Potato Disease Advisory #8 – May 31, 2012

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

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

Date

DSV

Total DSV

Accumulated
P-Days

Spray Interval Recommendation

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

5/24-5/28

8

65

279

5-days

5/28-5/30

3

68

294

5-days

 

The threshold of 18 DSV’s has been exceeded. Sixty-eight (68) DSVs have accumulated as of Wednesday, May 30. This includes any potatoes that established green row (approximately 50% emergence) prior to and on April 20. An additional three (3) DSVs accumulated from Monday, May 28 to Wednesday, May 30. The spray interval recommendation is 5 days.

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

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 294 P-days have accumulated at this site as of Wednesday, May 30. Airborne Early blight inoculum should rise 5-10 days after accumulating 300 P-days. Judging by the forecast, the 300-P day threshold will probably be exceeded in a day or two. A protectant fungicide application should be made once we exceed that threshold. Commercial fungicide recommendations can be found in the 2012 Delaware Commercial Vegetable Recommendations Guide at http://ag.udel.edu/extension/vegprogram/pdf/potatoes.pdf

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