A thorough garden cleanup in fall is one of the best ways to control for pest insect populations.
Many pest insects, including whiteflies, aphids and mealybugs, lay their eggs in fall to overwinter in weedy areas, inside “mummies” of dried fruits and vegetables, in bark crevices, just under the soil surface, and on the undersides of fallen leaves and garden debris. If your crape myrtle had a problem with aphids this year, it’s a good bet that the leaves falling from the tree will have quite a few aphid eggs stuck to them.
Two fairly recently arrived invasive pest insects, the bagrada bug (a stink bug) and the leaf-footed bug (closely related to stink bugs) are proving very difficult to control by either chemical means or by handpicking or vacuuming. They produce several generations throughout the year that feed on seasonal crops. Both bugs overwinter as adults and bagrada bugs lay their eggs in fall to overwinter. Removing their winter hideaways and egg clusters is critical in reducing the populations of these bugs.
Bagrada bugs’ main hosts are members of the mustard family, which includes several very popular flowering ornamental plants – sweet alyssum, stock and candytuft. Alyssum dies back in our summer heat, but self-sows readily, reappearing in other parts of the garden in spring and fall. They’re also serious pests of cole family vegetables (cabbages, cauliflower, broccoli, kale, turnip and mustard greens), which are cool-season crops in our climate. Monitor alyssum plants often and remove plants if bagrada bugs are present. (UC Davis’ www.ipm.ucavis.edu/PMG/PESTNOTES, has good photos of both bugs and their eggs).
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Use row covers to protect winter crops from the bugs, but set out the covers early to avoid trapping bugs inside. Feeding damage from bagrada bugs looks like small light green starbursts. Eggs are laid in small clusters of one to six, and are white at first but turn red before hatching. The eggs are laid on leaf surfaces or on the soil surface under plants. Scrape eggs off leaves and regularly cultivate the soil under plants. Favorite bagrada foods are ripe tomatoes and ripe pomegranates. Pull out tomatoes, pick up pomegranate culls, and cultivate the soil in those spots.
Leaf-footed bugs (3/4 to 1 inch long) are larger than bagrada bugs (1/4 inch long), and their leaf-shaped hind legs look as though they’re wearing swim fins, making them easy to identify. These bugs overwinter as adults in groups in protected areas such as woodpiles, sheds, inside palm fronds and in peeling bark crevices. They feed primarily on nuts and seeds in winter, especially weed seeds. Remove weeds or keep them mowed short, and check likely hiding places for adults. Leaf-footed bugs lay their egg clusters in spring.
Cold temperatures can kill off adult bagrada bugs and leaf-footed bugs, but warm, wet weather is predicted for this winter. Bagrada bug and leaf-footed bug (as well as other pest insect) populations will explode next spring unless we try to control for them now.