Integrate Your Insecticide Rotation in the Greenhouse with Biological Control
November 1, 2023 
Biological control can be used effectively as a part of an integrated pest management program. This image shows loose bran leftover from a predatory mite release. Photos: Juang Chong
In a perfect world, we can have our cake and eat it, too. Alas, this isn’t a perfect world. As much as we hope biological control can be a complete replacement for pesticides, it’s not. We may need to apply pesticides to prevent damage by a secondary pest. By a secondary pest, I mean a pest that’s not the primary target of your biological control program but can become a problem because it has no effective biological control option (such as lygus bug or striped mealybug) or its biological control agents are in short supply or unaffordable.
Multiple factors decide which pesticides to use when practicing biological control. You can consult Koppert’s Side Effects Database or Biobest’s Side Effect Manual to select compatible insecticides. But, understand that compatibility information isn’t available for all products, and databases from different companies may have different ratings for the same product. You’ll have to do a little homework. When multiple ratings are available, it’s prudent to go with the most conservative one or the “worst-case scenario.” The best aid in selecting compatible pesticides is the representative of your biological control agent supplier, who can help you select the most suitable products and fill information gaps, particularly information on sublethal impact of pesticides.
Today’s topic hasn’t been discussed in detail when folks talk about selecting compatible insecticides — how do you satisfy two critical requirements, i.e., insecticide rotation and compatibility with biological control agents, when selecting which insecticide to use against the secondary pest?
Avoid Pesticide Resistance
As part of an integrated pest management program, biological control is a great way to delay the development of pesticide resistance. Hopefully, a preventive biological control program is so successful that you don’t ever have to use pesticides. If you don’t use or use very little pesticides, then you don’t have to worry about pesticide resistance — as simple as that. But, if you need to make multiple applications to reduce a secondary pest population, you should consider rotating the pesticides you plan to use to avoid resistance development.
The process of developing an insecticide rotation program that’s compatible with your biological control program is the same as developing a rotation program for any other pest. This could be best illustrated by going through the steps of developing such a rotation program, say, against mealybugs (I’m too cheap to buy Cryptolaemus) while being compatible with the predatory mite, Neoseiulus cucumeris, used for thrips management.
Multiple pests can occur on the same plant, such as spider mites and thrips on this verbena. Designing an insecticide rotation program will need to consider both pests and their biological control agents.
The first step is to have a list of insecticides effective against mealybugs. I can find pesticide efficacy information from several resources. I can read IR-4’s Research Summaries or the Comparative Efficacy and Ecotox table from Rutgers University’s Protecting Bees website. Alternatively, I can call or email my favorite entomologist for recommendations. At the end of Step 1, my fictional list includes acephate, bifenthrin, buprofezin, dinotefuran, flonicamid, horticultural oil, insecticidal soap, and pyriproxyfen.
Now, let’s select insecticides that are compatible with cucumeris mite from my list. For this step, I consult with the technical representative of my biological control agent supplier, Do-Good Bug Company. Acephate and bifenthrin are out because they are broad-spectrum and have residual toxicity that may last for weeks. Dinotefuran can be very detrimental to cucumeris mite when sprayed, but is safe as a drench, so I’ll use that as a drench. Horticultural oil and insecticidal soap can also be detrimental when sprayed, but they have short residue, so I can use them just before releasing the predatory mites (the residue becomes harmless by release time) or at the end of the crop to clean up the mealybug population. Buprofezin, flonicamid and pyriproxyfen are compatible.
Steps for Mealybug Program
Here’s my mealybug program: I’ll start with a drench of dinotefuran followed with biweekly sprays of buprofezin, flonicamid, and pyriproxyfen. Remember that a good rotation program includes a sequence of non-repeating modes of action or IRAC (Insecticide Resistance Action Committee) numbers. I can find the IRAC numbers on the first page of the product labels, which are 4A for dinotefuran, 16 for buprofezin, 29 for flonicamid, and 7C for pyriproxyfen. All IRAC numbers in my rotation program are different, so I’m good to go. There you have it — an insecticide rotation program against mealybugs that’s compatible with cucumeris mite.
Of course, the example above is a simplified version of building an insecticide rotation program. Despite its simplicity, the same process can be repeated for any combination of (macro and micro) biological control agents and pesticides (insecticides and fungicides).
It is important to understand that insecticide rotation and compatibility with biological control should be considered within the context of the entire crop. Rarely do we deal with one pest or disease at a time. What we do to manage one pest or disease may have significant impact on the management efficacy against another pest or disease. Therefore, pesticide rotation and biological control programs should be designed carefully to consider multiple plant and pest species. It doesn’t matter how successful a biological control program is in managing the primary pest, a crop can still fail if a secondary pest management program ignores insecticide rotation and creates a resistant population that ultimately destroys the crop.
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