Q: The leaves on my azalea bushes have started to yellow in a speckled pattern. I noticed black splotches on the undersides of the leaves. What’s going on here?
A: The problem you describe sounds like azalea lace bug. This insect pest feeds by sucking plant sap from leaf tissue. Resulting tissue becomes speckled, and in high infestations can appear yellowish-white as the cell contents are removed. This can be a serious problem on evergreen plants like azaleas.
Lace bugs live on the undersides of plant tissue. The black splotches you notice on the leaf undersides are the fecal material of the lace bugs. Look closely, and you may notice the grayish adult lace bugs. Both the immatures and the adults cause damage.
While most lace bug infestations are in sunny locations, this is not always the case. To manage lace bug infestations, apply a strong spray of water aimed at the leaf undersides to dislodge the insects. This is most effective on young nymphs in spring. Insecticidal soaps can also be used to manage lace bugs, provided the soap coats the undersides of the leaves.
Q: All summer, my tomato plants have had spots on many of the lower leaves. Now most of those leaves have turned brown and have fallen off. What causes this?
A: The problem you describe sounds like septoria leaf spot of tomatoes. This disease is caused by a fungus. Infection usually shows up as tomato fruit begins to ripen in mid-summer. Small, circular spots gradually enlarge, beginning first on lower leaves. Wind and rain can spread the infection to new leaves or new plants. Abundant rainfall and relatively mild temperatures (between 60 and 80 degrees) favor this disease.
To manage this disease, clean out all plant debris at the end of the growing season. Control weeds, especially jimson weed, horse nettle and nightshade. These diseases can be spread via weed tissue.
Rotate growing sites as much as possible, being sure to rotate to a different plant family (grow cucumbers, for example, not peppers or eggplant, which are members of the tomato family).
Protectant fungicides may be necessary to control septoria when conditions are favorable. Always read and follow pesticide label instructions.
Q: What causes the large webbing on tree branches this time of year? I saw some on a small crab apple near my favorite grocery store.
A: The fall webworm caterpillar creates unsightly webbed nests at the ends of tree or shrub branches in late summer and fall. These pests do little lasting damage, but they can be unsightly. The caterpillars eat plant leaves under the protection of the webbing. Pull the nest out of the tree with a gloved hand, if it can be reached, to manage this pest.
Burning of the nest is not recommended, since this can cause much greater damage to the tree than letting the insects run their course. If practical, try to remove old nests from trees, since females are more likely to lay their eggs on trees with remnants of last year’s nests.
Q: Creeping Charlie has moved into my lawn. How can I get rid of it?
A: Ground ivy, also known as creeping Charlie, is a vigorous perennial weed of landscape beds and turf areas. Ground ivy’s creeping stems take root at leaf nodes, making this weed difficult to remove by hand, especially once the weed has moved into lawn areas. Crushed stems and leaves emit a disagreeable, mint-like odor.
Introduced as a gardening plant for hanging baskets, ground ivy escaped from cultivation and is now a common landscape weed.
Small pieces, cut when mowing, can take root, spreading ground ivy throughout the lawn and garden.
A broadleaf herbicide, applied in fall, can help to control this pest in lawn areas, although repeated applications may be necessary. Hand pulling or spot herbicide applications work best in landscape beds.
Denise Ellsworth directs the honeybee and native pollinator education program for the Ohio State University. If you have questions about caring for your garden, contact her at 330-263-3700 or click on the Ask Denise link on her blog at www.osugarden.com.