Landscape invaders

Asian long beetle

They come by boat, travel by plane, nestle in shipping crates and burrow into the soil of imported plants. Exotic species of pests travel to the United States and slip through ports of entry in spite of rigorous federal inspections, and once “exotics” get a foothold in a region and proliferate with no natural enemy to control their expansion, they can pose a threat to plants in the landscape – and in agriculture and our forests. Then, they become “invasive species.”

“What makes species invasive is that nothing preys on them – nothing kills them, nothing eats them, so they get all the food they want,” says Dan Suiter, a professor of entomology at the University of Georgia College of Agricultural & Environmental Sciences.

Over time, natural enemies emerge and can gradually control invasive species. Nature takes its course. But before that happens, invasive species can destroy desirable plants, trees and turf if left to their own devices.

Invasive species are especially a problem in states like Florida, where Steven Arthurs, assistant professor of entomology at University of Florida, says invasive pests enter the state at a rate of two new species per month. (That’s up from an average of one.) “They largely come in from the plant trade,” he says, relating that the best efforts to keep them out of the country just aren’t enough.

So that makes identifying invasive species and controlling them a priority. Some invasive species can be managed with insecticides and other lawn care products; while other pests require removal of infected plants or turf. Arthurs recommends that landscapers take a diligent course of action that begins with reporting the pest to a local extension by taking photographs (close up and long distance), and collecting a sample (if possible) to send to a lab, where the pest can be properly identified. “If it is a new species the government might want to take over and eradicate it,” he says.

That has been the case when treating the Asian long-horned beetle, says David Shetlar, entomologist known as the “Bug Doc” at The Ohio State University. This pest has been a threat in New York and Massachusetts, and along the eastern seaboard. “The federal and state governments have identified territories where they go in and do treatments to eradicate it,” he says of the eradication process.

This can involve removing trees in the affected zone, and treating areas in the perimeter. Landscapers who treat properties without taking the case to a local extension agency could be unintentionally thwarting the eradication effort, Shetlar says.

So, first identify then understand the proper course of action for managing invasive pests. Here is a cheat sheet to identifying “nasties” that are causing a problem now, how to spot an infestation and what courses of action are appropriate for controlling damage. For more information, always consult with a local county extension agency.
 

Kudzu bug

In 2009, pest control operators cited cases of the kudzu bug on the sides of white homes (that reflect light), and some genetic research uncovered that the pest was probably related to a group of bugs from Japan – and there happened to be a direct flight from Atlanta to Japan at that time, Suiter says.

By June 2010, the kudzu bug was infesting soybeans in northeast Georgia and South Carolina. “It became a tremendous soybean pest,” Suiter says, noting that the bug proliferated.

As the name implies, the preferred host plant is kudzu. They peak in early spring when kudzu emerges, and as the kudzu grows in summer they are less of a problem in the landscape as they nosh on their favorite plant. In fall, they become a problem again.

The problem for homeowners comes when kudzu bugs overwinter and burrow into cracks and crevices in the home, or underneath the bark of trees. They reproduce on legume plants, but you’ll find them hanging out on non-hosts like oak and pine trees and azaleas. The bugs are a nuisance, leaving behind a rust-colored stain and unpleasant odor, Suiter says.

Herbicide treatments can be effective in kudzu patches, before the kudzu bug overwinters and heads to the home to cause a nuisance. The pest is mainly a problem in the Gulf-coast states and north up into Tennessee, the Carolinas and parts of Virginia.
 

Emerald ash borer

The old EAB is still a concern in the Midwest and Eastern states, and its trail runs all the way west to Colorado, Shetlar says. Adults are bright, metallic green, ½ inch long and begin their damage in the top third canopy of ash trees. They progress downward until the tree is bare from leaf drop.

Symptoms include bark splitting, and underneath the bark you’ll find serpentine galleries (trails) and D-shaped exit holes. A side effect is increased woodpecker damage as the birds work to extract the insects.

“We grossly underestimated the power of this insect’s ability to expand its range,” Shetlar says, adding that the initial infestation of a tree is often missed for a couple of years until real damage sets in. “In the third year you see significant die-out in the middle of the tree, and that is often when treatments get started, and by that time you may have lost half of the tree.”

If emerald ash borer is within a 20-mile radius of your area, treatments are recommended to prevent infestation as opposed to curative treatment. Property owners will have to decide whether to continue the treatment investment, in spite of the fact that the tree may not be recoupable if damage was identified too late; or carefully take down and replace the tree. Control methods include a soil drench with imidacloprid applied in early spring.
 

Tuttle mealybug

Mealybugs generally aren’t a problem in turf, which is why this species caught the eyes of entomologists in Florida when it began infesting and damaging zoysiagrass. The tuttle mealybug is actually a native species, says Lyle Buss, manager of the insect identification lab at University of Florida. “It can cause some serious damage where it kills patches of grass, and you’ll notice it from brown patches or thinning out in the lawn,” he says.

The other common name for this pest is rice mealybug, and it was actually discovered in the U.S. in the late 1960s, infesting bermudagrass seed crops in Arizona. It was detected in California in 1970, and also in Texas, but it’s a problem mostly in southeastern states.

You can identify the insects by their tiny 2-mm pink bodies – they are difficult to spot in the turf because they surround themselves with a white, waxy material. They tuck in between younger leaf blades and the stem. Tuttle mealybugs seem to prefer ‘Empire’ zoysiagrass that is in lawns installed in the last two years.

Control methods can include some plant systemic products such as neonicotinoids that will reach the insects where they are feeding. In severe cases, lawn replacement with another type of grass might be necessary to avoid reinfestation. “If you really want to stick with zoysiagrass, you’ll have to treat with an insecticide,” Buss says.
 

Rugose spiraling whitefly

Whiteflies are such a problem in Florida that the state actually hosts a website on the topic at www.flwhitefly.org. This specific type of whitefly – the rugose spiraling white fly – feeds on a great number of plant species, including preferred hosts like coconut palms, white bird of paradise and black olive, Buss says.

“The population of whiteflies can build up to huge numbers on the undersides of leaves where they really make a mess,” Buss says. These sap-sucking insects take in plant liquids when they feed and exude honeydew as a waste product, which drips down from the tree. “It can make a mess on people’s cars, on their houses and in their pools.”

That honeydew sparks the formation of a fungus called sooty mold, which causes a blackening of leaves that is mainly an aesthetic problem, Buss says. But whiteflies also stress plants because they remove water and nutrients, and the honey and mold hinder plants’ abilities to produce nutrients. The honeydew attracts pests like stinging ants and honeydew wasps that protect the white flies and prevent natural control of the pest.

Good control using systemic insecticides, as soil drenches or trunk injections, can be achieved. But, reapplication is necessary to prevent re-infestation. You must commit to the program.
 

Brown marmorated stink bug

These sucking bugs can build up into significant populations on a variety of ornamental trees, including butterfly bush, fruit trees, berries, grapes, citrus, avocado and more – up to 60 host plant species. The bug feeds on the fruit, causing damage. You’ll spot this pest on the east and west coasts, says Mark Hoddle, biological control specialist and principle investigator at University of California Riverside.

The pest is a nuisance to homeowners when it migrates indoors during winter and goes outdoors in summer and destroys backyard crops. The stink bugs have shield-shaped bodies and are about 15 mm in length. Their piercing-sucking behavior leads to distorted fruit and fruit drop. They can contaminate grape vines and leave behind a strong odor.

Insecticides have proven effective, according to the University of California Riverside, though further research to identify control is ongoing.
 

Asian citrus psyllid

This citrus-grazing pest is persistent in Florida and Southern California in commercial groves and also on ornamental citrus trees in home lawns. “It likes to feed on the flush growth, causing leaves to curl up. It’s nasty looking,” says Mark Hoddle, Department of Entomology at University of California, Riverside.

“The bigger problem is that the psyllid spreads a bacterium that kills citrus.” Once infected with the bacterium, a citrus plant will die within five to eight years.

“The disease has killed 50 percent of the citrus trees in Florida, and we recently found it in Southern California,” Hoddle says. “Some experts suggest that if a cure is not found in five to 10 years, Florida may not have a commercial citrus industry. It is that bad of a problem.”

Asian citrus psyllid is often identified when a tree is already dying. Its leaves become yellow. The nyphs produce a toxin, causing the flush tips of leaves to die back or become twisted. The leaves then do not expand normally. The pysllids vector a bacterial disease that causes mottling of leaves and affects fruit maturation.

Control through pesticide can reduce the problem, but there is no “cure” for the disease.
 

Polyphagous shot hole borer

Polyphagous means “it eats lots of things,” Hoddle says, which is one reason why these beetles are a real problem in California. They are also difficult to detect because they are so small. “They are the size of Abraham Lincoln’s nose on the penny, and they tunnel into trees and carry fungal spores on the back of their heads in their small pockets,” Hoddle says.

Those are fusarium fungi. The beetles inoculate trees with the fungus, which destroys trees’ food and water conducting systems. The result is stress and dieback. The beetle larvae then feed on this fungus. “So, the beetles are not eating the tree, they are eating the fungus that they introduce into the tree, and that fusarium penetrates and kills the tree,” Hoddle says.

Fusarium dieback symptoms include a white powdery substance that looks like sawdust, dry or surrounded by wet discoloration of bark. (This marks the beetles’ exit holes.) Early injury is difficult to detect, though by lifting up bark you can see the beetle’s circular tunnels, called galleries.

Controlling this beetle so that it doesn’t spread in the landscape essentially involves removal of the tree, which is the case for wood-boring insects that are a threat (emerald ash borer, gold-spotted oak borer). The best landscaping practice is to chip the wood on site and transport by covering the waste with tarps. “If the wood cannot be chipped on site, it should be covered or buried so beetles cannot emerge and fly onto uninfected trees,” Hoddle says.