Posts Tagged ‘potato late blight’

Potato Disease Advisory #3 – May 17, 2012

Friday, May 18th, 2012

Late blight Advisory
Location: Art and Keith Wicks Farm, Rt 9, Leipsic, Kent County
Greenrow: April 20

Date DSV Total DSV Spray Interval Recommendations
4/20 – 4/30 12 12 None
4/30 – 5/1 8 20 7-days
5/1 – 5-8 15 35 5-days
5/8 – 5/10 4 39 5-days
5/10 – 5/13 0 39 10-days
5/13 – 5/16 5 44 7-days

The threshold of 18 DSVs has been exceeded. Forty-four (44) DSVs have accumulated as of Thursday, May 17. This includes any potatoes that established green row (approximately 50% emergence) prior to and on April 20. An additional five (5) DSVs accumulated during the recent wet, cloudy weather earlier in the week. While the spray interval has been lowered, the short-term forecast is predicting ample sunshine and warm temperatures. This should reduce the risk of late blight development.

Potato Disease Advisory #1 – May 10, 2012

Friday, May 11th, 2012

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu; Phillip Sylvester, Kent Co., Ag Agent; phillip@udel.edu

With my impending retirement only a week away, we were concerned that the Potato Disease Advisory email and FAX may not get done this year and would resume hopefully by my replacement. Phillip Sylvester, our Kent County Ag Agent, has volunteered to keep the late blight advisory part of the report operating for potato growers in our area for this season.

Late blight Advisory
We are using the E-WEATHER SERVICE from SkyBit, Inc as we have in the past. The service determines specific requested weather parameters (temperature, relative humidity and rainfall) based on calculations of data from the nearest National Weather Service stations. This weather data is used in the WISDOM software program for predicting late blight and early blight and making spray recommendations. Our location this year is:

Location: Art and Keith Wicks Farm, Rt 9, Leipsic, Kent County
Greenrow: April 20

Date DSV Total DSV Spray Interval Recommendations
4/20 – 4/30 12 12 None
4/30 – 5/1 8 20 7-days
5/1 – 5-8 15 35 5-days

The threat of late blight from seed infection was moderate since there was late blight in 2011 in the seed producing areas. Be vigilant since we have exceeded 18 DSVs already for 2012. The first late blight fungicide application is recommended once 18 Disease Severity Values (DSVs) accumulate from green row. Green row occurred on approximately April 20 at this location. Please be vigilant and keep a look out for suspect infections on young plants coming from infected seed pieces! Growers opting not to use the forecast system should put the first late blight fungicide application on when the plants are 6 inches tall or plants are touching down the row, and repeat every 7 days. There are numerous fungicides now labeled for late blight control; however, use of mancozeb (Manzate, Penncozeb, or Dithane) or chlorothalonil (Bravo) are still very effective early season protective fungicides to use. See the 2012 Commercial Vegetable Production Recommendations-Delaware for more information on products and rates.

The threshold of 18 DSVs has been exceeded. Thirty-five (35) DSVs have accumulated so far for any potatoes that established green row (approximately 50% emergence) prior to and since April 20. Spraying as soon as possible with a protectant fungicide would be advised if not already on a spray program. The forecast looks like favorable weather for late blight will continue. Scout your fields regularly for symptoms. Late blight was reported in northern North Carolina last week.

Potato Late Blight Confirmed in North Carolina

Thursday, May 3rd, 2012

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

Late blight has been confirmed on potato in a field in North Carolina on May 2, 2012. Growers in Maryland and Delaware should scout their fields and apply a preventative fungicide such as chlorothalonil, mancozeb or Polyram. If the disease spreads north to Virginia, be prepared to apply a more targeted fungicide.

Scout Emerging Potato Fields for Seed-Born Late Blight Infections

Thursday, April 19th, 2012

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

There have been several reports of late blight from Florida. The most recent was a report from north Florida in the Hastings area that was identified early, fungicides were applied and the situation is under control. This is a reminder that there was late blight in many of the seed producing areas last season. In spite of all the precautions and seed testing that occurs to reduce the chance of seed tuber infections, infections can occur if the weather is right and the seed is infected. Be sure to be checking fields as they emerge for any seed born infections. Apply fungicide sprays of mancozeb or chlorothalonil once the plants begin to touch down the row. There is a late blight monitoring website http://usablight.org/ that you can use to see what is happening around the country with late blight on tomato and potato.

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.

Potato Disease Advisory #15 – July 7, 2011

Friday, July 8th, 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*
6/16 1 67 328 7-days
6/17 0 67 336 7-days
6/18-6/19 0 67 352 10-days
6/20-6/22 1 68 377 10-days
6/23 1 69 383 10-days
6/24-6/26 0 69 407 10-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

Continue to scout fields for symptoms of late blight. Conditions will continue to favor early blight. Continued dry weather will not favor the spread of late blight.

Late Blight was reported last week 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

 

Potato Disease Advisory #12 – June 30, 2011

Friday, July 1st, 2011

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

Late blight Advisory

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*
6/13 0 66 301 7-days
6/13-6/15 0 66 318 7-days
6/16 1 67 328 7-days
6/17 0 67 336 7-days
6/18-6/19 0 67 352 10-days
6/20-6/22 1 68 377 10-days
6/23 1 69 383 10-days
6/24-6/26 0 69 407 10-days
6/27 1 70 416 10-days
6/28 1 71 424 10-days

 

Continue to scout fields for symptoms of late blight. Conditions will continue to favor early blight. We have surpassed the 300 P-day threshold for initiating early blight sprays.

Late Blight was reported this week in DE, on the eastern shore VA, and Long Island, New York. 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 near Leipsic in Kent County 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 specific fungicide recommendations, see the 2011 Delaware Commercial Vegetable Production Recommendations Book.