatment in 1990. Proper application timing and adequate soil moisture after treatment are important to the performance of nematodes against corn rootworms.

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Predators Reduce Black Cutworm Damage in No-till Corn

Dealing with increased crop residue is a fact of life for most Midwestern field crops farmers. While the transition may be difficult, research in Ohio has shown that natural soil predators can help control some crop pests under reduced tillage systems. Researchers compared the amount of corn plants that were damaged by black cutworms under various tillage systems. They compared three treatments: corn planted no-till after soybeans, no-till after corn and conventional tillage after corn, with and without soil insecticides. They found that corn planted no-till following soybeans had the greatest abundance of soil predators and the fewest cut plants of any treatment. Corn planted no-till after corn was next with conventional tillage corn having the least predators and the most crop damage.

Carabid ground beetles were the most common soil predators followed by wolf spiders, daddy long legs, rove beetles, centipedes and ants. The use of a soil insecticide reduced the number of predators and increased crop damage. They attributed the increased abundance of predators to the greater amount of winter crop and weed residue in the no-tillage treatments. Plant residues provide a sheltered microhabitat and the insects that feed directly on the residue (decomposers) may also form a constant food supply for the predators.

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