There have been many reports in certain areas of thrips populations that are not being controlled by registered insecticides. Resistance can be a major reason for pesticide failure. To slow down the development of resistance, IPM strategies are recommended. These include rotation of chemical products, timely sprays, introduction of beneficial insects, and the use of other tools, such as trap plants, sticky tape and insect screening. It should be noted, however, that when we talk about pesticide rotation and other pesticide use strategies, there are actually very few effective products available. Additional strategies, such as biological control, become important if not imperative. An increasing number of growers have made the move to biological control of thrips and are achieving good control.
WHAT DO I NEED TO DO?
a) Consult with biological control suppliers,extension specialists, other growers and consultants.
b) Monitor weekly:
i) Sticky cards
ii) Trap plants
c) Introduce beneficials at the correct time:
i) Amblyseius swirskii
ii) Amblyseius cucumeris
iii) Hypoaspis spp.
iv) Atheta (rove beetle).
v) Steinernema feltiae (nematodes).
d) Efficient use of chemicals, where possible, when necessary:
i) Check the effect of chemicals on beneficial insects and mites
ii) Spot treat only
iii) Rotate chemical families.
e) Other methods of control:
i) Mass trapping using sticky roller tape
ii) Insect screening.
WHAT CAN I EXPECT TO SEE?
a) Consult suppliers, extension specialists and consultants. Talk to growers who have used bios before and talk to those who work in the biocontrol industry.
b) Monitor weekly:
i) Monitor thrips population by counting sticky cards weekly.
ii) Use trap plants: Trap plants are useful either as a monitoring tool or as part of the thrips control strategy. Studies have shown that thrips can be more strongly attracted to certain crops and varieties. Recent research supported by Flowers Canada has shown that chrysanthemum is more attractive to thrips when compared to gerbera or eggplant (Shipp, et al., Final Report to Flowers Canada Ontario, May 2007).
Figures 1 and 2 show the chrysanthemum variety ‘Saskia’ planted as islands among other commercial chrysanthemum varieties. The variety ‘Saskia’ is very attractive to thrips in both the vegetative and flowering stage. Research demonstrated that the use of flowering chrysanthemums as trap plants lowered the number of thrips in the vegetative stage of the crop and reduced thrips damage (Shipp, et al).
Monitor trap plants weekly. Either release beneficial mites on the trap plants to create a “banker plant,” or replace the trap plants weekly and use them strictly as trap plants. Banker plants have been used in the greenhouse to build up beneficial insect populations. Trap plants are particularly useful for trapping ‘dispersing’ thrips, i.e., thrips on the move. Place trap plants close to intake vents, doors and in thrips-problem areas.
c) Introduce beneficials at the correct time. In contrast to chemical control of insect pests, biological control must be implemented before the pest reaches a high enough population to damage the crop. Release beneficials as early as possible.
d) Efficient use of chemicals, where possible, when necessary.
i) Whenever possible, spot-treat affected areas or varieties only.
ii) Rotate among different pesticide groups (listed in the table below) to reduce the chance of resistance to one product developing in the population. Refer to Ontario Ministry of Agriculture, Publication 370, Production Recommendations for Greenhouse Floriculture for more details concerning specific recommendations. Consult product label before using any pest control product.
e) Other methods of control
i) Install sticky roller tape above crop for mass trapping. Yellow roller tape placed just above the crop can be used to trap thrips and other flying insects, such as fungus gnats and shore flies. If using parasitic wasps, such as Aphidius spp or Encarsia, then hang blue roller tape. Blue roller tape will capture as many thrips as the yellow roller tape, but will trap fewer beneficial insects.
ii) Screening vents: Although this method seems costly, growers who have installed screens have observed a drastic reduction in insect pests.
A LONG-TERM SOLUTION
The adoption of biological control of thrips is a long-term solution, which is a different approach to pest control than strictly using chemical insecticides. We have become accustomed to a formula that has worked in the past: find thrips, spray thrips, kill thrips. Employing all tools of Integrated Pest Management is just that: management, not eradication. It is not a quick solution, but a long-term one. Be vigilant in monitoring other pests such as aphids, loopers and spider mites. Release beneficials for these pests as soon as possible.
Acknowledgments: Boekestyn Greenhouses; Graeme Murphy, OMAFRA; Mike Short, Eco Habitat; Biobest Canada; Dr. Les Shipp, Agriculture and Agri-food Canada; Dr. Rose Buitenhouse, Agriculture and Agri-food Canada; and Jennifer Hale, Plant Products Co Ltd.
Managing resistance pressures
An increasing number of growers are banking on biologicals for thrips control as part of their IPM programs.
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