By Zsofia Szendrei
Aphids are among the most common insect pests of vegetable crops. They can reduce plant vigor through feeding, contaminate produce with honeydew, and transmit numerous plant viruses. Although aphids are a common pest across many vegetable crops, the best management strategy depends on the production goal.
The first question to ask when aphids are detected is not "What insecticide should I spray?" Instead, ask “Is my crop primarily at risk from aphid feeding or from aphid-transmitted viruses?” The answer determines the most effective management strategy.
1. Crops where aphid feeding is the primary concern
In many vegetable crops, aphids become problematic only after they establish colonies and populations increase. Colonizing aphids remove plant sap, produce sticky honeydew, contaminate harvested produce, and may reduce plant vigor when populations become large. For these crops, growers can often allow small aphid populations to develop while relying on regular scouting and natural enemies to suppress population growth. Insecticides are applied only when populations reach economically damaging levels or when produce quality is threatened.
2. Crops where virus transmission is the primary concern
Some vegetable crops are highly susceptible to aphid-transmitted viruses. Cucurbits are a classic example because viruses such as cucumber mosaic virus, watermelon mosaic virus and zucchini yellow mosaic virus can cause severe yield and quality losses. Unlike colonizing aphids, even a few winged aphids moving through a field can introduce viruses. Many of these viruses are non-persistent, which means they can be transmitted by probing alone and do not require the aphid to stay and feed on the plant. This means plants can become infected within seconds of an aphid landing on a plant.
Because virus transmission frequently occurs before an insecticide can kill the aphid, simply applying foliar insecticides may do little to prevent primary virus infection. For virus-prone crops, the management objective shifts from killing aphids to reducing opportunities for virus transmission.
Source : msu.edu