Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Late Blight Advisory
Location: Shadybrook Farms, Little Creek, DE (Kent County)
Greenrow: May 1
| Date | DSV | Total DSV | Accumulated P-days* | Spray Recommendation |
| 5/3-5/6 | 41 | |||
| 5/7 | 2 | 43 | ||
| 5/8 | 1 | 44 | ||
| 5/9-5/13 | 0 | 44 | 10-day spray interval | |
| 5/14 | 1 | 45 | 10-day spray interval | |
| 5/15 | 3 | 48 | 10-day spray interval | |
| 5/16 | 2 | 50 | 7-day spray interval | |
| 5/16-5/25 | 0 | 50 | 7-day spray interval | |
| 5/26 | 3 | 53 | 10-day spray interval | |
| 5/27 | 3 | 56 | 217 | 7-day spray interval |
*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 217 P-days have accumulated at the site. Once 300 P-days have accumulated, the first fungicide for early blight control should be applied. This usually occurs when rows are touching.
Maintain the recommended spray interval. At 300 P-days, sprays will be need to control early blight. Growers who do not want to rely only on the DSV calculations for scheduling fungicide applications should apply at least 1-2 sprays of mancozeb (Dithane, Manzate, Pencozeb, Manex II) or Bravo (chlorothalonil) before plants canopy down the row. At this point weekly fungicide applications would be suggested.
For specific fungicide recommendations see the Delaware Commercial Vegetable Production Recommendations.