INSECT MANAGEMENT

IPM PRACTICES

IPM relies on a combination of practices to reduce damage by insects and related pests. Crop rotation and resistant varieties can be used to avoid some pest problems. Identifying pests promptly allows necessary and effective treatments to be applied before pest populations reach damaging levels. Treating a pest problem with either synthetic or natural pesticides is only a temporary solution. If a pest is recurring from year to year, then a new management strategy should be developed. As usually practiced, IPM includes judicious use of chemical pesticides applied only after scouting reveals pests at economically damaging threshold levels.

Scouting

An IPM program depends on good scouting. The scout walks through the field and inspects plants for insects at least once a week, sometimes more frequently when weather and season favor rapid pest buildups. Scouting for pests can prevent damage by identifying problems early, and it can save money if fewer treatments are needed (see Grower Example 1.)

Replacing automatic spray schedules with as-needed treatments based on scouting reports saved 62 percent of a group of Florida vegetable growers an average of $95 per acre. The remaining 38 percent reported costs of monitoring equalled pesticide savings. Thus all growers did at least as well economically as if they had used scheduled pesticide applications and most did better.

Scouts target specific insects and select search techniques accordingly. Grasshoppers, for example, appear first on field edges, spider mites next to harvested small grains, and armyworms next to wheat. Other specific scouting tips are given later in this chapter. As well as looking carefully at a random sample of plants, scouts may use sweep nets to sample highly mobile insects such as potato leafhoppers. Bean leaf beetles, cucumber beetles, Mexican bean beetles, and stinkbugs will drop onto a ground cloth or 'beat sheet' when the plant is shaken. Bright, adhesive-covered cards placed near plants will trap small, hard-to-see insects such as aphids, thrips, and whiteflies. Aphids and whiteflies are attracted to yellow cards and thrips to blue ones.

For some pests, adult populations are monitored for advance warning of egg-laying and larval stages. This gives the grower time to detect population buildup before damage from the larvae occurs and to schedule any necessary treatments. Black light traps are used to attract night-flying adults of such species as the European corn borer, corn earworm, armyworm, cabbage looper, hornworm, and some types of beetles. Adults of many moths, including most of those in the cabbageworm complex, can be lured to traps by manufactured sex signals (pheromones). The pheromones for each species are different and placement of the trap must be correct in terms of height, field location (edge or center) number of lures placed, and type of lure used. Manufacturers will provide these details, but some general guidelines are given below.

Economic Injury Thresholds

Economic injury thresholds are available for some, but not all, pests in the southern states. Economic injury levels given in this chapter are only intended as general guidelines. Information from cooperative extension agents and the experience of local growers are the best guides.

Insecticide Use

Before any insecticide is used in an IPM program, the presence of damaging levels of a pest insect should be confirmed by scouting. Unnecessary applications of insecticide increase costs, promote development of insecticide resistance, and degrade the environment. Use of insecticides sometimes increases the numbers of non-target pests.

On potatoes, for example, carbaryl (Sevin) application has produced peak green peach aphid populations that were more than ten times greater than those in untreated plots. The main factor in this population increase was direct stimulation of aphid reproduction by the carbaryl. Total nitrogen content, which has been shown to increase aphid populations, also increased slightly, but predator and parasite populations were not affected by carbaryl.

Once the need for an insecticide is confirmed, it should be applied as efficiently as possible. In the middle of hot, dry days, insects are less active and less likely to come in contact with the insecticide. It will also be difficult to get good coverage of wilted plants, and heat will volatilize some insecticides before they reach the plant.

Using the most appropriate sprayer will also increase efficiency as only chemicals deposited on plant surfaces kill insects. For aphids and other underleaf insects, only spray deposited on leaf undersides is effective. Conventional sprayers rely on gravity and inertia to deliver pesticides. By some estimates, only half the pesticide applied adheres to the plant. Electrostatic sprayers which apply an electrical charge to the material being sprayed reduce spraying time and improve insect and disease control per unit of chemical applied.

The charged chemical is attracted to the opposite electric charge on the leaf surface so that retention is better. To further increase efficiency, the charged spray can be delivered with a turbulent air blast, carrying the material deeper into the plant canopy. Such air-assisted electrostatic sprayers deposited four times more spray onto both upper and lower leaf surfaces than conventional mist-blower equipment. Higher amounts of sprays from air-assisted electrostatic units were also found deeper in the crop canopy compared to the amounts delivered by uncharged hydraulic sprayers. These sprayers also deposit more spray on any fruit present in the canopy, however.

Some systemic insecticides are applied to the soil at planting to control early season insects. Thoroughly incorporating granules of these soil-applied chemicals increases control efficiency, while reducing hazards to birds and wildlife from surface granules and granules spilled at the ends of the rows.

Weeds and Insects

Weedy areas may provide habitat for both pests and beneficial insects, but if plants in adjacent weedy areas are related to crop plants, weedy areas are more likely to be a source of insect pests. Morningglory is related to sweetpotato, for example, and nightshade to tomatoes, potatoes and eggplant. Pests with a wide host range such as armyworms, crickets, cutworms, darkling beetles, flea beetles, grasshoppers, lygus bugs, slugs and snails, stink bugs and thrips often inhabit weedy areas and in some cases will attack nearby crops. Mowing weedy areas for the first time after the crop emerges may encourage migration onto crop plants.It may be best not to mow weedy areas at all or to mow before the crop emerges and regularly after emergence.

Tillage Practices and Insects

Plowing under plant debris to speed up decomposition is a common method to lower pest populations by destroying overwintering stages. Seed corn maggots, for example, survive in decomposing plant material. However, tillage operations will also reduce populations of beneficial insects. A study of field crops showed lower populations of carabid beetles and spiders in conventionally tilled fields compared to no-till fields. Both of these predators can help control seed and seedling pests. Strip tillage preserves habitat for beneficial insects, while still destroying soil-dwelling insects in the plowed area.

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