Vegetable Crops News

Mulching Increases Spider Numbers and Reduces Insect Damage

Spiders move into new habitats by ballooning on air currents, but if conditions are unfavorable, the spiders will leave. Most spider migration into fields occurs early in the growing season, but newly cultivated fields generally do not provide optimum conditions for spiders. Spiders do best under conditions of high humidity and moderate temperatures. Mulch creates a more favorable environment for the spiders by providing higher humidity and protection from temperature extremes. Significantly higher spider densities were observed in test plots of mixed vegetables (spinach, radish, cabbage, brussels sprouts, potatoes, beans, corn, and tomatoes) that were mulched with 4 inches of grass hay between rows and around the plants than in unmulched plots. This type of habitat manipulation may also encourage ground beetles and other generalist arthropod predators that contribute to pest reduction. Flowering plants to attract an additional source of food for the spiders had no effect on spider numbers.

Although spiders are generalist predators, feeding on both pest and beneficial species, they can have a significant effect on pest insect populations. Insect damage to the radish, broccoli, potato and corn plants was significantly lower in the mulched plots, and there were fewer pest insects in these plots than in the control plots. A separate experiment showed the ability of spiders to control plant pests. Spiders were placed in cages over insect-infected broccoli plants. No insects remained at the end of the test, and plant damage estimates averaged only 32% compared to the control cages without spiders that averaged 93% damage.

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