Contributed by: Regional Extension Agent, Mallory Kelley
This seems to be the season for galls, from camellia galls to azalea galls and even pecan galls, the question is what should you do if you have them? Are they going to kill the plant, is it an insect or a disease?
Azaleas are a staple plant for the southern landscape with many different varieties and types. They prefer a shady environment with morning sun and acid soil (pH 4.5-5.5). If they get too much sun or the pH gets too high, they can develop some problems. Azaleas are most commonly affected by lace bugs and spider mites, but from time to time you will see galls which can be pale green, pink, white, or brown fleshy growths, caused by the fungus Exobasidium vaccinii, that may develop on leaves, branch tips, flower parts, and even on seedpods. The fungus overwinters within the infected plant. In the late spring and early summer, a whitish coating appears on the swollen plant tissue. This coating is composed of many microscopic fungal structures which produce spores capable of infecting more plants during moist weather. This disease is not usually a serious problem unless wet conditions prevail for long periods of time. To control this problem, the galls should be hand-picked and destroyed before they turn white. If the gall is removed you greatly reduce the chances of it occurring next year.
Camellias are also a staple landscape plant in the south and much like the azalea prefer a shady environment with morning sun and an acid pH. They too can be plagued with a gall forming fungal disease (Exobasidium camelliae) which is very closely related to that on the azalea (Exobasidium vaccinia), but these galls only form on leaves and young shoots and range from a cream to light green to a pink or reddish color.
As these galls mature, several layers of the lower leaf surface will peel away revealing a white color, which is the spores of the fungus. These spores are spread by the wind and splashing rain to the bark or buds of other camellias where they’ll lie dormant until next year and cause infection next spring. This disease is most commonly seen in April and May. Later in the season these galls will harden and turn brown and may fall to the ground or remain attached to the plants. Again, pruning the infected part of the branch and throwing it away is the best remedy.
Pecan galls are also a prevalent problem right now in the home garden. Unlike the azalea and camellia galls this one is caused by an insect, Phylloxera spp. The Pecan Phylloxera are aphid-like insects that emerge in spring and infest leaves and twigs. Big populations of this insect can cause loss of the pecan crop for the current year and also the following year and heavy infestations can cause the tree to defoliate. Often times if this occurs early in the year the tree will leaf back out before fall.
If you only enjoy your tree for its foliage and not the nuts, nothing needs to be done. Phylloxera populations vary widely from year to year depending on weather and predators. Controlling this problem in the home garden can be very difficult due to lack of equipment needed to spray a mature tree. If you want to harvest nuts, use a hose-end sprayer designed for trees to apply the active ingredient spinosad or carbaryl in early April and again two weeks later spraying as high as you can possibly reach, some control is better than no control.
Timing the pesticide application is critical. You won’t get ANY control if you wait until you see the galls. Spray your tree about the time the pecan buds show a half-inch to three-quarters of an inch of new growth, usually this is around the first week in April. Good control one year will often keep phylloxera damage low for several years unless infested trees are nearby.