NUMBER 1194 |
May 5, 2009 |
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SHADE TREES & ORNAMENTALS |
FRUIT CROPS |
TOBACCO |
CORN |
PESTICIDE NEWS & VIEWS |
Early Season Grape Disease Management |
Phomopsis cane and leaf spot. Caused by the fungus Phomopsis viticola, this disease is becoming increasingly important in Kentucky. Symptoms may include lesions along the vine (Figure 1). Early treatments are critical for Phomopsis management, especially for control of rachis infections (Figure 2), a common cause of disease loss in grapes. Fungicide applications need to be made during the early shoot growth period, at about 3 inches of shoot growth as bloom clusters first become visible. Applications now help to control rachis infections and provide significant control of berry infections by reducing rachis infection that leads to fungus spread from rachis to fruits. Repeat applications are helpful for Phomopsis management, but the greatest economic benefit comes from the first spray at 3 inches shoot growth. Early sprays also provide the greatest control of shoot infections, which in future years, serve as sources of Phomopsis spores from infected canes, spurs, or pruning stubs. Dead wood and canes may be particularly important sources of Phomopsis spores. Removal of dead wood during pruning operations is important for managing this disease. Furthermore, the fungus can remain active in dead wood and pruning stubs for at least several years. Based on studies in Michigan and New York, inoculum from these sources generally fades out by mid-summer. A minimal Phomopsis cane and leaf spot spray program should include at least one application during the period when shoots are a few inches long and soon after clusters are visible. If there is inoculum present in the vineyard along with rain, waiting to spray until shoots are 10 inches long and blooms are imminent is too late. Mancozeb, captan, and ziram all provide very good to excellent control of basal shoot and rachis infections. Strobilurin fungicides such as Abound and Pristine tend to be a little less effective. Sulfur does little for management of Phomopsis cane and leaf spot. Growers using alternate-row spraying during the early part of the season may wish to switch to every-row spray applications if the disease has been a problem over the years. What about other diseases? If powdery mildew, caused by the fungus Uncinula necator, has been a problem in the vineyard in previous years, fungicide applications should be considered now. Fungicides for black rot (Guignardia bidwellii) management can be used now, especially if black rot was a serious problem last year. Otherwise, growers could wait until further shoot growth and bloom development. Downy mildew (Plasmopora viticola) treatments can also wait. Treatments at 10-inch shoot growth and at early pre-bloom and bloom stages are important for management of black rot and downy mildew. Growers in warmer parts of the state may already be at the 10-inch shoot growth stage and will want to take steps to manage all four of these diseases. Conclusion: For the 3-5-inch growth stage with bloom clusters just visible, growers may want to consider mancozeb, captan, or ziram for Phomopsis cane and leaf spot. See U.K. Cooperative Extension Publication ID-94 “Midwest Commercial small Fruit and Grape Spray Guide 2009" for details of rates and timing. For powdery mildew, use one of the many fungicides listed for powdery mildew in that publication. Some of the material for this newsletter was adapted from an article, Grape Disease Control 2009 written by Wayne Wilcox of Cornell University. Trade names are used to simplify the information presented in this newsletter. No endorsement by the Cooperative Extension Service is intended, nor is criticism implied of similar products that are not named. Figure Legends:
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Bacterial Soft Rot Found in the Bluegrass |
Blackleg – A Crime of Opportunity
The bacteria that cause blackleg are essentially parasites of wounded or stressed tissue, and are plentiful in soil and on leaf surfaces. Because the pathogens are always present, development of disease is dependent on a favorable environment and plentiful food (in the form of plant debris or wounded/stressed tissue). Factors that may lead to outbreaks of blackleg include: high nitrogen levels (> 150 ppm), warm temperatures (>75 °F), high humidity, long periods of leaf wetness, and plant injury (stress and wounding). The latter occurs routinely during clipping and can lead to rapid spread of bacterial soft rot if carried out when plants are wet. Cultural practices are the most important ways to prevent of bacterial diseases. Provide adequate ventilation to shorten the length of time that foliage stays wet – this may be the most important of all management practices to reduce the incidence of blackleg. Most outbreaks we see in Kentucky are associated with warm temperatures and excessive moisture on float plants. Avoid over-fertilizing, a practice referred to as “pushing” seedlings, as this leads to dense, lush growth that is more susceptible to disease and takes longer to dry. Clip and handle plants only after they have been allowed to dry properly. Leaf debris left behind after clipping can serve as a starting point for the pathogens that cause blackleg and should be removed promptly. Along with maintaining good airflow in the float system, keeping as much leaf debris out of the beds as possible is a key to holding blackleg in check. Chemical options for control of blackleg are limited. Agricultural streptomycin can be used in outdoor plant beds to suppress bacterial diseases, but is not specifically labeled for use in transplant facilities. Because the use of agricultural streptomycin is not expressly prohibited in transplant production, however, EPA rules allow its use in the float system. Streptomycin provides only moderate suppression of blackleg, though, and growers who choose to apply the material in the greenhouse must accept all liability. Apply 3-5 gallons of a 100-200 ppm solution of streptomycin to 1000 sq. feet of float bed. This use rate translates to 0.5-1 lb per 100 gallons of water, or 1-2 teaspoons per gallon. Apply streptomycin before symptoms appear for best results, using the lowest rate. Use the 200-ppm rate immediately after the appearance of symptoms of blackleg. Some plant injury may be observed when applying the higher rate. Refer to the product label and the “2009 Kentucky-Tennessee Tobacco Production Guide” (ID-160) for more information. The guide can be found online at www.uky.edu/Ag/TobaccoProd/pubs/id160.pdf.
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| Cutworms Can Cause Early Problems in Tobacco Fields By Lee Townsend |
Dense low-growing weeds are selected by female moths as ideal places to lay a few eggs. These plants will serve as food for the developing cutworm larvae. When the weeds are killed or turned under, the cutworms suddenly are left without food. Newly-set transplants fill this void and the cutworm larvae quickly resume feeding. Cutworms are already present in infested fields before transplanting but there is not a good way to determine whether or not they are present or how abundant they may be. The extent of weed flush in the field over the last few weeks is the best indicator, along with reports of cutworm are in nearby communities from fields that have already been set. Capture and Orthene are labeled for cutworm control as transplant water applications. With this approach, the treated area is immediately around the plant roots. Control may not be considered satisfactory if there is a large number of cutworms in the field or if they are large (> 1.5 inches). Lorsban and Capture may be used as pre-transplant soil applications, as an alternative to the transplant water use. Capture, Orthene, or Warrior can be used as broadcast rescue treatments if cutworms are found transplants in the field. Cutworms feed at night or on overcast days and hide in the soil during the day. If soil is moist, they may feed on leaves in contact with the ground. In dry soil, they are more apt to stay below the surface and feed on stems, cutting off plants. The first signs infestations can be feeding holes at the leaf edge or cut, wilted plants. |
| IR-4 Project:Filling a Needed Role By Ric Bessin |
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| By Julie Beale and Paul Bachi |
On fruit and vegetable samples, we have diagnosed anthracnose on strawberry; Phytophthora root and crown rot on raspberry; leaf curl on peach; Sclerotinia stem rot on tomato. On ornamentals and turf, we have seen Botrytis blight (“fire”) on tulip; bacterial blight on lilac; Volutella canker on boxwood; Phyllosticta leaf spot on cherrylaurel; black root rot on holly; black spot on rose; fireblight on ornamental pear; Rhizosphaera needle cast on spruce; Phytophthora leaf blight on pieris and rhododendron; Phytophthora root rot on crabapple and pine (from nursery); Rhizoctonia large patch on bentgrass; and red thread on bluegrass. |
| By Patricia Lucas | |||||||||||||||||||||
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NOTE: Trade names are used to simplify the information presented in this newsletter. No endorsement by the Cooperative Extension Service is intended, nor is criticism implied of similar products that are not named.
European pine sawfly larvae are voracious feeders that can strip old needles from Mugo and Scotch pines; occasionally, they will attack Austrian and white pines. The green-gray larvae have shiny black heads and narrow dark stripes along the body. They are about 1-inch long when mature.
Warm, humid conditions in the float bed are the ideal environment for Erwinia carotovora subsp. carotovora and other bacterial species that cause blackleg. Initially, organic matter in trays, or wounded tissues, are colonized by the blackleg pathogen. Debris and leaf tissue infected by Erwinia appear necrotic and “slimy” (Figure 1, top left). Systemic infections, which arise when Erwinia moves from debris or wounded tissues into healthy plants, result in darkening of the stem that tends to move up one side of the seedling primarily, hence the name “blackleg” (Figure 2, top middle). Affected areas of the stem may also show splitting, and in advanced stages, seedlings will collapse. Under favorable conditions, blackleg will spread rapidly, causing significant loss of useable transplants in as few as 1-2 days (Figure 3, top right).
While serious black cutworm infestations in tobacco fields are not common, they occasionally can strike hard. The potential is greatest in conventionally-tilled fields where winter annual weed growth was evident for several weeks prior to final field preparation and a significant number of cutworm moths have been flying. Degree-day accumulations and moth captures indicate that the first black cutworms should be reaching the cutting stage during the first week of May in southern and western Kentucky. Moths have been flying since the second week of March and are still active so cutworm damage can be expected over the next 3 to 4 weeks.