My yucca had "depleting" leaf surface and damage to the leaf edge last year. Now I see multiplying black and red beetles again. I tried horticultural oil on the insects, but it only knocked down the numbers for a short period. Any magic bullets?
Yucca plant bugs have three generations a year, beginning in spring. After hatching, they go through several nymph stages, when they look like small adults. They feed by inserting their mouth parts into the leaf and sucking out plant juices, leaving leaves mottled or yellow. Monitor yuccas early in the season for signs of this pest. Knock down the first generation of bugs when they are still young nymphs by using insecticidal soap or a botanical insecticide such as neem.
Beneficial predator and parasite insects normally keep yucca-bug populations from exploding. Avoid broad-spectrum insecticides, because they kill beneficial insects along with the pests.
What is the best way to get rid of bugleweed in my lawn?
Ajuga, or bugleweed, is a popular groundcover that may escape into lawns. Dig up the occasional escapee. For major invasions, apply a broadleaf herbicide labeled for lawn use that contains the active ingredient Triclopyr. To prevent ajuga from spreading seeds, plant it behind a wide barrier, such as a walkway. To stop runners (horizontal growth that puts down roots), a narrower barrier should do.
Sow bush beans every two weeks to have a continuous harvest of fresh beans. Pick off Mexican bean beetle eggs, larvae and adults.
Don't be upset by the presence of defoliating caterpillars on shade trees. Orange-striped oak worm, green-striped maple worm and the red-humped caterpillar are three insects that typically cause little damage. Control measures may be warranted where infestations occur on small trees.
Jon Traunfeld, regional specialist, and Ellen Nibali, horticulture consultant, work at Maryland Cooperative Extension's Home and Garden Information Center, which offers Maryland residents free gardening information. Call the center's "hotline" at 800-342-2507 (Monday through Friday, 8 a.m.-1 p.m.) or e-mail plant and pest questions through the Send a Question feature at hgic.umd.edu.