Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu; Phillip Sylvester, Kent Co., Ag Agent; phillip@udel.edu
With my impending retirement only a week away, we were concerned that the Potato Disease Advisory email and FAX may not get done this year and would resume hopefully by my replacement. Phillip Sylvester, our Kent County Ag Agent, has volunteered to keep the late blight advisory part of the report operating for potato growers in our area for this season.
Late blight Advisory
We are using the E-WEATHER SERVICE from SkyBit, Inc as we have in the past. The service determines specific requested weather parameters (temperature, relative humidity and rainfall) based on calculations of data from the nearest National Weather Service stations. This weather data is used in the WISDOM software program for predicting late blight and early blight and making spray recommendations. Our location this year is:
Location: Art and Keith Wicks Farm, Rt 9, Leipsic, Kent County
Greenrow: April 20
| Date | DSV | Total DSV | Spray Interval Recommendations |
| 4/20 – 4/30 | 12 | 12 | None |
| 4/30 – 5/1 | 8 | 20 | 7-days |
| 5/1 – 5-8 | 15 | 35 | 5-days |
The threat of late blight from seed infection was moderate since there was late blight in 2011 in the seed producing areas. Be vigilant since we have exceeded 18 DSVs already for 2012. The first late blight fungicide application is recommended once 18 Disease Severity Values (DSVs) accumulate from green row. Green row occurred on approximately April 20 at this location. Please be vigilant and keep a look out for suspect infections on young plants coming from infected seed pieces! Growers opting not to use the forecast system should put the first late blight fungicide application on when the plants are 6 inches tall or plants are touching down the row, and repeat every 7 days. There are numerous fungicides now labeled for late blight control; however, use of mancozeb (Manzate, Penncozeb, or Dithane) or chlorothalonil (Bravo) are still very effective early season protective fungicides to use. See the 2012 Commercial Vegetable Production Recommendations-Delaware for more information on products and rates.
The threshold of 18 DSVs has been exceeded. Thirty-five (35) DSVs have accumulated so far for any potatoes that established green row (approximately 50% emergence) prior to and since April 20. Spraying as soon as possible with a protectant fungicide would be advised if not already on a spray program. The forecast looks like favorable weather for late blight will continue. Scout your fields regularly for symptoms. Late blight was reported in northern North Carolina last week.