Recall that the US EPA and the Kentucky Department of Agriculture granted approval on July 29, 2004 to use Quadris Flowable Fungicide in Kentucky burley and dark tobacco fields under a Section 18 Crisis Emergency Exemption. Foliar fungicide sprays were authorized from July 29, 2004 to October 15, 2004, unless ordered to stop earlier. EPA did not order earlier cancellation; consequently, this exemption expires at midnight, October 15, 2004. Applications of Quadris for use in tobacco are not authorized after this date, even if the product was purchased during the authorized period for tobacco use. Quadris is labeled for many other crops grown on Kentucky tobacco farms so finding legal applications for carry-over product is not anticipated to be a problem.
Representatives from Syngenta, the company holding the label, indicated that a national label for using Quadris on tobacco is being seriously pursued. However, best estimates are that the national label will not be available for use during the 2005 crop season.
The trade agreement established between the United States (U.S.) and The Peoples Republic of China (China) in 2001 allowed U.S. flue-cured and burley tobaccos to be imported into China. Those protocols allow China to import dried U.S. tobacco that is free of active tobacco blue mold oospores. This spore stage is the product of sexual reproduction by the agent causing blue mold, Peronospora tabacina, and is known to be an over- wintering, survival stage of some other downy mildews in the genus Peronospora. Fortunately, the oospore stage is not commonly found in U.S. tobacco during blue mold epidemics, but it does occur sometimes. The reasons for this difference and the conditions necessary for oospore formation in tobacco are not understood. Consequently, the trade agreement requires that all U.S. tobacco exported to China will be inspected for blue mold oospores at two points before shipment - in the production fields and in the shipping containers.
During July and August of 2004 the University of Kentucky College of Agriculture, coordinated by the Plant Pathology Department, assisted this marketing effort by conducting the field survey for oospores in direct support of Kentucky's burley growers, the Kentucky Office of State Entomologists, and USDA APHIS PPQ. The field inspection-survey for the 2004 crop involved County Extension Offices from 80 counties, because blue mold was widespread about the state this season. This survey involved collecting green leaf tissues from 80 counties with blue mold lesions taken directly from the field during the active period of the 2004 epidemic, as per the protocols established by USDA. The samples were submitted to an independent laboratory at North Carolina State University under contract with the USDA APHIS, which performed the required assays.
We recently learned that NO OOSPORES were found during microscopic examination of the Kentucky samples by the laboratory conducting these tests for the USDA APHIS PPQ. Their findings are consistent with our laboratory observations on companion samples from these sites as well as many other observations made during diagnostic events this season. These data should place Kentucky's tobacco in good standing for exporting again to China, assuming consistent results are obtained from neighboring states that also had blue mold since the burley tobacco exported from here also contains tobacco from our neighbors in Indiana, Missouri, Ohio, and West Virginia.
China has successfully imported burley tobacco in 2003 and 2004 from the Burley Tobacco Growers Cooperative Association based in Lexington, Kentucky.
For the latest blue mold status and other tobacco disease information, check the KY Blue Mold Warning System online.
Northern leaf blight (NLB) was more severe in Kentucky this past season than in any since I joined the faculty at UK in early 1990. The cool, wet, cloudy weather than prevailed during most of the 2004 season in many areas played a major role in disease development. Wet weather with temperatures in the range of 64-81oF favors infection and spore production by the fungus that causes NLB (called Setosphaeria turcica, but also known as Exserohilum turcicum and Helminthosporium turcicum). Furthermore, extended cloud cover favors the disease by making plants of a susceptible corn hybrid much more susceptible to disease activity than when growing under sunny conditions.
However, my concern is that the unusual weather was only part of the picture, as there are some indications of a possible trend of increasing pressure from NLB. A respected and highly experienced corn pathologist from a neighboring, major corn-producing state reported to me that the incidence of this disease has increased over the past 4-5 years. Records from the UK Plant Diagnostic Laboratories are certainly consistent with this. The weather this past season certainly played a role in the severe outbreaks observed, as explained above. However, the question is, are adequate levels of resistance to NLB available in the commercial hybrids being sown in the region? This question is especially critical given the high inoculum levels that are now present on many farms. At this time we don't know the reason for the apparent increased severity of NLB over the past several years. It could be due to a new race of the fungus. Alternatively, it could be due to an unintended erosion of partial resistance in the currently available hybrids to NLB as breeders focused on other priorities. It may simply be due to prevailing weather patterns. This issue is currently being researched by pathologists in the Midwest; I'll know more in a few months.
Some Biology of NLB
Symptoms of NLB are elliptical, grayish-green or tan lesions 1 to 6 inches long with smooth margins. The large ones are typical for a susceptible hybrid growing under cool, cloudy, wet conditions. During damp weather, greenish-black fungal sporulation is produced in lesions. Older leaves are affected first. Severely affected leaves can be killed when lesions coalesce.
The fungus survives in undecomposed corn residue. Spores are spread by air currents. Severe yield loss can occur when upper leaves become blighted during early grain fill. Strains of the fungus also infect sorghum, johnsongrass, and sudangrass, although strains that attack these plants do not attack corn.
Factors That Can Favor NLB Development
Producers should consider the level of susceptibility to NLB for all hybrids to be planted in 2005, but especially in or near fields under conservation tillage where NLB occurred this past season. The law of averages suggests that next season is not likely to be as cool, cloudy, and wet as this past season, in which case many producers would "dodge a bullet". However, with the high inoculum levels that are present in certain areas, especially in western Kentucky, a repeat of the same kind of weather could result in destructive epidemics on susceptible varieties in some localities.
There are two types of resistance to NLB: complete resistance (more or less) and partial resistance.
In hybrids with (nearly) complete resistance, lesions form which are yellow and limited in size, and sporulation by the fungus is very limited. These are hybrids with one or more Ht genes. For example, on hybrids carrying an Ht1, Ht2, or Ht3 resistance gene, long, yellow to tan lesions with wavy margins and no sporulation are observed on leaves infected with S. turcica. These lesions are a resistance reaction and can be easily confused with Stewart's wilt.
More commonly, corn hybrids have partial resistance. In that case, NLB can still develop on the hybrid but it usually does so more slowly that on a fully susceptible variety.
Under many circumstances, a moderate to high level of partial resistance would be sufficient to control the disease. However, high to very high disease pressure, a hybrid with complete resistance would often outyield a partially resistant hybrid. Consider the factors discussed in the preceding section to decide which fields might need a substantial level of resistance to NLB in 2005.
We don't know what the weather will be in 2005. However, inoculum levels of NLB are high in some areas of Kentucky. Producers should carefully consider planting corn hybrids with moderate to high levels of resistance to NLB in 2005.
Thanks to Bill Meacham of Pioneer Hi-Bred for observations of the association of volunteer corn with NLB.
For information about corn pests, visit
"Insect Management Recommendations".
Straw itch mites were mentioned in the July 26, 2004 issue of KPN (#1031) as one of the organisms, including mites, that can be found in hay or straw. Although not blood feeders, if these acarines find themselves on humans, they will bite and the results can be very uncomfortable. Most reported outbreaks are occupational, affecting people who harvest or handle grains or hay. But, mites also may be picked up from straw used for mulching or decoration, or apparently even from passing through infested areas.
Two infestations have been reported from Kentucky this fall but are within the traditional occupational exposure routes. Investigations of some itch incidents in other states this year have led investigators down a very different path. Complaints of itchiness from parts of Nebraska, Kansas, and Missouri ended in the discovery of unusually large numbers of straw itch mites in oak leaf galls. Favorable temperature, relatively cool and wet, apparently led to explosions of the mites.
The straw itch mite (about 1/125 inch long) feeds on caterpillars, beetle larvae, and other small arthropods. Proteins, injected as the mites feed on their normal arthropod hosts, can inflict people with moderate to severe skin reactions and itching. The itching typically is noticed from 2 to 12 hours after exposure and by then the mites often gone. Skin reactions can include lesions and small, solid, raise areas that may have white tops. They most often occur on the back, abdomen, and around the waist. The lesions disappear in a few days, with or without therapy. Severe reactions in some individuals can include fever and vomiting. Oral antihistamines and topical anti-itch creams have been reported to be useful in alleviating the discomfort caused by the bites. In most cases the bites clear in one to two weeks. Persons with prolonged discomfort should see a physician.
People working with hay / straw) can gain some protection by using a repellent, such as deet, and by a thorough washing with soap and water immediately after possible exposure. These mites should decrease in numbers or completely disappear after a hard frost. There is no evidence that the bites transmit disease, nor that there is a person to person transmission of the mite.
As the growing season comes to an end, gardeners ask questions about diseases that affected their garden flowers, especially during this late season time period. This short list of questions and answers may be helpful to County Extension Agents responding to inquiries from their clients.
1. Question: What is causing the small brick-red leaf
spots on my aster plants?
Answer: In late summer and fall, garden asters are often infected with rust disease. Severe leaf rust usually leads to death of aster leaves and reduced plant vigor. There are several species of rust that occur on aster and a common aster rust in Kentucky is caused by the fungus Coleosporium asterum. Most rust fungi spend part of their life cycle on more than one host, often times completely different hosts. The alternate hosts for this aster rust fungus are 2 and 3-needle pines which, when infected, show needle rust symptoms. One of the possible but often impractical means of controlling the rust is removal of the alternate host from the surrounding area. The remaining option is to spray the plants with a fungicide to protect the plants from infection by the rust fungus. There are several fungicides available to gardeners that will control rust diseases in the home garden. Check the fungicide label for spray rates and timing to manage aster rust.
2. Question: Why did rose leaves develop black spots,
turn yellow, and drop all summer long?
Answer: Black spot, caused by the fungus Diplocarpon rosae is the most common problem of roses grown in Kentucky gardens. This disease is favored by wet summer weather. Infected leaves develop black spots and the leaves respond by turning yellow and falling from the plant leaving the rose with less energy to produce flowers. Some popular roses are so susceptible that in order to produce acceptable flowers they require spraying every week. There are many home garden fungicide products available for rose disease management. However, black spot resistant roses are also available. Keep rose foliage dry by avoiding sprinkler irrigation. See U.K. Cooperative Extension publications ID-118 Roses, and Plant Pathology fact sheet PPFS-OR-W-06 Black spot of Rose for more information on growing roses and on rose black spot disease management.
3. Question: Why do peony leaves and foliage develop
spots and blotches and then die by late summer?
Answer: There are several peony leaf diseases which can cause foliage symptoms and death. The most common of these is Botrytis blight (gray mold) caused by the fungus Botrytis cinerea.
This fungus can infect shoots, stems, leaves, and flowers anytime during moist periods in spring and summer, causing infected parts to turn brown and die. Another disease, caused by the fungus Cladosporium paeoniae, causes small red spots which can coalesce to form irregular purple blotches on leaves and stems. Red spot can lead to deterioration of peony foliage by late summer as can several other leaf spots caused by fungi such as Alternaria, Cercospora, Septoria, and other fungi. All of these fungal diseases of peony are favored by wet weather and infections begun in spring may eventually cause severe symptoms later in summer. Gardeners can reduce disease in the following ways: increase plant spacing to improve air circulation and keep humidity lower, prune away shading vegetation from nearby trees and shrubs, avoid wetting foliage when watering, remove and destroy diseased foliage and blighted stems in the fall. Fungicides are available for home garden use to help prevent peony foliar diseases. Check fungicide labels for timing and rates to use for peony diseases.
4. Question: Why do leaves of phlox plants turn white
Answer: Perennial phlox plantings in Kentucky are subject to powdery mildew disease, caused by the fungi Erysiphe cichoracearum and Sphaerotheca humuli. Signs of powdery mildew appear as a superficial white powdery growth on leaf and stem surfaces. Infected leaves may shrivel up and die. Although the disease does not kill plants, it reduces aesthetics and flower production. Where possible, choose varieties that have resistance to powdery mildew. Reduce humidity in phlox beds through wider spacing, full sun exposure and judicious watering. Fungicides are sometimes beneficial. Check the fungicide label for rates, timing and use for garden phlox. See U.K. Plant Pathology fact sheet PPFS-GEN-2, for more information on powdery mildew on ornamentals.
5. Question: Why do zinnias in the garden develop leaf
blight or mildew, and decline and die?
Answer: There are two important zinnia leaf spots in Kentucky, one bacterial, caused by Xanthomonas zinniae, and the other fungal, caused by Alternaria zinniae. Bacterial leaf spots are small, angular, brown spots often surrounded by a yellow margin. Alternaria leaf spots are larger and reddish brown with grayish centers. Both diseases result in leaf blighting, and death of foliage, and eventually plant death. Powdery mildew, covering leaves with grayish white superficial growth also causes foliage to die. Some of these zinnia diseases are seed- borne, so purchase seeds from a reliable source. Fungicides may be beneficial for powdery mildew and Alternaria leaf spot, but will not control bacterial leaf spot. Avoid wetting foliage while watering. Fall garden clean-up will help to reduce carry over of inoculum for next year's plantings.
Clients soon will be calling about lady beetles congregating on the sides of homes and infesting buildings. This phenomenon has become an all-too- common autumn event throughout Kentucky and much of the United States. The culprit is the Asian lady beetle, Harmonia axyridis, in search of protected places to spend the winter. In Kentucky, movement into buildings typically begins in mid-October, continuing through mid-November.
Detailed information on this perennial problem is contained in ENT-64, Asian Lady Beetle Infestation of Structures. Key points include:
Homeowners insistent upon applying exterior treatments themselves will usually get the most for their efforts using over-the-counter versions of these products such as Spectracide Triazicide or Bayer Advanced Powerforce Multi-Insect Killer. Purchasing the concentrated formulations of these products that can be diluted will enable the homeowner to mix up and apply larger volumes of material with a pump-up or hose-end sprayer. In order to have any benefit, exterior treatments must be applied before the beetles enter buildings to overwinter.
Diagnostic lab samples over the past two weeks have included Diplodia and Fusarium ear rots on corn; Rhizoctonia root rot on alfalfa; white rust on mustard; black rot and Rhizoctonia stem rot on kale; and Cercospora leaf mold on tomato.
Ornamental samples were common and many showed symptoms of stress from abiotic causes, especially transplant shock in woody plants transplanted within the past two to three years. Other diagnoses in ornamentals included Phytophthora root rot on ginkgo; Verticillium wilt on maple; and Botryosphaeria canker on yellowwood.
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.
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