Begin monitoring for tarnished plant bug activity in strawberries

Use the sampling and thresholds process to determine whether treatment is necessary for tarnished plant bugs in strawberries.

Tarnished plant bug can be a major headache for strawberry growers by damaging blooms and causing deformed berries, or button berries, that are unsalable. Now that strawberry bloom is underway, growers should begin to monitor tarnished plant bug to keep damage below economic injury thresholds.

Adults overwinter in leaf litter, plant debris and brush piles, and move to broadleaf weeds, grasses and crops such as strawberry to lay eggs once temperatures get to 68°F. Eggs hatch in about 7 to 10 days and develop into small green nymphs that resemble aphids without cornicles. Cornicles are structures on the back end of the aphid that resemble tailpipes. Nymphs undergo five immature stages, or instars. Tarnished plant bugs move more rapidly than aphids. By the time they reach the third instar, they have developed small wing pads. The fourth and fifth instars begin to develop brown pigment and larger wings and look more like adult tarnished plant bug. Depending on temperature, the nymphs can develop into adults as rapidly as 12 days, or at cooler temperatures take up to 34 days.

Tarnished plant bug.
Tarnished plant bug nymph. Photo credit: Scott Bauer, USDA Agricultural Research Service, Bugwood.org

Although both adults and nymphs cause injury, the majority of the damage is done by nymphs. Tarnished plant bug feeding occurs on seeds or tissue near seeds. It stops the production of plant growth hormones in that area of the berry and results in deformed fruit – a condition known as “catfacing” or “button berries.” The earlier feeding by tarnished plant bug occurs, the more severe the damage is – at petal fall, damage is more severe than once seeds have developed and berry tissue starts to expand.

The Ontario Ministry of Agriculture, Food and Rural Affairs describes the sampling process and thresholds to use for tarnished plant bugs in their factsheet, Tarnished Plant Bug: a major pest of Strawberry. Monitor for tarnished plant bugs from beginning of bloom until the first picking. Place a shallow pan (choose a color other than white or green to make it easier to see the nymphs) under a cluster of flowers or fruit and tap the cluster to dislodge nymphs. Start by sampling 20 clusters at random. If no decision can be reached at this point, keep sampling by multiples of five up to a maximum of 50 clusters. After each multiple of 5 clusters, check Table 1 to see if a decision can be made.

For example, 20 clusters are sampled and two infested clusters are found. In referring to Table 1, for a sample size of 20 clusters, the “do not treat” decision number is zero and the threshold number is four. If 20 clusters are sampled and three infested clusters are found, that number is between the “do not treat” and “treat threshold,” so sample five more. Another five clusters are sampled, and one more infested cluster is found. At 25 clusters, the threshold number is four, so the treatment threshold has been reached and an insecticide should be used.

Consult the Michigan Fruit Management Guide, MSU Extension bulletin E-154, for recommended insecticides.

Table 1. Sequential sampling for tarnished plant bug in strawberry: Number of infested clusters.

Number of clusters Do not treat Treat with insecticide
20 0 4
25 1 4
30 2 4
35 3 5
40 3 5
45 4 6
50 5 6

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