Thrips Cocktail for the Year 2001 By Dr. Richard Lindquist Department of Entomology Ohio State University/OARDC, Wooster, OH There is not much new to report this year about pesticides effective in controlling western flower thrips, but this should not stop an extension specialist from reporting it, and taking a couple of pages to do so! The most important aspect of western flower thrips (WFT) management is to know what is happening in your greenhouse. A scouting and monitoring program is a requirement, preferably using sticky traps, indicator plants and plant inspections. The pesticide suggestions below have been divided into two categories: I. Products that can be used to reduce a well-established western flower thrips population, or on crops that are especially susceptible to INSV. II. Products that are not so-called "rescue" pesticides and which should be used when thrips numbers are low (Determined by scouting and monitoring, of course!), or on crops where thrips or viruses do not pose much of a problem. Rotate pesticide classes. Do not tank mix pesticides from the same or related classes. Avoid tank mixing entirely, if possible. Finally, use your scouting and monitoring data so that you will know when to stop spraying, or can extend the interval between applications. Some effective products are listed below, along with their chemical class. A spray interval is also suggested. However, this should not be a hard and fast rule. Use your own judgment based on greenhouse environment, crop, and your scouting and monitoring program, and adjust the application interval accordingly. I. Products and product mixtures that can be used in rotation to reduce a well-established WFT population. They do not have to be used in the order listed to be effective: A. Orthene 97 TT&O (8 oz/100 gallons). Orthene, an organophosphate pesticide, is labeled on only a relatively few crops, but has been effective against western flower thrips. Rose and orchid growers should use Orthene in their thrips programs. If necessary, repeat the application in two weeks. B. Avid (8 oz/100 gallons). Avid, a glycoside pesticide, is now registered for thrips control! Avid's manufacturer, Syngenta (formerly Novartis), does not encourage tank mixes containing Avid. However, tank mixes containing Azatin XL (12 to 16 oz/100 gallons) may improve thrips control. Azatin is a neem insecticide containing 3% azadirachtin. Make a second application in five to seven days. Another tank mix possibility is to add horticultural oil (e.g. Ultra-fine spray oil) at 0.5 – 1% by volume to an Avid spray. This will also increase the activity of Avid. If this is done, do not use Azatin in the mix. C. Thiodan 50WP (1 lb=1 bag/100 gallons), a chlorinated hydrocarbon pesticide, + a Pyrethroid (e.g. Astro, Decathlon, Talstar, or Tame – at suggested label rates). Make a second application after five to seven days. Note that thrips are not on the Thiodan label, but greenhouse ornamental plants are listed. It is legal in most states to use Thiodan to control non-labeled pests on labeled crops. Some growers have applied a tank mix of Thiodan and Avid with good results. If you are using Avid with Azatin or oil in your rotation, do not use it with Thiodan. D. Mesurol 75WP (8 to 16 oz/acre). Mesurol is a carbamate insecticide that has been very effective against western flower thrips. Note that the application rate for Mesurol is per acre, not per 100 gallons. Closure 76WP, which replaces Dycarb, is another carbamate pesticide that can be used in place of Mesurol. Application rates for Closure are 11 to 20 oz/100 gallons. Make a second application of either product after five to seven days. Do not apply carbamate insecticides following organophosphate insecticide applications (or vice-versa), because the two chemical classes have similar modes of activity. Closure will lose its' registration as of 6/31/2001. E. Conserve SC (6 oz/100 gallons). Repeat after five to seven days. Conserve, a spinosyn insecticide, is the newest, and most effective, thrips control product for the greenhouse market. It is especially useful as crops mature because it kills thrips in flowers, generally without injuring the flowers. Make two or three applications, five to seven days apart. Activity is very rapid, but residual life is short. Do not rely only on Conserve for thrips management. Use other products in a rotation. II. Products and product mixtures that can be used when western flower thrips populations are low, or to help suppress thrips numbers: A. Marathon II (50 mls/100 gallons). Marathon is a liquid nicotinoid insecticide formulation that is most effective against aphids and whiteflies – but it also will help control thrips when applied as a foliar spray for control of those pests. Marathon II will control thrips on leaves, not in or on flowers. Make one or two applications, 14 days apart. It will be necessary to use other products in between Marathon II applications. There have been some reports that a tank mix of Marathon II and Beauveria bassiana will improve thrips control. B. BotaniGard or Naturalis-T&O. These are classified as mycoinsecticides, and contain strains of a naturally-occurring fungus, Beauveria bassiana. Make at least three applications, five to seven days apart. Use when thrips numbers are low. These products, used alone, will not control high thrips populations very well, but will help to maintain them at low levels. Beauveria bassiana products seem to be effective in controlling thrips in or on flowers. A tank mix with Azatin XL will help increase the activity of the B. bassiana. See the comments under Marathon II for another tank mix possibility. C. Precision 25 WP (2-4 oz/100 gallons), or Preclude Total Release Aerosol (rate depending on can size). Repeat after seven days. Precision is classified as a carbamate insecticide but it also is an insect growth regulator. As such, it will not directly affect adult thrips, only larvae. Precision 25WP is applied as a foliar spray and Preclude is applied as a pre-packaged aerosol.