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Greenhouse Updates: Feb 28, 2017

Reviewing Thrips Biocontrol
Feb 28, 2017

Before releasing biocontrols, check with your supplier to determine if long residual pesticides have been applied to incoming plant material that may adversely affect the biological control agents. For successful thrips management using biocontrol, begin introductions of natural enemies on young plants or in propagation areas before thrips are detected.

Growers begin thrips management by using the predatory mite (Neoseilus  cucumeris).  N. cucumeris feeds on first instar nymphs residing on leaves and in flowers and for many growers, has been working very well. N. cucumeris is available in different formulations including in bulk with a bran carrier that can be placed on the foliage; with a vermiculite carrier so that the mites can be blown onto the foliage with a mite blower; and slow release sachets and mini sachets. Predatory mites should emerge from the sachets for 4 to 6 weeks unto the crop.  If using sachets in bench crops, the foliage should be touching, so that the mites can move from plant to plant. Sachets are best placed in the plant canopy, protected from bright sunlight. Direct sunlight reduces relative humidity inside the packet so the predatory mites lay fewer eggs. Sachets are scientifically designed to provide the proper environment for the mites. Do not tear larger holes in the sachets, leave them as is. Remove sachets if they become moldy.

Growers also use minute pirate bugs (Orius), beneficial nematodes (Steinernema feltiae) and BotaniGard (beneficial fungi, Beauveria bassiana) as part of their biological control program for thrips.  Orius are primarily used in biocontrol programs when the weather warms in (mid -March) with other biocontrol agents already being used. Orius feed on all stages of thrips on leaves and in flowers and are most effective at temperatures of 68F – 86F. They are commercially available as adults and nymphs mixed with inert materials that can be shaken over plants but can take several weeks to become established. Because Orius is slow to establish in the greenhouse and expensive to purchase, banker plant systems have been used to encourage their development and establishment in the greenhouse. Some growers use ‘Purple flash’ ornamental pepper plants and lobularia as banker plants to provide a pollen food source and egg laying sites to rear Orius. Banker plants allow an Orius population to establish, develop and disperse within the greenhouse. One recommendation is to make three, weekly releases of Orius  onto banker plants beginning in mid-March. The appearance of bright orange nymphs while scouting indicates that they are reproducing. Liners of ‘Purple Flash’ ornamental peppers and lobularia are becoming commercially available. For example one local supplier is Pioneer Gardens in Deerfield, MA

BotaniGard (Beauveria bassiana) is an insect-killing fungus that works best under high humidity and is best used in propagation areas. Rove beetles, Atheta (=Dalotia) coriaria, and predatory mites, Hypoaspis miles (= Stratiolaelaps scimitus) that are used primarily for fungus gnat larvae will also feed upon thrips pupae found in the growing media. Beneficial nematodes, (S. feltiae) also used for fungus gnat larvae will kill thrips pupae. The general predatory mite Amblyseius swirksii  has been effectively used for both thrips larvae and whiteflies. A swirskii  is most effective at warmer temperatures (70˚F to 80˚ F) and a relative humidity of 70%.

Mass trapping of thrips using yellow sticky cards and tape is a practice successfully being used by some growers in Canada to reduce thrips populations when using predatory mites (not Orius) or chemical based management programs. See more information below.

Tina Smith, UMass Extension and Leanne Pundt, UConn Extension