Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Disease Severity Value (DSV) Accumulation as of July 9, 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* |
| 6/15-6/18 | 0 | 44 | 10-day interval | 376 |
| 6/19-6/22 | 0 | 44 | 10-day interval | 409 |
| 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 |
* 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, 536 P-days have accumulated at the site.
The recent thunder showers and increased humidity have produced conditions favorable for both late blight and early blight. Maintain fungicide applications. There have been no reports of late blight on either potato or tomato in the region.
Early dying was confirmed this past week. One-sided brown discoloration was present and the causal fungus, Verticillium, was isolated from the discolored areas. Lesion nematodes can often be present as well which can greatly increase the symptoms and reduce yields. As most of you know ‘Superior’ is pretty susceptible to early dying. Resistant varieties, long rotations away from potatoes or fumigation are the most recommended treatments. There is some evidence that using Sudan grass in the rotation can reduce early dying as well.
For specific fungicide recommendations, see the 2008 Delaware Commercial Vegetable Production Recommendations Book.