Several weeks ago, I reported on Diplodia ear rot activity (http://www.uky.edu/Agriculture/kpn/kpn_04/pi040816.htm). This disease was favored by the very wet weather most areas experienced through the silking period this summer. Diplodia ear rot appears as a white, cottony fungal growth between kernels. The rot commonly progresses from the ear shank upward and from the cob outward, the result of infection of the shank. This year, infections have often progressed downward from the tip of the cob. These "topdown" infections appear to occur through the silk channel and were probably favored by the unusually sustained periods of cloudy, wet weather this summer. Grain affected by Diplodia ear rot has reduced feed value and may even be unpalatable in some cases, but it is not known to be contaminated with mycotoxins here in the U.S.
Regional reports indicate that another ear rot disease Gibberella ear rot is also present in some corn fields. Normally, weather conditions are too cool for this ear rot in Kentucky, but the sustained periods of unusually cool, wet weather after silking put many corn crops at risk this season. Gibberella ear rot appears as a white to pinkishwhite mold that grows from the tip of the ear downward. The fungus that causes this ear rot also causes the very familiar disease, Fusarium blight of wheat, also known as "head scab". Like wheat, corn infected with this fungus can be contaminated with mycotoxins. There are two mycotoxins of concern: deoxynivalenol (DON, also known as vomitoxin) and zearalenone. Although these toxins can pose risks for all livestock feeds and human foods, swine are particularly sensitive to DON and zearalenone. Details on the risks these mycotoxins pose to humans and livestock are available in the Kentucky Cooperative Extension publication, Fumonisin, Vomitoxin, and Other Mycotoxins in Corn Produced by Fusarium Fungi, available through county Extension offices or at http://www.ca.uky.edu/agc/pubs/id/id121/id121.pdf. Because silk end infections of Diplodia ear rot have been common this year, it may be difficult for field observers to distinguish these ear rots this year. Thus, corn with a notable level of ear rot should be checked for mycotoxins before being utilized. Laboratories specializing in testing grain for mycotoxins include the UK Grain Quality Testing Laboratory in the UK Department of Biosystems and Agricultural Engineering and other laboratories listed in the publication available at http://www.ca.uky.edu/agcollege/plantpathology/PP AExten/PPFShtml/ppfmisc1.htm.
For information about corn pests, visit
"Insect Management Recommendations".
Soybean Sudden Death Syndrome (SDS) has been fairly common this year, but in my opinion, few fields will be significantly impacted. Often this disease does not live up to its name: it is usually not sudden, and it is often not death. A better name would be "Soybean Slow Occasional Death Syndrome".
SDS is usually a disease of fullseason soybean; doublecrop soybean is rarely affected, at least not significantly. This has to do with the fact that SDS is primarily a root disease and infection of roots by the causal organism, Fusarium solani f. sp. glycines (now being called F. virguliforme by some) is favored by cool, wet soils conditions that tend to exist when fullseason soybean is in the seedling to preflowering stages. Conversely, soil conditions tend to be warm and on the dry side when doublecrop soybean is in the same stage range.
This year, probably due to the unusually cool and moist early summer conditions, SDS is fairly common in many doublecrop fields. This situation has many producers concerned, and rightly so, since SDS in doublecrop soybean is so rare. Fortunately, the dry late summer conditions has tended to stop SDS in its tracks where it is occurring. Thus, it does not appear that SDS will cause serious yield damage in most doublecrop fields.
For more information about soybean pests, visit
"Insect Management Recommendations".
According to pheromone trap catches, early September fall armyworm moth flight at the UKREC at Princeton has been about 10x that of the comparable period for last year. This can mean damage to earlyseeded cover crops, forages, rights of way, or lawns. FAW prefers grasses but also can show up in alfalfa.
Egg hatch and larval development slows with cooler temperatures so we are just reaching the time to check for spreading brown patches in new seedings. The initial damage is clumped around the sites where females lay masses of several hundred eggs. These clumps can spread rapidly as the larvae grow and feeding increases.
Be suspicious of and investigate dry spots that might be written off to shallow soils or lack of rain. Careful hands and knees evaluation of the edges of these areas can catch damage early. Look for damaged seedlings, droppings of the worms, and check in soil cracks and under surface litter for the striped caterpillars. They will be hiding during the day. Averages of more than two one half to 3/4inch long worms is a good indication that treatment is justified. Limited treatment of "hot spots" can keep damage from spreading over larger areas of the field.
Year in and year out, Sclerotinia crown and stem rot is the most serious disease threat to fallseeded alfalfa in Kentucky. However, this year, the unusually wet weather in August and September in some areas provided infection opportunities for another common fungus called Rhizoctonia solani. A latesummer seeding into soil with a high content of fresh organic matter, such as disced crop residue, coupled with sustained wet weather, favors this disease.
Affected plants appear stunted, yellow, and possibly wilted or red. Careful examination of the lower stem and upper taproot reveals small light brown to dark brown lesions. If the symptoms are not evident on the plant surface, sometimes cutting into the tender plant will reveal the discolored stem/root tissue. Even small areas of discoloration inside can result in severe stunting, since this rot interferes with the vascular system of the plant.
There is no specific control measure for this disease, although it is usually a serious problem only in the establishment year in Kentucky. Thus, if an acceptable and vigorous stand remains after spring greenup, the disease has probably done all the serious damage it is likely to do.
See Insect Recommendations
for more alfalfa pest recommendations.
When harvesting fruit this fall, growers should watch for insect pests that may have escaped detection during the season. One serious pest that can affect the health of the tree is the woolly apple aphid. This aphid is not usually controlled by the insecticides that are commonly used in commercial orchards, and in years following periodical cicada attack, they may be found infesting wounds on the trunks and branches.
The woolly apple aphid differs from other apple aphids in appearance, life cycle, and the type of damage inflicted. A colony appears as a cottony mass generally clustered in wounds and pruning scars on the trunk and branches of the tree. The aphids themselves are purplish in color surrounded by white, cottony, threadlike secretions. Woolly apple aphid is a sucking insect pest that weakens the tree by feeding on limbs and roots. It gets its name from the woolly appearance of its colonies. Long strands of white wax are produced that help to protect the colony of purple aphids from predators and pesticide sprays.
Woolly apple aphid is a serious pest of apples, particularly young trees. Colonies form at wound sites on trunks, limbs, and twigs, where they feed on tender bark. Pruning and hail damage can create the wound sites for attack by this pest. Egglaying wounds by the periodical cicada are ideal sites for infestation. As populations grow, aphids are commonly found on water sprouts in the center of the tree. The tree will begin to swell and form galls at the feeding sites.
As the number of aphids on the above ground portion of the tree increase, many work their way down to the roots and trunk below ground surface. It is the feeding on the roots that produces the greatest damage. Mature trees usually suffer little damage from the root infestations, but the root infestations are very damaging to young trees. Control of these aphids is very difficult when they attack the roots. Yellowish foliage is a sign that woolly apple aphid may be infesting roots. The root systems of nursery stock can be damaged, and severe root infestations can stunt or kill young trees. Infested trees often have short fibrous roots, which predisposes them to being easily uprooted. Swollen galls also form on roots; galls increase in size from year to year and are sites where fungi can attack. Aphid feeding on the root systems also disrupts the nutrient balance of root tissue, which can affect growth of other parts of the tree. Trees can have aboveground infestations of woolly apple aphid but no root infestations. Rootstocks vary in susceptibility to woolly apple aphid and susceptible rootstocks will form galls around the infestation sites. Use M111 or M106 if woolly apple aphid is a serious problem. Rootstocks appearing more susceptible to woolly apple aphid infestation include B9, M9, M26 and the P series.
During the summer, repeated woolly apple aphids generations of wingless individuals are produced. In the fall, winged individuals are produced which fly to search for elms on which to lay overwintering eggs, while some wingless forms may remain on both above and below ground parts of the apple tree throughout the winter.
Woolly apple aphid colonies produce honeydew, which results in development of black sooty mold. The wax and the honeydew are bothersome to pickers when it brushes off the tree and onto clothing of pickers.
It is relatively easy to find where the colonies have formed. When monitoring for woolly apple aphid, examine four pruning scars on each of 5 scaffold limbs per tree. Carefully examine woolly apple aphid colonies to determine if live aphids are present. Predators, such as lady beetles, Syrphid fly larvae, and lacewing larvae can completely destroy the colony, but the waxy residue will remain. When examining colonies, blow hard on the branch to remove the waxy filaments to reveal live aphids. Treatments for woolly apple aphid are recommended when 10% of the pruning scars are infested with live colonies.
There are few insecticides specifically labeled for control of woolly apple aphid. Thiodan is recommended for control of aboveground infestations. There are no insecticides to control root infestations on bearing apple trees.
Despite publicity about the threat of Sudden Oak Death disease, caused by the funguslike Phytophthora ramorum (which has not yet been confirmed in Kentucky), we must not lose sight of the fact that we continue to lose trees to bacterial leaf scorch caused by Xylella fastidiosa. Symptoms of scorch and defoliation are very visible now. Especially hard hit are the mature pin oaks lining many urban streets and red oaks growing in the landscape. Even mature sugar maples are seen now losing leaves to this disease. Where trees are being lost, replacements will be needed. Do not give up on replanting where trees have died from bacterial leaf scorch!
Where bacterial leaf scorch has been a problem, avoid species that are susceptible to this disease. In Kentucky, the disease has been found on pin, red, bur, white, scarlet, shingle, and willow oaks; sycamores and London planes; sugar, red, and silver maples; hackberry; elm; mulberry; and sweetgum. To prevent catastrophic tree losses due to diseases or insects, the diversity of the urban forest should be increased by not planting the same kinds of trees that are already present in high numbers in neighborhoods, cities and towns.
The following is a list of trees that mature to a large size. These trees are not known to be susceptible to bacterial leaf scorch and thus might make suitable replacements for trees lost along streets, in parks and in yards. Some may have other drawbacks. Readers are urged to learn more about the habits of these trees and, if they are to be used as street trees, to ascertain whether or not they are permitted by the local municipal arborist or tree authorities. One good source of information, with illustrations, is a CD, "Large Trees for Kentucky Landscapes," written and developed by Robert Geneve and Christy Cassidy of the U.K. Horticulture Department.
Large trees not yet affected by bacterial leaf scorch. Alder. European black alder, Alnus glutinosa, and cultivars. Ash. Blue Ash, Fraxinus quadrangulata; white ash, F. americana, and cultivars; green ash, F. pennsylvanica, and cultivars. Beech. European beech, Fagus sylvatica, and cultivars. Black gum. Tupelo, Nyssa sylvatica. Buckeye. Yellow buckeye, Aesculus flava. Catalpa. Northern catalpa, Catalpa speciosa. Cork tree. Amur cork tree, Phellodendron amurense, and fruitless male cultivars. Elm. Lacebark, or Chinese elm, U. parvifolia Ginkgo. Ginkgo biloba, and fruitless male cultivars. Hackberry. Sugar hackberry, Celtis laevigata; however, since common hackberry, C. occidentalis is susceptible, sugar hackberry may be a risky choice. Hickory. Shagbark hickory, Carya ovata; shellbark hickory, C. laciniosa; and pignut hickory, C. glabra. Katsura. Katsuratree, Cercidophyllum japonicum. Kentucky Coffeetree. Gymnocladus dioicus, and fruitless male cultivars. Linden. American linden, Tilia americana; littleleaf linden, T. cordata. Magnolia. Cucumbertree, Magnolia acuminata. Maple. Black maple, Acer saccharum subsp. nigrum. Although the disease has not been detected on black maple, the fact that it occurs on three other maples in Kentucky might make this a risky choice. Oak. Chestnut oak, Quercus prinus; chinkapin oak, Q. muehlenbergii; sawtooth oak, Q. acutissima; shumard oak, Q. shumardii; and swamp white oak, Q. bicolor have not been seen with bacterial leaf scorch. However, the fact that it occurs on seven other oaks in Kentucky would make any of these risky choices. Osage Orange. Maclura pomifera, and fruitless male cultivars. Sassafras. Sassafras albidum. Tulip poplar. Tuliptree, Liriodendron tulipifera. Zelkova. Japanese zelkova, Zelkova serrata, and cultivars.
|UKREC-Princeton, KY, September 13 - 17, 2004||Black Cutworm
||European Corn Borer
||Southwestern Corn Borer
|UKREC-Princeton, KY, September 20 - 24, 2004||Black Cutworm
||European Corn Borer
||Southwestern Corn Borer
You can now view trap counts for the entire season on the IPM web site. From the opening page found at http://www.uky.edu/Agriculture/IPM/ipm.htm , click on Pheromone Trap Counts. Then click on "2004 Data" to view or you can go directly to the 2004 data at http://www.uky.edu/Ag/IPMPrinceton/Counts/2004trapsfp.htm.
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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