In the past week, there have been several reports of whiteflies, aphids, spider mites, and thrips attacking tomatoes in high tunnels or greenhouses. It is not unusual to have an upturn of insect activity in high tunnels as the season changes and the weather warms. Insects are more active outdoors and more ventilation with outside air is occurring. Once inside, these pest populations will develop more rapidly than outdoors. This article discusses whitefly management in high tunnels.
High tunnel insect management can be challenging, and whiteflies (Figure 1) on tomatoes and other vegetable crops can be one of the more common challenges. While there are several species of whiteflies that are routinely found in high tunnels, silverleaf whitefly can be more difficult to manage than the others. Whiteflies damage plants in several ways:
- They remove plant sap, reducing efficiency of plants
- Honey dew produced by whiteflies covers leaves reducing photosynthesis and contaminating fruit (Figure 2)
- Silverleaf whitefly can transmit tomato yellow curl virus.
Prevention is the first and best tactic used with whiteflies.
- Before starting a new crop in the high tunnel, be sure the structure is free of weeds and other plants.
- Prior to planting a new crop, eliminate whiteflies by allowing the high tunnel to freeze in winter or by allowing a sealed tunnel to heat up in summer.
- Side wall curtains can be screened to exclude whiteflies moving into the high tunnel.
Managing whiteflies with insecticides is challenging. Table 1 lists recommended insecticides for whitelfies available for use in high tunnels and greenhouses. Producers must manage whiteflies, reduce the potential for development of insecticide resistance, and pay attention to preharvest intervals close to or after harvest begins. Generally, applications to growing media have much longer preharvest intervals than foliar applications.
Table 1. Recommended High Tunnel Insecticides for Whiteflies
|Insecticide||IRAC group||Target||Maximum usage per crop|
|Admire Pro||4A||Adults and nymphs||6.7 fl oz|
|Assail 30 SG||4A||Adults and nymphs||16 oz|
|Courier 40 Sc||16||Nymphs||2 applications|
|Knack 0.86 EC||7C||Nymphs||20 fl oz|
|Requiem 25 EC||UN||Adults and nymphs||10 applications|
|Rimon 0.83 EC||15||Nymphs||36 fl oz|
|Sivanto Prime 1.67 SL||4D||Adults and nymphs||28 fl oz|
|Venom 70 SG||4A||Adults and nymphs||6 oz|
Ric Bessin,UK Extension Entomologist