Saturday, June 16, 2012

Pest News for Week of June 18th

From: Steve Frank, Extension Entomologist

Time to Target Bagworms

Bagworms have hatched and are still quite small. They can be difficult to find although they have constructed tiny bags that can be seen on leaves and needles of infested plants. It is easier to look for the large bags left from last year’s bagworm adults. These will be empty but are a good indication that small bagworms are likely roaming a plant. This is because female bagworms are flightless and overwinter and lay eggs in their bags on trees and shrubs. Thus baby bagworms hatch and grow up on the same plant as their mother was on the previous year.

Early in the year the before eggs hatch bags can be hand-picked from bushes with light infestations. Now caterpillars are still small and have not yet eaten much of your plant. Damage increases dramatically as caterpillars grow and they will easily defoliate branches. Small caterpillars are also much easier to kill than large ones. This is because they have less body mass to dilute toxins and their protective bags are not as thick. Therefore less toxic chemicals such as Bt formulations can be very effective when targeting small caterpillars. Other chemical options that are considered compatible with natural enemies are Acelepryn, TriStar, and spinosad. More information can be found at

From: Adam Dale, Department of Entomology, and Steve Frank, Extension Entomologist

Maple Spider Mites Active on Nursery and Street Trees

Maple spider mites (Oligonychus aceris) are common and damaging pests of maple trees throughout the Eastern United States. These spider mites overwinter on the trunk and branches of maple trees and migrate to the underside of leaves in the spring. Once there, they use their mouthparts to tear into leaf tissue and feed on cell sap, causing fine flecking or browning of the leaf. Maple spider mites have multiple generations per year which enables them to become quite abundant during a single season. These pests are a more serious problem in nurseries due to the close proximity of potted trees and applications of broad spectrum insecticides like permethrin. Studies have shown that over-application of permethrin can wipe out natural enemies and result in secondary maple spider mite outbreaks. However, they are still an issue on landscape trees around Raleigh. The first red maple that I sampled from in Cameron Village had a severe abundance of maple spider mites and the effects were obvious. The use of a hand lens or stereo microscope is necessary for correct identification of these mites but damage is a good indicator of infestation. They are dark brown or red with hairs along their backs and have eight legs while some immature forms exhibit green coloration and have six legs. Red eggs of these mites can be found on tree limbs and yellow or clear eggs can be found on leaf surfaces. Treatment for these pests includes foliar applications of acaricides. It has been observed that maple spider mites are more successful on trees in warmer temperatures. We are currently researching the effects that elevated temperatures have on maple spider mite biology and their natural enemies to uncover the mechanisms that are behind this. For more information on general spider mite management, please visit

Debris-carrying Green Lacewing Larvae are Active and Everywhere!

Green lacewing larvae are common predators of several soft-bodied pest arthropods across the United States. Their prey includes but is not limited to: scale insects, spider mites, aphids, thrips, and eggs of pest insects. They are useful in biological control because of their generalist and voracious feeding habits. Lacewing larvae are often compared to alligators due to their elongate, slender body shape and are typically yellow and brown in color with six legs. These larvae have large pincer mouthparts that they use to penetrate bodies of prey, paralyze them, and literally suck out their insides. They use these mouthparts to devour several hundred prey per week. Lacewings are known to be cannibalistic if they cannot find any other food source. This is one reason that they deposit their eggs individually on long hairs that suspend them above the leaf surface out of reach. These eggs are common and can be easily found on leaf surfaces.

Some but not all green lacewing larvae develop a camouflage cover which hides them from predation by other insects.  These are called debris-carrying lacewing larvae because they pick up plant tissue debris and other insect debris and attach it to their back. This camouflage makes them difficult to recognize by natural enemies and the inexperienced human eye. Often times they will appear to be a cluster of tree lichen until you notice small legs underneath or it start to move. They can currently be found on most plants just by scanning leaf surfaces. I have seen several recently without looking for them. These insects remain larvae for two to four weeks at which point they develop into winged green lacewing adults. Adult lacewings are not predators and primarily feed on plant nectar. The adults are commonly attracted to lights at night and can often be found around your home.

From: Kelly Ivors, Extension Plant Pathologist

Impatiens Downy Mildew Detected in Multiple Landscape Locations in North Carolina

Downy mildew of impatiens is caused by the ‘fungus-like’ organism Plasmopara obducens. The group of organisms that cause downy mildew diseases are not true fungi - they are more closely related to the well-known plant pathogens Phytophthora and Pythium than they are to true fungi. This is an important distinction to understand because many of the traditional fungicides used to control fungal diseases of plants do not have efficacy against the downy mildews. All types of propagated Impatiens walleriana, including double impatiens and mini-impatiens, and any I. walleriana interspecific hybrids, such as Fusion® impatiens, are susceptible to downy mildew; however, all New Guinea impatiens (I. hawkeri) and interspecific hybrids such as SunPatiens® are tolerant to downy mildew. No other bedding plants are known hosts of this particular downy mildew, although there are a few other downy mildew species that attack other floriculture plants like coleus and basil.

What does downy mildew look like?

A really good resource about identifying the disease, as well as disease control information, can be found at

In addition, a webinar presented by Dr. Colleen Warfield of Ball Horticultural Inc. can be found at

Downy mildew likes cool, wet/humid environmental conditions. The current conditions we’ve experienced recently across the state of North Carolina are conducive for this disease. The important thing to remember is that downy mildew is spread by wind currents, water splash or by the movement of infected plants. We know that the disease is now in our area and that the spores of the pathogen have the ability to spread long distances in air currents. Be on the look-out for it! So far it has been confirmed in both the western and Piedmont areas of North Carolina.

Fungicide treatments are not recommended for plants in the landscape; instead, all infected impatiens should be pulled from the landscape and destroyed. Fungicides are not always 100% effective at eliminating the disease. Allowing infected plants to remain in the landscape may allow the pathogen to overwinter as resting structures (called oospores), which can start a new epidemic later in the year or in following years if impatiens are replanted in the area. New Guinea impatiens, coleus, begonia, or other available bedding plants are safe to reset in the affected area.

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by North Carolina State University, North Carolina A&T State University or North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact an agent of North Carolina Cooperative Extension.

For more information contact your local Cooperative Extension Center and ask for the Commercial Horticulture Agent.