Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Disease Severity Value (DSV) Accumulation as of July 23, 2008 is as follows:
Location: Broad Acres, Zimmerman Farm, Rt. 9, Kent County
Greenrow: April 27
| LATE BLIGHT | EARLY BLIGHT | |||
| Date | Daily DSV | Total DSV | Spray Recs | Accumulated P days* |
| 6/22-6/23 | 1 | 45 | 10-day interval | 418 |
| 6/23-6/25 | 0 | 45 | 10-day interval | 435 |
| 6/26-6/30 | 0 | 45 | 10-day interval | 466 |
| 6/30-7/2 | 0 | 45 | 10-day interval | 482 |
| 7/2-7/3 | 0 | 45 | 10-day interval | 489 |
| 7/4-7/5 | 1 | 46 | 10-day interval | 496 |
| 7/5-7/6 | 2 | 48 | 10-day interval | 505 |
| 7/6-7/7 | 3 | 51 | 7-day interval | 514 |
| 7/7-7/9 | 0 | 51 | 7-day interval | 536 |
| 7/9-7/10 | 2 | 53 | 7-day interval | 544 |
| 7/10-7/13 | 0 | 53 | 10-day interval | 566 |
| 7/13-7/14 | 1 | 54 | 10-day interval | 575 |
| 7/14-7/16 | 0 | 54 | 10-day interval | 589 |
| 7/16-7/20 | 0 | 54 | 10-day interval | 608 |
| 7/20-7/23 | 0 | 54 | 10-day interval | 622 |
* 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 greenrow. To date, 622 P-days have accumulated at the site.
Maintain fungicide applications for plants that are still green. There have been no reports of late blight on either potato or tomato in the region. There was a report on potato from Erie County, PA late last week. We probably received enough rain last night and humidity to accumulate several DSVs last night but the hot dry weather has not been favorable for late blight. No reason to change the spray interval. All the best to the growers as they begin harvest.
For specific fungicide recommendations, see the 2008 Delaware Commercial Vegetable Production Recommendations Book.