Ferguson: Prevent insect problems in the vegetable garden

Published 11:40 am Tuesday, May 10, 2022

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Growing vegetables is a source of both food and pleasure for many of us. It’s disappointing when pests take away from the fruits of our labor.

Most insects are not pests, but there are some insects and mites that damage vegetables and other plants. They may directly damage the part that we eat, injure the plant so that it isn’t able to produce as much, or transmit a pathogen that reduces the plant’s productivity.

There are things we can do to prevent or reduce insect and mite problems.

If you’re planting transplants, obtain them from a reputable source and check them before you buy them to make sure there are no obvious signs of insect or mite infestation.

Grow healthy plants so that they are better able to defend themselves from pests or can produce well in spite of injury. Varieties suited to our climate should be chosen. Plants or seeds should be planted at an appropriate time, planted in a site with sufficient sunlight and drainage, spaced appropriately, and provided with appropriate amounts of nutrients and water.

While plants need adequate nutrients, excessive fertilizer can cause problems. For example, aphids tend to be more problematic when nitrogen levels are high.

Planting time can affect insect pressure. Some insects have multiple generations during the growing season. Their populations start out relatively small and get larger as the season goes on. Because of this, vegetables planted in the spring tend to experience less insect pressure than fall plantings of the same thing. For example, corn earworm/tomato fruitworm (it’s the same insect) tends to cause more problems on summer plantings of sweet corn and tomatoes than on those planted in the early spring.

Vegetables should still be planted at an appropriate time for good growth. For example, don’t plant okra or southern peas (black-eyed peas, crowder peas, purple hull peas, cream peas) too early, since they grow poorly if planted when soil is cool.

Just as good weed management is part of disease management because weeds can serve as alternative hosts for pathogens, this is also part of insect management, since weeds can serve as hosts for some pest insects.

Observe plants often so that, if you have a pest issue, you can catch it early. Some insects can be removed by hand.

Avoid spraying broad spectrum insecticides when possible. In nature, a variety of beneficial insects — such as lady beetles, green lacewings, minute pirate bugs, assassin bugs, and parasitoid wasps — prey on or parasitize pest insects. Use of broad-spectrum insecticides can cause secondary pest issues. In other words, pest insects that are normally kept in check by beneficial insects sometimes become problems when the beneficial insects are killed by insecticides. Vegetable leafminer is an example of an insect pest that sometimes becomes more problematic when beneficial insects are killed by insecticides.

With good cultural practices, pest problems can be reduced. Insecticides are sometimes necessary, though, to avoid significant losses. I’ll discuss insecticide options for different types of insect and mite pests in next week’s article.

Let me know if you have questions.

Dr. Mary Helen Ferguson is an Associate Extension Agent with the LSU AgCenter, with horticulture responsibilities in Washington and Tangipahoa Parishes. Contact Mary Helen at mhferguson@agcenter.lsu.edu, 985-839-7855 (Franklinton) or 985-277-1850 (Hammond).