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Tarnished Plant Bugs in Strawberries

Have you ever heard of a “cat-faced” strawberry? Maybe not, but have you ever come across a strawberry with seedy areas that didn’t expand? (And how did someone think those symptoms look like a cat?)

Regardless of the name, cat-facing may not be apparent until the berries are ripe, but the damage occurs when the plants are flowering. Frost or poor pollination can cause similar distortions, but most often the culprit is the tarnished plant bug (TPB, Lygus lineolaris).

Though all bugs are insects, not all insects are bugs – but the TPB is a true bug in the order Hemiptera and family Miridae. Like all true bugs, it develops through metamorphosis. Immature bugs progress through five growth stages – from looking like an aphid to having partially developed wings – and then molt and become reproductively mature adults with fully developed wings. There are typically three or four generations per year in Wisconsin.

Adult TPBs are approximately ¼ inch long, oval-shaped, mottled bronze to tan, with reddish to white markings behind the head and on the wings.  Typically there’s a tan, triangular or heart-shaped spot in the center of the back, which helps to differentiate them from similarly sized beneficial insects. At all life stages, TPBs are highly active and move quickly.

Adult tarnished plant bug. Photo by Russ Ottens, University of Georgia, Bugwood.org.

TPBs may have first been found in the United States as early as 1781. Since then, it has been documented feeding on more than 385 plant species, including 130 of commercial significance. Along with strawberries, they are common on apples, pears, apricots, plums, many flowers, vegetables, and field and forage crops.

To protect your strawberries, it’s important to understand the TPB’s life cycle. It overwinters as an adult in weedy areas, under leaf litter, in bark crevices and under rocks. When temperatures rise in the spring, adults begin to feed on weedy plants by ingesting plant juices through their piercing/sucking mouthparts. Females lay eggs on weedy plants or strawberry flowers, and the eggs hatch about 10 days later.

Feeding coincides with the flowering of strawberries, and TPBs target sap within the blossom, which kills the developing seeds in that portion of the flower. During and after bloom, TPBs also feed on the developing seeds and the part that will eventually be the fleshy fruit. As the fruit grows, the damaged areas do not expand, resulting in sunken, deformed, seedy sections. These berries are called cat-faced berries or button berries.

Control measures vary by the size of the strawberry patch and the TPB population. They feed and reproduce on weeds, so good weed management is key, as is mowing nearby grassy areas to minimize feeding and reproduction grounds. Cleaning up leaves and removing weeds in the fall reduce overwintering sites.

Then check for TPBs in the spring, when strawberry buds are forming. Carefully inspect the plants by tapping the leaves and flowers over a light-colored tray to see whether any fall off. Do this early in the morning when it’s cooler and the bugs are slower. Tapping the plants over a tub of soapy water is an effective way to kill them in a small patch.

TPBs favor some plants such as alfalfa and clover even more than strawberries, so avoid planting strawberries next to alfalfa or clover fields. When such a field is mowed, they will migrate and likely end up in your strawberry patch, resulting in a higher damage risk if this migration coincides with strawberry bloom.

If you find more than one bug per four flower clusters in your strawberry patch before bloom, you may choose to use an insecticide. Do not use an insecticide during bloom, however, to avoid killing pollinators. Insecticides available to the general public include products containing carbaryl (e.g., Sevin), permethrin and malathion.

When using any pesticide, read the entire label before purchase and use. Make sure the product is labeled for use on strawberries, and carefully follow the recommendations for application rates, personal-protection equipment, and the interval between the last spray and when the fruit can be harvested.

The longer strawberries – and other crops – are grown in the same place, the more pest pressure will increase, so rotate strawberries to a different area every three to four years. This will help reduce the number of TPBs, other insect pests and plant diseases.

Severely deformed strawberries may have a poor texture, but otherwise, TPB-damaged fruit is perfectly safe to eat. With any luck, your harvest will be so abundant that a cat’s face is the last thing on your mind.

To learn more about controlling tarnished plant bugs, call the Door County Extension office at 920.746.2263, or email me at [email protected].