Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Disease Severity Value (DSV) Accumulation as of June 16, 2010 is as follows:
Location: Art and Keith Wicks Farm, Rt. 9, Little Creek, Kent County
Green row: May 6
| LATE BLIGHT | EARLY BLIGHT | |||
| Date | Daily DSV | Total DSV | Spray Recs | Accumulated P- days* |
| 5/29-5/30 | 1 | 31 | 10- days | – |
| 5/31 | 0 | 31 | 10-days | 199 |
| 6/1 | 1 | 32 | 10-days | 206 |
| 6/2 | 0 | 32 | 10-days | 214 |
| 6/3-6/5 | 0 | 32 | 10-days | 232 |
| 6/6-6/8 | 0 | 32 | 10-days | 257 |
| 6/9–6/10 | 4 | 36 | 7-days | 275 |
| 6/11-6/12 | 1 | 37 | 7-days | 292 |
| 6/13-6/14 | 2 | 39 | 7-days | 305 |
| 6/15–6/16 | 0 | 39 | 7-10 days | 325 |
Maintain the recommended spray interval. At 300 P-days fungicide sprays will be needed to control early blight. At this point weekly fungicide applications would be suggested. There have been no confirmed reports of late blight on potatoes in the region.
* P days– We use the predictive model WISDOM to determine the first fungicide application for prevention of early blight as well. 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. To date, 325 P-days have accumulated at the site. The first fungicide for early blight control should be applied. This usually occurs when rows are touching.
For specific fungicide recommendations, see the 2010 Delaware Commercial Vegetable Production Recommendations Book.