inspector findings in kentucky · aliette, banol, segway, stature, and subdue maxx. homeowners may...
TRANSCRIPT
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