Last week, I discussed the cicada killer wasp and hydrangea leaf spot - two concerns that popped up recently in Troup County landscapes. This week we have a couple of additional concerns – dodder and the azalea caterpillar.
Dodder (Cuscuta spp.) is a parasitic weed that infects a wide range of herbaceous and woody plant material. There are about 12 species of dodder and each species has a different host range. Dodder is generally brought into ornamental plantings via infected plant material.
Dodder is a rootless, leafless, parasitic flowering plant. It is in the morning glory (Convolvulaceae) family. Dodder has flowers and produces seed like any other flowering plant.
Seeds can remain dormant in the soil for years before germinating. Under the right conditions, dodder seed will germinate, sending up a tendril that attaches to a suitable host plant. If no suitable host is available, the plant will die within a few days.
Dodder attaches itself to the host plant’s vascular system with a peg-like haustoria or food-absorbing outgrowth. Once attached, the root system of the dodder plant shrivels and the plant feeds off the host.
Dodder contains no green tissues because it does not need to photosynthesize and produce its own food. The stem color of dodder is generally yellow to orange, but can also be shades of red or white. Flowers are small, white or pink, and usually grow in clusters.
Dodder infects a wide range of plants, including plants in the Aster or Daisy family (chrysanthemums, marigolds and sunflowers), Fabaceae or Bean family (alfalfa, clovers, soybeans and vetches), and the Ericaceae family (azaleas and rhododendrons).
Remove all plants or portions of plants infected by dodder. Ideally it should be removed before the dodder flowers and produces seed.
To date, dodder cannot be controlled through a selective postemergent herbicide application. However if the host plant is killed, the dodder plant will also die. Dodder seed can be controlled with preemergent herbicides (check label to see if these herbicides are safe to host ornamentals) and soil sterilization.
Why is the caterpillar eating the leaves on my azalea plants? Azalea caterpillars are true to their name – caterpillars that feed on azalea leaves. They often feed together, especially when young.
This large caterpillar has a red head and legs with rows of yellow spots and a few white hairs. When disturbed they may arch their heads and tails backwards.
If you only have a few caterpillars, pick them off and crush them. If there are too many for this, you can spray them with liquid Sevin, cyfluthrin or other appropriate insecticide. Read and follow all label directions when using pesticides.
A few caterpillars may not hurt anything but many can strip an azalea of all its leaves. Bacillus thuringiensis (or Bt) dust or sprays (Dipel, Thuricide and others) may work if the caterpillars are small. Bt is less toxic to people than traditional insecticides.
Randy Drinkard is a technical writer for The University of Georgia Center for Urban Agriculture and ANR Agent for Troup/Meriwether Cooperative Extension. The Troup County Extension office is located at 114 Church St. It can be reached at 706-883-1675.