Blossom end rot of bell pepper

The very hot temperatures and dry periods over the last month have been stressful for peppers and tomatoes, resulting in the appearance of blossom end rot. While blossom end rot, as the name implies, typically occurs on the blossom end of tomato fruits, in some cases (see figure) it occurs on the shoulder and sides of the tomato fruit. In peppers it occurs commonly on the sides of the fruit but can appear anywhere on the fruit surface.

Blossom end rot is the result of plant stress brought on by periods of dry vs moist soil.  Calcium deficiency in the plant is the cause but applying calcium to the foliage won’t help.  Calcium is relatively insoluble and plants under stress can’t move it to flowers and developing fruit.  It is a vital component of plant cell walls and the matrix that holds the cells together. When fruits start to form without sufficient calcium the tissues soften and die.  Secondary molds often colonize the dead tissue.

Severe case of blossom end rot of a green tomato, starting at the blossom end.

Blossom end rot of a green tomato.

The disorder is especially disappointing to home gardeners, because fruits with blossom end rot are often the first to ripen but usually inedible. I don’t recommend cutting off the affected parts and consuming the rest due to the risk of mold growth and presence of potential toxins to which some people may be sensitive.

Blossom end rot becomes less problematic with more consistent soil moisture and as the plants grow and develop their root systems.

Thanks to Carri Jagger for the blossom end rot of pepper photo.

Powdery mildew colonies on the underside of a pumpkin leaf. Fungicide applications should start when these colonies are first observed during scouting. It is important to check both surfaces of the leaves. Photo by Josh Amrhein.

Powdery mildew will soon be appearing on squash, pumpkins, and other cucurbits.  Organic growers should always start with varieties with some degree of resistance to powdery mildew – seed catalogues often call partial resistance “tolerance”.  Although resistance will generally not be complete, efforts to manage powdery mildew with organic-acceptable products will be more productive if growers start with a variety that can put up a fight on its own than one that is highly susceptible.

In 2021 we evaluated  OMRI-approved fungicides for efficacy against powdery  mildew  in our standard bioassay. Young pumpkin plants were produced in a greenhouse, one plant per pot, sprayed with a fungicide, and taken to a pumpkin field with active powdery mildew.  After about  24 hours of exposure, the plants were returned to the greenhouse and evaluated for disease development 7 and 10 days after exposure.

Seven days after exposure (DAE) to powdery mildew in the field, disease severity was moderate (24.2%) on non-treated control bioassay plants. All of the OMRI-listed products significantly reduced powdery mildew severity compared to the non-treated control. Regalia, Milstop, and Microthiol Disperss reduced disease severity to <1%, providing 96-100% control, significantly lower than severity on plants treated with Badge X2 (7.8%; 68% control) or Serifel (9.5%; 61% control). Powdery mildew severity on pumpkin plants treated with Sonata (4.2%; 83% control) was statistically similar to that of plants treated with Milstop (1%; 96% control), Badge X2 and Serifel. Ten DAE to powdery mildew, disease severity on non-treated control plants increased to 42.1%. Powdery mildew severity was lowest on plants treated with Regalia (0.6%) and Microthiol Disperss (0%), followed by Milstop (9.8%), and Sonata (23%), corresponding to 99, 100, 77 and 45% control, respectively. Treatment with Serifel or Badge X2 did not significantly reduce powdery mildew on pumpkin plants 10 DAE compared to the non-treated control.

Best results are obtained when these products are used preventatively or at the very first signs of powdery mildew (see photo above), usually in mid-July in Ohio.  If you wait until powdery mildew has progressed significantly, it will probably be too late to get it under control.

Powdery mildew colonies on the underside of a pumpkin leaf. Fungicide applications should start when these colonies are first observed during scouting. It is important to check both surfaces of the leaves. Photo by Josh Amrhein.

Powdery mildew usually appears on pumpkins and other cucurbits in Ohio beginning in early July. The pathogen does not overwinter in Ohio; infections result from spores blown into the area on the wind.  Powdery mildew is favored by moderate to high temperatures and high humidity. However, unlike most other fungal plant pathogens, it is inhibited by free moisture on the leaf surface.

Signs of infection are small circular powdery growths on either side of the leaf. These spots enlarge and can eventually cover most of the leaf surface and kill the leaves. Stems and leaf petioles are also susceptible, but the disease is not observed on fruit. In pumpkins, powdery mildew may also attack the “handles”, which can be further damaged by secondary pathogens. It is time to start scouting cucurbits for powdery mildew.

Powdery mildew is managed using disease-resistant varieties and fungicides. Pumpkin and squash varieties vary in resistance to powdery mildew; in general, the more susceptible the variety, the more fungicide needed. The choice of fungicide is important because insensitivity to overused fungicides is common. It is critical that a fungicide resistance management program is followed. Alternate fungicides in different FRAC (Fungicide Resistance Action Committee) groups, indicating different modes of action against the fungus. Fungicide applications should begin when the disease first appears and incidence is low. Fungicides that are labeled for use against cucurbit powdery mildew can be found in the searchable Midwest Vegetable Production Guide for Commercial Growers.

OSU evaluations of efficacy of powdery mildew fungicides in Ohio in 2021 indicated that Aprovia Top, Luna Experience, Inspire Super, Rally, Miravis Prime, Luna Sensation, Microthiol Disperss, Vivando and Procure provided very good control of powdery mildew on pumpkins (see table below).  Velum Prime, Cevya, Prolivo and Gatten provided good control of powdery mildew on upper leaf surfaces but poor control on the lower surfaces.

Quintec provided good control in 2021 but in other years and other states has failed due to resistance. Fontelis, Bravo Weather Stik, Merivon Xemium, Pristine, and Torino have been shown to provide poor or variable control in Ohio or other states and are not recommended.

Always check label for full list of allowed crops and use recommendations and restrictions.

Alternaria leaf spot on cabbage

The OSU Vegetable Pathology Lab carried out an active field research program in 2021, with ten full field trials spread across three research sites in Wooster, Celeryville and Fremont, OH, and three bioassays for downy and powdery mildew management. We tested fungicides, biological control products, and disease-resistant varieties to manage diseases of tomatoes, peppers, cucumbers, pumpkins, cabbage and collards. Our vegetable disease diagnostic lab service for commercial growers, led by Dr. Francesca Rotondo, diagnosed 241 physical samples and 20 digital samples for Ohio growers at no cost. You can click here Plant Pathology Series 2022_Veg Pathology Research Rpts 2021_final to read the research trial and diagnostic lab reports. Most of these trial results will be published in 2022 in Plant Disease Management Reports (subscription required).

Research projects (those with an * were supported financially by the Ohio Small Fruit and Vegetable Research and Development Program):

*Tomato anthracnose – fungicide evaluation

Tomato black mold, Septoria leaf spot and anthracnose – fungicide evaluation

Pepper bacterial canker – evaluation of cultivar resistance

Pepper Pseudomonas leaf spot – evaluation of cultivar resistance

*Pepper anthracnose – fungicide evaluation

Cucumber downy mildew – evaluation of cultivar resistance

Cucumber downy mildew – fungicide resistance screening (bioassay)

*Pumpkin powdery mildew and Plectosporium blight – fungicide evaluation

*Pumpkin powdery mildew – fungicide resistance screening (bioassay)

*Pumpkin powdery mildew – OMRI-listed products evaluation (bioassay)

Cabbage Alternaria leaf spot and soft rot – fungicide and biological product evaluation

Cabbage white mold – fungicide and biological product evaluation

Collards black rot and peppery leaf spot- biological product testing

*Vegetable disease diagnostic report

Downy mildew symptoms on untreated pumpkin leaves in Clark County, OH. Photo by Jim Jasinski.

Downy mildew was reported for the first time in pumpkins in Ohio in Clark County at the OSU Western Agricultural Research Station. Jim Jasinski noticed possible symptoms in an untreated control in a pumpkin research trial as many as 10 days ago, but the disease did not progress rapidly in last week’s heat. However, we were able to confirm downy mildew today. This is so far the furthest north that downy mildew has been found and reported on pumpkins or squash in the US. It is likely caused by Clade 1 of the pathogen, which comes from SE US and is more aggressive on pumpkins, squash and watermelons than other cucurbits.  Pumpkin and squash growers throughout Ohio should apply appropriate protectant fungicides now and scout fields thoroughly. Growers in Clark County should begin a fungicide program with downy mildew-effective fungicides now.

In the last week or so Ohio Master Gardener Volunteers in our Citizen Science project to monitor this disease have also reported downy mildew on cucumbers in Belmont, Jefferson and Geauga counties. Rainy or cloudy weather and moderate temperatures are expected this week in much of Ohio – these conditions are ideal for downy mildew.

For all cucurbits: If favorable conditions for downy mildew persist and downy mildew is present in your area, add effective fungicides shown in green in the Table to the spray program. Tank mix with a protectant fungicide, alternate fungicides with different modes of action (FRAC codes) and follow the label restrictions and requirements. Shorten the application interval to 7 days under favorable weather for downy mildew.

1. Forum, Presidio, Quadris, Zampro and Revus are not recommended. Curzate may be moderately effective in some locations.
2. Follow this blog, Twitter @OhioVeggieDoc or the Cucurbit Downy Mildew IPM PIPE for downy mildew reports.

Map of US counties with cucurbit downy mildew reports. https://cdm.ipmpipe.org/

Cucumber downy mildew, Hardin County OH. Photo by Francesca Rotondo.

Just after posting yesterday, July 30 I received a confirmed report of downy mildew in cucumbers in Hardin County. See that post for recommendations.

Cucurbit downy mildew outbreaks in Ohio counties. Red color indicates reports less than 7 days ago. https://cdm.ipmpipe.org

Cucurbit downy mildew outbreak map. https://cdm.ipmpipe.org.

We have three new reports of downy mildew on cucumbers this week, all from home or community gardens in Coshocton, Muskingum and Geauga counties. Thanks to OSU Extension educators David Marrison and Clifton Martin for the finds in Coshocton and Muskingum counties. The Geauga County outbreak was reported by one of our Ohio Master Gardener Volunteers participating in a multi-state Citizen Science project to monitor and report cucurbit downy mildew (thanks Annie!). Numerous reports in other states show that downy mildew is on the move (see map), mostly still in cucumbers and melons. In Ohio the cucumber/melon outbreaks have been in the northern and central counties, likely caused by the downy mildew “pathotype” that circulates in the Great Lakes region and infects only cucumbers and melons. However, last week downy mildew was reported on squash and pumpkins in Central Kentucky and on squash in Western New York. The downy mildew “pathotype” that infects squash and other cucurbits moves up into the Midwest from the deep South, so Ohio growers, especially in the southern counties, should step up scouting of all cucurbits and apply protectant fungicides such as chlorothalanil products. When downy mildew is confirmed nearby and conditions are conducive (cool, rainy, humid, overcast), more effective fungicides should be applied.

Spray Program Recommendations for Ohio Cucurbit Growers

1. Northern and Central Ohio cucumber and melon growers: add effective fungicides shown in green in the table to the spray program now. Tank mix with a protectant fungicide such as chlorothalanil (Bravo, Equus, etc.), alternate fungicides with different modes of action (FRAC codes) and follow the label restrictions and requirements. Shorten the application interval to 7 days under favorable weather for downy mildew.
2. Southern and Central Ohio cucurbit growers (all types): apply a protectant fungicide on a 7-10 day schedule now.

If favorable conditions for downy mildew persist and downy mildew is present in your area, add effective fungicides shown in green in Table 3 to the spray program. Tank mix with a protectant fungicide, alternate fungicides with different modes of action (FRAC codes) and follow the label restrictions and requirements. Shorten the application interval to 7 days under favorable weather for downy mildew.

1. Forum, Presidio, Quadris, Zampro and Revus are not recommended. Curzate may be moderately effective in some locations.
2. Follow this blog, Twitter @OhioVeggieDoc or the Cucurbit Downy Mildew IPM PIPE for downy mildew reports.

Click to enlarge.

Downy mildew map. https://cdm.ipmpipe.org

After last week’s very wet weather, downy mildew has appeared on cucumbers in a research plot on the OSU Muck Crops Research Station (Huron County) and on cucumbers and melons in sentinel plots on the OSU CFAES Wooster campus (Wayne County) and the OSU North Central Agricultural Research Station in Fremont (Sandusky County). In addition, downy mildew continues to spread in commercial fields in Seneca County. Downy mildew is likely to be present in cucumbers and/or melons in other northwest and northcentral Ohio counties and growers should protect these crops with appropriate fungicides. Fungicides must be applied preventatively – once plants are infected they will show symptoms within ~5-7 days even if fungicides are applied after infection. Only the fungicide Curzate has moderate “kick-back” activity.

OSU is part of a multi-state cucurbit downy mildew monitoring project, for which this year we have enlisted the help of Master Gardener Volunteers (MGVs) as Citizen Scientists in counties throughout Ohio. Most (25) are monitoring cucumber and squash plants in their gardens, while six groups of MGVs are managing and monitoring full sentinel plots. We have had no reports of downy mildew on cucurbits outside of northern Ohio and none in squash, pumpkins, gourds, or watermelons in any part of Ohio. We will continue monitoring and reporting downy mildew occurrences as they happen.

Cucumber downy mildew – photo by J. Amrhein.

If you suspect cucurbit downy mildew on your farm or in your garden, please send pictures (as close-up as you can) of the tops and undersides of affected leaves to me by text (330-466-5249) or email (miller.769@osu.edu).  Please include your name and the name of the town or city nearest you.

Downy mildew sporulating in a lesion on the underside of a cucumber leaf. Photo by F. Rotondo.

Basil plants with severe downy mildew symptoms in a big box store garden center in Wooster, OH. Photo by F. Rotondo.

This is shaping up to be a summer of downy mildews in Ohio. Rainstorms, high humidity, overcast skies and cool-ish nighttime temperatures are very conducive to downy mildew occurrence and spread. We reported the first “sightings” of cucumber downy mildew last week in Seneca and Wayne Counties in Ohio, and today OSU diagnostician Dr. Francesca Rotondo spotted a very severe outbreak of downy mildew in potted basil in a big box store garden center in Wooster (see photos). The pathogens that cause downy mildew in cucurbits and basil are different and don’t cross-infect among the two different plant groups.  However, they do respond similarly to environmental conditions.

Basil plants with severe downy mildew in a garden center in Wooster, OH.

The garden center manager in Wooster was notified and will have the diseased basil plants removed and destroyed promptly.

Management options for commercial  growers are 1) resistant varieties and 2) fungicides applied preventatively. Dr. Andy Wyenandt and colleagues at Rutgers University recently published an excellent discussion of available management tactics, including those for conventional and organic commercial basil producers. Information is also available on the Basil Ag Pest Monitor website, including photos of symptoms, management options and a map of basil downy mildew reports.

Management options are limited for home gardeners – resistant varieties are the most viable choice. In established garden basil plantings of susceptible varieties, monitor plants closely and remove and destroy leaves and stems with downy mildew symptoms. This may or may not slow disease progress, depending on environmental conditions and the presence of inoculum in nearby plantings. Leaves without symptoms are safe to eat, so if downy mildew appears in one’s garden basil, it may be time to make pesto or a nice Caprese salad before the disease spreads.