Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Disease Severity Value (DSV) Accumulation as of July 1, 2009 is as follows:
Location: Shadybrook Farms, Little Creek, DE in Kent County.
Greenrow: May 1
| LATE BLIGHT | EARLY BLIGHT | |||
| Date | Daily DSV | Total DSV | Spray Recs | Accumulated P-days* |
| 6/17-18 | 10 | 106 | 7-day interval | 406 |
| 6/19 | 4 | 110 | 7-day interval | 410 |
| 6/20-6/21 | 1 | 111 | 5-day interval | 434 |
| 6/22-6/23 | 0 | 111 | 7-day interval | 462 |
| 6/24 | 1 | 112 | 7-day interval | 470 |
| 6/25-6/28 | 0 | 112 | 10-day interval | 495 |
| 6/29 | 0 | 112 | 10-day interval | 503 |
| 6/30 | 0 | 112 | 10-day interval | 511 |
| 7/1 | 2 | 114 | 10-day interval | 519 |
There have been no new reports of late blight in the neighboring states since the last report. It looks like we are going to get a break in the weather in that it will not be favorable for late blight again for the next few days but will continue to be favorable for early blight. If several sprays of a late blight targeted fungicide have been made, the next spray could be a preventative spray of Bravo or mancozeb at the highest labeled rate. None of the targeted late blight fungicides such as Previcur Flex, Curzate, Ranman and now Revus should ever be used more than twice in a row to prevent resistance development in the fungus. When they are used, read the label for mixing partners with a protectant fungicide and possible need for adjuvants.
Note: As of last Friday Syngenta announced that Revus (mandipropamid) received a supplemental label to add potatoes and tomatoes to its label for late blight control at 5.5-8.0 fl oz/A on a 7 to 10-day interval. Addition of a non-ionic surfactant is recommended. It is another late blight specific fungicide that can be used.
Remember if you sprayed Curzate it has a short residual activity period especially when the temperatures are above 80 so you will need to make another fungicide application 5 days later at the maximum.
If the fields are dry enough and you have the ability to ground-apply fungicides now would be a good time to get good coverage of any areas that an aerial application may not have covered well or at all (under power lines, next to buildings, fence rows, etc).