Dear Lisa,

Thank you for reaching out to the UVM Extension Master Gardener Program with your question.

The damage to your plants is consistent with damage from the four-lined plant bug. This insect can feed on a wide variety of plants including herbs, vegetables and ornamentals. The insect has piercing, sucking mouth parts so when it feeds on the leaves it results in small almost angular spots. The spots can appear almost clear or brown but later appear more black. There can be drop out of tissue leaving holes in the leaves. The four-lined plant bug is quick and difficult to detect so the fact that you have not seen the insect on your plants is not unusual. Both the nymphs and adults feed on plants but there is only one generation each year. Nymphs emerge in late spring and the adults feed until early July so the damage is seen in May and June. The good news is that the damage is usually cosmetic although large numbers of the four-lined plant bug can be destructive to herbs.

You could use row covers to protect the plants. If you can tolerate the damage the plants should recover. Usually treatment is not necessary. Adults lay eggs on the plant stems so you should remove damaged plants in the fall to remove eggs. Transport the damaged plant material away from your landscape, bury or compost the damaged plant material.

Selected Resources:

Fourlined plant bugs | UMN Extension