Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Location: Art and Keith Wicks Farm, Rt 9, Little Creek, Kent County.
Greenrow: May 3
| Date | Late Blight | Early Blight | Spray Interval Recommendation | |
| DSV | Total DSV | Accumulated P-days | ||
| 6/6 | 1 | 58 | 251 | 10-days |
| 6/6-6/8 | 0 | 58 | 263 | 10-days |
| 6/8-6/9 | 0 | 58 | 267 | 10-days |
| 6/10 | 2 | 60 | 274 | 10-days |
| 6/11 | 4 | 64 | 282 | 5-days |
| 6/12 | 2 | 66 | 291 | 5-days |
| 6/13 | 0 | 66 | 301 | 7-days |
| 6/13-6/15 | 0 | 66 | 318 | 7-days |
| 6/16 | 1 | 67 | 328 | 7-days |
| 6/17 | 0 | 67 | 336 | 7-days |
| 6/18-6/19 | 0 | 67 | 352 | 10-days |
| 6/20-6/22 | 0 | 67 | 377 | 10-days |
Continue to scout fields for symptoms of late blight. Conditions will continue to favor early blight. We have surpassed the 300 P-day threshold for initiating early blight sprays.
Early Blight and Black Dot
Many fields have flowered and this is a good time to consider switching to an application or two of Gem, Headline, Quadris, or Evito (no black dot label) for early blight susceptible varieties. This can also be helpful for late season varieties including russets if stress makes plants susceptible to black dot later. Make one or two applications at the end of flowering and repeat 14 days later. Apply mancozeb or chlorothalonil 7-days later between the two applications. Another product that is labeled for early blight is Revus Top from Syngenta. Revus Top is a combination product of Revus (mandipropamid, Group 40) plus difenoconazole which is triazole fungicide (Group 3). Difenconazole has been used in Europe very successfully for early blight control. Since it is a different mode of action than the strobilurin fungicides (Group 11) it would be a good alternative if resistance is an issue if Gem, Quadris, or Headline are not controlling early blight.
For specific fungicide recommendations, see the 2011 Delaware Commercial Vegetable Production Recommendations Book.