August 31, 2014. Downy Mildew on Pumpkins in Ross County, Ohio

Ross County educator Chris Bruynis sent us samples from an 8-Acre commercial pumpkin patch in his county that he suspected had downy mildew.  The farmer noticed symptoms several weeks ago.  We confirmed downy mildew, as well as a pretty severe case of powdery mildew.  This is our first report of downy mildew in southern Ohio, and first on pumpkins.  However, we don’t hear from everyone when downy mildew is suspected, so it is likely to be more widespread than on this farm in Ross County.  Downy mildew symptoms on pumpkin appear as irregular, brown (necrotic) lesions that eventually coalesce into larger necrotic areas.  Powdery mildew also will eventually kill the leaves, so it is important to seek confirmation if downy mildew is suspected.  Downy mildew fungicide recommendations are posted at  Powdery mildew fungicide recommendations can be found at


Downy mildew on pumpkin. Dark brown (necrotic) areas are downy mildew lesions. Sporangia (spores) of the downy mildew pathogen are produced on the underside of the lesions. This leaf also has powdery mildew.



Close-up of brown (necrotic) downy mildew lesions on a pumpkin leaf. The white powdery-looking spots are powdery mildew.


A severe case of powdery mildew on pumpkin.



August 28, 2014. Downy Mildew Now in Sandusky County, Ohio

Downy mildew was found in cucumbers in our non-fungicide-treated sentinel plot in Fremont, Ohio (Sandusky County).  The severity of the disease was about 25%.  Growers in northern Ohio counties should already have fungicide programs in place to manage this disease.  See for fungicide recommendations.

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Typical symptoms of cucumber downy mildew. Note chlorotic (yellow) angular lesions.

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Light fuzzy mold with dark purple-black “dots” (sporangia of the downy mildew pathogen) on the underside of a cucumber leaf.


August 23, 2014. Downy Mildew Getting Started in Northern Ohio Cucurbits


Downy mildew lesions on a cantaloupe leaf.

We  found cucumber downy mildew in our non-fungicide treated sentinel plot in Celeryville, Huron County, Ohio yesterday.  The incidence was very low – my field tech Jhony Mera found just one leaf lesion. Later in the day Jhony also spotted a low incidence of downy mildew in cantaloupe in our sentinel plot in Wooster, Wayne County, OH. We found downy mildew in cucumbers in the Wooster sentinel plot last week, at a low incidence – about 6%.  This week the incidence was nearly 50% in the same cucumbers.

These outbreaks are coming nearly 6 weeks later than we have seen in previous years.  We normally  see the disease around the end of June or early in July.  Growers in northern Ohio should begin applying fungicides effective against downy mildew to cucumber and cantaloupes crops, if they have not been doing so already.  Scouting fields for the disease is also recommended.  Effective fungicides are listed in my July 3, 2014 post.

August 20, 2014. Late Blight Management in Organic Systems

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Potato late blight. See August 13, 2014 post for tomato late blight photos.

We confirmed late blight in heirloom tomatoes from an organic farm in Ashland County, Ohio yesterday.  Although the hot weather we have experienced the past week does not promote late blight as much as cool weather – the cooler daytime temps, rain and cool nights of last week were very conducive for the disease. During hot weather the disease may continue to build slowly and then spread quickly with rain and cool weather. The disease was reported on potatoes on the OSU student farm in Columbus on August 1 and last week on tomatoes in Trumbull County, Ohio (see my August 13, 2014 post).  It is fair to assume that the potential for late blight is widespread in Ohio at this time, and tomatoes and potatoes need to be protected with appropriate fungicides.   I talked about fungicide programs for conventionally-produced tomatoes in my August 13 post – photos of symptoms are also posted there.  This post expands on information for organic tomato and potato growers, who have a bit tougher job than conventional growers in keeping late blight at bay.  There is a good webinar on late blight and its management in organic potatoes and tomatoes originally presented in January 2014 and featuring leading researchers on late blight from New York, Pennsylvania, Wisconsin and Florida.  They mention Actinovate AG, EF-400 and Zonix as products approved for organic that can be effective in reducing late blight – but will not completely control the disease.  OMRI-approved copper fungicides (Champ  WG, Nordox 75 WG, and others) generally rank highest for control among organic approved products. Actinovate, EF-400 and Zonix might be used in a program with copper.   NOTE: It is critical to apply  fungicides prior to infection – these fungicides (and most for conventional use as well) are not effective once plants have become infected.   Scouting programs must be carried out in earnest now; scouts need to be sure to look within the tomato or potato canopy for the tell-tale dark brown to black stem and petiole lesions and leaf spots.  Infected tomato fruits develop copper-colored irregular lesions that may cover half the fruit or more.

If possible, diseased plants should be removed from the field and destroyed.  It is best to bag the plants and discard them.  Infected fruit should not be allowed to remain in the field.  If it is not feasible to remove individual plants from the field, they can be killed in place by cutting them at the base or by flaming.

For next season’s planning, consider including late blight -resistant tomato or potato varieties.  There is a good deal of discussion on these varieties in the webinar mentioned above.



August 15, 2014. An Update on our Tomato Work in Tanzania

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Tomatoes in a market in Tanzania.

This is a little different post than usual, because it is not about Ohio vegetable diseases and management. Instead, I’d like to go quite a bit far afield – all the way to Tanzania, to talk a little about work we are doing to help improve tomato disease management and soil quality in the Morogoro region.  Tanzanian farmers produce tomatoes for fresh market that look a lot like our processing tomato varieties. However, due to diseases, soil problems, lack of access to improved varieties, and other factors, yields are well below the world average.  Last year we started a project funded by the USAID iAGRI program, in cooperation with Sokoine University of Agriculture and the International Institute of Tropical Agriculture (IITA) in Tanzania.  The goals are to understand which diseases are causing the most damage, train farmers in disease diagnosis and best management practices, introduce soil testing and management techniques, and test varieties with robust disease resistance. We are working with Dr. David Francis and OSU’s processing tomato breeding program to provide varieties for testing in participatory experiments called Mother-Baby trials.  My Ph.D. student Anna Testen has been working in the Morogoro region since April, and presented the results of her work so far in a special symposium during the Annual Meeting of the American Phytopathological Society this week in Minneapolis.  Anna also has funding for this work from the US Borlaug Graduate Fellowship program. You can see her 30-minute presentation by clicking here. Her presentation is about 1 hour, 25 minutes into the session.  You can read more about Anna’s adventures on her blog at


Go Bucks! Anna Testen (left), Dr. Delphina Mamiro of Sokoine University of Agriculture (secod from right) and Sally Miller (right), with one of our cooperating Tanzanian farmers.


August 13, 2014. Late Blight Reported in Ohio Tomatoes

Eric Draper, OSU Extension Geauga County Extension Educator, called me today to report late blight on two tomato farms in western Trumbull County, OH.  Cool nights and rainy conditions are very favorable for the development of late blight.  Once you have seen late blight a few times it is usually pretty easy to recognize, since the symptoms are quite distinct. Leaf lesions appear soon after infection (Figure 1A, 1B), with a dead center and a fuzzy white white border visible on the underside of the leaf.  The fuzzy material contains the sporangia that can be blown in the air or splashed in water to other parts of the plant or to new plants.

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Figure 1A. Late blight lesion on tomato leaf (top). Late blight is caused by Phytophthora infestans.

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Figure 1B. Late blight lesion – underside of leaf. The white fuzzy border of the lesions contains sporangia of the pathogen.

Stem lesions are dark brown to black (Figure 2), and diseased fruit appear coppery in color (Figure 3), often with what appears like a dusting of white material.  This white material also contains the sporangia that spread the disease.

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Figure 2. Brown stem lesions caused by late blight.


Figure 3. Tomato fruit with late blight symptoms.

It is very important that both potatoes and tomatoes be scouted regularly (at least twice per week) for late blight.  If late blight is suspected, it can be confirmed by bringing or sending a sample to the OSU Vegetable Pathology Lab in Wooster  or the OSU C. Wayne Ellett Plant and Pest Diagnostic Clinic in Reynoldsburg.   We appreciate hearing from you if late blight is suspected so that we can confirm and alert others.

Growers need to maintain an effective fungicide program on tomatoes and potatoes.  This should continue as long as rainy conditions, high humidity and/or heavy dews are expected.  If late blight has not been observed and weather conditions are generally dry and warm, use a protectant fungicide on a 7-10 day schedule, depending on how fast the plants are growing.  Good protectants are chlorothalanil (Bravo, Equus, Echo), mancozeb (Penncozeb, Manzate, Dithane), and to a lesser extent, copper-based products – use according to label instructions.  Under cool wet conditions when late blight is likely, or if late blight has been found on the farm, use one of the following, tank mixed with one of the above protectants: Curzate (3 day PHI), Gavel (5 day PHI), Presidio (2 day PHI), Previcur Flex (5 day PHI), Ranman (0 day PHI) or Tanos (3 day PHI) to the spray tank with a protectant fungicide.  Note the Pre-Harvest Interval (PHI) for these fungicides ranges from 0 – 5 days.  So far, Ohio late blight strains have been sensitive to Ridomil, so that is another option (but may be risky). Organic producers must rely on applications of approved copper-based products.

If the disease is mainly found in one or a few foci, it is a good idea to remove and destroy the diseased plants.  This is particularly important for organic tomato or potato growers.  Home gardeners should consider spraying tomatoes and potatoes with a fungicide containing chlorothalanil, and should prune out diseased tissue.  Pack up diseased plants in a plastic garbage bag and discard – don’t leave them in the field or garden or on a compost pile, where the pathogen can be released into the air and spread to other plants.