Managing tarnished plant bug injury to strawberries

Check strawberry fields for tarnished plant bugs and prevent economic injury by following treatment thresholds.

Tarnished plant bug (Lygus lineolaris) can cause serious fruit injury in strawberries. Since both adults and nymphs feed, there is considerable potential for economic damage. Adults overwinter in dead weeds and leaf litter in areas in and around woods and fence lines, ditch banks and alfalfa fields. They become active in early spring, feeding on shoots and flowers of early-blooming plants. Adult females lay eggs in grasses, broadleaf weeds (such as dandelion and chickweed), and in some crops like strawberries once temperatures reach 68°F or higher.

There are three to five generations per year, with each generation lasting about three to four weeks. Nymphs cause the most damage, and the earlier they feed, the more severe the damage they cause. “Button berries,” cat facing, result from nymphs feeding during petal fall; later feeding produces fruit that is slightly deformed, but still marketable. Strawberry varieties that flower later have greater potential for injury by tarnished plant bugs.

Control of broadleaf weeds in and around strawberry fields is important. Some preferred hosts for tarnished plant bugs include dandelions, chickweed, wild mint, creeping charlie, mustards and alfalfa. Growers should avoid establishing strawberry fields near weedy ditches, fence-lines with scrub vegetation, woodlot areas and alfalfa fields, as these are ideal feeding and overwintering sites for tarnished plant bugs.

Monitoring for tarnished plant bug activity should take place from first bloom through first pick, ideally, twice a week. Using a shallow pan held under the fruit or flower cluster, randomly sample 20 to 50 flower or fruit clusters by tapping the cluster into the pan and counting the number of nymphs that fall into the pan. Thresholds for treatment are shown in the table below.

Table 1. Sequential sampling for tarnished plant bugs in strawberries: Numbers of infested clusters

Number of clusters examined

Do not treat

Threshold   (Treat)

20

0

4

25

1

4

30

2

4

35

3

5

40

3

5

45

4

6

50

5

6

Reference: Tarnished Plant Bug: A Major Pest of Strawberry, OMAFRA, 1997, P. Cermak and G. Walker

A decision to treat or not to treat is made when the number of infested clusters is equal to or less than the "do not treat" number, or equal to or greater than the threshold. If the number of infested clusters is between the "do not treat" number and the threshold, sampling is continued. The threshold or treatment column in Table 1 is equal to or greater than a population of 0.15 nymphs per cluster (2.25 nymphs per 15 clusters). Applying control measures as soon as this threshold is reached will result in about 2 percent of fruit with severe injury. Delaying insecticide applications for three to five days after the threshold is reached could result in 5 percent cat faced – damaged fruit of the overall crop. Consult the MSU 2012 Michigan Fruit Management Guide (E-154) for current insecticide recommendations.

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