Posts Tagged ‘potato’

Potato Disease Advisory #6 – May 24, 2012

Thursday, May 24th, 2012

Phillip Sylvester, Kent Co., Ag Agent; phillip@udel.edu and Nancy Gregory, Plant Diagnostician; ngregory@udel.edu

LATE BLIGHT ON POTATO ALERT:
From Andy Wyenandt, Extension Vegetable Pathologist, Rutgers University: Late blight was confirmed on actively sporulating leaf lesions from an 8 acre potato field in Burlington County, New Jersey. The few infected plants were found at the end of a row where the boom sprayer was most likely turned off. The grower had preventative applications of manzate followed by chlorothalonil prior. Seed pieces were sourced from Maine. This is the first report of Late blight in New Jersey on potato or tomato this year.

Continue to scout for Late blight symptoms in local potato fields. Please notify and submit samples with symptoms to your local county extension office (Kent: 302-730-4000 Sussex: 302-856-7303) or contact the UD Plant Diagnostic clinic (302-831-1390) to have the sample confirmed. You may also email Nancy Gregory at ngreogry@udel.edu or Phillip Sylvester at phillip@udel.edu if you have a sample to submit.

Good coverage with preventative fungicides application is very important for Late blight control. Commercial fungicide recommendations can be found in the 2012 Delaware Commercial Vegetable Recommendations Guide at http://ag.udel.edu/extension/vegprogram/pdf/potatoes.pdf

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

Date

DSV

Total DSV

Accumulated P-Days

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

149

10-days

5/13 – 5/16

5

44

177

7-days

5/17-5/20

0

44

209

7-days

5/20-5/22

11

55

229

5-days

5/22-5/23

2

57

238

5-days

The threshold of 18 DSVs has been exceeded. Fifty-seven (57) DSVs have accumulated as of Wednesday, May 23. This includes any potatoes that established green row (approximately 50% emergence) prior to and on April 20. An additional thirteen (13) DSVs accumulated from Sunday, May 20 to Wednesday, May 23. Recent weather conditions have been favorable for late blight development since the last report. The predicted hot weather would make conditions less favorable for Late blight. The spray interval recommendation has been lowered to 5 days.

Early Blight
We are using the predictive model WISDOM to determine the first fungicide application for prevention of early blight. The model predicts the first seasonal rise in the number of spores of the early blight fungus based on the accumulation of 300 physiological days (a type of degree-day unit, referred to as P-days) from green row. A total of 238 P-days have accumulated at this site as of Wednesday, May 23. Once 300 P-days have accumulated, the first fungicide for early blight control should be applied. This usually occurs when rows are touching.

Spray to Prevent Late Blight on Potato and Tomato

Thursday, May 24th, 2012

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

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 http://ag.udel.edu/extension/vegprogram/publications.htm#vegrecs.

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.

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.