On July 16, a fairly significant outbreak of blue mold was found in several fields located along the Clark - Montgomery county line.  The disease appeared to have started roughly 2 weeks earlier, based on the appearance of older lesions, and the origin of the outbreak has not been determined.  The incidence of disease was near-100% in two fields, and severity was quite high.  Actively sporulating lesions were abundant, making this a strong source for disease.  Additional cases have not been reported as of July 20; however, there’s a good chance that we’ll find more in the vicinity of the current outbreak, and to the east of this area in the coming days.

For now, the areas facing the strongest threat blue mold are located in the immediate area of the current find, and eastward.  Within the “danger zone”, growers are advised to begin application of fungicides as quickly as possible to help protect tobacco and to contain the outbreak.  If blue mold is active on tobacco at the time of fungicide application, I recommend treatment with Quadris at 12 fl oz/A; use 8-10 fl oz/A for protection.  Growers may also use the combination of mancozeb (Dithane, Penncozeb, or Manzate) plus dimethomorph (Acrobat or Forum).  In this case, apply 2 lb/A of mancozeb and 3-7 oz/A of dimethomorph (user higher rates on bigger tobacco or if active disease is found).  Actigard will probably not be a good choice in the areas affected by the blue mold warning, as they may have been exposed to the pathogen, and Actigard needs to be in place 4-5 days before exposure to the blue mold pathogen in order to activate plant defenses. 

When applying fungicides for control of blue mold, good coverage is critical for getting adequate control of disease – this means using an appropriate application volume and drop nozzles to get fungicide materials down into the lower plant canopy.  The need to get after blue mold is really strong in the threatened area, because we are looking at some very favorable conditions for blue mold in the coming days.  According to the forecast, we are going to have cooler-than-normal day and night temperatures, and mostly clear days.  Long-distance transport will not be favorable, but we could see an explosion of blue mold within a field that has the disease and also short distances from these fields, mainly due to very favorable night-time temperatures.

Another point to consider is that tobacco that has been topped, or will be topped in a few days, will be less susceptible to blue mold, and may not need an application of fungicide.  However, blue mold loves suckers, so good sucker control will be important.

Finally, in areas west of the current outbreak, the need to protect against blue mold is not as critical as for the affected zones.  Those wishing to “play it safe” can follow the protectant guidelines listed above; if Quadris is used, they can also count on protection against target spot and frogeye if these diseases are present.  The other approach is to monitor the blue mold situation and be prepared to spray immediately if movement is predicted from known sources of blue mold, or when blue mold is first found.

Please keep a close watch on tobacco in your area, and let me know if you find or suspect blue mold in your area.  Now that it’s here, having a good fix on the extent of the outbreak helps me keep us all up to speed.  And don’t hesitate to call if you have any questions.

If the blue mold situation changes, we’ll post an alert through the Kentucky Blue Mold Warning System and on the Kentucky Tobacco Disease Information Page (www.uky.edu/Ag/KPN/kyblue/kyblue.htm).   Please urge producers (particularly in eastern KY)to check their crops regularly for blue mold, and let me know if you suspect or find the disease in your area.

Figure 4. Tobacco leaf collapsed due to stink bug feeding.

Single wilted leaves on scattered plants in a field may be the result of feeding by brown or one-spotted stink bugs. Both are about 1/2" long brown, shield-shaped insects. Enzymes that they inject into the plant during sap removal can cause adjacent tissue to wilt or collapse. The collapsed area may recover leaving about a quarter-sized yellow area immediately around the feeding site. On hot sunny days these areas can become scalded and the affected tissue will eventually turn brown and die. Affected plants often are most common along field margins but usually are not noticeable until several days after feeding has occurred.

Symptoms require several hours to develop so the culprits are long gone by the time the injury is apparent. 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.

Grape Black Rot, caused by the fungus Guignardia bidwellii, is being found commonly in vineyards across Kentucky.  Wet weather this spring has certainly contributed to disease outbreaks and made preventive sprays difficult.  Being seen now in the field and in the plant disease diagnostic laboratory are infected leaves and fruit (Figure 5).  Leaf spots due to black rot can be diagnosed by close examination of the tan centers of the angular spots and observing the tiny dark specks (pycnidia) arranged towards the edges of the spot (Figure 6).  These pycnidia produce spores that in turn cause additional infections of leaves and fruit.  Rotted fruits turn black and form mummies (Figure 7).  About a month after bloom, grape fruits become resistant to new black rot infections.  Thus, sprays applied now will not reduce black rot, but may help with other fruit rot diseases.  Lesions may also develop on the grape vine (Figure 8).  These lesions will need to be pruned out early next spring and any remaining mummies will need to be removed at the same time.  If not, the black rot fungus in the lesions and in the fruit mummies will be a source of inoculum for new infections next year.

Fall webworms are pale yellow, hairy caterpillars with two rows of black spots along the body. They are gregarious caterpillars that live together in silk tents spun at the ends of branches. Larval development takes about 6 weeks. These webworms feed on about 90 species of trees and shrubs and can be seen from late summer to early fall. Fall webworm infestations are unsightly and if present in sufficient numbers they may defoliate small trees.

Physical removal of tents and caterpillars may provide suitable control. Registered insecticides may be used for control if necessary.

Leafhoppers are about 1/8 inch-long wedged shaped insects that feed on plant sap. Small numbers of them are common in turf every year but these light gray to green insects can be very abundant, especially in irrigated turf. As grass gets tall, they may accumulate on yard chairs, pet dishes, children’s toys, etc.  They can be a temporary nuisance but are harmless to humans and pets, and rarely affect turfgrass.