On July 16, a fairly significant outbreak of blue mold was found in several fields located along the Clark - Montgomery county line.  Since that time, we have confirmed cases in Fleming, Lincoln, Garrard, and Madison Counties.  Continued rainfall and periods of overcast weather mean that we will see further spread of blue mold in Kentucky and surrounding areas.

Growers with susceptible crops in the field should 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 for tobacco that may have been exposed to the pathogen, and Actigard needs to be in place 4-5 days before exposure to the blue mold pathogen to activate plant defenses.  However, for late-set crops that have not been exposed, Actigard could be an attractive option for controlling blue mold.  It offers the advantages of having a fairly long (10 days) residual period, and is very systemic.  The latter part means that using drop nozzles for full coverage is not as critical as for other products.

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 outbreaks, 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.  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.

If the field will be topped within about a week (or has been topped), aphids have already done their damage; there is no benefit to an insecticide application that is limited to aphid control. Topping the plants not only removes the greatest concentration of aphids but also the tender tissue on which they prefer to feed and where they cause the most new damage. Aphids present on the discarded tops will remain there and will continue to feed until the leaves dry completely. Few, if any, will find their way back to a plant. Aphids present on tobacco that has been topped are not a cause for concern at this time in the season.

Aphids can be a problem in late set fields that are still several weeks from being topped. Foliar sprays can be effective if applied when about 20% of the plants in the field are infested with aphids. Judge the benefit of control by looking at new foliage at the top of the plant. If aphid build ups are not seen on these leaves, then the sprays are working – they are more effective at protecting uninfested foliage than at killing aphids lower down on the stalks.

Hornworms and grasshoppers are the most common insect pests that are active in tobacco that has been topped. They can be very destructive during the 3 to 4 weeks the crop remains in the field before harvest. Most insecticides used on tobacco should be effective for about a week. After that time, weekly field checks should be made to detect any late pest buildups.

The unprecedented cool weather we’ve had in July, coupled with above-normal precipitation, has been stressful on Kentucky’s tomato growers – commercial and homeowners alike.  Diseases have added to this stress load, and we are seeing a fair amount of early blight and Septoria blight show up at the Plant Disease Diagnostic Lab.  These are serious problems and can cause losses if left uncontrolled; however, they pale in comparison to another problem that has literally exploded in the past week – late blight.  This is a fairly uncommon disease in Kentucky, and rarely causes widespread losses.  In the eastern U.S., though, a massive epidemic is underway that has caused some severe damage to tomatoes and potatoes in 16 states.  According to Dr. Meg McGrath of Cornell University, it is unprecedented to see this disease so early and widespread.  Part of the blame goes back shipments of infected tomato transplants from a large supplier that went out to garden centers and home supply stores across the region.  I don’t know if this is the root of our epidemic, but it’s certain that we are now facing a crisis on tomatoes and potatoes in Kentucky.

Back around the 9th of July, I sent out an e-mail alert that we’d confirmed late blight in Laurel and Larue counties.  Since that time, we’ve had very favorable conditions for late blight in terms of temperature and moisture.   Reports began rolling in during the week of July 27, and by the end of that week we’d confirmed cases in Breathitt, Jackson, Johnson, Montgomery, and Wolfe Counties.  All reports thus far have been on tomatoes and epidemic seems to be confined to eastern Kentucky for the moment, although there have been unconfirmed cases in central Kentucky as well.  Growers in eastern Kentucky are at greatest risk, but all areas in the state need to be on the lookout for late blight.  Prevention should be our focus at this stage, since we don’t know where this disease is headed next!

The Disease.  Late blight is caused by Phytophthora infestans, a fungus-like organism, and is a fast-moving and highly destructive disease of tomatoes and potatoes under cool and wet conditions.  Late blight epidemics in the late 1840’s were responsible for the Irish potato famine and subsequent migration of millions of people to the United States.  All plant parts are affected, including fruit and tubers.  Total losses are common in gardens and fields if control measures are not put in place.  Late blight can easily enter greenhouses and high tunnels as well.

Symptoms.  Early symptoms of late blight are large water-soaked blotches on foliage that will enlarge and form green-to-brown lesions.  Sporulation may be evident on the undersides of lesions under moist conditions; this sporulation will be gray to white in color.  Necrotic leaf tissue will blacken and shrivel, giving affected plants a blighted appearance.  The pathogen will also attack petioles and stems, killing the plant in some cases.  Tomato fruit affected by late blight develop as darkened spots that enlarge over time, and fungal growth may be seen in rotted tissue.  Infected fruit are invaded by secondary organisms and develop soft rot.  Potato tubers can become infected from spores washed from leaves into the soil and will decay.

Control – Commercial Growers.  Preventive application of fungicides is necessary to prevent losses to late blight.  Protectant fungicides such as chlorothalonil (Bravo and generics), maneb, and mancozeb (Dithane, Penncozeb, or Manzate), and fixed coppers can help when disease pressure is low; however, when inoculum levels increase or if disease is found in fields, stronger products are recommended.  Late-blight-specific fungicides are summarized below (as published by Dr. Meg McGrath, Cornell University):

Curzate 60DF (Group 27). 3.2-5 ounces per acre (3.2 ounces for potatoes). 5 oz on 5-day interval when late blight present. 30 oz/A seasonal max.  3 d PHI.EPA Reg No. 352-592.  Active ingredient is Cymoxanil.  12 h REI.  Must be tank-mixed with a protectant fungicide.

Forum (Group 40). 6 fluid ounces. 30 fl oz/A seasonal max.  2 consecutive spray max.  4 d PHI. EPA Reg No. 241-427.  Dimethomorph. 12 h REI.  Must be applied with another fungicide.

Gavel (Group 22). 1.5-2 pounds. 16 lb or 8 application seasonal max. 5 d PHI tomato; 3 d PHI for potato (14 d in some states).  Latron surfactant recommended. EPA Reg No. 62719-441.  Zoxamide + mancozeb. 48 h REI.

Omega 500F (Group 29).  5.5 fl oz for potatoes only.  3.5 pts/A seasonal max. 14 d PHI. EPA Reg No. 71512-1-100.  Fluazinam. 48 h REI.

Presidio (Group 43).  3-4 fl oz for tomatoes only. 12 fl oz/A seasonal max.  2 consecutive spray max.  EPA Reg No. 59639-140.  Flupicolide. 12 h REI. 2 d PHI

Previcur Flex (Group 28). 0.7-1.5 pint (1.2 pints max for potatoes).  7.5 pts/A seasonal max for tomatoes; 6 pts/A for potatoes.  5 d PHI for tomato; 14 d PHI for potato.          EPA Reg No. 264-678.  Propamocarb hydrochloride. 12 h REI.

Ranman (Group 21). 1.4–2.75 fluid ounces (2.1-2.75 for tomato). 16.5 fl oz or 6 application seasonal max for tomatoes; 27.5 fl oz or 10 applications for potatoes. 0 d PHI for tomatoes; 7 d for potatoes.         EPA Reg No. 71512-3-279.  Cyazofamid. 12 h REI.

Revus (Group 40). 5.5 to 8 fluid ounces. 2 consecutive spray max.  32 fl oz/A seasonal max.  1 d PHI for tomato; 14 d PHI for potato.         EPA Reg No. 100-1254.  Mandipropamid. 12 h REI.

Strobilurins, such as azoxystrobin (Quadris), pyraclostrobin (Cabrio/Headline), and fenamidone (Reason) have not performed as well as the products listed above in university trials.  Ridomil Gold Bravo and Ridomil Gold Copper are not recommended due to widespread resistance in pathogen populations to Ridomil.  Consult ID-36 (KY Production Guide for Commercial Vegetables) for specific use rates.  Keep in mind that some of these products may be difficult to find in local dealerships and may have to be special-ordered.  Of the materials listed above, Previcur Flex, Forum, Curzate, or Gavel may be the easiest to obtain in Kentucky, and are effective against late blight when used as directed.

Growers need to scout plantings regularly for late blight and other diseases.  Preventive fungicide applications are recommended at this point for all Kentucky tomato and potato growers to help combat late blight, and also early blight and Septoria (tomato).  Growers should not wait to see symptoms of late blight before treating.   A good protectant program aimed at late-blight prevention will also aid against other foliar fungal diseases.  During favorable conditions, sprays need to be made every 5-7 days, and every 7-10 days during drier weather. 

If late blight is found, growers should immediately destroy plants in the affected area plus bordering plants (as these are likely infected).  Plants can be sprayed with an herbicide, or removed and disked under.  Do not handle plants when they are wet, as this may spread disease; perform this operation when conditions are sunny and dry if possible.  At the end of the season, promptly destroy crop residues.  Do not leave cull piles out in the open, as the pathogen can spread or potentially survive in this residue.  Bury this material if at all possible.

Control – Homeowners.  The general management practices listed above apply also to the homeowner.  Regular scouting of plantings, and prompt removal of infected plants is an important consideration.  The bulk of cases reported thus far have come from home gardens, where regular application of fungicides is less common than in commercial fields.  Few fungicides are available to home gardeners; however, products containing chlorothalonil, maneb/mancozeb, or fixed copper are the tools of choice.  These should be applied regularly, and the user should refer to the product label for rates, PHI, and safety precautions.  These products, as mentioned earlier, will not function well if pressure is high or if disease is present before spray programs are started.

Control – Organic Producers.  Control measures for organic producers are similar to those recommended for home gardeners.  OMRI-approved fungicides such as fixed-copper (depends on the product) can be used in a preventive program.  Other OMRI-approved products include:  Sporatec, Sonata, Serenade Max, Oxidate, and Companion.  As with the protectants recommended for home gardeners, these products do not perform well under high disease pressure or if disease is present prior to treatment.  Consult product labels for rates, PHI, and safety precautions.

In recent weeks, downy mildew has been active on cucurbits in the eastern seabord, Michigan, and parts of Canada.  Earlier this week, the disease was confirmed in northwestern Illinois.  Since our weather usually moves west-to-east, this means that are now looking at the chance that downy mildew could move into Kentucky.  We don’t have confirmed cases at the moment, either from the field or the sentinel plots that we have near Owensboro, Lexington, and Quicksand; however, there is an unconfirmed report from Wayne County.  As you’ve seen, the weather has been great (unfortunately) for downy mildews to develop judging from the amount of blue mold on tobacco and late blight we’re seeing on tomatoes.  Please be on the lookout for downy mildew on cucurbits in the field, and note that we will have conditions that favor development and spread of this disease in the coming days.  Downy mildew on cucurbits is an aggressive, fast-moving disease and can be really hard to stop when it gets started. Under the right conditions, infection levels can go from 10% of leaf area infected to 90-100% in less than a week!

Identifying downy mildew on cucurbits can be a little tricky, because symptoms on each species vary to some degree. What's more, downy mildew can be confused with powdery mildew. Both of these diseases are similar in that they are caused by obligate pathogens, meaning that the pathogen must be associated with a host plant to survive. The downy mildew pathogen, Pseudoperonospora cubensis, is not a true fungus. It belongs to the Oomycetes and is related to the pathogen that causes blue mold of tobacco; however, powdery mildew is caused by Podosphaera xanthii and belongs to the Ascomycete group of "true" fungi. Although downy mildew is more common in wet weather, fogs and heavy dews can contribute enough moisture to allow infection during "dry" weather. Powdery mildew is more likely to be a problem when conditions are warm and dry, and it tends to develop gradually over the course of several weeks. In terms of symptoms, the two diseases can be confused. Early on, both can cause yellow spots on the upper surface of a leaf. In the case of downy mildew, leaf spots tend to be small, blocky, and are limited by leaf veins, while spots associated with powdery mildew are round and somewhat diffuse.  On the underside of a leaf with downy mildew, lesions will initially appear sunken and slightly water-soaked. As downy mildew progresses, infected leaves will take on a scorched appearance.  Leaf yellowing (chlorosis) is more common with powdery mildew, and infected leaves will be covered with a white, talc-like, superficial growth (from which powdery mildew takes its name) that tends to favor the upper leaf surface; however, it is not uncommon to find colonies of the powdery mildew fungus on lower leaf surfaces, stems, or vines and even fruit if disease is severe. One of the key features of downy mildew is the pattern of sporulation, which occurs only on the underside of an infected leaf and has a faint, fuzzy or "downy" appearance.  It is easier to observe sporulation with downy mildew in the morning when there's plenty of leaf wetness. It's very easy to distinguish the downy and powdery mildew pathogens at the microscopic level; sporangia of downy mildew are formed on sporangiophores that have a distinctive branching pattern that gives them the appearance of "deer antlers". Conidia of powdery mildew are formed in chains on relatively simple structures. If downy mildew is suspected, send a sample in to the Plant Disease Diagnostic Lab in Lexington or Princeton for examination.

At this point, and as weather permits, growers who are not on a preventive fungicide program should consider an application as soon as possible; spray intervals need to be fairly tight – in the 7-day range if possible.  Chlorothalonil and, to a lesser extent, mancozeb (or maneb for pumpkin and winter squash) offer reasonable protection against downy mildew if sprayed on a regular schedule; there are several downy mildew-specific materials that can be used as well, such as Acrobat (or its liquid counterpart, Forum), Ridomil Gold Bravo (Ridomil-resistant strains of the downy mildew pathogen are common, so this option is questionable), Revus (a new fungicide from Syngenta – very active against downy mildew), Presidio (a new material from Valent, and a strong performer), and Ranman (ISK / FMC product).  Previcur Flex is another effective alternative.  Please see ID-36, the Vegetable Production Guide for Commercial Growers, for rate.  Note that we are not recommending strobilurins (Quadris, Cabrio, Reason, Flint) for control of downy mildew, as resistance to this class of chemistry is high in the strains of P. cubensis in the U.S., and these compounds have lost much of their effectiveness against downy mildew.