May 2012 Volume XVI, Issue III

Inspector Findings

in Kentucky Office of the State Entomologist

www.KyStateEnt.org

Picture key: 1: Azalea lace bug

2. Elm leaf beetle

3. Pine Bark Adelgid

4. Dogwood borer

Pictures from insectimages.org

Inside this issue:

Downy Mildew On

Roses

2

Pine Sawflies 3

Fire Blight 4

Asian Longhorned

Beetle

6

What To Look For In

May

7

University of Kentucky

Department of Entomology

Office of the State Entomologist

S-225 Ag Science Ctr—N

Lexington, KY 40546-0091

Page 2 Inspector Findings in Kentucky

What’s this Spot? Downy Mildew Showing Up on Roses this Spring

By Nicole Ward and Julie Beale, University of Kentucky Plant Pathology

There’s a new disease in town. Downy mildew of rose is showing up across the state. It has been several years since

downy mildew has been diagnosed on rose in KY, but we have already seen multiple cases this spring. During the

past weeks, there have been reports of an “incurable black spot” that is “unresponsive to fungicides.”

The downy mildew pathogen is a water mold, not a true fungus. Thus, humid greenhouse conditions are ideal for

disease spread. So far, all reports originate from greenhouse-grown roses. Additionally, retail centers who purchased

finished roses indicated that roses arrived with early stages of the disease.

Symptoms of downy mildew occur primarily on young apical leaves. Initial symptoms begin as purplish-red irregular

spots (Figure 4). Rapid spread occurs with high moisture and reduced air circulation. Within days, lesions coalesce,

resulting in leaf yellowing and/or leaf drop. The fuzzy sporulation of rose downy mildew occurs on the lower leaf

surface, but it is typically very sparse and difficult to see. This season, infection has been diagnosed on hybrid tea

roses and some varieties of Knockout rose.

Roses are susceptible to a variety of leaf spots (Figure 5). Black spot, the most common foliar disease of rose, begins

as circular spots with feathery margins. While hybrid tea roses are extremely susceptible to black spot, Knockout

roses are mostly resistant. Cercospora leaf spot, common on many shrub roses, produces circular lesions with pur-

plish red edges and light gray or tan centers. Both of these leaf spots can be confused with early symptoms of downy

mildew.

Management of downy mildew requires a combination of cultural and fungicidal controls. This first step requires re-

duction of humidity. Greenhouses should be well ventilated. Nursery and greenhouse plants should be spaced for

sufficient air circulation to promote leaf drying. Drip irrigation can greatly reduce leaf wetness, as well. Growers

should practice good sanitation, removing fallen leaves and pruning away diseased plant parts, as the pathogen can

survive for several weeks on debris. Fungicides registered for use in commercial greenhouses and nurseries include

Aliette, Banol, Segway, Stature, and Subdue MAXX. Homeowners may apply copper + mancozeb. Refer to labels for

rates and application intervals.

Figure 4. Downy mildew on rose begins with irregularly-

shaped lesions that are purple to reddish in color

(photo N. Ward).

Figure 5. Leaf spots of rose can appear similar.

Black spot lesions are circular with feathery edges

(left, photo by J. Hartman). Cercospora spots have

dark halos with light centers (right, photo by A.

Windham). Downy mildew infections often cause

blotches, not spots (center, photo by D. Hull)

Page 3 Inspector Findings in Kentucky

Loblolly Pine Sawfly

By Lee Townsend, UK Entomology, and Jody Thompson, KY Division of Forestry

Reports of feeding by the loblolly pine sawfly came in from western Kentucky late last

week. This species is an important defoliator of loblolly and short leaf pine in the south-

east. Significant defoliation in early spring can reduce tree growth and vigor but usually

does not directly cause tree death.

The dull green caterpillar-like larvae have brown heads and black stripes running along

the sides of their bodies. At first, clusters of them feed on soft outer tissue of old

growth needles so the remains of them turn reddish brown. Larger larvae feed by

themselves and consume entire needles except for a small stub. Full grown larvae

(about 1 inch long) drop to the ground and spin individual cocoons in soil and leaf litter.

There is one generation each year.

First Generation of Introduced Pine Sawfly Feeding

By Lee Townsend, UK Entomology

The distinctive introduced sawfly larva has a black head and black body that is covered with yellow and white spots.

The larvae prefer to feed on the needles of eastern white pine but also will eat Scotch, red, Austrian, jack, and Swiss

mountain pine. Short leaf and Virginia pines have been attacked but usually are not heavily damaged.

Defoliation is most severe in the crown to upper half of the tree but heavily infested trees can be completely defoli-

ated. If this occurs after the winter buds have formed, many branches or even the entire tree can be killed. There

are two generations each year. Larvae of the first generation feed on needles from the previous year. Young saw-

flies eat the more tender outer parts of the needles while older larvae consume them entirely. They are full-grown

(about inch long) in July. The second generation of this sawfly feeds on both old and new needles during August and

September.

Sawfly larvae are not true caterpillars in the sense of being immature stages of butterflies or moths so they are not

susceptible to Bt (Bacillus thuringiensis) sprays.

Page 4 Inspector Findings in Kentucky

What You May Not Know About Fire Blight

By Nicole Ward, UK Plant Pathology

Fire blight can be a devastating bacterial disease of apple, crabapple, pear, and flowering pear, but disease epidemics are often sporadic. In fact, optimal conditions must be met for severe disease to occur. Our current conditions are an indication that fire blight may be severe this spring.

Initial fire blight infections occur through flowers. We call this symptom “blossom blight”. Petal browning is the first sign of petal blight, but many growers do not notice it. Browning of pedicels (stems that attach flowers to stems) follows. Often, droplets of bacterial ooze can be seen coming from pedicels. Bacteria quickly travel down the spur and into the twig. Cankers that form around the spur-attachment site girdle branches, and then branch parts above the canker also die.

Most growers are familiar with shoot blight, the most obvious fire blight symptom in which infected shoots die quickly, causing branch tips to form a distinct crook. Shoot blight, however, does not result from infection of blossoms. Direct penetration of bacte-ria into green shoots or the upper leaves of young shoots after bloom typically causes shoot blight symptoms.

Erwinia amylovora, the causal agent of fire blight, infects trees initially through flowers. However, large numbers of bacterial cells must be present during flowering in order for the disease to develop into an epidemic. The fire blight pathogen favors rain and temperatures above 60˚F. Under these conditions, bacterial cells multiply quickly. Thus, if conditions are favorable during flowering, infection can be severe.

Predictive systems are available for growers. University of Kentucky’s Cougarblight model evaluates the potential for infection by analyzing temperature and leaf wetness data from the previous four days in order to estimate potential risk for infection. Trees must be in bloom for this predictor to be effective. Cougarblight is an excellent decision-making tool for growers and can be ac-cessed at http://wwwagwx.ca.uky.edu/plant_disease.html .

Fire blight control measures include bactericides applied during bloom. Applications made after bloom are ineffective. When fire blight risk is high (warm temperatures combined with rain) during bloom or if fire blight was a problem last year, the spray schedule below should be followed:

1. Apply fixed copper at silver tip. Do not use copper fungicides after bud break.

2. Apply streptomycin beginning at pink stage, repeating every 4-5 days, through petal fall. At least 2 applications are re-quired, but up to 4 sprays may be applied, depending on rain and temperature conditions. Pay extra attention to suscepti-ble varieties (i.e. Gala, Jonathan, and Rome). Utilize Cougarblight or MARYBLIGHT predictive systems for determining specific risks. Mycoshield (oxytetracycline) is also available for management of fire blight but is not as effective as strepto-mycin.

3. Copper is the only bactericide product recommended homeowner use. Thus, homeowners must rely on the copper application at silver tip for management of fire blight.

More information on fire blight can be found in PPA-34 and PPFS-FR-T-7. Spray recommendations for commercial growers (ID-92) and homeowners (ID-21) are also available online.

Page 5 Inspector Findings in Kentucky

Figure 9. Initial infection by the fire blight pathogen

occurs through blossoms. Notice bacterial ooze coming

from the pedicel.

Figure 10. Bacteria can spread through flowers

and spurs into twigs. Resulting cankers can

girdle entire limbs and branches.

Figure 11. Blighting of shoots, also called shepherd's crook, is

the most recognized symptom of fire blight on apple.

Page 6 Inspector Findings in Kentucky

Asian Longhorned Beetle

The following is a postcard mailed to individuals residing in Clermont County, OH where Asian Longhorned Beetle

(ALB) was found last year. The mailings were designed to keep residents informed of the most recent ALB develop-

ments in their community as well as provide information on what they can do to help and who to contact if they

have any questions. Click here to view the full pdf on http://www.beetlebusters.info/ohio/ . ALB has not yet been

found in Kentucky.

Page 7 Inspector Findings in Kentucky

Taken from Calendar for Common Kentucky

Shade Tree and Woody Ornamental Pests

What to look for:

May

Azalea lace bug Azaleas, especially evergreen varieties and mountain laurel

May and July

Bagworm Foliage of host, especially arbovitae, juniper

mid-May through mid-June

Birch leaf miner Birch early May and mid-June

Boxwood leaf miner Boxwood foliage mid-May through mid-June

Boxwood psyllid Underside of boxwood leaves mid-May to mid-June

Bronze birch borer Bark, especially upper branches of birch

late May to early June

Dogwood borer Dogwood trunks and branches May to mid-June

Elm leaf beetle Elm mid-May through early July

European red mite Foliage of host May through June

Fall webworm Tents at end of branches in various trees

late May through June

Juniper scale Juniper and arbovitae twigs and branches

Egg hatch in May

Linden looper Oaks, maples, elm, hickory, ash May through June

Oystershell scale Twigs and branches of willow, lilac, apple, others

Crawlers in early May

Pine bark adelgid Twigs and branches of white and Scotch pines

early to mid-May but several genera-tions

Pine webworm Va pine, short and longleaf pines May

Poplar tentmaker Poplar and willow May through October

Taxus mealybug Trunk and branches of Taxus, apple, cedar, linden, maple

Active in late May, 2 to 3 generations/year

Walnut caterpillar Black walnut, pecan, hickory May

White pine aphid White pine terminal needles mid-May

Yellow poplar weevil Poplar, sassafrass, and magnolia mid-May