This is a difficult blue mold advisory to develop so early after a week of wet weather followed by a weekend of very hot weather events, complicated furthermore by highly variable crop stages. But the news is good. The immediate threat of a blue mold epidemic in Kentucky should be over for most crops and greatly reduced even for the worse cases, following the very hot and sunny weather of this past weekend. But, crops located in communities and field sites experiencing cooler temperatures could still have blue mold. Tobacco growers should adjust their controls accordingly.
Blue mold is highly weather-sensitive, so its activity fluctuates sharply with weather extremes. The most favorable conditions for blue mold development in burley tobacco are: a strong source of active disease located in the prevailing wind path, the presence of rapidly expanding tobacco leaf, wet leaves at nights with temperatures between 65-70, and overcast days with temperatures not reaching the mid 80's, plus a light wind to move the spores. When all these favorable conditions are present, blue mold can cause great damage. However, if any one condition is missing, the disease potential declines, and when multiple factors are missing, the potential for economic damage is not present. Most of the factors necessary for blue mold to seriously threaten Kentucky's tobacco crop do not currently exist, following the major change in weather.
During the past week, blue mold development in Kentucky has gone from approaching epidemic potential to near cessation of activity. The potential for an epidemic in late July is over for most crops. Therefore, growers should carefully reconsider the current disease potential and economics of their particular situation before making decisions about future fungicide use. There will be individual cases where fungicide use is clearly warranted (e.g., shady fields, irrigated fields, river bottoms, and low-lying areas), but in most areas of Kentucky the blue mold potential has declined so sharply that fungicide applications are no longer needed this season for crops within 10 days of topping or older. Younger crops will need to be monitored closely and fungicide decisions reconsidered regularly, based on current situations. Tobacco crops at all stages throughout most of Kentucky will remain at low risk of blue mold development, however, until cooler and wetter conditions return.
Based on close monitoring in several fields and research plots in central and eastern Kentucky late last week and over the weekend, here is my evaluation of the situation. Much of Kentucky's tobacco crop experienced ideal conditions for blue mold infections between July 18 and 24, resulting in a rapid increase in activity (massive sporulation, new infections, and lesion expansion), especially in central and eastern Kentucky. The visible symptoms and signs resulting from these events will still be occurring until the end of July. However, very hot weather (the hottest of the crop year) was experienced on July 25-27, which will immediately impact the developing lesions, altering sporulation and symptoms.
The stage of fungal development within the leaf at the time of the high-temperature events will greatly determine symptom and sign development. Lesions developing from infections of July 21 and 22 could have developed symptoms faster than normal, within 4-6 days, and would have been ready to sporulate strongly on July 26 and 27 had high daytime temperatures not interrupted the process. Where infection rates were high, the amount of necrotic leaf tissue can be large, resemble scalds, and be easily confused with other disorders, because fungal sporulation is not obvious. Where high temperatures occurred before the fungus was ready to sporulate, host damage may occur as yellow spots, without sporulation - sterile lesions. Where high temperatures occurred within 2 to 4 days of infections, developing lesions should be much smaller than normal, occurring as small spots to flecks, either necrotic or yellow, but without sporulation - very different from normal blue mold. Where temperatures did not reach the mid-90's long enough, lesions may appear near normal, but with reduced sporulation. How much of this type lesion is present needs to be determined in ALL communities. In contrast, lesions resulting from infections on July 18-20 were typical for blue mold on July 24-25. One agronomist described them on July 24 as: "This morning's new lesions are a pathologist's dream and a tobacco farmers nightmare." However, most of these same lesions and even newer ones did not sporulate (production of new spores) on the mornings of July 26 and 27, plus the center of these lesions rapidly became necrotic (dead tobacco tissues) with small yellow margins. On the morning of July 28, I observed 6-day-old lesions that appeared to be 10-14 days old.
An abundance of new blue mold symptoms (lesion) may still appear during late July and cause damage, because of infection events of last week that were not controlled. However, they should not pose a new and serious threat unless they are producing NEW spores. Sporulation should be very limited from lesions of all ages following the high temperatures experienced recently, thus, greatly reducing the disease potential because inoculum is limited.
Are new spores being produced from either new or old lesions? This is the key question to be answered in each tobacco producing community with the next cool and wet events. Only if new spores are being produced, does the fungus still threaten. Until the fungus has enough time to rebuild its spore-load, little damage can occur, unless a large mass of spores blows in from other production areas, such as western North Carolina or east Tennessee.
Active blue mold has been confirmed during the past 10 days in the following Kentucky counties:
Two other counties have had confirmed cases earlier but no active cases were reported in the past 10 days - SHELBY and HARRISON.
Single, wilted leaves on tobacco plants usually are the result of feeding by stink bugs. Usually, the damage is done by either the brown or the one-spotted stink bug. Both are about " long brown, shield-shaped insects with a light yellow underside.
Enzymes injected into the plant by the sucking mouthparts as stink bugs remove sap will cause that leaf to wilt or collapse. On hot sunny days wilted leaves can be scalded. Frequently the leaf will recover and the only permanent damage is death of tissue in about a quarter-sizes or larger area immediately around the feeding site. The dead tissue will drop out leaving holes surrounded by yellow to brown areas.
Initial symptoms require several hours to develop so the culprit is long gone by the time the injury is apparent. Consequently, insecticide sprays in response to symptoms are useless. Stink bugs are good fliers and move frequently from plant to plant as well as into and out of the field. Because of their transient nature and generally minimal damage, insecticide applications specifically for stink bug are rarely justified.
Tobacco hornworms can be found in virtually all fields at this time of year. They do the bulk of their feeding from the time they are 1-1/2" long until they are full grown (about 4"). If control is necessary, treat when most are 1" to 2" long. While it is convenient to apply an insecticide with the sucker control material, the timing may not be good. The effective life of most of the insecticides used at this time is 3 to 7 days. If hornworms happen to be present, then control should be good. However, moth flight lasts for many days and hornworms that escape the treatment can be very damaging. Continue to examine fields at weekly intervals between topping and harvest. Treat when there are 5 or more healthy hornworms per 50 plants. See ENT-15, Insecticide Recommendations for Tobacco.
Parasitized hornworms can be recognized by the small, white, football shaped cocoons along their backs. Fields should not be treated if a significant proportion of them are parasitized.
Throughout the state, second generation corn borers are active. Moths from the first generation have emerged and begun to lay eggs. Producers of corn and peppers need to be monitoring for this pest. Corn producers should give special attention to late planted fields by searching plants for egg masses and signs of borer feeding. Examine closely the lower surface of leaves and at the ear. Check the middle one-third of each plant for damage and live larvae. Second generation larvae are usually found feeding at the base of leaf sheaths.
Treatment is suggested in field corn if egg masses average one per plant and egg hatch has begun or if 50% of plants inspected have live larvae feeding on the leaves or tassels in leaf axil or behind sheaths. If your examination indicates that half of the larvae have entered the stalk, insecticide treatment is not recommended. See ENT-49 for more information.
Wheat spindle streak mosaic (WSSM) is an annual problem in many Kentucky wheat fields. However, only rarely does this soilborne virus disease become as widespread, severe, and long-lasting in susceptible varieties as it did this spring. Normally some fields will show the characteristic yellow dashes of WSSM, but symptoms will disappear as temperatures warm in late April. In contrast, symptoms this spring often remained visible throughout the season, and contributed to premature crop maturity and apparent reduced yields. Increased problems with WSSM this spring are thought to be due to the abnormally cool weather we experienced in April and the first half of May.
Wheat producers do not like to see diseases in their fields and this is understandable. However, big disease years give us the opportunity to assess varietal differences which can help farmers avoid disease problems in future years. The last year we were able to make "good" WSSM ratings was in 1993.
The following table indicates our most current WSSM ratings according to level of resistance or susceptibility . If you had a problem with WSSM this spring, it would be prudent to select a variety for planting this fall which is rated at least moderately resistant. You never know when we'll have another serious WSSM year, so it is best to only plant varieties with some resistance in fields which have a history of the disease.
| Variety | WSSM Reaction | Variety | WSSM Reaction |
|---|---|---|---|
| Beck 103 | MS | Becker | MS |
| Caldwell | S | Cardinal | MS |
| Clark | R | Clemens | MS |
| EK 102 | S | EK 114 | S |
| EK 309 | S | Elkhart | S |
| Ernie | MS | Featherstone 520 | S |
| FFR 523 | S | FFR 525 0 | VS |
| FFR 555 | MS | FFR 558 | S |
| Foster | MS | Glory | R |
| Hopewell | MR | Jackson | S |
| KAS Justice | MS | KAS Patriot | MS |
| Madison | R | NK Coker 9543 | MS |
| NK Coker 9663 | S | NK Coker 9704 | S |
| NK Coker 9803 | MS | P2510 | R |
| P2540 | R | P2548 | VS |
| P2568 | R | P2552 | R |
| P2684 | MS | P2737 | MR |
| Patterson | MR | Pocahantas | S |
| Terra SR 204 | MS | Terra SR 205 | MS |
| Terra SR 211 | MS | Verne | MR |
| Voris 6044 | MS | Wakefield | S |
Ratings are based on observation of replicated plots and/or multiple field observations.
Good news with beet armyworm. Pheromone trapping by USDA-APHIS gypsy moth surveyors indicates that beet armyworm moth activity remains low. The USDA scouts are monitoring beet armyworm moth activity in 34 counties in western, central, and eastern Kentucky. Past trapping efforts have suggested that detectable fields problems are usually associated with moth captures of 30 or more per trap per week. So far this year, they are finding an occasional moth in the pheromone traps with no location exceeding 2 moths per trap per week. Since 1992, beet armyworm has been a sporadic and serious pest of peppers and tomatoes in Kentucky. Check the KPN for further updates.
Producers considering raising a fall crop of cabbage, broccoli or cauliflower to follow their spring crop need to use good cultural practices to avoid excessive insect problems. Because the spring cabbage crop was late this year, growers may need to make a special effort to quickly destroy remaining crop residues two to three weeks before setting their fall crop. Even though the marketable portions of the plant have been remove, the remaining leaves will allow insect pests to continue to develop and multiply.
Simply rotating the fall crop to a new field is not sufficient to avoid the problems caused by insect pest carry over from the spring crop. The common pests, including imported cabbageworm, diamondback moth, cabbage looper, and cross-stripped cabbageworm, can readily locate and move between fields. As soon as harvesting is complete, fields need to plowed or disked to destroy residues.
Application of a cattle grub treatment is one of the Kentucky CPH requirements. Cattle grub infestations necessitate more trimming of carcasses and decrease the value of hides. Grubby carcasses are routinely docked by packers.
Cattle grub control is a part of producing quality steers for the feedlot. While the damage (cysts or swellings long the backline) will not be evident for several months, control measures must be applied to Kentucky cattle before October 31 to kill the pest without harming the animal.
Host Reaction to Cattle Grubs
Depending upon the species, cattle grub larvae move either
to the esophagus (common cattle grub) or spinal column
(northern cattle grub)during their migration to the back.
The grub larvae are in these sensitive areas during
November and December. If large grubs are killed there, the
surrounding tissue can become severely inflamed and
additional symptoms can develop.
In animals infested with the common cattle grub, the esophagus can swell shut, and produce difficulty swallowing, drooling, or bloat. Northern cattle grubs killed in the region of the spine can put pressure on the spinal column. This results in stiffness in the hind quarters, loss of balance, or inability to lift the hind feet.
Be careful when treating for grubs. Use accurate weight estimates to determine the proper dose. Undertreating may not provide satisfactory control. At best, overtreatment will waste money; at worst, it may cause the animal to become sick.
There are a variety of formulations of cattle grub insecticides. Pour-on or Spot-On products are convenient if god handling facilities are available. High pressure sprays are a good choice when chutes or working pens are not an option. Animals must be wet to the skin when high pressure sprays are used. Ivomectin, used as a dewormer in the fall, will also control cattle grubs. There is no need to treat with an insecticide, too.
Several calls are received each year about spiders. Typically, the caller wants to know if the spider they've seen is dangerous --- and what -- if anything, should be done in terms of control.
Many different kinds of spiders live in and around buildings. Some, such as the house, cellar, and garden spiders, construct webs to help entrap their prey. Others, including the wolf spiders, are free-roaming and make no webs. The vast majority of spiders are harmless, and in fact are beneficial, because they prey upon flies, crickets and other insects. They generally will not attempt to bite humans unless held or accidentally trapped. Moreover, the majority of spiders have fangs too small or too weak to puncture human skin. Of the hundreds of species found in Kentucky, only the black widow and brown recluse are dangerous. Fortunately, both are relatively uncommon, and have markings which can be used to distinguish them from other non-threatening species.
Even though most spiders are harmless, few people are willing to tolerate them inside the home. Their unsightly webbing and fecal spots further negate the beneficial aspects of spiders to most homeowners. This column provides practical tips on spider control for concerned clients.
General Control Measures (all species)
Brown Recluse/Black Widow
As noted earlier, both the brown recluse and black widow
are potential health threats. Both spiders are timid,
however, and will only bite in response to the threat of
being injured. Most bites occur while putting on a shoe or
piece of clothing in which a spider has hidden, or while
unpacking boxes, sorting through clutter or lifting
objects.
The female black widow is about 1/2-inch long, shiny black and usually has a red hourglass mark on the underside of the abdomen. In some varieties the hourglass mark may be reduced to two separate spots. Most adult brown recluse spiders are about the size of a dime to a quarter with legs extended. Coloration ranges from tan to dark brown, with the abdomen often darker than the rest of the body. The feature that most distinguishes the brown recluse from many other harmless spiders is a somewhat darker violin-shaped marking on the top of the leg-bearing section of the body. The neck of the violin "silhouette" points toward the rear (abdomen) of the spider. Although each species has distinctive markings, a "spider is a spider" to most people. Concerned homeowners or victims of spider bites should be advised to bring the specimen in for confirmation.
Spider bites are difficult to diagnose, even by physicians. Black widow venom is a nerve toxin and its effects are rapid. The victim suffers painful rigidity of the abdomen and usually tightness of the chest. Victims should seek medical attention promptly. The bite of the brown recluse is usually painless until 3 to 8 hours later when it may become red, swollen and tender. Later the area around the bite site may develop into an ulcerous sore from 1/2 to 10 inches in diameter. Healing often requires a month or longer, and the victim may be left with a deep scar. Prompt medical attention can reduce the extent of ulceration and further complications. Not all brown recluse bites result in ulcerations and scarring.
The brown recluse may be found living indoors or outdoors. Black widows are more often encountered outdoors. Thorough inspection of cracks, corners, and other dark, undisturbed areas with a bright flashlight will help determine the location and extent of infestation. Indoors, pay particular attention to basements, attics, crawl spaces, closets, under/behind beds and furniture, inside shoes, boxes of stored items, and between hanging clothing. Brown recluse spiders also may be found living above suspended ceilings, behind baseboards, and inside ductwork or floor/ceiling registers. Another way to detect infestations in these areas is to install glueboards or sticky traps. These devices, designed to capture mice and cockroaches, can be purchased at grocery or farm supply stores. Placed flush along walls and in corners, glueboards and sticky traps are useful monitoring tools and will also capture large numbers of spiders.
Brown recluse and black widow spiders also live outdoors in barns, utility sheds, woodpiles, and underneath lumber, rocks, and accumulated debris. To avoid being bitten, wear work gloves when inspecting inside boxes or when moving stored items.
Each of the management tips (1-6) noted above for spiders in general are also useful against the black widow and brown recluse. Removal of unnecessary clutter is especially helpful in making areas unattractive to these pests. Indoor infestations of brown recluse and black widow also warrant treatment with insecticides. Insecticides should be applied into areas where spiders are living, making an attempt to contact as many spiders and webs as possible with the treatment. Most household insecticides with spiders listed on the label will kill spiders provided the spider is treated directly. Spot treatment with synthetic pyrethroids such as those mentioned earlier (including Raid Max) are especially effective. In attics, storage sheds, and other inaccessible or cluttered areas, total-release foggers will have a better chance of contacting spiders that are hidden.
Severe infestations of brown recluse or black widow spiders require specialized skills, persistence and equipment to eradicate. In these situations, it would be prudent to call a professional pest control operator.
Black shank and soreshin, continue to be active in tobacco fields across the state; other diagnoses on tobacco last week included blue mold, Fusarium wilt, alfalfa mosaic virus, tobacco ringspot virus, and flea beetle injury.
Landscape plantings are showing many stress related symptoms; abiotic stresses and various leaf spot diseases (tar spot, Phyllosticta leaf spot) are apparent on woody plants. On fescue, samples with brown patch, anthracnose, and rust (Puccinia) were diagnosed. Heterosporium leaf spot of iris and Cladosporium leaf blotch of peony were diagnosed from landscapes; commercial chrysanthemums were submitted with Rhizoctonia root rot and environmental stress.
Vegetable diseases last week included common scab on potato, wet rot on squash, stinkbug injury on sweet corn, Septoria leaf spot, early blight, late blight, and Fusarium wilt on tomato.
Insect Trap Count for July 18 - July 25, 1997
| Princeton | |
| True Armyworm | 5 |
| European Corn Borer | 4 |
| Corn Earworm | 1 |
| Southwestern Corn Borer | 0 |
| Tobacco Budworm | 0 |
| Allen Co. | |
| European Corn Borer | 0 |