Tuesday, September 18, 2012

Pest News for Week of September 17


From: Steve Frank, Extension Entomologist

Fall Pest Cleanup

Fall is a good time for nurseries and landscapers to consider dormant oil applications for spider mite and scale management. It is also a great time to scout for these critters. After leaves drop you can get good coverage of trunks and branches where scales and mites are overwintering. Scouting is also easy in the fall because scales are often overwintering in their adult, or near adult stages, which are (a little) larger and easier to see. Without leaves it is also much easier to see the scales. Trees that have scales should be examined in spring to determine if live scales are still present and if further treatment is necessary. The squish test will give you a good idea if scales are alive. If you squish some scales with your finger nail and juice comes out they are alive. If it is dry and crumbly they are dead. Most horticultural oils have a low and high rate listed that may even indicate that they should be used on growing or dormant trees respectively. On dormant deciduous trees you can safely use the high rate. 

As a side note, I have seen a lot of wax scale on conifers and broad leaf evergreen plants. I probably see them a lot because they stand out so much. Right now most are juveniles about half the size of the adults.

Rose Bud Caterpillars

This is not a species of caterpillar but several generalists that will feed on rose plants and particularly the buds. Tobacco bud worm and corn earworm are the most common culprits. They are active throughout the year and I found some on my knockout roses this week. This does not usually cause extreme damage but can reduce flowering if you have a lot of caterpillars present. 
There are many incidental and beautiful caterpillars out now such as the American dagger moth. I have catalogued some pictures and information on my blog: http://ecoipm.com/

From: David Orr, Extension Entomologist

Soldier Beetles on Flowers

The margined leatherback (Chauliognathus marginatus) is one of two soldier beetles commonly seen feeding on nectar and pollen on garden flowers in the late summer and early fall. Sometimes they can be quite numerous and cause concern for gardeners. However, they do not damage plants and can be considered beneficial. The adult of this beetle can be predatory on small insects such as aphids, while the larvae feed on ground-dwelling invertebrates such as slugs and insects. Occasionally, the larvae can be found inside of damaged produce such as tomatoes that have split from rainfall, or been opened up by caterpillars.

Adult margined soldier beetles have somewhat flattened bodies and soft, leathery wing covers rather than the hard covers found in many beetles. They can appear clumsy as they 'stumble' around flower heads on their long legs looking for both food and mates. Margined soldier beetle larvae look velvety and soft, and their legs are small and hard to see. This can make them appear similar to caterpillars. However, if you watch them carefully they have no legs near their rear end so they move by dragging their bodies along using the 3 pairs of legs under their thorax. Caterpillars, on the other hand, use either an "inchworm" or slinky type movement to lift up and bring their back legs closer to the front ones. 

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

Monday, September 10, 2012

Pest News for September 10

From: Steve Frank, Extension Entomologist

Yellownecked Caterpillars

Adult yellownecked caterpillars, Datana minstra, occur in June or July and lay eggs on deciduous shrubs and trees. They will feed on many fruit and ornamental trees including birch, elm, oak, maple, Prunus spp. and others. They feed gregariously in late summer. They consume entire leaves except large mid-veins and can rapidly defoliate trees or cause significant damage. I found the caterpillars pictured below in the forest on a bush I couldn't identify because every leaf was gone. Scouting for small caterpillars can help reduce damage and improve control if it is needed. Caterpillar management information is available: http://www.ces.ncsu.edu/depts/ent/notes/O&T/shrubs/note07/note07.html. See more caterpillars on my blog: http://ecoipm.com/.

Redheaded Pine Sawfly

The redheaded pine sawfly, Neodiprion lecontei, is a pest of pines in ornamental landscapes, nurseries, and plantations. Adults emerge in spring and a second generation occurs in mid-summer. Eggs are laid on many 2 and 3 needled pine species such as Jack pine, loblolly pine, and red pine. Sawflies are not flies and the larvae do not turn into butterflies. They are non-stinging herbivorous wasps. They can defoliate trees and bushes in the landscape. Since they are gregarious it is sometimes possible to prune off an infested branch and remove all the larvae. Management for sawflies is similar as for caterpillars though not all the insecticides will work so check the label. Horticultural oil is a good bet especially for small larvae. Formulations that contain azadirachtin or spinosad are also effective. For sawflies and caterpillars, management of full grown caterpillars is generally not warranted. The damage is already done and they are hard to kill.

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

Poinsettia Scab

Poinsettia scab, caused by the fungus Sphaceloma poinsettiae, was found on a sample from a commercial greenhouse this week. It has been six years since the PDIC last diagnosed this disease in a North Carolina poinsettia crop. As the name implies, this fungus causes leaf spots and stem lesions, but the most noticeable effect is an abnormal elongation of the poinsettia stem. The purple leaf spots may develop a light tan center, and they sometimes have a yellow halo. The surface of the spot is characteristically puckered, which is best seen under magnification. An olive-colored, velvety layer of spores may be present on the spots and stem lesions. These spores are spread to other plants via water splash. Long-distance transport occurs on infected planting material. This disease cannot survive between seasons in North Carolina in the absence of a poinsettia crop. For a good summary of the disease, see the 2001 APSnet publication by Mike Benson et al. (http://www.apsnet.org/publications/apsnetfeatures/Pages/PoinsettiaFlower.aspx). Growers should be sure they get clean stock and should scout points for leaf and stem symptoms. Keeping leaf wetness to a minimum will help reduce the advance of the disease. Apply azoxystrobin (Heritage), trifloxistrobin (Compass O), triflumizole (Terraguard) or triadimefon (Strike) to protect plants.

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

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.