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.