Insect Note #43

Dated 4/94
Placed on the Web 4/95 by the Department of Entomology, NCSU

Insect Management for the Home Gardener

Every year the home gardener is faced with some sort of insect problem in the vegetable garden. These problems can be prevented or overcome easily by proper use of pest management strategies and tactics. Several insect management techniques follow and merit concerted attention by the conscientious gardener.

1. PREVENTION - Start with Quality!

• Start the season with healthy plants and seeds. A healthy transplant should not contain mites or insects such as aphids, leafminers, or whiteflies. Germination is checked easily by sprouting the seed (10-15) in a rolled moist paper towel in a warm room for a few days. The better the percentage sprouted, the better the bag of seed, and the better chance for uniform and established stands.
• In order to keep those quality plants healthy, be sure to use proper and adequate fertilization, cultivation, and irrigation. Healthy plants are less attractive to insects and also tolerate some damage. Proper planting methods are essential. Seeds planted too deep may be slow to germinate making them more susceptible to soil insect damage before they can emerge. A good soil texture and soil pH will help ensure productive plants that may outgrow insect damage.
• Plants resistant or tolerant to insect damage are available to the home gardener. These plants can be effective in reducing insect damage. Some examples are Jewel sweet potatoes which are resistant to the sweetpotato flea beetle; Resisto and Regal sweet potatoes to many soil insects; Blue Hubbard squash to pickleworm, and Wade or Black Valentine snap beans to Mexican bean beetle.
• Planting and harvesting on time will help prevent many garden vegetables from being damaged by insects. Some insect pests are killed by cold weather in NC. Sweet corn planted early may avoid the ravages of the corn earworm and fall armyworm, especially if harvested prior to July 15 in the Coastal Plain. Early squash may reach maturity before the pickleworm arrives. During the last week of May through the first week of June there are few cabbage maggot flies to lay eggs on cabbage or broccoli plants in Western NC.
• Destroy crop refuse after harvest by working it into the soil or putting it in a compost pile. Plants left in the garden provide shelter for many insects such as Mexican bean beetle, squash bug, imported cabbageworm, diamondback moth, European corn borer, hornworms, corn earworm, bean leaf beetle, asparagus beetle, harlequin bug, cowpea curculio, and others.
• Plant a garden large enough to allow for some insect damage and still provide for your enjoyment.
• Diversify your planting (interplant) to prevent overpopulation of an insect species. Many insects only enjoy one type of plant. For example, the cucumber beetle feasts on little other than cucumbers, squash, and melons. Plant these crops in with the corn or beans. Interplant your different cole crops such as broccoli, collards, and cabbage. This may reduce damage from the cabbage looper. Other insects are not extremely mobile and enjoy having their favorite foods close together. So separate like vegetables to lessen the chance for insect establishment and buildup. Plant flowers or herbs between your crops to add color and add further protection to your garden vegetables.

1. IDENTIFICATION

If an insect problem does arise, the first step in managing it is identifying the pest. There are about 150 species of insects that are considered damaging to crops. However, there are more than 91,000 species that are either beneficial to a garden and/or non- damaging to crops. The gardener should be cautious about assuming no insect is a good insect. The insect you see may be eating the pests. Identification can be done through your local County Cooperative Extension Office or County Plant Clinic, the NCSU Plant Disease and Insect Clinic, or through various gardening manuals or garden centers.

2. ECONOMIC THRESHOLDS

It is most important to assess the amount of damage the insect is causing in your garden. Look for the identified insect: its stages and damage. Turn over the leaves and check undersides. Look for holes in the fruit and chewing injury on leaves. This assessment of the pest number or damage is called economic threshold. This is the pest number or resulting damage where some sort of management practice should be used to minimize or prevent economic loss. This should also show if the cost of the control measure would exceed the value of the crop. You will need to check with your local County Cooperative Extension Office for assistance in determining a threshold number, or you may develop your own. Keep good records to document pest trends and the need for action.

3. CONTROL MEASURES

Even after all the preventative measures have been taken, some insect populations may get out of hand. There are harmless methods of insect control that should be tried before bringing out the sprayer or duster. Most insects can be picked by hand and dropped into a can of oil, oil plus water, or kerosene. Look for the eggs of these insects also. This method allows you to save the beneficial insects that may be killed by a spray.

Various formulations and trade names of Bacillus thuringiensis (B.t.), a biological insecticide, are available. B.t. is mainly directed towards Lepidopterous (moths) caterpillars of most leafy and some fruiting vegetables. Cabbage loopers and Imported cabbageworms are the primary targets. However, new strains B.t. exist which are directed at Diamondback moth and Colorado potato beetle.

With B.t. control is complete and there are no widespread cases of resistance to B.t. B.t. is also safe to the applicator, the host plant and the environment. Direct injection of B.t. into squash vine borer tunnels has also proven effective.

Biological control results from the action of parasites, predators, and various diseases. Biological control agents are usually present, but often at levels too low to offset economic damage. However, if some damage can be tolerated, one can encourage or introduce such biologicals as lady beetles, whitefly parasites (Encarsia formosa), lace wings, aphid midges, beneficial mites, nematodes, preying mantids, or other parasites or predators. For more information on biological control, consult organic gardening literature.

Safer soap for aphids and other soft-bodied insects, mineral oil on corn silks for corn earworm, and the use of such other natural products as pyrethrum, ultra fine oil, rotenone, ryania and nicotine are other viable alternatives to synthetic pesticides for the serious gardener.

The use of physical barriers such as cardboard collars around transplants for cutworms or various row covers are other insect management tactics.

Insect light traps attractant traps and pheromone (sex) traps are also available for home garden use and in addition to detecting and monitoring pests, some traps exert control through mass trapping or confusion of adult insect pests. Provide a clean environment free of weeds and some insects. Aluminum reflective mulches are effective in confusing aphids and delaying the incidence of watermelon mosaic virus II on yellow squash grown in the fall.

If a spray is necessary, USE CAUTION! Read the label carefully and follow the directions exactly. Wear protective clothing. Follow the label guidelines for when it is safe to harvest.

4. SUMMARY