Nursery Tour Uncovers Insect Friends, Foes

7/26/2014 7:00 AM
By Philip Gruber Staff Writer

EAST EARL, Pa. — From algaelike bacteria to grubs to big, benign wasps, nurseries are home to many species.

Developing a cost-effective, responsible pest management program requires knowing which ones are helpful, only minor concerns or truly devastating.

Tim Abbey, a Penn State Extension educator, led growers and landscapers around Conestoga Nursery on Tuesday, talking about pests and beneficial insects.

Abbey first pointed the group to yellowing and stunting on the ends of a maple tree’s branches. It was caused by potato leafhopper, a problem in field and container agriculture but not, as far as Abbey has seen, in landscapes.

Potato leafhoppers do not overwinter in Pennsylvania. They arrive from the South each year around early May. Often, they attack alfalfa first, but they have a range of hosts, Abbey said.

“It doesn’t take a lot of adults or immatures” to cause noticeable damage, and potato leafhoppers produce multiple generations in a year, Abbey said.

“Once this growth sort of hardens off, they go off and find something else to feed on,” he said.

Synthetic pyrethroids can be used on potato leafhoppers and may provide some residual protection, he said.

Abbey found evidence of another tree pest on the underside of some sycamore leaves.

Lace bugs, named because parts of their body resemble a lace doily, cause stippling or bleaching of the leaves because they drain the fluids and chlorophyll.

They also leave feces behind, Abbey said.

Lace bugs overwinter as adults and emerge in May when plants start their new growth. Besides sycamores, they can also be pests of rhododendrons, Japanese andromeda and other ornamentals, he said.

Immature and adult lace bugs feed together, so one spray can get the bugs at all of their life stages at once, he said.

“On deciduous plants, they can be pretty noticeable,” but the damage is short-lived because those plants drop their leaves every year, Abbey said. Damage on evergreen plants takes longer to cover with new foliage.

“The picky customers, they might want this dealt with,” he said.

For effective lace bug control, sprays need to cover the undersides of the leaves, not an easy task, Abbey said.

Like lace bugs, spider mites stipple leaves. Boxwood spider mites and spruce spider mites overwinter as eggs, though other species spend the cold months at other stages, Abbey said.

Mites can produce several generations a year and mature quickly. “Two-spotted spider mites can go from an egg to an adult in like 10 days,” Abbey said.

To scout for mites, shake the plant over a piece of white paper and then wipe your hand across the page. “It’s a really good way to scout because they’re small,” Abbey said.

Many new miticides have come out in the past 10 years. Abamectin is one type that is translaminar, meaning it can be sprayed on the tops of the leaves and make its way to the underside of the leaves where the mites feed, Abbey said.

Some nursery insects are many times the size of mites but are not necessarily destructive.

The large, buzzing green June beetle, or June bug, is not much of a nursery pest, even though its grubs can grow 2 inches long, Abbey said.

The grubs can be a problem for golf courses, as they tunnel to the surface at night, leaving unsightly holes and mounds. June bugs can also cause problems for fruit growers, he said.

A group of another big but basically harmless nursery insects was humming around a boxwood planting.

Female cicada killer wasps can grow up to 2 inches long and use their stinger to paralyze annual cicadas. The females take their still-living victims to their burrows in the ground and lay an egg next to them. The cicada serves as food for the young wasp, Abbey said.

Males are smaller and do not sting. “The females aren’t aggressive” and would likely not sting a person unless the person tried to grab the wasp, he said.

Abbey has so far avoided being stung while handling the insects, which he admitted are one of his favorite insects.

The wasps like loose soil, so they can sometimes make a mess of golf course sand traps and baseball fields. “People freak out when they see them,” Abbey said.

Cicadas are not a major pest for ornamental plants, and cicada killer wasps cause neither help nor hurt to growers. “I wouldn’t do anything for them (for control) anywhere,” Abbey said. “They’re hard to kill anyway.”

“Plus, it’s neat to be able to pick up a wasp that’s that big and not get stung,” he said.

There is even a place of sorts in the nursery for infamous pest insects like aphids.

Keeping an aphid colony going in grasses or small perennials at the edge of the nursery can supply beneficial insects with a food source and a hub from which adult predator insects can spread out to other areas of the nursery, Abbey said.

One tree planting had one of the highest concentrations of lady beetles Abbey had ever seen. If the nursery owners had been spraying the planting, “you’re not going to see this complex of beneficials,” he said.

If cultural practices can restrict bad bugs to small areas, they can also keep some away entirely.

In a residential setting, greater peachtree borers are often attracted to roots by lawn mower-inflicted injury. They also exploit soft bark behind a tree tube that is left up too long or under mulch piled around the trunk, he said.

The greater peachtree borer is a moth that mimics a wasp. Its caterpillars pupate inside trees, and when they emerge, they leave behind a “brown, papery thing” that often sticks out of their holes, Abbey said.

Once the insects are inside the tree, “there’s not really much you can do about it,” Abbey said.

The trick, then, is to use a pheromone trap to time a bark spray so the borers never get into the tree. The spray should be applied 10 days after the first male is caught. Onyx (bifenthrin), Dursban (chlorpyrifos) and other products are effective, Abbey said.

Growers need to spray only the bottom few feet of the tree because that is where the greater peachtree borers attack, he said.

Properly managed nurseries rarely have problems with peachtree borers, Abbey said.

While Abbey spent much of the tour talking insects, he also took time to talk about the brown-green goo that often lurks in low, wet areas at nurseries.

Cyanobacteria resemble algae but prefer to rest on solid surfaces like soil or stone rather than float on water. “It likes water, but it’s not aquatic,” Abbey said.

The bacteria, which can photosynthesize, are not really a pest, but they can pose a hazard to workers because they get very slick when they are wet, Abbey said.

Some sprays can break down the scum, but it is not always practical to control it. Areas under overhead irrigation, for example, are almost always wet, providing good conditions for the bacteria to grow, he said.

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