Inspector Findings in Kentucky

Transcription

1 Inspector Findings in Kentucky Volume XVI, Issue III Office of the State Entomologist May 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 Picture key: 1: Azalea lace bug 2. Elm leaf beetle 3. Pine Bark Adelgid 4. Dogwood borer Pictures from insectimages.org University of Kentucky Department of Entomology Office of the State Entomologist S-225 Ag Science Ctr N Lexington, KY

2 Page 2 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 purplish 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 reduction 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 irregularlyshaped 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)

3 Page 3 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 southeast. 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 defoliated. 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 sawflies 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.

4 Page 4 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 bacteria 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 accessed at 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 required, but up to 4 sprays may be applied, depending on rain and temperature conditions. Pay extra attention to susceptible 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 streptomycin. 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.

5 Page 5 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.

6 Page 6 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 developments 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 ALB has not yet been found in Kentucky.

7 Page 7 What to look for: May Azalea lace bug Azaleas, especially evergreen varieties May and July and mountain laurel Bagworm Foliage of host, especially arbovitae, mid-may through mid-june juniper 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 late May to early June birch 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 late May through June trees Juniper scale Juniper and arbovitae twigs and Egg hatch in May branches Linden looper Oaks, maples, elm, hickory, ash May through June Oystershell scale Twigs and branches of willow, lilac, Crawlers in early May apple, others Pine bark adelgid Twigs and branches of white and Scotch pines early to mid-may but several generations 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, Active in late May, 2 to 3 generations/ cedar, linden, maple 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 Taken from Calendar for Common Kentucky Shade Tree and Woody Ornamental Pests