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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 pollinators in mind when spraying for TPB in strawberries, since they are both present during bloom
- Both synthetic and organic insecticides can be toxic to bees
- Multiple conventional insecticides control TPB, and they vary in
pollinator risk level. Beleaf and Rimon have the lowest pollinator risk while also being effective on TPB. 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 a concern as long as strawberries are in bloom.
TPB
has several generations of nymphs (immature stage of the insect) from June through August. Nymphs pierce and suck liquid from the flowers and young fruit.
They are responsible for "catface" deformation on fruit. The fruit is less appealing for fresh-eating but it is still edible and can be used for
processing. Because it makes the fruit smaller, extensive TPB damage will reduce overall yield.
Protecting Pollinators While Controlling TPB
A challenge with this insect in strawberries is that they feed on blossoms, and bees are actively pollinating the flowers during bloom. Growers must control TPB without killing the local bee population.
Thankfully, not all
insecticides impact pollinators equally. There are a few lower-risk options effective on TPB - keep reading to find that list. First, let's go through five important tips for protecting pollinators:
- Only spray insecticides if necessary. Scout your field for TPB before deciding to spray.
- Control weeds in and around the field to reduce TPB habitat. Using exclusion
netting can also drastically reduce TPB pressure.
- Choose insecticides with low pollinator
risk if possible. The Minnesota Department of Agriculture maintains a Pesticides & Bee Toxicity List
where growers can easily compare the toxicity of many insecticides. Check the labels of your insecticides
for pollinator advisories.
- Spray in the very early morning or late at night when pollinators are less active.
- A pesticide's certified organic status does not necessarily mean it is bee-friendly. For example, Entrust and Pyganic are both broad-spectrum insecticides that are toxic to bees. Additionally, neither of these insecticides have been proven effective against TPB.
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 according to MDA.
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 plan for how to rotate products and 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 on TPB is not known.
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 at least weekly for TPB nymphs while strawberries are in
bloom. This doesn't take much time and can be done while you are in the field doing other tasks.
Scouting tells us whether or not an insecticide application is warranted.
If you find no TPB 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 stands to reason that supporting healthy crop growth through good fertilization and irrigation practices, weeding, rotating crops, and doing annual post-harvest renovation will all help mitigate TPB.
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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