Two new concerns have popped up recently in landscapes and lawns in the west central Georgia area – one issue being insect related and the other issue involving a disease.
Cicada Killer Wasp
The cicada killer wasp is the largest wasp in Georgia. The cicada killer wasp is almost two inches long. Although intimidating in appearance, these wasps are not something we humans have to worry about. Cicadas, on the other hand, should be very afraid. Cicada killer wasp adults feed on nectar but use paralyzed cicadas to feed their young.
Female cicada killers are hard to provoke to sting. The female uses her stinger to paralyze her prey (cicadas) rather than in self-defense. The female’s attention is focused on providing food for her babies, so she poses little threat to humans.
Cicada killers prefer to nest in sandy open sunlit areas. As the female digs, she kicks out soil that forms a semicircle around the burrow opening. She burrows six to ten inches into the ground, prepares a chamber, catches a cicada to fill the chamber, lays an egg on the cicada, and seals the chamber. She may do this over a dozen times in one burrow.
When a female finds a cicada, she paralyzes it with her stinger, straddles it, and attempts to fly with it to her burrow. Because the cicada typically weighs more than she does, these flights are usually hops, with more dragging than gliding.
The egg hatches in a few days and the larva feeds on the paralyzed cicada until nothing is left but a shell. Then the wasp larva pupates within the burrow, remaining there until the next spring.
Males cannot sting; their only defense is intimidation. They patrol the nesting area, trying to divert attention away from the female, allowing her to provision her nest with cicadas. Meanwhile, the male is using threatening tactics to distract potential predators. He may even dive bomb perceived threats. Since the males do not have stingers, they are completely harmless. They must rely on bluff, bluster, and bravado to protect their families.
Because cicada egg laying can be damaging to trees and shrubs, cicada killer wasps are very beneficial, providing free biological control. However, homeowners who do not want these wasps around can modify their lawn to be unappealing. A thick healthy turf with no bare spots will exclude cicada killer wasps. If turf is thin in nesting areas, identify turf problems that make the turf weak and correct them.
Many areas in Georgia are experiencing warm, humid weather with spotty rain showers. This is the perfect weather for fungal leaf spot development in the landscape. Most leaf spots are benign and will not damage the plant.
Cercospora Leaf Spot of Hydrangea is an example of a leaf spot disease that commonly occurs during hot, humid weather, especially under sprinkler irrigation. As with most leaf spots in the landscape, chemical treatment is rarely needed for light infections, but may become necessary for major infections.
Management of leaf spot diseases involves removing sources of the disease and protecting the plant. Start by selecting plants that will thrive where they are sited.
The fungi that cause these diseases mainly survive on the infected leaves that fall to the ground, so removing and destroying diseased leaves can help lessen the amount of disease next year.
Stressed plants are more susceptible to disease, so check the cultural conditions and optimize them with fertility management and mulching. Good air circulation around plants will lower the humidity and leaf wetness, thereby reducing disease.
Avoid wetting the leaves when irrigating landscape plants. If the plant is repeatedly defoliated each year or appears to be dying back because of the disease, prune out the affected stems and use fungicides preventatively (before the symptoms) to protect new growth.
Randy Drinkard is the ANR Agent for The University of Georgia Troup/Meriwether County Cooperative Extension. The Troup County Extension office is located at 114 Church St. and can be reached at 706-883-1675. Open Monday through Friday, 8 a.m. to 5 p.m.