Saturday, September 1, 2012

Pest News for September 1

From: Steve Frank, Extension Entomologist

Lacebugs Other Than Azalea Lacebugs

Numerous additional lacebugs were discovered in the landscape this week. These lacebugs have been around most of the year, but the damage is becoming especially apparent. Sucking insects damage plant cells and as the cells die necrotic spots and stippling become more apparent. This can be exacerbated by plant stress and drought. Lacebugs and damage on service berry and oak were discovered this week. Of course, sycamore and cotoneaster always incur damage from the sycamore and hawthorn lacebugs, respectively. A pyracantha plant on campus was especially loaded down with hawthorn lacebugs. Upon closer look, fire ants tending aphids on the tips of the branches were seen. Often ants that are tending aphids will kill all other herbivores that would compete with the aphids and predators that would kill the aphids. In this case the ants didn't seem to be tending the lacebugs, but were also not destroying them. The lace bugs were definitely benefiting from not having predators around though!

At least six species of scales can be found on liriope. Most of the time scales do not cause extensive damage. Whatever building you are located, it probably has liriope planted outside and that liriope probably has scale. However, plants in stressful environments or nurseries may be more susceptible to infestations that could degrade plant aesthetics. The armored scales most common on liriope are hard to distinguish, but cause small yellow spots where they feed. Often they are at the base of leaves out of site of you and predators.

From: Mike Munster, Ornamental Pathologist, Plant Disease and Insect Clinic

Rose Rosette on the Rise

Those of you living in the Raleigh, North Carolina, area may have read the article in the News and Observer on Saturday, August 25, 2012 about the removal of several rose bushes from the Raleigh Rose Garden and from a traffic circle on Hillsborough Street. The reason: they had been diagnosed with rose rosette. This disease has been known in North America for decades, but it has become more common in our area over the last two years. Only roses are affected.

Symptoms and Diagnosis. Symptoms of rose rosette can vary depending on the variety of rose involved. They include elongated flexible shoots, proliferation of shoots leading to “witches' brooms”, excessive development of thorns (soft or not), leaf deformation, retention of juvenile red coloration in shoots, flower abnormalities, decreased cold hardiness, and plant death. There is a molecular test that can be used to confirm the presence of the virus that causes rose rosette, but we do not currently offer that service at the North Carolina State University Plant Disease and Insect Clinic. Instead the diagnosis is based on symptoms and can range from definitive (when the “hyperthorniness” is seen) to tentative. Not all symptoms may be present in any given plant. In particular, shoot proliferation and leaf deformation can be misleading, since they can be caused by exposure to low doses of the herbicide glyphosate. If you observe these two symptoms alone, do some sleuthing to see if drift might have occurred.

Cause and Spread. Rose rosette was only recently proven to be caused by a virus, but it has long been known to be transmitted by the microscopic eriophyid mite Phyllocoptes fructiphilus. These are not the same as the more familiar spider mites. Small size makes up for their lack of wings, and these mites can be carried about on air currents, perhaps by other insects. There is some experimental evidence that rose viruses can move through natural root grafts, but no published studies have looked specifically at rose rosette transmission via this mechanism. The risk of spreading the virus on pruning shears appears to be very low, but it is a good general practice to sanitize knives and shears frequently during pruning operations anyway. Of course propagating from infected plants or grafting onto infected rootstocks would be very likely to result in infected roses.

Management. The jury is still out on how to best manage rose rosette, so the following recommendations are provisional. This could be called the "RSVP" approach: removal, spacing, vigilance, and patience.

Removal. Since viruses become systemic in their hosts, pruning may not be sufficient. If a bush has only one affected cane, pruning that cane as close to the ground as possible might get ahead of the infection, but we have no data to show that this is effective. Removal of infected plants is the safer course of action. Plants should be bagged before digging or as soon thereafter as possible, to reduce the chance that the mites will scatter on the wind and carry the virus to nearby roses. Remove enough of the roots so that the infected plant does not re-sprout. Also remove any nearby (within 100 to 150 meters) weedy multiflora roses that may be serving as a reservoir of the virus. The virus and mites should die quickly after plants are chipped, so properly composted municipal mulch should not be a source of the disease. As a precaution, vehicles used to transport diseased plants should be closed or covered.

Spacing. Given the mobility of the mites and the possibility of root grafts, plant roses far enough apart that roots or branches don’t touch. Fragments of small roots left in the soil after plant removal should pose no risk. As long as there are no other infected roses nearby, replanting can be done immediately.

Vigilance. Examine any new plants (purchase, trade, or gift) to be sure they are symptom-free. That does not guarantee that they are healthy, since symptoms can take from 17 days to 9 months or longer to show up. Keep an eye on established plantings, too. Finally, keep a close watch on areas were diseased plants were removed, to be sure they do not sprout again.

Patience. As plant pathologists and entomologists continue to do experiments over the next several years, we'll be in a better position to know what works and what doesn't. Breeding also takes time. Perhaps some of the resistance in our native species like Rosa setigera and Rosa carolina can be brought into cultivated types.

What about spraying? There is no effective chemical treatment for plants infected with rose rosette or any other virus. According to Steven Frank in the North Carolina State University Department of Entomology, there is no evidence to suggest that pesticide applications directed at the mites will reduce the spread of rose rosette. It is certainly no substitute for removing an infected plant from the landscape.

From: David Orr, Extension Entomologist

Grub-Killing Wasps For Your Lawn

The large colorful hunting wasps, Scolia dubia (Order: Hymenoptera; Family Scoliidae) may look intimidating, but are harmless to you unless you grab one and force it to sting in self defense. Adults are most numerous late in summer (usually August) and are present now on flowers (see August 17 post for example) and hovering over lawns in search of food for their young. Their larval food is actually grubs, primarily green June beetle larvae that feed on and damage grass roots in lawns.

The adult grub-wasps dig into the soil when they “smell” (anyone who has seen holes made by skunks in their lawn knows this is possible) a grub, sting it to paralyze it, then lay an egg on it. The paralyzed grub is then helpless to defend against the hatched grub-wasp larva that will consume this fresh food supply until it is fully grown. The grub-wasp larva then pupates in the soil, ready to emerge as an adult the following summer. If there are enough of these wasps in your yard, they can help reduce the numbers of grubs in your lawn, providing natural control of pests

Here's a video of a grub-wasp feeding on nectar:
 Grub Killing Wasp

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