One of the more common pest issues across a range of vegetable crops in greenhouses is aphid management. Vegetable production in protected environments is generally used to extend seasons and during these times of the year problems with aphids are often more common. While there are a number of aphids that can cause problems, most common are the green peach aphid, melon aphid, and potato aphid. Despite their names, they attack a wide range of vegetable crops.
Aphids feed with piercing-sucking mouthparts and remove large amounts of plant sap. They can cause leaf cupping, stunting, and discoloration, but one very noticeable sign of aphid infestation is the honeydew they produce. Honeydew is how aphids get rid of the excess sugar in plant sap. It falls onto the leaves and fruit below their colonies, leaving a sticky residue that is a food source for sooty mold.
Typically in high tunnels/greenhouses, there are winged and wingless aphids, but they are often all females, which reproduce asexually (without mating). Reproduction without mating shortens generation times because females give birth to live aphids rather than eggs, and the entire population is producing more aphids. The result is rapid population buildup, if the conditions are correct.
Integrated pest management (IPM) of aphids in high tunnels relies on a combination of physical, cultural, biological, and chemical controls. High levels of sustainable management are achieved when multiple tactics are used in harmony.
Windows, ventilators, and intakes for fans should be screened to reduce insect movement into structures. Curtains that are opened on the sides of high tunnels for ventilation can be fitted with insect screening.
Weed management and sanitation are two key tactics to prevent aphid problems. Weeds should be eliminated inside structures and weed-free zones should be maintained around the perimeters of houses. The wider the zone, the more effective it can be. Many producers use weed mats in high tunnels/greenhouses to reduce labor. A crop-free period during mid-winter or summer will help to disrupt most pest populations. This way pests are not carried over from one crop to another. When bringing in new plants or plugs into greenhouses/high tunnels, it is best to keep them separated for a couple of weeks to be sure they are not harboring aphids or other pests.
There are a number of biocontrol predator and parasitoid options for aphid control inside enclosed structures. Common predators released include lady beetles (adults) and green lacewings (eggs or larvae). Each predator will consume many aphids during its life. There are several different parasitoid wasps that can be released, but it is important to match the aphid species with the appropriate wasp species. UK Extension Entomology can identify samples submitted to county Extension offices. With biological control, it is also critical to manage insecticides so that they don’t harm these natural enemies.
There are systemic and foliar sprays that can be used for aphid control; these are listed in Vegetable Production Guide for Commercial Growers (ID-36) for each vegetable crop. Pre-harvest interval, potential for impact on natural enemies, efficacy against aphids, and possible greenhouse prohibitions play a role in selecting an appropriate aphid insecticide. Care should also be taken to not harm pollinators with insecticide sprays. This may involve removing pollinator nests for a day or more while sprays are applied.
The final comment on aphid management is to monitoring throughout the crop cycle. Use weekly scouting, as well as yellow sticky cards, to monitor aphid populations. For weekly monitoring, use five groups of three plants for weekly monitoring. Yellow sticky cards hung just above the plant canopy are used to monitor for aphids, thrips, fungus gnats, and whiteflies. Circle any of these that are found so that cards can be reused for multiple weeks and newly captured pests can be recognized. Monitoring is much more valuable if pest observations are written down in order to track pest levels from week to week and year to year.
By Ric Bessin, Extension Entomologist