UMass Extension Landscape Message #15 - 2011 | UMass Extension Landscape Nursery & Urban Forestry | UMass Amherst

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UMass Extension Landscape Message #15 - 2011 June 10, 2011 Quick Links Scouting Information by Region Scouting Information Regional Notes Regional Notes Cape Cod Cape Cod Region (Barnstable) – General Conditions: The weather for this reporting period has been temperate for the most part but with no precipitation for the second week in a row. Heat and humidity Southeast moved in on Wednesday, June 8, and many plants in the landscape are beginning to flag. Soils are very dry. East The Cape has gone from chilly and wet, to hot and dry. Early summer perennials are coming into bloom and Metro West irrigations systems are being turned on. Pests/Problems: Leucanium scale is being reported on both Oak Central and Linden; Cottony Maple scale has been identified on Kousa dogwood and Styrax. Cottony Taxus scale Pioneer Valley oviposition in evident on Taxus and Ilex. Winter moth is finished for this season with pockets of defoliation Berkshire scattered across the Cape. Spittlebug, cutworms, aphids, rose slug sawfly, boxwood psyllid, and clover mites Environmental Data are all being reported. Mosquitoes are very numerous this season, making repellants a necessity when Phenology working outdoors. Deer tick nymphs are active. In the disease department, black spot of rose, apple scab Woody Ornamentals and frog-eye leaf spot on crabapples, peach leaf curl, maple anthracnose, and sycamore anthracnose are all present in the landscape. Red thread has been reported on turf. Landscape Turf

Southeast Region (Hanson) – General Conditions: Warm weather and dry soils have been the norm, Archived Messages this past week and many unirrigated flowering trees and shrubs are dropping flowers earlier than usual. Hanson received 0.0 inches of rain this past week and soils are dry. Yellowwood, Cornus kousa, Physocarpus opulifolius (Eastern Ninebark), Liriodendron tulipifera (Tuliptree), Weigela, Lilac (Syringa x prestoniae) ‘James Macfarlane’, late-flowering viburnums, Chionanthus virginicus, Cytisus scoparius (Scottish broom), Calycanthus, Indigofera sp., Rosa rugosa, Roses, Clematis, Paeonia (Peony), Foxgloves, Tradescantia, Allium, Nepeta sp., Salvia ‘May Night’, Baptisia australis and Baptisia hybrids, Anemone canadensis, Amsonia sp., Thalictrum aquilegifolium, Oriental poppies, Geranium sp., Doronicum sp., Corydalis lutea, Siberian Iris, Dianthus, and Centaurea montana are in full bloom. Remind clients to water trees damaged by winter moth caterpillars and also to water newly planted trees, shrubs and perennials. Pests/Problems: The White- spotted pine sawyer, a native beetle, has begun to emerge and many people mistake it for the Asian Longhorned Beetle. This beetle is considered an Asian Longhorned Beetle (ALB) ‘look-alike” but does not do the damage that ALB does. Iris bud fly larvae are showing up on Siberian iris. The tiny white maggots can be found inside the damaged flowers, and/or at the base of the flower and flowers often appear ‘shredded’. Dogwood sawfly, cottony camellia scale on blue holly and Taxus, Aphids, four-lined plantbug, slugs, snails, cutworms, lily leaf beetle (adults, larvae and eggs), wasps and hornets, carpenter bees, mosquitoes, and ticks are all active. Roseslug sawfly larvae continue to feed on the undersides of rose foliage and if left untreated, these larvae will skeletonize the foliage. Monitor for foliar diseases like black spot on roses, apple scab on apples and crabapples, and anthracnose on sycamore, maple and dogwood. The tiny deer tick nymphs are active and it is the deer tick stage often associated with the transmission of Lyme disease. Dog ticks are also active. Check frequently for ticks after working outdoors especially in grassy and wooded areas. Mosquitoes continue to be numerous. Plymouth County Extension does not spray for mosquitoes. The number for residents of Plymouth County to call is 781-585-5450. White clover and oxalis are in full bloom. White pine pollen continues to fall, coating everything with yellow ‘dust’. Deer are browsing Hosta.

East Region (Boston) – General Conditions: We started out the week with cool temperatures, but ended with a rapid heating, reaching a high of 86° F on June 7th. This shift in temperatures resulted in an average gain of 100 GDDs, reaching 489 GDDs for the year. The soil is becoming extremely dry and in sunny areas, turf is showing signs of stress. Trees in bloom: Liriodendron tulipifera (tulip tree) and Paulownia tomentosa (royal paulownia). Shrubs in bloom: Cultivars of Calycanthus sp. (sweetshrub), Cotinus sp. (smoketree), Hydrangea bretschneideri, Stephanandra incisa ‘Crispa’ (stephanandra), Styrax japonicus (Japanese snowbell) and Symphoricarpos x doorenbosii ‘Kordes’ (coralberry). Perennial in bloom: Clematis albicoma (erect mountain clematis), Hypericum buckleyi (blueridge st. johnswort) and cultivars of Paeonia sp. (peony). Vines in bloom: Actinidia [A. arguta (bower actinidia) and A. purpurea (purple actinidia)], Bignonia capreolata ‘Tangerine Beauty’ (crossvine), Clematis [C. japonica (Japanese clematis) and C. viticella (clematis)], Lonicera sempervirens (trumpet honeysuckle), Menispermum dauricum (Asiatic moonseed), many Vitis sp.

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(grape) and Wisteria [W. frutescens (American wisteria)and W. macrostachya (Kentucky wisteria)]. Especially eye catching at this time is Salix integra var. albo-marginata. Pests/Problems: Lilac borer (Podosesia syringae) is flying in large numbers and lacebugs continue to be active. Aphids are easily spotted, however lady bug populations are increasing and can be also be easily spotted among the aphids. Hydrangea leaf tier (Olethreutes ferriferana) adults have emerged. Mosquitos continue to readily feed, however their numbers have significantly dropped compared to a couple of weeks ago. Weeds continue to grow; Acalypha virginica (Virginia copperleaf), Chenopodium album (lambsquarters), Digitaria sp. (crabgrass), Euphorbia maculata (spotted spurge) and Trifolium sp. (clover) continue to germinate. Others are in flower: Persicaria maculosa (formerly Polygonum persicaria) (lady’s thumb), Rumex obtusifolius (broadleaf dock), Urtica dioica (stinging nettle). Alliaria petiolata (garlic mustard) and Chelidonium majus (greater celandine) continue to set seed.

Metro West (Acton) – General Conditions: The Metro West area gained 90.5 growing degree days this past week and received 0.75” of rain. This year’s growing degree days are 98.5 GDD behind of last year’s total. There were some cool nights during this past week’s reporting period. The month started out with a wicked rain and lightening event. The metro west area fared much better than areas west of it. Woody plants in bloom are: Cornus canadensis (Bunchberry), C. sericea (Redosier Dogwood), C. x rutgersensis ‘Ruth Ellen’ (Rutgers Hybrid Dogwood), Kerria japonica (Japanese kerria), Laburnum x watereri (Goldenchain Tree), Leucothoe axillaris (Coast Leucothoe), Physocarpus opulifolius (Common Ninebark), Rhododendron spp., Rosa rugosa (Rugosa Rose), Spirea thunbergii (Thunberg Spirea), Syringa spp. (late blooming Lilac), Viburnum plicatum var. tomentosum (Doublefile Viburnum) and V. sargentii (Sargent Viburnum). Herbaceous plants in bloom this week are: Alchemilla mollis (Lady’s mantle), Allium giganteum (Giant Onion), A. schoenoprasum (Chives), Amsonia hubrichtii (Arkansas Blue Star), Aquilegia spp. (Columbine), Aruncus dioicus (Goat’s Beard), Baptisia austrailis (False Indigo), Coreopsis verticillata (Threadleaf Coreopsis), Dicatamnus albus (Gas Plant), Galium odorata (Sweet Woodruff), Geranium maculatum (Wild Geranium), G. macrorrhizum (Bigroot Geranium), G. sanguineum (Cranesbill Geranium), Gillenia trifoliata (Bowman’s Root), Hemerocallis ‘Stella D’Oro’ (Daylily), Iris germanica (Bearded Iris), I. sibirica (Siberian Iris), Lupinus ‘Russell Woodfield Hybrids’ (Lupine), Myosotis sylvatica (Forget-me-not), Nepeta spp. (Ornamental Catmint), Paeonia spp. (Peony), Penstemon digitalis ‘Husker Red’ (Beardtongue), Phlox divaricata (Canadian Phlox), P. stolonifera (Creeping Phlox), Potentilla tridentata (Wineleaf Cinquefoil), Salvia nemerosa (Sage), Tradescantia virginiana (Spiderwort). Pests/Problems: Rosa multiflora (Multiflora Rose) is in full bloom; is easy to see out in the landscape and is engulfing whatever it is growing on or near. Mosquitoes continue to thrive especially with the recent rains as are the weeds that are popping up everywhere. Evidence of spittlebug has been seen. Ticks and mosquitos are feeding and very active.

Central Region (Boylston) – General Conditions: Heavy thunderstorms tore through our area on Wednesday June 1st, but fortunately did not develop into the tornadoes that devastated other parts of the state. With the exception of that evening rain has been scant, sun prevalent, and now temperatures are soaring. Pests/Problems: Turf is beginning to show stress in un-irrigated areas and soils are drying out. The symptoms of fireblight on apples are becoming apparent with new shoots wilting and leaves quickly turning brown.

Pioneer Valley Region (Amherst) - General Conditions: A soaking rain along with several tornadoes happened to the Pioneer Valley Wednesday/Thursday last week. The well-timed moisture followed by moderate temperatures has kept things green, thriving, and growing. Irises, columbines, and a host of flowering annuals bloom in neighborhood gardens while Kousa dogwood, old-fashioned weigela, mountain laurel, and Catawba rhododendrons add color to the yard and foundation beds.

Berkshire Region (Great Barrington) - General Conditions: Soil moisture levels are low and a combination of irrigation and mulching are necessary for most herbaceous plants. Hazy, hot, and humid! Take precautions when working outdoors to avoid heat exhaustion. There are many web sites that describe the symptoms of heat exhaustion and provide first aid information. Pests/Problems: Skunks are digging holes in lawns, flower gardens, and in patio containers, most likely searching for grubs. Browsing by deer, rabbits, and voles continues to be a problem in many gardens. Mosquitoes, ants, deer ticks, slugs, and snails abound. Foliar diseases observed this week include: apple scab and rust on leaves of apples and crabapples, twig blight on cherry, leaf blight on Hamamelis and Parrotia, powdery mildew on numerous herbaceous plants and shrubs, and Phyllosticta leaf spot on maples. Insect observed include: Imported Willow Leaf Beetle (larvae), Azalea sawfly (larvae), Lily Leaf Beetle (adults and eggs), aphids, leafhoppers, spittlebug (on herbaceous plants), and Honeylocust Pod Gall. Viburnum Leaf Beetle larvae can no longer be seen on plant foliage.

Environmental Data The following growing-degree-day (GDD) and precipitation data was collected for an approximately one- week period, June 2 through June 8, 2011. Soil temperature and phenological indicators were observed on or about June 8, 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.

2011 GROWING DEGREE DAYS Soil Temp (°F at 4" Precipitation (1-Week Region/Location 1-Week Total accumulation for depth) Gain) Gain 2011

Cape Cod 91 476 68° 0.00"

Southeast 79 476 81° 0.00"

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East 100 489 74° 0.70"

Metro West 90.5 519.5 68° 0.75"

Central 94 482 70° 0.98"

Pioneer Valley 100 527 70° 1.32"

Berkshires 72 412 70° 0.00"

AVERAGE 90 483 72° 0.54"

n/a = information not available

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:

Indicator Plants - Stages of Flowering (begin, b/full, full, f/end, end)

SOUTH METRO PLANT NAME (Botanic/Common) CAPE EAST CENT. P.V. BERK. EAST W.

Catalpa speciosa (Northern Catalpa) * * * * * * begin

Syringa reticulata (Japanese Tree Lilac) begin b/full begin * begin * begin

Philadelphus spp. (Mockorange) begin full full full full * begin

Cladrastis lutea (Yellowwood) * full full full full * begin

Cornus sericea (Red Osier Dogwood) begin full * full full * begin

Kalmia latifolia (Mountain-laurel) begin full b/full full b/full full begin

Hydrangea anomala petiolaris (Climbing begin full full * begin * b/full Hydrangea)

Cornus kousa (Kousa Dogwood) full full full full full full full

Robinia pseudoacacia (Black Locust) full full * full full f/end full

Chionanthus virginicus (Fringe Tree) full f/end full full full f/end f/end

Kolkwitzia amabilis (Beautybush) full full full f/end full full full

Weigela florida (Old Fashioned Weigela) f/end f/end end f/end full full full

Syringa meyeri (Meyer Lilac) f/end end end f/end full f/end *

Deutzia spp. (Deutzia species) end end full f/end full * f/end

Enkianthus campanulatus (Redvein end end f/end f/end end f/end f/end Enkianthus)

Rhododendron catawbiense (Catawba f/end f/end f/end f/end full f/end f/end Rhododendron)

* = no activity to report/information not available

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) - HWA infestations remain actively feeding and developing at this time. Infested trees with live HWA can be treated with a summer rate horticultural oil spray when weather conditions are conducive for such sprays. However, be aware of tender new foliage at this time and/or very hot and humid weather which tends to slow the drying time of the spray thus increasing the risk of phytotoxicity. Systemic imidacloprid can also be effective but uptake by the plant and translocation to the growing points where HWA feeds can take anywhere from weeks to months given the size of the tree and

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delivery method (soil-applied vs. trunk injection). Systemic imidacloprid should only be applied (soil or trunk injection) when soil moisture is adequate. Dry soils greatly reduce the ability of trees to uptake the product; water prior to application and up to 2 weeks after application if drought conditions prevail.

Elongate Hemlock Scale (aka: Fiorinia Scale) has become more prevalent in MA in recent years and is commonly found attacking hemlocks that are also under assault by hemlock woolly adelgid. This very small, elongate and light brown scale is found on the undersides of needles and can be difficult to see even when occurring in large numbers. Inspect for both pests on Eastern (Canada) hemlock. Systemic imidacloprid is not very effective for this scale nor are oil sprays. This scale is atypical given that it produces crawlers (first instar stage that is the easiest to manage for most scale species) throughout the growing season where other species have 1-2 crawler stages per year. Dinotefuran (Safari™), another neonictinoid, like imidacloprid, has systemic uses and does have this scale specifically listed on the label. Safari™ in MA is a restricted-use insecticide given its high water solubility.

Winter Moth (WM) caterpillars have finished feeding in MA at this time and have entered into the soil to begin pupation. No more damage will occur from this pest this year. Trees that were attacked by this pest should be considered to be stressed trees, especially if defoliated, and should be watered once a week during dry periods for the rest of the growing season. Fertilizer is not necessary nor is it recommended.

Mountainash Sawfly caterpillar remains active. These yellow sawfly caterpillars with dark spots feed mostly in clusters on host plant branches. Small clusters can be pruned away and destroyed. Larger infestations can be sprayed with insecticidal soap sprays (when caterpillars are still small) or with a product that contains Spinosad (any time during the larval period).

Lily Leaf Beetle nymphs have appeared and are feeding on Asiatic lily foliage. The larvae, which are active now, are easily treated with a product that contains Spinosad (e.g. Conserve SC™).

Viburnum Leaf Beetle larvae are virtually finished feeding in MA at this time and are now in the soil pupating to become adult beetles starting in mid-July. Much damage is now noticeable and in some cases, entire plants are defoliated. This pest is commonly moved on nursery plants from other states that have had this pest for a number of years; carefully inspect any new plants arriving for installation. Adult beetles will begin to appear in mid-July and will feed on the same host plants, potentially defoliating them a second time. Water injured plants if less than one inch of rain falls within a week.

Lacebugs on Shrubs - Many of the lacebug species that attack shrubs that over-winter as eggs embedded within the shoots or foliage of the host plant are now 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.

Boxwood Leafminer adults will be active soon. Either inspect the undersides of affected foliage to see the pupae hanging down from the undersides of the leaves and/or hang yellow sticky cards from host plant stems to monitor for the adult flies. Once adult flies are active, spray with a pyrethroid or with one of the other chemical insecticides registered for this pest.

Cottony Maple Scale has been reported from Cape Cod as well as parts of Rhode Island within the past week, primarily on Kousa dogwood. This large, ‘soft scale’ has been producing white and cottony egg- masses, which are currently still attached to the dark-colored adult female body. More than 1000 eggs may be within each egg mass. These can be found on stems as well as foliage. Crawlers (immature scales) will hatch from now into August. Being a soft scale, there is also a problem with honey dew/sooty mold. This scale can also be found on red and silver maples, linden, honeylocust and other deciduous hosts. Treat for the crawlers with an insecticidal soap (more than one application may be necessary) or with a systemic imidacloprid treatment. A horticultural oil spray at the summer rate may also be effective. This can be a challenging scale to get under control.

Cottony Camellia Scale is active. This pest has a wide host range but certain holly is mostly affected in MA. Inspect for the white cottony egg masses, sooty mold, and stunted growth. Yellow foliage may be present in heavier infestations. See ‘Cottony Maple Scale’ (above) for treatment options.

Native Holly Leafminer, which primarily attacks American Holly, will be active soon as an adult fly. Hang yellow sticky traps now to monitor for adult emergence and spray when the traps begin to collect many flies. Treat with a pyrethroid or with one of the other labeled chemical insecticides.

Arborvitae Leafminer adult moths will be active soon, which provides an opportunity for treatment. This leafminer is not attracted to yellow sticky cards as are many other leaf mining insect species. Monitor affected arborvitae by gently shaking foliage, which causes the dull-white and small moths to fly off of the foliage. When abundant, apply a registered pyrethroid insecticide to limit the number of female moths that lay eggs on the host foliage. A summer rate of horticultural oil can be effective if correct timing is achieved but this necessitates very close examination of the foliage undersides to identify the presence of new eggs. The leaf-mining caterpillars of this species hatch from the eggs and then chew their way into the foliage, usually from the undersides of the foliage. Eggs are small, oblong and whitish in color and are generally tucked into leaf folds.

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

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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

Bronze Birch Borer (BBB) adult beetles are becoming active. This native Buprestid beetle is remarkably similar to the Emerald Ash Borer (EAB) in size and body shape given their relationship. However, where the EAB is an emerald green color, the BBB is quite dark on the dorsum (back) and more of metallic bronze on the ventral (under) side. The BBB is not considered to be a threat given that it is a native species and only attacks already weak and dying trees. Birches that are stressed by extended drought, poor growing sites or other factors are strong candidates for attack by BBB. Trunk sprays with a pyrethroid, for protection of identified weak trees, may be necessary in some cases.

Rhododendron Borer adult moths will become active soon, if not already in some parts of the state. The females of this species lay their eggs near the base of shoots of host plants. Hang specific pheromone traps to monitor for adult flight. If numerous moths are captured then a pyrethroid spray may be necessary to prevent egg-laying. The tunneling larvae (caterpillar) can eventually kill the entire within which it is mining. Inspect shoots, especially within a foot of the ground, for signs of sap streaking, which may indicate the beginning of a new entry point by the caterpillar. Adults of this species will remain active through August.

Leopard Moth. This large white moth with black spots is an introduced pest that has been in North America for more than 100 years. Its host range is rather large and includes many deciduous tree species. Although each adult female is capable of producing hundreds of eggs, only a few survive. Exit holes on shoots, trunks, and larger branches are large and round and greatly resemble the exit holes of the Asian longhorned beetle (approximately ½” - 5/8” in diameter). However, the exit holes of Leopard Moth usually are at an angle where those of ALB exit straight out of the trunk. Test by placing a pen or pencil into the exit hole. If the pen points downward from the trunk towards the ground, then it is most likely that of leopard moth. With ALB, the pen usually will be at a 90 degree angle (perpendicular) to the trunk.

Asian Longhorned Beetle - 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

White-spotted Pine Sawyer Beetle (WSPS) became active starting last week in MA. This native insect that only attacks already weak and dying pines is not considered to be a pest species in MA. However, it does greatly resemble the Asian Longhorned Beetle (ALB) in appearance and is often confused with that exotic insect. The WSPS has one white spot behind the head, in the center of the body directly between the wing covers (elytra = front wings); the ALB does not have this one distinctive white spot.

Brown Marmorated Stink Bug has been officially found in MA 5 times within the past 4 years. This exotic pest caused millions of dollars in damage in some of the mid-Atlantic states this past fall in such crops as apples, peaches, corn and others. It is expected that this pest will become established in MA at some point. This pest is commonly confused with the Western Conifer Seedbug (WCSB) that is a common house invader but other than being a nuisance is not considered to be a pest in MA. A newspaper and on-line article published last week in the Springfield area discussed BMSB but failed to distinguish the similarities and differences between WCSB and BMSB thus resulting in a multitude of e-mail and phone messages from readers certain that they had BMSB. Thus far, all reports this last week were for WCSB and no new finds of BMSB have resulted. Please report any findings to MDAR or UMass Extension (Robert Childs: [email protected] ). A 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 Oak leaf blister is showing up on red, white, and pin oak leaves as faint, yellow green, puckered spots. This is a not a serious fungal disease problem in our area, but leaf browning that follows in early summer disfigures foliage and may cause premature leaf loss. If a severe outbreak is occurring on high value trees, next spring, start chemical control activities just as buds open and repeat at labeled intervals if rainy weather persists.

Maximize the effectiveness fungicide treatments in the management of black spot on rose by monitoring rainfall and if needed, making repeat applications per label directions into the fall. Remove spotted leaves and first year canes with numerous reddish-purple to black lesions/cankers to reduce Marssonina inoculum around roses. 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.

Horsechestnut (Guignardia) leaf blotch is becoming more evident, as scattered, irregular-shaped orange- brown blotches on infected leaves. They are primarily affecting lower and inside leaves. As the late spring

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and summer progress, rainy conditions can allow the disease to become more noticeable. However, fungicide interventions at this time of this season provide little benefit to disease management. Keep in mind that horsechestnut infected year after year often continue to grow vigorously in spite of Guignardia leaf blotch.

Powdery mildew fungi are visible as a dusty, gray to white spots on leaves of leaves of roses, horsechestnut, and lilac. Additional common host plants include sycamore, phlox, and rose are not showing signs of powdery mildew as of yet in the Amherst area. Once established on plants, powdery mildews grow superficially on both upper and lower leaf surfaces as well as on green shoots and flower buds. Generally, if unsightliness is not a critical concern, the damage caused by powdery mildew is of minor consequence to healthy trees and shrubs and does not warrant chemical control. However, if considering chemical control there are a number of biorational/unconventional applied materials labeled to protect susceptible plants. They include summer horticultural oil, commercial baking soda preparations (sodium bicarbonate and potassium bicarbonate) and combinations of these, as well as a number of conventional fungicides. Chemical spray programs are most effective when begun just as symptoms of powdery mildew begin to show. Once powdery mildew is extensive on the plant, there is little benefit from chemical control for that season. Applications need to coat both surfaces of all susceptible plant parts to prevent infection. Spray on a regular schedule per labeled intervals, and repeat more often during warm humid weather.

Close observation of trees on the UMass campus indicates that sycamore anthracnose, maple anthracnose, oak anthracnose, and ash anthracnose is becoming evident. Symptoms now appear as water-soaked dark-green leaf spots along with tan-brown curling leaves and shoots on sycamore, maple, and white oak. Early ash anthracnose symptoms are occurring as young green leaves often without discernable spots falling from the trees. Anthracnose is widespread on early leaves and shoots this year due to the abundance of inoculum on overwintering twigs and fallen leaves as well as the consistently wet early spring weather. It is too late this spring to apply protective fungicides. However, even though these diseases cause leaf discoloration and some premature leaf loss that does not seriously harm an otherwise healthy tree. Collect and dispose of fallen leaves to reduce anthracnose fungal inoculum around trees. If practical, promote drying of foliage by pruning and spacing trees to increase sunlight penetration and air circulation. During rainy future springs, consider fungicide protection of high value trees beginning as buds open/new leaves emerge. If rains persist, reapply 1-2 times at label intervals.

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 May 23 through May 27, 2011:

Norway maple – six of twenty 17 year old trees exhibited scattered leaf wilting and some branches with buds that swelled but failed to open; Botryosphaeria cankers found on branches with bark wounds likely due to last summer’s drought and/or winter wind and heavy ice/snow load damage. Austrian pines – 20-year old tree with many partially to mostly browned needles but with new candles appearing from the branches, which are as healthy and the same size as those on adjacent Austrian pines with only minor browning; Dothistroma needle blight. Canadian hemlock – mature tree with some relatively uniform pale-green to yellowing needles on some branches and scattered branches dying back from the tips; no disease-causing fungi grew out of needles, but the canker fungus Phomopsis girdled/girdling branches with bark wounds probably caused by water shortage and soil compaction and/or winter wind and ice damage. Corylus species – well-established tree with some of this year’s leaves and flowers browned coupled with branch and twig dieback; eastern filbert blight. Cornus kousa – ~7 year old tree that grew on site for one year that is now showing diffuse branch tip dieback throughout its crown; Botryosphaeria cankers are exacerbating damage primarily caused by transplant stress and water shortage during last summer’s drought.

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

United States Department of Agriculture National Institute of Food and Agriculture

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