Kunkel hosts lesson on pest insects at expo
DOVER, Del. — “Bugs, they truly suck!” was the title of a presentation by Dr. Brian Kunkel of the University of Delaware, who addressed the Delaware Horticulture Industry Expo on Jan. 16.
If anyone can get excited about bugs, Kunkel can. For his 50-minute presentation, he prepared 185 slides on whiteflies, mealybugs and various scales.
There are a number of whiteflies which are a problem in such crops as poinsettias and salvia.
Symptoms of whitefly include honeydew, leaf yellowing or stem blanching, chlorotic spots, leaf shedding and sooty mold.
Whiteflies also transmit viruses.
Two species are greenhouse and silverleaf (or sweet potato) whiteflies. The adults look different from each other.
Compared to sweet potato whiteflies, greenhouse whiteflies have flatter wings over their back, more like a tent. To determine other differences requires a microscope.
Greenhouse whiteflies have hairs or spikes off the pupae. Sweet potato whiteflies do not.
“Whiteflies are true bugs. They suck,” Kunkel said.
For whitefly management it is important to use sticky cards. They are for scouting and monitoring; they’re not meant to control.
There are three ways to attempt control:
• Cultural control, which requires knowledge of the insect’s biology and sanitation;
• Biological control, using generalist predators and parasitoids; and
• Chemical control, using compatible products.
Kunkel said, “I bring insects inside so I can learn what works to kill it. Others try to keep insects out!” Kunkel said. He wants to know their biology — their life stages and how adults feed, mate and transmit viruses.
Eggplant can be used as a trap plant.
The insects go there first, he said. After hatching, they crawl a little, then settle. There they go through nymph stages.
It is important to identify the pest and to know which species you are dealing with so you know which parasitoid to use, Kunkel emphasized.
The minute pirate bug (Orius sp.) is a true bug. It feeds on aphids, thrips, whiteflies and mites.
Encarsia formosa is also a parasitoid of whitefly.
Using banker plants, you can grow your own natural enemies among the plants you want to sell.
The idea is not to let them move to valuable plants. Parasites and predators will move, he cautioned.
‘Purple flash,’ an ornamental bell pepper, is a good banker plant for minute pirate bug.
Amblyseius swirskii, or “Swirski mite” is a predatory mite sold in sachets or in bran.
Available since 2006, it feeds on whitefly pupae or eggs and helps keep populations low.
Kunkel observed that mealybugs will feed in crotches. They have piercing, sucking mouthparts. Mealybugs lead to distortion and wilting of plants, rendering them unacceptable to sell.
In tests, plants were treated, then exposed to mealybugs. There were significant reductions on plants treated with Acelepryn and Mainspring. All of the treatments left very few to no bugs compared to the untreated control.
Where treatment was used on plants already infested, Mainspring and Acelepryn did not do well, Kunkel said. “I’m not surprised, because they work better if the chemical is on the plant before the bug shows up,” he said. Insecticides are more effective as a preventive than as a curative.
Kunkel then moved on to scale. Identification is incredibly important in integrated pest management, he said. There are critical stages for controlling scales, and there are some natural enemies.
Crape myrtle bark scale is a “newish” problem. It is not an armored scale, but a felt scale, similar to azalea bark scale. Crape myrtle bark scale feeds on twigs, stems and the trunk of plants and produces much honeydew. It makes them look unacceptable. Unfortunately, it is hard to notice the initial infestation.
The nymphs/crawlers are pink; settled nymphs are pink, gray or brown. This scale usually overwinters as nymphs. It moves well from nursery to nursery. Crape myrtle is its main host; American beautyberry is another.
The females lay 200-300 eggs. They form crawlers, settle, pupate. Males come out and can fly to females. After females produce eggs, their bodies shrink. There can be two to four generations per year in the Southeast.
This pest is not in Delaware yet. The closest confirmation is in southeast Virginia or North Carolina.
The first generation appears in late March to April; the second in July. The third generation, in October, feeds into winter, and the fourth generation is active in February. Overlapping generations make this scale difficult to manage.
Hort oil does not work well; neonics work better. Insect growth regulator gives you an extended time to try to manage. If you are concerned, an application of soil-applied systemic insecticide in March should give protection. The crawlers are the most vulnerable.
With limited time, Kunkel ran through cottony camellia or taxus scale, tulip tree scale and armored scale.
“Target crawlers. They are most sensitive,” he said. He warned that hundreds to thousands of eggs are produced by soft scale; armored scale produces a few hundred. They look like aphids.
For control, try oil soap or contact insecticides. “Don’t be afraid to prune out infested areas of a host plant,” he said. For example, with Japanese maple scale, you can prune out a branch and remove a couple of thousand eggs.
Soft scales have no shell; their bodies are covered with a leathery exoskeleton.
They are usually large and oval in shape, an eighth inch or larger. They produce honeydew. Nymphs and early females remain mobile. With short mouthparts, they feed from phloem sap. Their eggs are like globules.
Soft scale moves back to woody tissue in fall. Once armored scale settles, its legs atrophy and are no longer functional.
Cottony camellia scale is seen in June at 830 growing degree days. It has one generation per year. Look for flat, brownish insects. You’ll see white ova sacks in November, but by then it is too late to treat. They’re done feeding, Kunkel said. Hosts are hollies, sweet box, camelia and taxus.
Calico scale crawlers are active between 519 to 902 growing degree days. Look for nymphs feeding on leaves. Some birds and parasitoids attack this scale. Hosts are dogwood, magnolia, sweetgum, honeylocust, elm, tuliptree and others.
Armored scale often has more than one generation. They are not mobile. They are tiny, difficult to see, and difficult to manage. They don’t produce honeydew.
Work at the University of Maryland on Japanese maple scale indicates Distance and Talus (insect growth regulators) provided good control at crawler stage.
Arena (clothianidin) provided better control than Safari. Merit did not control.
Out of time, Kunkel gave only mention to assassin bugs, predators that do great feeding on insect pests. “They’re good guys,” he said. So is the spine soldier bug. Spiders also have piercing mouthparts and eat aphids and caterpillars, so they are beneficial also.
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