Posts Tagged ‘tomato late blight’

Late Blight on Tomato Confirmed in Baltimore County, MD

Monday, August 20th, 2012

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

Late blight on tomato is now confirmed in Maryland (Baltimore County). We do not yet know what strain or genotype it is. Until additional information is available, growers should assume that both tomatoes and potatoes are at risk. The pathogen is very aggressive and can complete its life cycle and sporulate in as little as 7 days. Tomato growers should scout their crop aggressively and modify their spray program. Conventional growers should add translaminar fungicides, which can move into and through leaves are more effective than a protectant only program. The following are some fungicides that have performed well on tomato in our region. Growers should apply them with a protectant and rotate among them based on rotation of products that are in a different FRAC grouping.

  • Curzate–3.2 to 5.0 oz 60DF/A
  • Forum–6.0 fl oz 4.18SC/A
  • Presidio–3.0 to 4.0 fl oz 4SC/A
  • Previcur Flex–1.5 pt 6F/A
  • Ranman–2.10 to 2.75 fl oz 400SC/A
  • Reason–5.5 to 8.2 fl oz 500SC/A
  • Revus Top–5.5 to 7.0 fl oz 4.16SC/A
  • Tanos–8.0 oz 50WG/A

The best option for organic growers is an OMRI approved copper product. While research results indicate that copper is the best available option in organic production, remember that it is a protectant. That means it must be present on tissue to work. Keep protecting plants with repeated applications as new tissue forms.

Different products are available on potato. Please refer to Maryland, Extension Bulletin 236 (in Delaware, Extension Bulletin 137) for additional information.

Because this disease can spread rapidly by air, advise home gardeners with infected plants to use fungicides – or to kill their plants and bag them or place them under a tarp. This will avoid allowing the spores to spread to neighboring farms.

Spray to Prevent Late Blight on Potato and Tomato

Thursday, May 24th, 2012

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

Late blight has been found on potato in central New Jersey. The grower was applying preventative fungicides, however lesions occurred in a part of the field that the sprayer missed. All potato and tomato crops are susceptible to this disease. Growers should scout and apply preventative fungicides to protect their crops. Chlorothalonil, mancozeb or Polyram can be applied to potato and chlorothalonil, Gavel, or mancozeb can be applied to tomato. Complete coverage of the field is extremely important. Once late blight has been found close to a grower’s field, switch to a fungicide that is late blight specific. More information on available fungicides for this disease can be found at

Controlling late blight in organic systems is extremely difficult. Organic growers should apply a protectant such as copper to their crop. Serenade, Sonata and Sporatec are OMRI listed, and labeled for late blight. (However, there are very few research trials on efficacy of these products). It is critical to apply these materials with adequate coverage and at short spray intervals.

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.

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


Late Blight Report

Friday, July 1st, 2011

Bob Mulrooney, Extension Plant Pathologist;

Late blight caused by the fungus-like organism, Phytophthora infestans, was confirmed this week in DE, eastern shore VA, and the South Fork on Long Island, NY on potato. See the Potato Disease Advisory. Late blight was confirmed on tomato on Long Island, NY. Growers should be checking fields daily and maintaining preventative fungicide sprays. The weather conditions have been favorable the past few days but the hot weather forecasted for this weekend should help reduce the threat. The Delaware find was a small area at the end of a field next to woods and under power lines that obstructed the aerial application of fungicide applied to the whole field. Late blight specific fungicide has been applied.

For more information on controlling late blight on potato and tomato, see the 2011 Commercial Vegetable Recommendations. In addition to the information in the Commercial Veg Recs guide there is a very good table on fungicides for late blight on tomato and potato from Cornell University summarized by Dr Tom Zitter:


Late April 2011 Late Blight Status

Friday, April 29th, 2011

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

Currently there are a few reports of late blight (caused by Phytophthora infestans) from elsewhere in the United States. In Connecticut late blight was confirmed on tomatoes grown from farmer-saved seed, and on potatoes grown from organic seed pieces (cultivar ‘Australian Crescent’). In Wisconsin, late blight has also been confirmed on potatoes seed. Again, these confirmations are not local; however, increased scrutiny of tomato and potato for symptoms is warranted.

Symptoms on tomato leaves are lesions that initially appear as light green or grey water soaked areas that expand. Sporulation is white to grey on the under surface of the leaf. Infected leaves die. Petioles and stem lesions are dark brown and irregular.

Figure 1. Symptoms of late blight on a tomato leaf and stem (Courtesy of E. Gugino, The Pennsylvania State University).


Watch for Tomato Late Blight

Friday, August 20th, 2010

Bob Mulrooney, Extension Plant Pathologist;

Late blight has not made an appearance in Delaware so far this year. Late summer and fall is when we usually see it on home garden and truck crop tomatoes. For late tomatoes continue with Bravo and/or mancozeb as your protectant fungicide and add a late blight specific fungicide if late blight should occur in the region. See the 2010 Delaware Commercial Vegetable Production Recommendations for products and rates.

Potato Disease Advisory #17 – July 22, 2010

Friday, July 23rd, 2010

Bob Mulrooney, Extension Plant Pathologist;

Disease Severity Value (DSV) Accumulation as of July 21, 2010 is as follows:
Location: Art and Keith Wicks Farm, Rt 9, Little Creek, Kent County
Green row: May 6

Date Daily DSV Total DSV Spray Recs Accumulated
P- days*
6/26- 6/27 0 42 10-days 391
6/28 – 6/30 0 42 10-days 408
7/1 – 7/5 0 42 10-days 444
7/6 -7/7 0 42 10-days 449
7/8 1 43 10-days 454
7/9 8 51 7-days 462
7/10 0 51 7-days 471
7/11- 7/12 0 51 7-days 484
7-12 -7/13 3 54 7-days 490
7/13 – 7/14 10 64 7-days 499
7/15 -7/16 1 65 7-days 508
7/17- 7/20 0 65 10-days 526
7/20- 7/21 1 66 10- days 530


Late blight was found in a commercial potato field north of Bridgeton, NJ. Potatoes and tomatoes in the region could be at risk. It is important to keep scouting and maintaining fungicide applications at this time. Potato harvest has begun here in DE and there are still some fields with green tissue that could become infected. The hot weather forecasted for the rest of the week and the weekend will not be favorable for late blight infection and development but be aware of the presence of the disease in the region.

For specific fungicide recommendations, see the 2010 Delaware Commercial Vegetable Production Recommendations Book.