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| Photo: Flowers that were fed on by tarnished plant bug nymphs during bloom develop into "catfaced" fruitlets. University of Maine Extension. |
Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production
Key Points:
- Tarnished plant bug (TPB) is the most economically significant pest of strawberries in the Midwest
- Keep pollinator health front-and-center when spraying for TPB in day neutral strawberries, since they are always in bloom
- There are multiple conventional insecticides available for TPB, which vary in pollinator risk level. The most effective organic insecticide on TPB, based on existing research, is azadirachtin.
- Scout weekly to determine the need to spray for TPB
- Manage weeds in and around the field to reduce TPB populations
Tarnished plant bug (TPB) is a significant insect pest of strawberries that remains throughout much of the day neutral strawberry growing season.
TPB has several generations of nymphs (immature stage of the insect) per season. Nymphs pierce and suck liquid from the flowers and young fruit. They are responsible for "catface" deformation on fruit that renders the fruit unmarketable for fresh-eating but still usable for processing.
Protecting Pollinators While Controlling TPB
A challenge with this insect + crop combination is that day neutrals are always in bloom from May through October or November. Spraying insecticides during bloom is risky for pollinators. Thankfully, not all insecticides impact pollinators equally. There is a short list of lower-risk options that are effective on TPB.
1) The first way to reduce harm to pollinators is to only spray insecticides if necessary. Scout your field for TPB before deciding to spray (read on for details on how to scout). Reduce TPB habitat by controlling weeds in and around the field. Growers who use exclusion netting can drastically reduce their insecticide applications or avoid them altogether.
2) Choose insecticides with low pollinator
risk whenever possible. The Minnesota Department of Agriculture maintains a Pesticides & Bee Toxicity List where growers can easily compare the toxicity of many insecticides and active ingredients. You can also check the labels of your insecticides for pollinator advisories.
3) Additionally, spray in the very early morning or late at night when
pollinators are less active. This goes for both organic and conventional
insecticides.
Note: Just because a pesticide is certified organic does not necessarily mean
it is bee-friendly. For example, the common organic insecticides Entrust and Pyganic are both broad-spectrum insecticides that are toxic to bees. Additionally, neither of these insecticides have been proven effective against
TPB. Read on to learn which products are effective.
Conventional insecticides
Two effective conventional insecticides for TPB that have lower risk for pollinators according to the Pesticides & Bee Toxicity List include Beleaf (flonicamid) and Rimon (benzoylureas). Both are rated "practically non-toxic" to pollinators.
All other conventional insecticides recommended for TPB in the Midwest Fruit Pest Management Guide are rated "moderately" or "highly toxic" by the MDA. These include: Admire Pro, Assail, Brigade, Danitol, and Sevin XLR Plus.
Read the product labels for information on spray intervals, residual period, maximum per-season application rates, REIs and PHIs, etc. This will help you make a plan for how to rotate products and for how often to spray.
Organic insecticides
Among the organic insecticides, products containing azadirachtin have shown the best efficacy in research studies. Products containing azadirachtin as the active ingredient include AzaMax, AzaSol, Azatrol-EC, Azera, and Ecozin Plus. Azera also includes pyrethrins. It should still be noted that the evidence of their efficacy is not as strong as with the conventional products above, as they are not as widely used or studied.
While azadirachtin has relatively low pollinator risk, the risk to bees is still not zero. It has to be ingested to be toxic and has a short residual period. However, foraging bees can transport it back to the nest where bee larvae are present. Source. Therefore, it is still best to spray it in the early morning or late at night. Check the re-entry interval (REI) to help decide when to spray. For example, Azera has a 12-hour REI.
Other organic products that have not
been sufficiently studied in controlled, subjective studies include
Pyganic, Grandevo, garlic juice, and insecticidal soap; therefore, their efficacy is not known, and these
products are not currently recommended for TPB control.
Scout Before Deciding to Spray
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| Tarnished plant bug nymphs are small and green; try not to confuse them with aphids. Photo: Jeff Hahn. |
Scout weekly for TPB nymphs while day-neutral strawberries are in bloom. This doesn't take much time, can be done while you are in the field doing other tasks, and is virtually free.
Scouting tells us whether or not an insecticide application is warranted.
If there are no TPB found during scouting, or the number found is below the "economic threshold" then you can save on an application or spread out the application intervals in order to use less product.
The best way to scout
for TPB is to hold a white paper under fruit/fruit clusters, shake the
clusters, and check for TPB that fall on the paper. Do this at 5-10
random spots in the field or tunnel, shaking several clusters at each
spot. Decide whether to spray based on the number of green TPB nymphs found.
Economic thresholds: Insecticide application is recommended if there are more than 0.15 nymphs per cluster. In other words, spray if you find:
- 3 nymphs on 15 clusters
- 4 nymphs on 20-30 clusters
- 5 nymphs on 40 clusters
- 6 nymphs on 50 clusters
What if you find a couple TPB, but not very many? The idea of economic thresholds is that if the number of TPB is below these thresholds listed above, it is not economically beneficial or necessary to spray. The cost of the spray will not make up for the small amount of fruit potentially saved by spraying!
Economic thresholds are developed through extensive research - see the UMass article listed below for more information. See an example of a study that informed economic thresholds for strawberries, from University of Minnesota's own Suzanne Wold Burkness and Bill Hutchison.
Other Key Management Tips
- Weedy fields tend to attract more TPB. Good weed management in and around the field is key to reducing TPB populations
- Highly
productive varieties seem to be less susceptible to TPB than less
productive varieties. This may be because they develop faster and spend
less time in the growth stages vulnerable to TPB. Therefore it also
stands to reason that supporting healthy crop growth through good
fertigation and irrigation practices, weeding, and using white-on-black
plastic mulch should also reduce TPB incidence.
Sources:
2021 Organic Production and IPM Guide for Strawberries - Cornell University
2021-2022 Midwest Fruit Pest Management Guide
Strawberry IPM - Tarnished Plant Bug - University of Massachusetts Extension Fruit Program
Tarnished Plant Bug - UMN Extension
Disclaimer: Please read the pesticide label prior to use. The information contained at this web site is not a substitute for a pesticide
label. Trade names used herein are for convenience only; no endorsement
of products is intended, nor is criticism of unnamed products implied.
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