Saturday, May 19, 2012

Pest News for Week of May 21st


From: Steve Frank, Extension Entomologist

Thrips are Early and Abundant in Greenhouses

Western flower thrips have several life history traits that make them notoriously difficult to manage. In particular of the four primary life stages (egg, larvae, pupae, adult) only larvae and adults are susceptible to insecticide applications. Eggs are inserted into leaves and pupae are in the soil. Thus, right after you make an application eggs start hatching and adults start emerging from pupae and you feel as though you are right back where you started. This is why we recommend that growers make 3 applications 5 to 7 days apart to help break the lifecycle of the population present in their greenhouses. This initial round of applications could be done with a single chemical but rotate to a new chemical with new mode of action for subsequent applications. Since many plants are starting to bloom we have several chemicals that are generally not phytotoxic to foliage or flowers though mixing chemicals (insecticides, fungicides, etc.) or addition of adjuvants can have unexpected phototoxic results. Consider a rotation that includes Conserve (spinosad; label indicates potential spotting on African violets), Avid (abamectin; label indicates potential phytotoxicity on Adiantum ferns and Shasta daisy), Flagship (thiamethoxam), and/or bifenthrin. Complete list of chemicals can be found at:

Lilac/Ash Borer Adult Flight

The lilac/ash borer, Podosesia syringae, has been captured in phermone traps this week in the Piedmont and foothills. This particular clearwing borer is not a major pest. Others such as the banded ash clearwing typically cause more damage. However, this critter will cause lilac canes to wilt suddenly as larvae bore within. So, it is good to be aware of this even though we do not recommend preventative insecticide treatments. The lilac/ash borer overwinters as larvae in twigs then adults emerge over several weeks to mate and lay eggs. Later in the summer dogwood borers, lilac borers and other will be emerging.

Second Generation Euonymus Scale Crawlers

Euonymus scale has three generations per year in North Carolina the first of which we reported on in the spring.  It is best to treat euonymus (or any) scale in the crawler stage. So if you forgot in the spring or didn’t get sufficient control, now is your second chance. Crawlers are active at research sites on campus and in Raleigh neighborhoods. In the first generation crawlers come out all at once but become less synchronized in second and third generations. Thus you may find all developmental stages present at this time. There are many predators that feed on scale insects such as the lacewing larva in this video ( However, euonymus scale still tends to reach damaging levels once established. There are a number of products that can be used to treat armored scale. We have found neonicotinoids Safari, Flagship, and TriStar to be very effective also plant growth regulators Distance and Talus. Note that imidacloprid is not labeled for or effective against armored scale. Please check our blog and the updated insect note for recommendations and up-to-date information

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

Controlling Botrytis in the Greenhouse

Due to weather conditions, Botrytis epidemics are currently occurring in greenhouses across the state. A wide range of floriculture crops can be affected. Symptoms of Botrytis infection range from flecking of blossoms, blossom blight, and even leaf and stem rot. On rose canes it can cause a tan-colored canker. The characteristic gray mold may be visible under high humidity conditions. The two keys to Botrytis management are keeping the relative humidity below 85% and maintaining the greenhouse free of dead or injured plant material (spent flowers, fallen leaves, pruned branches, culls, etc.) on which the fungus can produce new spores. Irrigate at times of day when foliage will dry quickly, and if possible ventilate greenhouses in the evening to bring down the humidity. Avoid wounding plants, which allows Botrytis to invade healthy tissue. Keep fertilization at optimal levels to avoid premature leaf senescence. Plants with bloom infection or crown rot should be discarded along with the potting mix. NEVER REUSE POTTING MIX WITH THIS PATHOGEN. Clean up all plant debris from the block and discard it. Do not compost any of this material, as the sclerotia of the fungus are capable of surviving adverse conditions. Spores of this fungus can be windborne, so be sure there are no cull piles nearby on which the fungus could produce them.

If re-using pots, first clean thoroughly and then sanitize with either steam (150 to 160 F for at least an hour at the center of the pile) or one of many chemical disinfectants available.

Fungicides may help prevent new infections, but won't cure plants that already have symptoms like those submitted. Effective products for Botrytis control include Chipco 26019/26 GT (Iprodione), Decree, Medallion and Pageant. Chlorothalonil (e.g., Daconil) can also be used; however chlorothalonil can cause phytotoxicity on blooms so this product should not be used on flowering plants. Decree is probably the most effective product for Botrytis control; however, it is only labeled for controlling Botrytis and should be used in a rotational program. In addition, there is a new Syngenta product named Palladium that just got registered for use in greenhouses and it is very effective against Botrytis. Be sure to rotate fungicides of different modes of action (FRAC groups) so as not to pressure the fungus into becoming insensitive (resistant) to any particular chemical. Note that one of the active ingredients in Palladium (fludioxonil) is the same as that found in Medallion. Get good coverage of the stems/crowns. Test any new treatments on a small number of plants first, to ensure that there are no adverse effects.

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.