Posts Tagged ‘late blight’

Vegetable Disease Updates – August 5, 2011

Thursday, August 4th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

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.

Watermelon
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.

Potato Disease Advisory #18 – July 19, 2011

Thursday, July 21st, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Location: Art and Keith Wicks Farm, Rt 9, Little Creek, Kent County.
Greenrow: May 3

Date

Late Blight

Early Blight

Spray Interval Recommendation

DSV

Total DSV

Accumulated P-days*

6/27

1

70

416

10-days
6/28

1

71

424

10-days
6/29

0

71

432

10-days
6/29-7/2

0

71

456

10-days
7/3

1

72

462

10-days
7/4

0

72

468

10-days
7/5

1

73

474

10-days
7/6

0

73

481

10-days
7/7

3

76

486

7-days
7/8

3

79

493

5-days
7/9

0

79

499

5-days
7/10

0

79

506

5-days
7/11-7/14

0

79

530

10-days
7/15-7/18

0

79

558

10-days

 

Continue to scout fields for symptoms of late blight. Maintain spray programs if plants are still growing.

There have been no further reports of late blight in the region.

For specific fungicide recommendations, see the 2011 Delaware Commercial Vegetable Production Recommendations Book.

Potato Disease Advisory #17 – July 15, 2011

Friday, July 15th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Location: Art and Keith Wicks Farm, Rt 9, Little Creek, Kent County.
Greenrow: May 3

Date

Late Blight

Early Blight

Spray Interval Recommendation

DSV

Total DSV

Accumulated P-days*

6/27

1

70

416

10-days
6/28

1

71

424

10-days
6/29

0

71

432

10-days
6/29-7/2

0

71

456

10-days
7/3

1

72

462

10-days
7/4

0

72

468

10-days
7/5

1

73

474

10-days
7/6

0

73

481

10-days
7/7

3

76

486

7-days
7/8

3

79

493

5-days
7/9

0

79

499

5-days
7/10

0

79

506

5-days
7/11-7/14

0

79

530

10-days

 

Continue to scout fields for symptoms of late blight. Conditions will continue to favor early blight. The recent rains and the amount of humidity we have been having have made conditions for late blight more favorable. Maintain spray programs if plants are still growing. The shortened spray interval reflects the more favorable conditions and is a very conservative recommendation but with no recent detections, 7-day intervals should be fine.

Late Blight was reported two weeks ago in DE, on the eastern shore VA, and Long Island, New York. There have been no further reports of late blight in DE or VA but late blight has been reported on the North Fork on Long Island, NY in addition to the earlier find on the South Fork.

For specific fungicide recommendations, see the 2011 Delaware Commercial Vegetable Production Recommendations Book.

Vegetable Disease Updates – July 8, 2011

Friday, July 8th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

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: http://cdm.ipmpipe.org.

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 April 2011 Late Blight Status

Friday, April 29th, 2011

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

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).

 

Potato and Tomato Late Blight Update

Friday, June 25th, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Late blight on tomatoes was found on Long Island in a home vegetable garden this past weekend. There have been no reports of late blight in DE, NJ or eastern shore VA to date. The high temperatures this week (above 90°F) are not favorable for late blight.

Information on Potato and Tomato Late Blight Management

Thursday, March 25th, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

With the widespread occurrence of late blight last season on tomato and potato. There is some new information available from other universities that might be of interest. Dr. Meg McGrath, Cornell plant pathologist on Long Island, has written two articles on managing late blight organically, both of which are available online: Managing Late Blight in Organically-Produced Potato and Managing Late Blight in Organically-Produced Tomato.

Dr. Tom Zitter, also from Cornell, compiled a list of tomato varieties with reported resistance to late blight and early blight that might be helpful: Table of Late Blight and Early Blight Resistant Tomato Cultivars

Vegetable Crop Diseases – September 11, 2009

Friday, September 11th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Lima Beans
Continue to scout for downy mildew. The recent weather is very favorable for downy mildew. If downy is found apply RidomilGold/Copper, Phostrol or other labeled phosphorus acid (phosphonate) fungicide. If disease has not appeared in the field Headline, Forum or fixed copper fungicide can be applied preventatively in addition to Ridomil Gold/Copper and phosphorus acid fungicides.

Sweet Corn
Field corn is not the only host for the fungus that caused Northern corn leaf blight. I have seen several fields of sweet corn recently with very high levels of infection clear to the top of the plant. Ears from badly infected plants were not filled out and will not be worth harvesting. Northern has been favored by the cooler and wetter season.

Northern corn leafblightTypical large lesion (3-4 inches long) caused by Northern corn leaf blight

Tomatoes
Late blight
is resurging on backyard tomato plantings at the present time. There is nothing besides chlorothalonil and mancozeb for homeowners but late season commercial planting should be protected from late blight with any of the late blight specific fungicides.

Cole Crops
Downy mildew and Alternaria
can be a problem in fall cole crops (cabbage, collards, broccoli, cauliflower, and kale). When the disease first appears apply a fungicide every 7 to 10 days. Quadris, chlorothalonil, Cabrio, Endura (Alternaria only) Maneb, Ridomil Gold Bravo, Switch (Alternaria only), Actigard (downy mildew only) and Aliette (downy mildew only) are labeled for control. For more information on control please see the 2009 Delaware Commercial Vegetable Production Recommendations.

Late Blight on Tomato

Friday, July 24th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Late blight on tomato was identified in a backyard garden near Ellendale in Sussex County this week. Conditions have been favorable lately for late blight. Commercial tomato growers should be including a late blight specific fungicide in their fungicide rotation. Previcur Flex plus Bravo, Tanos, Ranman, or Forum could be used. Check label for specific information and all should be tank mixed with a protectant fungicide. Potatoes are rapidly reaching maturity and late blight should not be an issue at this stage of the season. Organic growers only have copper as a fungicide choice which is not very effective. If backyard tomatoes are badly infected the best control measure is pull them up, place them in sealed plastic bags and dispose of them. Do not put them on a compost pile. Backyard tomato growers have several protectant fungicides that can be used namely mancozeb and products containing chlorothalonil or Daconil. Sprays should be applied at 5 to 7-day intervals before symptoms appear.

late blight on a tomato leafLate blight on the underside of a tomato leaf. Note the white cottony growth on the dying tissue.

Late Blight Present on Tomatoes in Maryland

Friday, June 19th, 2009

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Late blight of tomato is present in fields in Somerset County, Maryland. The disease can be recognized by large grey to brown lesions on the leaves. Associated leaf tissue becomes necrotic leading to the “blighted” symptom. In wet weather the lesions may have a downy appearance due to sporulation of the pathogen, Phytophthora infestans. Late blight can move quickly through a field causing large yield losses. It infects leaves, stems and fruit. Tomatoes are at particular risk now because of our rainy weather and moderate temperatures, conditions that are highly conducive to disease. 

Because late blight has been confirmed on the Delmarva, growers are advised to switch to a spray program that rotates some of the following combinations:
● Forum plus a protectant, such as chlorothalonil
● Previcur Flex plus a protectant
● Ranman plus a protectant
● Tanos plus a protectant

Continue using these materials until conditions no longer favor development of late blight.

There are some OMRI (Organic Material Review Institute) approved products that list late blight as a target disease. However there is limited information on their efficacy and the information available usually indicates that they are not as efficacious as “conventional” non-organic materials. With those caveats, the OMRI approved materials include basic copper sulfate (check for formulations that state that they are OMRI approved) and Sonata.

tomato late blight symptoms

Symptoms of tomato late blight