05-18-07

2007 GROWING DEGREE DAYS

Soil Temp
(°F at 4" depth)

Precipitation
(1-Week Gain)

Total accumulation for 2007

n/a = information not available

* = no activity to report/information not available

Defoliators:

Lepidoptera (moths/ butterflies, but their caterpillar stage):

Forest Tent Caterpillar (FTC) is once again in big numbers and very active. The warmer regions are already experiencing defoliation, especially on oaks. The Connecticut River Valley region in MA (e.g., Greenfield) already has experienced complete defoliation of trees that are typically late to have bud break, such as pin oaks. However, fully leafed and blossoming crabapples have also been defoliated. In Greenfield, FTC is now around 1.5 inches in length while just 10 miles from there, in the slightly higher elevations, FTC larvae are only about 0.75 inches in length. Last year, an Entomophaga fungus, similar to the one that attacks gypsy moth, was observed having an effect on FTC, and it is not yet known to what extend it reduced population numbers, if at all. This pest, when occurring in large numbers, can quickly defoliate trees. If necessary, treat the caterpillars with a product that contains spinosad or with one of the labeled pyrethroid insecticides. Oaks, maples, birches, crabapples, and many others are common host plants.

Gypsy Moth is not expected to be in large numbers across the state, but it is not uncommon for small, localized areas to experience gypsy moth in outbreak proportions. This pest has hatched in most of the state and is settled and feeding, but no reports of large populations have yet been received. Monitor for their activity and treat in a similar fashion, if necessary, as for winter moth or FTC.

Eastern Tent Caterpillar has been active for a few weeks and is rapidly gaining in size. Webs on cherries and apples are numerous and quite large in the areas of heavy infestation. Some areas that have experienced outbreaks of this pest in recent years are reporting much lower numbers this year. If this pest is active in your area, it should be obvious by now. Treat the same as the above-mentioned pests, if necessary.

Fall Cankerworm should just be beginning its activity now. Large numbers of FCW similar in appearance to winter moth but has two and a half pairs of prolegs on the abdomen where winter moth only has two pairs. They are sometimes found in mixed populations with winter moth on the same host plant. Treat, if necessary.

Hymenoptera:

European pine sawfly has the potential to completely defoliate branches and entire plants. Monitor mugo pine, in particular, for clusters of this green caterpillar, which are almost the same color of the needles. The very young caterpillars can be successfully treated with an insecticidal soap spray while caterpillars of all ages can be treated with a product that contains spinosad or with one of the labeled pyrethroid insecticides. This pest has mostly been reported in the eastern regions of the state, including Cape Cod, in past years. Monitor oaks, in particular, for this (currently) tiny looper (inchworm) caterpillar.

Azalea sawfly caterpillar is now active in much of the state. This pale green caterpillar is almost the exact color of the host plant foliage and often hugs the leaf margin while it feeds. Therefore, it is very cryptic, and much damage can be created before it is noticed. Treat established populations with a product that contains spinosad or with one of the registered pyrethroid products that is labeled for this pest.

Coleoptera:

Lily leaf beetle has been active in the adult stage for several weeks now. Feeding injury, showing up as notches to leaf margins and holes in the foliage, is becoming noticeable. Eggs, on the undersides of leaves, in the form of an irregular tan-colored line about one inch in length have not yet been seen or reported, but they will be appearing within the next couple of weeks. Treat the adults with a registered and labeled pyrethroid. Later on, treat the larvae with a product that contains spinosad. NEEM products do work to deter feeding activity, but they need to be reapplied every 10-14 days for as long as the pest is active, which is much of the growing season. NEEM, therefore, is a good choice in smaller plantings of true lilies.

European chafer adults should start to appear within the next few weeks, especially in the warmer regions. This large scarab often goes unnoticed due to its nocturnal habits, BUT it sometimes clusters by the hundreds or even thousands on individual plants for mating purposes. While there, they can often create plant injury in the form of ragged notches on the leaf margins. Rhododendrons are common host plants along with many others. If suspected, inspect at night with a flashlight for their presence. Treat with a pyrethroid, if necessary.

Piercing-Sucking Pests :

	Many spider mite species are now active. Inspect foliage with a hand lens for their presence; also, make note of the ratio of predatory mites to spider mites. Spider mites are often present on plant foliage, and predatory mites usually keep their numbers in check. Treatments for spider mites are usually only necessary if populations of them are high and when numbers of predators are low.
	Many aphid species are now very active, such as snowball aphid on many different species of viburnum, aphids on various species of maples (including Japanese maple), and balsam twig aphid. Inspect for clusters of aphids, honeydew, sooty mold, and distorted foliage. Unlike most of the other piercing-sucking pests, aphid feeding usually does not result in yellow stippling injury. Treat large populations, if necessary, with a spray of insecticidal soap, or with a systemic application of a product that contains imidacloprid.
	Hemlock Woolly Adelgid - is active, and the white cottony masses are quite obvious right now. Once foliage has fully expanded, treat with a horticultural oil spray at the summer rate. Small populations can be treated with a systemic application of imidacloprid. This pest is actively feeding and will produce one more generation within the next several weeks.

Leafminers:

Birch Leafminer is active, and in the warmer regions it may be too late to treat for the adults in those areas. Monitor for emergence with yellow sticky cards and treat with a pyrethroid to break the cycle of reinfestation. If larvae are already active within the foliage, consider using an insecticide that has translaminar activity for the larvae within the mines. For the past several years and for unknown reasons, this pest has been at very low levels statewide.

DISEASES -

Flowering dogwoods (Cornus florida, not Cornus kousa) susceptible to dogwood anthracnose are vulnerable to infection during wet seasons. Apply fungicide to protect developing leaves on high value trees, as the buds break open, again when bracts have fallen, and ~4 weeks later. If this is a persistent problem, consider planting one of the many resistant cultivars of flowering dogwood and Kousa dogwood now available.

Apply fungicides to protect emerging apple and crabapple leaves from apple scab as the buds turn pink, again around petal fall, followed by 1-2 additional times at 7-10 day intervals (assuming wet conditions linger). In addition, prune densely branched trees to increase air circulation and sunlight penetration that speeds drying of foliage. There are numerous resistant varieties of apple, crabapple, and mountainash to grow and simplify disease management.

It is difficult to determine based on field symptoms alone whether or not junipers with browning foliage have the disease juniper blight or suffered damage from another agent. Environmental stresses such as soil compaction, snow and ice damage, deicing salt exposure, and physical bruises often result in browning of foliage that looks like a juniper blight disease. During dry weather remove and destroy dead foliage to improve the plant’s appearance as well as reduce juniper blight inoculum if that should be present. If it clear there is juniper blight caused by Phomopsis juniperovora, begin fungicide control as new growth emerges, and repeat applications if wetness persists. If the problem persists, gradually replace problem junipers with disease-resistant shrubs better adapted to the site.

Maximize the effectiveness fungicide treatments in the management of black spot on rose by initiating them now as buds swell and repeat applications per label directions into the fall. Provide good air circulation and irrigate early in the day to minimize the period of plant wetness to further suppress the disease. If the problem persists, gradually replace susceptible varieties of roses with those resistant to black spot to reduce buildup of inoculum and the need for fungicide treatment.

Gymnosporangium rust fruiting structures are noticeable on eastern red cedar (really a juniper) and Rocky mountain juniper, as well as the occasional Chinese, common, creeping, and savin juniper. Specifically, cedar-apple rust galls are visible on eastern red cedar as eruptions of orange, gelatinous masses protruding from pea- to golf ball-sized galls. These fruiting structures release spores that infect the leaves of alternate hosts such as apple and crabapple at this time of the year during cool, rainy periods. Likewise, fruiting structures of quince rust are visible as red-orange “cracks” in the bark of infected branches on several of these junipers. Leaves and fruit of amelanchier, crabapple, and hawthorn are common alternate host of quince rust. Because the damage to tree health is so minor, chemical interventions are seldom worthwhile except with specimen or nursery plants. Now is the time to begin fungicide applications to protect leaves, green shoots, and fruit of the susceptible, high value alternate rosaceous hosts from Gymnosporangium rust infections. Treat susceptible rosaceous host plants 2-3 times at labeled intervals.

Status of Phytophthora ramorum in 2007:

Forest Detection Survey - There was no report this week.

Federal Regulation, State Inspection, Nursery Survey, and Other Finds - There was no report this week.

Reported by Dan Gillman, Plant Pathologist, UMass Extension Plant Diagnostic Lab, Amherst

WEEDS -

There are a large number of weeds of the mustard family in ornamental beds this spring. Attempt to control them before they seed. Species include bittercress, whitlowwort, shepard’s-purse, pennycress, and Virginia pepperweed. Visit the UMass Weed Herbarium, click on Sort list by Family Name. Then, select Brassicaceae (Cruciferae) - Mustard Family to see images.

WEEDS -

Forsythia has completed its flowering period. Therefore, preemergence herbicide applications should be finished by now. Any remaining preemergence applications should be made with dithiopyr products and, preferably, those that are a sprayable formulation. See last week's message for explanation.

Still more calls and emails on star-of-Bethlehem infestations. First, let me state that paraquat is not a viable control strategy for us in the north who are managing cool-season turfs despite what information many are finding on the Internet’s web. Some control strategies include: 1) ignore them and wait until they go away as we get warmer days, 2) diligently dig up clumps and reseed, or 3) apply an herbicide product that contains the active ingredient carfentrazone.

Wild garlic is noticeable now. Ignore it and it will go away, or treat it with a broadleaf turf herbicide. Control is increased if weed is stepped on or rolled before application. Granular broadleaf herbicide formulations should not be used.

Dandelion and violet can now be treated with postemergence broadleaf herbicide products.

Reported by Randall Prostak, Weed Specialist, UMass Extension Landscape, Nursery and Urban Forestry Program, Amherst.

IMPORTANT INFORMATIONAL RESOURCES

The MNLA/MFGA Summer Meeting and Trade Show is Wednesday, July 18, 2007 at the Tower Hill Botanic Garden in Boylston, MA. Visit http://www.mnla.com for complete information.

For a complete listing of upcoming events, see our Conferences and Workshops page.

Don't forget to visit the UMass Extension Online Weed Herbarium!

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UMass Extension Landscape Message #12 May 18, 2007

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