All of the leaves on some of my tomato plants have curled down, except a few twisted in all directions. They were growing great for a while. It looks contagious because they're all together. What is this?
Tomato plants are like canaries in the coal mine when it comes to herbicide injury. They are super sensitive to the chemical 2,4-D and its family of growth-regulating herbicides, including clopyralid. Twisted growth is a classic symptom. Most likely an herbicide sprayed in your area was carried by wind and drifted onto the tomato plants. Clopyralid also could have been present in mulch or compost used on your garden. It is a very persistent herbicide — it can travel from treated pasture through the digestive system of a foraging animal and into the manure, surviving composting and remaining toxic to plants. Severely damaged tomato plants should be replaced. However, if you suspect clopyralid in the soil, it will takes several years before that soil can be used for growing successfully. For more info, visit the Home and Garden Information Center website.
My oak's leaves are starting to brown again, mainly on the bottom branches. This has been going on for years, and by the end of the summer it looks bad. Otherwise it's OK except for a few dead branches. Do I need to water this tree?
This is likely bacterial leaf scorch, a relatively new disease of shade trees in Maryland. It affects a large number of species, including elm, catalpa, hackberry, ginkgo, oak, sycamore, maple, mulberry and sweetgum. In severe cases, it can cause tree death. This bacterium is introduced by an insect feeding and spreads through the tree's vascular system. Symptoms typically appear in mid- to late summer on lower interior leaves in the form of irregular browning on leaf margins, sometimes with a yellow halo depending on the tree species. The symptoms progress along the branch toward the tip and recur yearly, moving through the crown. Reduced growth and dieback are common in severely infected plants. The effects of this disease might be mistaken for drought or other stresses. Drought symptoms, however, are more uniform and first appear on upper branches and younger leaves near branch tips. There is no treatment for this disease, though infected trees may continue to persist in the landscape if affected branches and dead wood are pruned out promptly. See photos at extension.umd.edu/learn/bacterial-leaf-scorch.
University of Maryland Extension's Home and Garden Information Center offers free gardening and pest information. Call 800-342-2507 or send a question to its website at extension.umd.edu/hgic.
Plant of the week
Blanket flower, Gaillardia
Gaillardia x grandiflora
Add sizzle to your summer garden in shades of orange, burgundy and yellow with this perennial flower. Its daisy-like flowers bloom from spring to early fall. Blanket flowers are easy-to-care for plants, handling drought and heat with ease. They can even grow in almost pure sand. In fact, planting in very well-drained soil is key to its winter survival. There are many cultivars of this hybrid cross of Gaillardia aristata and Gaillardia pulchella, including "Arizona sun," "goblin" and "fanfare." The plant is listed as deer resistant and is attractive to butterflies. Remove spent flowers to prolong blooming. With few associated diseases or pests, it is a wonderful, though short-lived, perennial for a low-maintenance flower bed and often self-seeds.
— Debbie Ricigliano