UMass Extension Landscape Message #21 - 2011

Scouting Information by Region

Regional Notes

Cape Cod Region (Barnstable) – General Conditions: August has seen a change in the weather pattern, with cooler temperatures and more frequent precipitation. The Cape received and average of 4” of rain over the past two weeks. However, depending on where the storms tracked, some towns have received much more. The series of storms that passed over the Cape on the 15th and 16th dropped over 4” in Falmouth, while only giving Chatham 1.5". Soil moisture levels are good. Late summer perennials are providing good color. Pests/Problems: Powdery mildew is quite evident on lilac, phlox, flowering dogwood, and other susceptible trees, shrubs and perennials. Horsechestnut leaf blotch is causing horsechestnut to appear scorched. Susceptible roses are defoliating from Black Spot. Leaf spot, possible Cercospora, is prevalent on Bigleaf hydrangea. Terminal leaders are flagging and turning brown on white pine and white spruce due to damage from white pine weevil. Northeastern Sawyers are coming into the office for identification. Many people mistake them for the ALB. Japanese beetles are almost gone.

Southeast Region (Hanson) – General Conditions: Hanson received 3.00 inches of much needed rain. Clerodendrum trichotomum (Harlequin Glorybower), Albizia julibrissin, Hydrangea macrophylla, Hydrangea arborescens (Smooth Hydrangea), Hydrangea paniculata, Rubus odoratus, Clematis, landscape roses, Echinacea, Lysimachia clethroides, Perovskia atriplicifolia, Hosta plantaginea, Corydalis lutea, Heliopsis ‘Summer Sun’, Lavender, Rudbeckia sp., Persicaria polymorpha, Lobelia sp., Veronicastrum virginicum (Culver's Root), Astrantia major, Campanula sp., and Gentiana ‘True Blue’ are in full bloom. Goldenrod and ragweed are starting to bloom. Pollen from ragweed may cause allergies in some people, but goldenrod is often mistakenly blamed. Pests/Problems: Asiatic beetles are still active but are starting to wind down.  Oriental beetles and Japanese beetles appear to be done for the year and while Oriental beetle numbers appeared to be high this year, Japanese beetles were thought to be low. Fall webworm, earwigs, dogwood twig borer, Rhododendron borer, lily leaf beetle, wasps, slugs, sharpshooter leafhopper, snails, ticks, biting flies, katydids, cicada killing wasps, Hibiscus sawfly and Pieris or andromeda lacebug and aphids are all active. Beneficial insects are also active. Black spot is common on susceptible roses. Giant tar spot is showing up on Norway maple. Anthracnose is showing up on a number of plants including dogwood, sycamore and oak. Powdery mildew continues to persist on a wide variety of plants including oak, lilac, beebalm, dogwood, and garden phlox. Beneficial insects are also active. It has been a banner year for mosquitoes and along with Eastern Equine Encephalitis (EEE), which was found in mosquitoes a few weeks ago, it has recently been reported that mosquitoes are carrying the West Nile Virus in some areas of Plymouth County. Plymouth County Extension does not spray for mosquitoes. The number for residents of Plymouth County to call is: 781-585-5450. Goldenrod, ragweed, fleabane, Queen Anne’s lace, and yellow toadflax are in bloom.  Crabgrass is everywhere. Deer, voles, woodchucks, rabbits and chipmunks remain active. Many trees are dropping leaves prematurely, probably due to heat stress, drought and disease, or a combination thereof. During dry weather, continue to remind clients to water trees damaged by winter moth caterpillars and also to water newly planted trees, shrubs and perennials.

East Region (Boston) – General Conditions: We received a much needed and welcomed 5.03” of precipitation over the past two weeks.  That is 2.34” greater than the historical average for the entire month of August.  The landscape is looking lush again, with the combination of precipitation and moderate temperatures plants and turf that appeared water stressed are recovering.  Plants in bloom: Albizia julibrissin (mimosa), Franklinia altamaha (Franklin tree),  Rhus chinensis (Chinese sumac), Styphnolobium japonicum (Japanese pagotatree), and the uncommon Poliothyrsis sinensis.  Many Chaenomeles (flowering quince), Crataegus (hawthorn), Malus (crabapple), Prunus (cherry) and Sorbus (mountain ash)’s fruit is maturing and adding color to the landscape. Pests/Problems: The recent rains averted a drought – weeds continue to thrive.   Arctium minus (common burdock), Solanum carolinense (horsenettle) and Solanum dulcamara (bittersweet nightshade) are in flower.  Cynanchum nigrum (black swallowwort) fruit is maturing but not yet releasing seed.  Be on the look- out for the European Hornet (Vespa crabro) and its distinctive girdling patterns especially on lilacs, rhododendrons and viburnums . Cicadas and Cicada Killers (Sphecius speciousus) are active. Viburnum Leaf Beetle (Pyrrhalta viburni) is confirmed in Boston.  Take a close look at your viburnums – low level infestation does not equal skeletonized leaves.  Look for chewing of leaves - it is an inconspicuous beetle.

Metro West (Acton) – General Conditions: A total of 4.09” of rain fell on the area since the last report raising total rainfall for the month of August to 4.62” which has surpassed the historical average monthly rainfall of 3.54”. The current growing degree day total is 2028.5.  Last year on this date the growing degree day total was 2215.  Woody plants seen in bloom are: Hibiscus syriacus (Rose-of-Sharon) and Hydrangea paniculata and its many cultivars including ‘Tardiva’.  Herbaceous plants seen in bloom are: Achillea filipendula (Yarrow), Astilbe spp. (False spirea), Boltonia asteroides (White Doll’s Daisy), Coreopsis verticillata ‘Moonbeam’ (Threadleaf Coreopsis), Echinacea purpurea (Coneflower) and its cultivars, Eupatorium purpureum (Joe Pye Weed), Hemerocallis spp. (Daylily), Hosta spp.(Plantain Lily), Liatris spicata (Spike Gayfeather), Lythrum clethroides (Gooseneck Loosestrife), Macleaya cordata (Plume Poppy), Malva alcea ‘Fastigiata’ (Hollyhock Mallow), Monarda didyma (Bee-Balm), Patrinia gibbosa (Patrinia), Perovskia atriplicifolia (Russian Sage), Phlox carolina (Carolina Phlox), C. paniculata (Phlox) and its many cultivars, Rudbekia fulgida ‘Goldsturm’ (Black-Eyed Susan), Solidago sp. (Goldenrod), Thalictrum rochebrunianu (Meadow Rue) and Veronicastrum virginicum (Culver's Root). Pests/Problems: Webs of the Fall webworm have been seen on Betula (Birch), Syringa (Lilac), and Prunus (Cherry).  Lots of Fireblight has been seen on Prunus (Cherry). With the moisture and humidity powdery mildew has been seen on susceptible Filipendula sp. (Meadow Sweet), Phlox paniculata (Summer Phlox), Rosa spp. (Roses) and Syringa spp. (Lilacs). Other fungal diseases appearing in the landscape are: fungal leaf spots on Amelanchier spp. (Serviceberry), diplodia on Pinus spp. (Pine), rust on Alcea (hollyhock) and anthracnose on Cornus florida (Flowering Dogwood) and Platanus spp. (Sycamores). Be on the lookout for Cynachum nigrum (Black Swallowwort) and Phytolacca americana (Pokeweed). Both are flowering and will be setting seed and soon either the wind or the birds will be dispersing the seed. Also in seed now and quite visible is Ailanthus altissima (Tree of Heaven). Most importantly, monitor the 13 host genera: Acer (Maple), Betula (Birch), Ulmus (Elm), Salix (Willow), Aesculus (Horsechestnut), Fraxinus (Ash), Platanus (Plane Tree), Populus (Poplar), Celtis (Hackberry), Sorbus (Mountain Ash), Albizia (Mimosa), Cercidiphyllum (Katsura) and Keolreuteria (Golden Raintree) for the Asian Longhorned beetle because the adult beetles are active.

Central Region (Boylston) – General Conditions: No conditions report available, see Environmental Data & Phenology below.

Pioneer Valley Region (Amherst) - General Conditions: Mild weather was the rule during the last two weeks with episodes of rain during the two-week period totaling over 4 inches.  Soil moisture remains adequate in most but is puddling in low-lying areas.  Goldenrod, panicle hydrangeas, daylilies, and summer annuals add color to landscapes and gardens.  Lawns were beginning to show symptoms of moisture stress, but now they should be greening up again. Pests/Problems: Mosquitoes continue to be plentiful.  Spring leaf spot and shoot blight diseases are causing extensive spots, yellowing, browning, and premature leaf loss on many trees and shrubs.

Berkshire Region (Great Barrington) - General Conditions: Despite the high rainfall figure, almost all of that fell in 2 days, leaving soils saturated.  However, the rain was needed.  Landscapes remain lush but many plants are showing the worn look typical of plants at this time of year.  Mildew, leaf spot and other foliar diseases, and leaf-eating insects have taken their toll in these plants.  There is still plenty of color in the landscape with species and varieties of Echinacea, Phlox, Rudbeckia, Helenium, Hosta, and Oriental lilies. Pests/Problems:  One of the more interesting observations this week included seeing Western Conifer Seed Bug boring into cones of Korean fir.  The insect feeds on young cone scales and developing seed in the cone.  Another curiosity was the sight of a row of street-side Norway maples, each with its foliage heavily coated with powdery mildew.  The trees almost looked like they were snow-covered.  Mosquitoes are numerous but so is the population of dragonflies.  Dragonflies prey on mosquitoes, gnats, and flying ants. Large numbers of slugs, snails, and earwigs are troublesome in most gardens.  Continue to take precautions to protect yourself from deer ticks as Lyme Disease remains a common occurrence in Berkshire County.  Viburnum Leaf Beetle adults are still active. The purple box traps set up earlier in the year to monitor for Emerald Ash Borer (EAB) have been examined. No EABs were found.  With EAB having been found just 25 miles to the west of Berkshire County, it is almost inevitable that the pest will appear in the county eventually.

Environmental Data

The following growing-degree-day (GDD) and precipitation data was collected for an approximately two-week period, August 4 through August 17, 2011.  Soil temperature and phenological indicators were observed on or about August 17, 2011.  Total accumulated GDDs represent the heating units above a 50° F baseline temperature collected via our instruments for the 2011 calendar year.  This information is intended for use as a guide for monitoring the developmental stages of pests in your location and planning management strategies accordingly.

Phenology

Phenological indicators are a visual tool for correlating plant development with pest development. The following are indicator plants and the stages of bloom observed for this reporting period:

• CAPE COD REGION - Roberta Clark, UMass Extension Horticulturist for Barnstable County, Barnstable.
• SOUTHEAST REGION - Deborah Swanson, UMass Extension Horticulturist for Plymouth County - Retired, Hanson.
• EAST REGION - Kit Ganshaw & Sue Pfeiffer, Horticulturists, reporting from the Arnold Arboretum, Jamaica Plain.
• METRO WEST REGION – Julie Coop, Horticulturist, reporting from Acton.
• CENTRAL REGION - Joann Vieira, Superintendent of Horticulture, Tower Hill Botanic Garden, Boylston.
• PIONEER VALLEY REGION - Dan Gillman, Plant Pathologist, UMass Extension Plant Diagnostic Lab, UMass, Amherst.
• BERKSHIRE REGION - Ron Kujawski, Horticultural Consultant, reporting from Great Barrington.

Woody Ornamentals

Insects

Hemlock Woolly Adelgid (HWA) - This insect is in summer dormancy now but can still be treated, if necessary, with a summer-rate horticultural oil spray.

Garden Fleahopper (which is a small piercing-sucking insect) remains active and has become rather numerous and destructive in some parts of the state this summer.  There are numerous generations throughout the growing season and many host plants can be affected.  Although usually found feeding on weeds, this pest does attack landscape foliage as well as certain vegetable plants.  Look for foliage that is very chlorotic whereupon close inspection reveals very fine yellow stippling (similar to that of spider mites) on the foliage.  The insects are small and dark in coloration.  However, when magnified, this insect has yellow markings as well.  The adult females have reduced wings and almost appear to be beetle-like. When this insect occurs in large numbers and is problematic, treat infestations with a pyrethroid insecticide.  Repeated applications may be necessary given the multiple generations.

Fall Webworm caterpillars remain active.  This species has a large deciduous host plant range.  They become obvious when their silken webs, which are formed at the tips of the branches, become larger.  They will continue to feed into August and the webs will become ever larger as the larvae expand them from the tips of branches downward on towards the trunk and engulfing the foliage.  The caterpillars scrape the foliage within the webs causing the leaves to die and turn brown.  In most cases, populations are limited and go untreated.  Unsightly webs that are reachable can be pruned away now before they become too large.  Products that contain Spinosad work well as sprays, if necessary.

Red-Headed Pine Sawfly larvae remain active.  Mugo pine is one of the more common hosts for this species. The caterpillars are yellow with black spots and a rust-colored head capsule.  They feed gregariously and can be pruned away and destroyed when occurring in small numbers.  Insecticidal soap sprays or horticultural oil sprays are effective against the small and young larvae.  Spinosad products work well on sawfly larvae of all ages and sizes.  This insect can feed well into October if the weather remains warm.

Viburnum Leaf Beetle adult beetles are very active and are creating much feeding damage. New adult beetles will continue to appear and feed until the first frost. Water injured plants if less than one inch of rain falls within a week for the rest of the growing season. Treat for the adult beetle with a registered pyrethroid spray, especially if they appear on plants previously damaged by the larvae.  Damage, in many cases, is now quite severe in the state.

Lacebugs on Shrubs - Lacebug species that attack shrubs remain very active.  All of these species feed and develop on the undersides of the foliage while their yellow stippling feeding injury will appear on the upper leaf surface.  Small nymphs can be controlled with insecticidal soap sprays or horticultural oil sprays (summer rate); all feeding stages can be managed with a soil applied systemic treatment of imidacloprid. Given that soaps and oils are contact sprays, the sprays must be directed to the leaf undersides.  Plants in sunny locations are more susceptible to severe injury from lacebugs, especially if dry periods prevail.  Japanese Andromeda, azaleas, rhododendrons, and cotoneaster are some of the common hosts for these lacebugs.  The 4-5 weeks of drought that much of the state experienced earlier this summer has greatly enhanced lacebug populations. 

Two-spotted Spider Mite remains very active.  This mite has a large host plant range.  Damage appears as chlorotic foliage and close inspection reveals thousands of tiny individual piercing-sucking type wounds.  Shake foliage over a white piece of paper to find the actual mites.  Large numbers of mites and noticeable damage may indicate the need for treatment.  Horticultural oil sprays at the summer rate can be effective.  Hot and dry conditions, such as experienced within the past 2 weeks in MA greatly encourages outbreaks of this mite.  Predatory mites that often keep their numbers in check tend to become inactive during hot weather thus allowing the spider mites to explode in population numbers.  Water affected plants well during drought.  Use of chemical insecticides can be harsh on beneficial mites (when present) and also lead to the development of pesticide resistance within the spider mite population.

Emerald Ash Borer - Although not yet found in MA, it was found in a roughly 30 mile by 15 mile area in New York State just 25 miles from the western borders of MA and CT last July (2010).  Both states are actively preparing now to monitor for this unwanted exotic invader.  Traps will be set out throughout Berkshire County (MA) soon to monitor for the adult beetles, which begin to appear in June. The traps are 2 feet long, triangular-shaped, and baited with Manuka Oil, which contains 4 compounds that stressed ash trees emit.  These traps are common sights now in all of Berkshire County and in parts of other Franklin, Hampshire, and Hampden Counties in MA, as well as western CT and parts of southern VT.  The traps are suspended in trees with rope and coated with a sticky material to catch any emerald ash borer beetles.  For more information consult:  http://www.emeraldashborer.info

Japanese Beetle adults remain active. Chemical insecticide sprays, such as pyrethroids, are usually necessary when this insect reaches unacceptable population numbers.  Repeated sprays may be necessary as new beetles emerge.

Asian Longhorned Beetle - August is the most common time to find adult ALB attacking trees from the outside.  Inspect closely for these large and showy beetles and their associated signs (sawdust, exit holes, new egg-laying sites, etc).  Survey work continues in the Worcester and Jamaica Plain Regulated Areas.  No new finds have occurred in the Boston (Jamaica Plain) area since the original 6 trees at Faulkner Hospital were discovered and removed last July (2010).  Within the Worcester Regulated Area, new pockets of infestation have been found. The latest find, in Worcester but bordering the town of Auburn, has lead to an expansion of the Regulated Area to now include a part of Auburn.  No infested trees or beetles have been found in Auburn as of this time. The Worcester Regulated Area has expanded from being 94 sq. miles to now being 98 sq. miles.  For more information consult: http://massnrc.org/pests/alb

Brown Marmorated Stink Bug remains active. See the Rutgers web site (http://njaes.rutgers.edu/stinkbug/identify.asp ) for photographs of various life stages.  Please report any potential BMSB findings to MDAR or UMass Extension (Robert Childs:  rchilds@psis.umass.edu).  Another source for information and quality photographs for this pest is: http://ento.psu.edu/extension/factsheets/brown-marmorated-stink-bug

Reported by Robert Childs, Extension Entomologist, Plant, Soil and Insect Sciences Department, UMass, Amherst.

Diseases

Browning of leaves on deciduous trees is a common cause of concern.  When symptoms include leaf spots and blotches or sometimes leaves turn yellow-brown, curl up, and fall off prematurely, they are very likely a result of leaf spot and shoot blight disease infections.  These symptoms were widespread on immature leaves and shoot tips this summer but they began during the persistent rainy spring this year.  Even though these diseases cause leaf discoloration and premature leaf loss that does not seriously harm an otherwise vigorous tree.  As long as 50% or more of a tree’s foliage is green, it can photosynthesize the carbohydrates needed to sustain the tree so it can leaf out again next spring.

Collect and dispose of fallen leaves to reduce fungal disease inoculum around susceptible trees.  If needed, promote drying of foliage by pruning trees to increase sunlight penetration and air circulation.  It is too late this growing season to control these diseases with fungicides.  If desired, fungicides can maintain the appearance of high value trees during future rainy springs, by protecting immature leaves.  Begin as buds open/new leaves emerge.  If rains persist, reapply 1-2 times at label intervals.

In addition, it is often not possible to diagnose what is causing leaf browning and premature loss based on visible symptoms alone.  For example, leaf browning occurred on some trees because of insect feeding damage, water shortage/water-logged soils, soil compaction, and root damage as well as root rot diseases, vascular wilt diseases, and bark wounds subsequently colonized by secondary canker disease fungi.

Gymnosporangium rust infections are visible as orange-yellow spots on susceptible hawthorn, apple, and crab apple leaves.  In addition, tiny yellow-white tube-like fruiting structures are extending from the underside of infected leaves and fruits.  From mid-summer to autumn, spores are wind-carried from the broadleaf host’s leaves and, when conditions are wet, they infect green shoots and needles of junipers.  Pea-sized to 2” diameter round and elongated galls/swellings develop on susceptible juniper needles and branches between 12 and 20 months after infection.  Galls caused by Gymnosporangium rust infections cause little or no damage to health of susceptible junipers.  However, to maintain appearance of high value junipers, apply fungicides per label intervals to protect eastern red cedar and other susceptible junipers from early July through early September.  An alternative approach to manage this disease is to grow Gymnosporangium rust resistant hawthorn, apple, and crab apple as well as juniper varieties.

Plant Problem Diagnostic Lab Woody Plant Report: The following are some of the interesting woody plant disease/abiotic disorder samples received at the UMass Extension Plant Diagnostic Lab in Amherst during the period from July 25 through August 5, 2011:

• Spruce - mature tree with scattered branch tip dieback last year but more extensive this year; Sirococcus shoot blight.
• Flowering dogwood - 25 year old tree with many lower and inside leaves having gray blotches; dogwood anthracnose.
• Hornbeam - 10-12 year old tree exhibiting branch dieback scattered throughout crown; water shortage, compacted soil, heat stress/secondary Nectria canker.
• Cornus alternifolia - newly transplanted shrubs in a landscape with small, round, gray spots with purple margins; Septoria leaf spot.
• Kwanzan cherry - 15-year-old tree with browned leaves on ~20% of branches throughout crown; probably winter damage, splitting branch crotches, and sunscald with secondary/opportunistic Leucostoma cankers.

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

Weeds

Japanese knotweed is beginning to flower now and therefore it is time to treat with an herbicide.  Use a 2% spray solution of glyphosate sprayed to the initiation of spray drip.  Do not use herbicide formulations that contain diquat (Reward™) and do not tank-mix pelargonic acid (Scythe™) with the glyphosate.  Diquat and pelagonic acid are contact herbicides and have the potential to decrease the efficacy of glyphosate.  Non-chemical products containing clove oil, citric acid, acetic acid or orange extract will not effectively control Japanese knotweed.

Inspect areas of the landscape where new trees or shrubs, especially those that were field grown, have been planted in the last year.  Look for perennial weeds that may be growing from the root ball.  Canada thistle, mugwort, quackgrass, bindweed and horsenettle are some of the possible culprits.  Treat will a non-selective systemic herbicide (ex. glyphosate). Contact herbicides (Sycthe™, Reward™) or the non-chemical burndown materials that contain clove oil, citric acid, acetic acid or orange extract will not provide adequate control.

Summer annual weeds are headed toward the end of their life cycle and this means seed production, so any strategy that can be implemented now to remove plants before seed falls will be helpful in the long run.

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

Landscape Turf

No report this week.