Posts Tagged ‘cucurbit downy mildew’

Cucurbit Downy Mildew Present Early in North Carolina

Thursday, May 24th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

Cucumber growers should monitor their crops for downy mildew. Symptoms of downy mildew on cucumber are angular yellow to tan lesions on the upper surface of the leaf and brown to black sporulation on the lower surface.

Downy mildew was found a second time last week in North Carolina on greenhouse grown cucumbers. This outbreak may have started two months ago. Although there are no reports north of the Carolinas, it is extremely troubling that downy mildew is present there so early in the season. Growers should scout their fields and monitor the Cucurbit Downy Mildew ipmPIPE site for the progress of the disease. Preventative fungicide applications should begin when disease occurrence is predicted in our region.

Downy mildew on cucumber leaf. Angular necrosis on upper leaf surface and dark sporulation on lower leaf surface.

Cucurbit Downy Mildew Fungicide Decisions

Friday, May 11th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

Downy mildew on cucurbits has been a problem on Delmarva beginning in early July for the last few years. Good fungicides for management are available. However, last year in my trials, one of these fungicides, Presidio, was not as effective as expected. Looking ahead to your spray program, be careful not to rely on one fungicide class. It is difficult to know which fungicides will be effective here, because our population does not overwinter and is reintroduced from the South each year. Therefore use excellent resistance management practices to avoid allowing the pathogen to develop resistance and to improve the efficacy of your fungicide management program.

Fungicide Resistance management guidelines by crop are available online and hard copies are available in Delaware at the county Extension offices.

Vegetable Disease Update – September 16, 2011

Friday, September 16th, 2011

Bob Mulrooney, Extension Plant Pathologist;

Lima bean downy mildew was found by a CCA and confirmed on Wednesday from a field of ‘C-elite’ near Galena, MD. Growers need to be scouting carefully and applying fungicides as needed. If seen in the field apply either Ridomil Gold/Copper 2.0 lbs/A or ProPhyt (3.0 pts/A). See the 2011 Delaware Commercial Vegetable Production Recommendations for other fungicide choices as well as last week’s WCU for more detailed information.

Basil downy mildew was found in New Castle County this week. Any specialty crops growers might want to protect basil with one of the phosphorus acid products, such a ProPhyt, at this time.

Powdery and downy mildew are widespread in cucurbits especially pumpkins and winter squash at this time. Maintain fungicide programs until fruit develop fully.

Unfortunately Phytophthora fruit rot is very prevalent on a number of cucurbits especially pumpkin at this time. The excessive rainfall just made a bad problem worse. A few growers have asked about dipping fruit in a 5-10% bleach solution or using Zerotol to prevent fruit rot. My experience has been that is not effective if the fruit are infected in the field. You may get reduced spread in a bin but it will not control Phytophthora fruit rot.

There were a few reports of late blight in New York and Connecticut this week, but nothing in the Mid-Atlantic to worry tomato growers so far. To track the progress of late blight in the US you can go to

Vegetable Disease Update – September 2, 2011

Friday, September 2nd, 2011

Bob Mulrooney, Extension Plant Pathologist;

Cucurbit Downy Mildew
Cucurbit downy mildew was confirmed on pumpkin, summer squash and winter squash this week in DE. It will likely be more widespread following the storm. Maintain fungicide sprays specific for downy mildew if the foliage is still green and harvest is still planned.

Late Blight
Late blight was reported in a central New York county this past week on tomatoes in a homeowners garden. After the hurricane we might see some late blight develop on tomatoes.

Lima Bean Downy Mildew
Be sure to scout for lima bean downy mildew after the hurricane. Symptoms may take 7-10 days to develop after the rain ended. See previous issues for recommendations, or the 2011 Commercial Vegetable Production Recommendations.

Cucurbit Downy Mildew Update – August 19, 2011

Friday, August 19th, 2011

Bob Mulrooney, Extension Plant Pathologist;

There were reports of downy mildew on pumpkin in northern New Jersey at the beginning of the week. This was sent to the WCU mailing list to make you aware that downy mildew was beginning to appear on more than just pickling cucumber in the area. With the recent thunderstorms, cooler nights and morning fog, conditions will be more favorable for disease development. Maintain your fungicide program at this time. Growers should be aware that the fungicides that have been the most effective on downy mildew on cucumber (namely Presidio, Ranman, and Previcur Flex) will also be very effective on pumpkin, cantaloupe and any other cucurbit. Tanos and Curzate could be added to that list as well for cucurbits other than cucumber. Be aware that Presidio has some plant back restrictions for crops not on the label. The link will take you the new supplemental label: Wheat can be planted 30 days after treatment. This was added in the supplemental label.

Vegetable Disease Updates – August 12, 2011

Friday, August 12th, 2011

Bob Mulrooney, Extension Plant Pathologist;

Sweet Corn
With a return to some cooler weather be on the lookout for corn leaf rust on sweet corn. Scout the plantings and if you see rust on plants at the whorl stage or younger, rust could become an issue if the hybrid is not resistant to rust. Rust, when heavy, can affect plant health and reduce ear size. The best control is to plant resistant hybrids, but the strobilurin or triazole fungicide work well. On fresh market corn rust on the husks makes ears unsightly to consumers.

Cucurbit downy mildew
was recently observed on cantaloupe in the sentinel plot in Newark. These lesions resemble the same symptoms as seen on cucumber but spore production appears to be very sparse. It has not moved to any pumpkin, winter squash or watermelon so far. The susceptible cucumber in the plot is almost totally defoliated.

Lima Beans
So far weather conditions have not been favorable for downy mildew. It looks like the weather may be changing and getting a bit cooler with more dew and possibly fog in the early morning hours. If it should start raining soon growers and crop consultants should be scouting for downy mildew. Race F of Phythophthora phaseoli was the only race identified in 2006, 2008, 2009, and 2010. Preventative applications of 2 lbs fixed copper, 2 lbs Ridomil Gold/Copper, or 3- 4 pts Prophyte have provided control of downy mildew in the past. The newest formulation of fixed copper from DuPont is Kocide 3000 and it performs as well as the other formulations of copper at the rate of 1.3 lbs/A. The best controls continue to be Ridomil/Gold Copper, Prophyte, or other labeled phosphonate fungicides, and Omega, especially when disease pressure is high. Application at flowering or when pods are first forming is recommended if weather is favorable for disease. If disease is present Ridomil/Gold Copper and phosphonate fungicides have shown to provide some curative activity if applied when downy mildew is first seen. If downy is present in the field do not use copper fungicides alone for curative control, they will not provide control. Another product that is labeled on lima beans for white mold control is Omega but not downy mildew, but in DE this would be a 2ee use that someone like me can recommend since the fungicide is labeled on lima beans. I have three years data that show excellent control of downy mildew at 5.5 fl oz and 8.0 fl oz/A as a preventative application (before disease is found in the field). Omega is not labeled for aerial application, however. Headline from BASF is also labeled for downy mildew. I have tested it and it has provided good control of downy when applied on a 10-day schedule at 6.0 fl oz /A. It does not give as good disease control as Ridomil Gold/Copper or the phosphonates preventatively but the yields have been comparable. It is also labeled for anthracnose which the other products do not control.

Downy mildew caused by Phytophthora phaseoli

Downy mildew on raceme and petiole

Phytophthora capsici on lima bean pod.

Phytophthora capsici will infect lima bean pods as well and can look very similar to downy mildew. P. capsici or lima bean pod rot is usually found in wet low spots in the field. The fungus growth looks more granulated or “pebbly” than downy mildew, microscopic confirmation is encouraged.

Downy mildew on the upper pod and lima bean pod rot on the lower pod. Note the granular appearance of the fungus on the lower pod and the lack of a reddish brown border on the pod infected with lima bean pod rot or Phytophthora capsici.

Vegetable Disease Updates – August 5, 2011

Thursday, August 4th, 2011

Bob Mulrooney, Extension Plant Pathologist;

Basil Downy Mildew
Basil downy mildew has been seen in nearby NJ. Any sweet basil growers should be scouting for this disease. Phosphite fungicides such as Prophyte have shown the best efficacy for controlling basil downy mildew.

Cucurbit Downy Mildew
Cucurbit downy mildew continues to be seen at low levels in commercial cucumber fields. The dry hot weather has been helping the fungicides to keep it in check. So far we have not seen it move into other cucurbits such as pumpkin. Keep scouting and check the 2011 Commercial Vegetable Productions Recommendations for fungicide suggestions. Once the cooler weather returns, and hopefully some rainfall, look for this disease to increase. Keep up with preventative fungicide applications.

Late Blight
We just received a confirmed report of late blight from Ann Arundel County in MD and in New Brunswick, Canada. Keep on the lookout for this disease on tomato and potato.

Cercospora leaf spot was diagnosed on watermelon last week. Cercospora leaf spot symptoms occur primarily on foliage, but petiole and stem lesions can develop when conditions are highly favorable for disease development. Fruit lesions are not known to occur. On older leaves, small, circular to irregular circular spots with tan to light brown lesions appear. The number and size of lesions increases, and eventually they coalesce and cause entire leaves to become diseased.

Lesion margins may appear dark purple or black, and may have yellow halos surrounding them. Severely infected leaves turn yellow, senesce, and fall off. On watermelon, lesions often form on younger rather than older foliage. Cercospora leaf spot can reduce fruit size and quality, but economic losses are rarely severe. Fungicides such as chlorothalonil (Bravo) and mancozeb including Gavel, as well as the triazole fungicides such as Inspire Super and strobilurins (Cabrio and Quadris) should provide good control of Cercospora leaf spot. As wilthall vine crops be sure to apply in enough water to get good coverage, usually a minimum of 15 gal/A.

Vegetable Disease Updates – July 8, 2011

Friday, July 8th, 2011

Bob Mulrooney, Extension Plant Pathologist;

Late Blight
There have been no new late blight detections in DE or VA on potatoes. The disease apparently is under control and the weather has not been very favorable, especially where the temperatures have been over 90°F. Besides the two finds in DE and VA the only active late blight at present appears to be on Long Island, NY on both potato and tomato.

Downy Mildew on Cucurbits
As most of you know by now downy mildew was found in Sussex County on Tuesday and Dorchester County, MD. Both finds were on pickling cucumber. Since then downy mildew was found in an additional field near Bridgeton, NJ, Talbot County, MD, Wyoming County, PA, and several more cucumber fields in NC. Now is the time to be spraying specific fungicides for downy mildew on cucumbers. Continue to check the IPM pipe website for more information on the spread of downy mildew:

Root Knot Nematode
Root knot nematode can be a very yield limiting pathogen on very susceptible crops like cucumbers and other vine crops, lima beans, snap beans and tomatoes to name a few. They are often worse in very sandy soils or sandy knolls in fields. With the temperatures that we have seen here in DE you can begin to see the swellings or galls on the roots in about 21 days from seeding or transplanting. Plants in infested areas of the field will be stunted and if the plants are dug carefully, if root knot is present, you will see galls of varying sizes on the roots. We have no chemical controls except for vine crops once the nematodes are seen. Vydate should be applied preventatively in fields with known root knot infestations at seeding and/or later when plants are still small. See label for details. Treating early is always better than waiting until galls can be seen.

Root knot galls on baby lima bean roots, 23 days from planting

Pepper Anthracnose
Be on the lookout for anthracnose on peppers. It has been reported in southern NJ. Anthracnose fruit rot can be a very difficult disease to control if it gets established in a field. Fields should be scouted frequently especially if peppers or tomatoes have been planted in the past. It is best controlled by preventative fungicide sprays beginning at flowering. Apply Bravo or another chlorothalonil product every 7 days and alternate with a stroblilurin fungicide (FRAC code 11) like Cabrio or Quadris plus Bravo. If anthracnose fruit rot appears, removing infected fruit from heavily infected areas will help to reduce spore loads and reduce spread if done early and often enough. Fruit will need to be removed from the field and not just thrown on the ground.

Anthracnose on pepper fruit


Cucurbit Downy Mildew Alert – July 1, 2011

Friday, July 1st, 2011

Bob Mulrooney, Extension Plant Pathologist; and Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

Downy mildew was confirmed on seeded cucumbers in Cumberland County, NJ near the city of Vineland. There were no reported downy mildew infections on any transplanted cucurbits in this area. This is the first report of downy mildew on cucurbits in the Mid-Atlantic region this year. Downy mildew has also been increasing in North Carolina the last several weeks. This is a very long leap from NC to NJ if this infection was from air transported spores. Traditionally we can expect downy mildew to arrive here sometime around the 4th of July. DE and MD have sentinel plots for monitoring downy mildew on cucurbits and have been negative for downy so far. These are scouted regularly in addition to reports and samples that we receive from the field. Hopefully we can provide an early warning when it appears here so that timely fungicide applications with downy mildew specific fungicides can be made.

What growers should do:

● Now that downy mildew has been detected in the region growers should be scouting on a daily basis.

● In areas where rainfall has occurred, growers may want to apply targeted fungicides to cucumbers. Tank- mix Presidio, Ranman, or Previcur Flex with a protectant fungicide and alternate sprays with a material with a different mode of action. Because downy mildew has only been found in adjacent states on cucumber, targeted sprays on other cucurbits crops (pumpkin, squash, watermelon, etc.) are not necessary, at this time. Instead scout aggressively and continue a broad-spectrum spray program.

● All abandoned cucumber and summer squash fields should be sprayed with gramoxone or disced under immediately after last harvest to kill the foliage! Abandoned fields left unattended after use will only serve as a source of inoculum for other fields once downy mildew makes its way into our area.

● Please see the 2011 Commercial Vegetable Recommendations Guide for specific fungicide recommendations

● To track the progress of cucurbit downy mildew in the eastern US and to keep up with reports of Downy mildew from other states please visit North Carolina State University’s Cucurbit Downy Mildew Forecasting Center at


Downy Mildew Updates – June 24, 2011

Friday, June 24th, 2011

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

Basil Downy Mildew
Downy mildew on basil has been confirmed in Dunkirk, MD (Calvert County between the DC metro area and Southern Maryland). The infected plants are in a homeowner’s yard, but commercial growers should be on the lookout.

Cucurbit Downy Mildew
As a result of slightly more favorable conditions, Downy mildew on cucurbits is moving northward. Within the last week there have been three reports of downy mildew on CUCUMBER in North Carolina, including one on the border of Virginia. The Cucurbit Downy Mildew forecaster says that disease spread is possible in the mid-Atlantic region, including areas in southern Maryland, the eastern shore, and in Delaware. Scout plants rigorously and monitor the CDM website

Lower leaf surface of a cucumber leaf infected with downy mildew. Courtesy of Gerald Holmes, Valent USA Corporation,

Downy mildew symptoms on upper leaf surface of cucumber.

Downy mildew symptoms on watermelon, note the differences.