June 25, 2015. Cucumber Downy Mildew in Seneca County, OH

Cucumber downy mildew was confirmed in Seneca County in pickling cucumbers.  The grower first saw symptoms on June 22.  This is the first report of cucumber downy mildew in Ohio; we were expecting to find it given the rainy conditions and proximity of other recent first reports (Kent County Ontario and Monroe County, MI.   Please see the recommendations posted on June 20, below.

Zing! is an additional fungicide to consider, preferably before symptoms appear.  This fungicide contains zoxamide, similar to Gavel, but instead of mancozeb is pre-mixed with chlorothalanil.  So the preharvest interval (PHI) for Zing! is 0 days for cucurbits, compared to 5 days for Gavel.

CDM1 compr CDM-2 compr

June 22, 2015. Cucumber/Melon Downy Mildew Update

Well, wouldn’t you know it?  In my last post only 2 days ago, I reviewed the downy mildew situation in Ohio and the Great Lakes Region in general, commenting in bold that there were no reports of outbreaks north of North Carolina.  That has all changed now, with reports of downy mildew TODAY from Kent, Ontario and Monroe County in SE Michigan.  It is likely that downy mildew is also in Ohio – we just don’t know about it yet. So Ohio cucumber and melon growers should begin preventative sprays of fungicides effective against this pathogen.  See the June 20, 2015 post below for details.

Once again, we would appreciate samples of suspected downy mildew, or let me know if you suspect downy mildew in your crop, at miller.769@osu.edu or by commenting below.

June 20, 2015. What’s the Cucumber/Melon Downy Mildew Situation?

Last year downy mildew appeared on cucumbers considerably later than in previous years. The table shows the dates and locations of first Ohio reports in 2014 vs. 2013. Even in 2013, downy mildew appearance was later in some counties than previously. The first report of downy mildew on cucumbers generally occurred around the 4th of July in the northern third of Ohio.

Cucurbit First Report 2013 First Report 2014
Cucumber July 3 Aug 15 (Wayne); Aug 25 (Huron)
Cantaloupe August 2 Sep 8 (Clark)
Pumpkin August 19 Sep 3 (Ross)
Watermelon August 22 ?
Squash         ? Sep 12 (Guernsey)

We don’t know why downy mildew appeared later than “usual”. Weather conditions were generally favorable in both 2013 and 2014 in early summer. However, it is possible that better control of early sources of inoculum in the Great Lakes Region may be slowing spread of the disease. There have been no reports of cucurbit downy mildew north of North Carolina to date. However, given the gravity of a downy mildew outbreak in cucumbers, and to a slightly less extent, melons, cucumber and melon growers in the northern third of Ohio and especially in the lake counties should start the following this week:

  1. SCOUT cucumber and melon fields for symptoms. Early symptoms on cucumbers are yellowish angular lesions on the tops of the leaves. Lesions on melon leaves are less angular than on cucumbers. A downy mold growth with tiny dark purple/black specks may be seen on the underside of the leaves.
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Downy mildew on cucumber


Downy mildew on melon

Cucumber DM sporulating1.JPG

Downy mildew sporulation on underside of leaf

  1. SEND downy mildew-suspected samples to the OSU Vegetable Pathology Lab (http://www.oardc.ohio-state.edu/sallymiller/t08_pageview3/Diagnostics_Services.htm; miller.769@osu.edu or 330-263-3678) for confirmation. There is no charge for diagnosis of vegetable diseases from Ohio growers. Samples may also be dropped off at OSU-OARDC facilities: Wooster Campus (234 Selby Hall); the North Central Agricultural Research Station in Fremont; the Western Research Station in Urbana; and the Muck Crops Experiment Station in Celeryville.
  2. FOLLOW me on Twitter @OhioVeggieDoc for reports of downy mildew in Ohio; tweets will direct you to more information and recommendations on this site. You can also see forecasts and sign up for alerts on downy mildew throughout the US on the Cucurbit Downy Mildew IPM PIPE website http://cdm.ipmpipe.org/ (don’t use Chrome for your web browser for this site).
  3. TREAT cucumbers and melons preventatively with fungicides.  Given the recent rainy weather, you should be applying a protectant fungicide to prevent anthracnose, gummy stem blight and other diseases. Add the downy mildew fungicides once the disease starts moving in the Great Lakes Region. See the Midwest Vegetable Production Guide for more details.

Fungicide application:

General protection: Apply Bravo, Manzate, Dithane or other broad-spectrum protectant fungicide on a 7-10 day schedule to prevent a number of diseases. 

Protection before downy mildew appears but is “on the move” in the Great Lakes Region: Apply one of the following fungicides on a 7-10 day schedule, tank mixed with Bravo, Manzate or Dithane: Presidio, Ranman, Previcur Flex, Tanos, Curzate, Gavel (Gavel already contains mancozeb), Zampro or Omega (melons only).  Alternate products.  The application interval can be lengthened under dry conditions.  Use the shorter interval under cool, moist conditions.

Management after disease appears: Apply one of the following fungicides on a 5-7 day schedule, tank-mixed with Bravo or Dithane: Presidio, Ranman, Previcur Flex, Zampro or Tanos.  Alternate products.  The application interval can be lengthened under dry conditions.  Use the shorter interval under cool, moist conditions.  See product labels for fungicide rates.

Always tank mix targeted fungicides with a protectant fungicide and alternate targeted fungicides with different modes of action (see FRAC Codes below). Note that the fungicides recommended above have different pre-harvest intervals (PHI).  Keep this in mind when fungicides are applied after harvesting begins. Note also that some fungicides have plant-back restrictions that may affect decisions regarding crop rotations.

Product PHI (days) FRAC Code Comments
Chlorothalanil e.g. Bravo Weather Stik 0 M5 Protectant; tank mix with targeted fungicides below
Mancozeb e.g. Dithane or Manzate 5 M3 Protectant; tank mix with targeted fungicides below
Ranman 0 21 No reports of reduced efficacy
Previcur Flex 2 28 Reduced activity suspected in some Ohio counties
Tanos 3 11 + 27 Up to 2 days curative activity but low residual (3-5 days)
Gavel 5 22 Contains mancozeb
Presidio 2 43 Likely resistance in some CDM populations
Curzate 3 27 Up to 2 days curative activity but low residual (3-5 days)
Zampro 0 40 + 45 No Ohio data; moderate efficacy in Eastern US
Omega 500F 30 29 Use only for Cucurbit Vegetables Subgroup 9A – includes muskmelons/cantaloupes/honeydew; use early for protection: note 30 day PHI


June 12, 2015. The Scourge of Vegetable Gardens: Early Blight of Tomato

One of the most common diseases of home garden tomatoes is early blight.  Gardeners usually describe spots, leaf yellowing, and defoliation, beginning at the bottom of plants and moving upwards.  Typically, spots contain irregular concentric rings, and are surrounded by irregular zones of yellow tissue. Stem lesions may also be observed. Fruit symptoms are usually seen on the stem end – the lesions often contain concentric rings.  Another tomato disease that also causes defoliation and leaf spots, and can be confused with early blight, is Septoria leaf spot. This disease is most severe in rainy weather. It does not cause symptoms on fruit.

Tomato early blight_1_1

Symptoms of early blight on a tomato leaf.


Stem lesion caused by early blight.


Fruit symptoms of early blight (photo by JP Jones).

There are a couple of management approaches for early blight.  These approaches will be helpful for other fungal disease of tomatoes as well.

Rotation – if the garden is big enough, move the tomatoes around from year to year, with at least 2 years between tomatoes in the same location.

Sanitation – Remove diseased leaves from the plant and destroy; at the end of the season, remove and destroy all of the tomato plants.  Don’t allow fruit to rot on the ground.

Irrigation – only water plants during the day so that they are not wet going into evening.  When free moisture is present on leaves the fungus that causes early blight can germinate and infect the plant.  Drip irrigation is preferable, but if not possible, avoid watering the foliage.  Lately the irrigation issue has been pretty much overshadowed by the rainy summers, but irrigation management is still useful during dry periods.

Disease resistance: Not a lot available but there are some varieties with partial resistance.  

Fungicides: A weekly spray with Daconil or other product containing chlorothalanil will help quite a lot.  Spray intervals can be extended to 10-14 days if the weather is very dry and there isn’t much dew in the morning.  I always recommend washing fruit (there are a number of products for this purpose) prior to consumption if fungicides are used.

June 9, 2015. Very Early Report of Powdery Mildew in Squash

OSU Extension entomologist Jim Jasinski found powdery mildew on squash in Champaign county today.  The find is unusual since 1) it is very early and 2) the disease was more severe on the underside than the top of the leaves.  We normally advise scouting in earnest for powdery mildew at the end of June or early July.  However, southern OH growers should start looking carefully for the disease in cucurbits, checking the lower side of leaves as well as the tops.

It is not necessary to apply fungicides for powdery mildew control before it has appeared in the field.  However, fungicide applications should begin when the disease is first spotted, and at a very low incidence.  Powdery mildew can get away from you and cause a lot of damage.  See the Midwest Vegetable Production Guide for Commercial Growers, page 98 for fungicides labeled for treatment of powdery mildew.  Product ratings are included on page 109.

Cuke PM3

CukePM2 Powdery mildew



June 8, 2015. Rain, Rain Go Away…

We received several samples of squash plants in the last 2 weeks with bacterial disease, either bacterial spot or angular leaf spot.  With the rainy weather in many parts of the region, we can expect to see more bacterial diseases on cucurbits and other vegetable crops.  On squash, pumpkins, cucumber and other cucurbits, symptoms are typically necrotic spots, sometimes surrounded by a yellow halo.  In the morning or after a rain, water-soaked spots may be observed on the leaves.  If unsure, contact the OSU Vegetable Pathology lab to send us a plant sample for confirmation.

Unfortunately, once bacterial diseases become established in the field, they are very difficult to manage.  Traditionally fixed copper products have been applied, but their efficacy is generally low; many bacterial pathogens are insensitive to some degree to copper.  The plant activator Actigard may be applied at 0.5 to 1 oz per acre, and may provide some control.

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Squash angular leaf spot