Controlling sweet gum tree sticky balls, arborvitae leafminer

DEAR JESSICA: Could you please tell me how often and exactly what months green emerald arborvitaes should be sprayed with a systemic spray to protect them from the leafminer insect?

— Regina Redmond, via email

DEAR REGINA: It isn’t entirely clear from your email whether you’re trying to prevent or control a leafminer infestation. I wouldn’t recommend using chemicals as a preventive measure on healthy arborvitaes, especially since the control, or “cure,” is so effective. The best advice I can offer as far as prevention goes is that you avoid planting only arborvitaes. In general, it’s best not to plant more than 5 percent of any one species.

The arborvitae leafminer is a caterpillar that develops into a small tan moth that lays its eggs between leaf scales. Its larvae overwinter in plant tissue and then tunnel into the foliage for feeding, repeating the cycle, resulting in brown leaf tips, which is first noticed in late winter or early spring.

If that’s what you’re seeing, the good news is that affected trees can make a really nice comeback with the help of a systemic insecticide containing either acephate or spinosad, as long as at least 20 percent of its foliage has survived the attack.

If you’re certain trees are infested, treat with acephate or spinosad in mid-May and again in August.

DEAR JESSICA: When we moved into our house years ago, we bought a sweet gum tree sapling and planted it in the front yard. We knew nothing about that type of tree, and the garden store mentioned nothing either except to say it’s a great shade tree. Today, the mature 60-foot tree is a nightmare. In the spring it drops tons of pollen clumps, then in the fall it drops tons of itchy balls. Sometimes it drops a second batch of itchy balls later in the early winter. The cleanup is almost continuous; the neighbors complain, and our cars and front property and street are mostly covered with tree junk.

A few years ago I called a tree service, and for three years they injected a fluid in the tree that was supposed to control this stuff. The injections were once in the spring before the tree flowered and once in late summer. However, the tree continued dropping its loads as usual and the tree service gave up and told me that any further treatments would be useless and risk killing the tree. So, short of cutting down the tree, which we won’t do because it provides great shade for our house and is a beautiful tree (when it’s not dropping things), we are at a loss. Anyway, just wondering if you have any other suggestions.

— Frank and Pattie Farello, West Babylon

DEAR FRANK AND PATTIE: Many a homeowner has lamented the seemingly never-ending task of cleaning up after a sweet gum tree. Its spiky seed pods litter lawns, walkways, sidewalks and cars, and cleanup can be painful — literally and figuratively.

One method of control is the use of a product called Florel Fruit Eliminator, which stimulates the release of a plant hormone. When flowers are exposed to that hormone, they drop off and never develop into seed pots. Applications need to be timed with the right stage of flowering in order to be effective, however, and timing can be extremely difficult as the target window is only about a week long. It also needs to be repeated every year to stimulate the drop of each season’s blossoms.

Alternately, a product called Snipper can be injected into the tree when male flower buds reach exactly 1 inch in size. To complicate matters further, trees can produce buds in two or three stages throughout the season. As you might imagine, timing injections also can be quite challenging. When effective, a hormonal reaction kills off part of the male and female flower cells, disrupting maturation so gum balls never develop.

I can’t be sure the injections your tree received were properly timed, but the information you received was correct: Too many treatments can, indeed, be harmful to the tree.

There really aren’t any other controls available.