Potato Disease Advisory #7 – June 14, 2013

June 14, 2013 in Vegetable Crops

Phillip Sylvester, Kent Co., Ag Agent; phillip@udel.edu

Location: Art and Keith Wicks Farm, Rt 9, Leipsic, Kent County
Greenrow: May 5

Date

DSV

Total DSV

Accumulated

P-Days

Spray Interval Recommendation

5/15 – 5/20

11

32

5-days

5/20 – 5/23

2

34

5-days

5/23 – 5/27

5

39

5-days

5/27 – 5/30

0

39

10-days

5/30 – 6/6

2

41

251

10-days

6/6 – 6/7

10

51

261

5-days

6/7 – 6/9

10

61

280

5-days

6/9 – 6-13

4

65

314

7-days

 

Late Blight
The threshold of 18 DSVs has been exceeded. Sixty-five (65) DSV’s have accumulated so far for any potatoes that established green row (approximately 50% emergence) prior to and since May 5. Favorable conditions have lowered the spray interval recommendation to seven (7) days. Late blight was reported in greenhouse tomatoes in Morgan County, WV over 7 days ago. The website USABlight tracks tomato and potato late blight across the nation and can be found here: http://usablight.org/ Continue to scout your fields regularly for symptoms. Any suspicious samples can be sent to the UD Plant Diagnostic Lab or dropped off at your local Extension office. See the 2013 Commercial Vegetable Production Recommendations-Delaware: http://extension.udel.edu/ag/files/2012/03/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. We have now exceeded 300 P-days as of Thursday, June 13. Airborne Early blight inoculum should rise 5-10 days after accumulating 300 P-days. A fungicide for early blight control is recommended. Commercial fungicide recommendations can be found in the 2013 Delaware Commercial Vegetable Recommendations Guide at http://extension.udel.edu/ag/files/2012/03/Potatoes.pdf