Ga. Drought Means Less Turf Insects, More Diseases

Bluegrass Billbug

The ongoing drought in Georgia has had many negative side effects when it comes to turfgrass. However, with Landscape professionals daily struggle with insect damage, the drought has been a help. Most notably, it has diminished the Japanese beetle population.

In the United States, controlling the beetles’ larval (grub) and adult stages cost more than $460 million a year.

Adult Japanese beetles feed on the leaves of some 300 different landscape plants from roses to crape myrtles. As grubs, they burrow underground and feed on plant roots. Turfgrass roots are among their favorites, Braman said.

The tiny destroyers’ numbers are down because their life cycle relies on moisture. If it’s too dry, the larvae can’t complete their development.

Young Japanese beetle larvae need moisture to tunnel and search for food. If they survive in the drought to adulthood, they need wet areas to lay their eggs in, and there haven’t been many wet areas to be found this summer.

The drought also has reduced the population of another turfgrass pest, the two-lined spittlebug.

They like it hot, but they need moisture, too. So there aren’t as many around this year to harm centipede grasses and holly bushes.

Less and different diseases

The drought has reduced the typical diseases found on turfgrass and landscape plants during high humidity conditions, but it has also opened the door for other diseases, said Alfredo Martinez, a plant pathologist with UGA Cooperative Extension.

In a drought, turfgrass is stressed, “and we have a good amount of stressed turf areas in Georgia,” he said. “We are seeing more cases of anthracnose and dollar spot, which are caused by organisms that take advantage of the turf’s stressed state.”

Martinez says homeowners actually help give these diseases a foothold by the adjustments they make in reaction to the drought.

“When there’s not sufficient water, people tend to reduce or avoid fertilization all together,” Martinez said. “They think it will burn the turf if they do. But low fertility promotes disease like dollar spot.”

Jean Williams-Woodward, a UGA Extension plant pathologist who specializes in ornamentals, agrees.

“Generally with less water there is less disease, but any plant that is being irrigated can still become diseased,” she said. “During drought conditions, plants become weak and are more susceptible to infection.”

Leylands hit hardest

She says Leyland cypress trees are being hit harder by the drought-related diseases than most other trees and landscape plants.

“Seiridium canker disease is the main cause of tree decline,” Woodward said. “Drought stress causes the cankers to enlarge about three times faster than they would on nonstressed trees.”

Cankers form on the branches when the fungus enters through wounds or natural openings on the tree. Collectively the cankers interfere with water flow, and, as a result, the branches die.

Roots stressed