Originally Posted on July 18, 2014 at 5:25 PM
Late Blight Alert!
On Wednesday afternoon Chuck Bornt found late blight (LB) in a potato field in Columbia County. A sample has been sent off to Dr. Fry at Cornell University for confirmation and isolate identification. The outbreaks in Erie County and Long Island, both in potato, are the US 23 strain which is sensitive to Ridomil. The US 23 strain of LB is equally aggressive on tomato as it is on potato.
Growers will need to evaluate the threat to their crops based on scouting, weather, proximity to known outbreaks, spray materials (protective vs. systemic) and spray intervals. At this time, for most growers, it is likely protection from LB is adequate using protective materials such as chlorothalonil (Bravo Weather Stik or OLF) or mancozeb (Dithane DF or OLP), and for organic growers copper compounds such as Champ. Keep in mind that new growth needs to be covered and that rain over an inch and in particular a hard pounding rain is considered a wash off for many of these materials. LB may first appear in areas of the field with poor air circulation by wooded edges and low areas. Infected tissue is initially water soaked (olive green color) then becomes brown or black. The lesion is often surrounded by a light green halo. Under humid conditions, sporulation (white fuzz) may be seen on the underside of the leaf surrounding the lesion.
Once you see LB on your farm, or if you are downwind of a farm in your area that has LB, you will want to use the systemic or translaminar products such as Curzate + protectant, or Revus Top. Because of resistance issues Ridomil should only be used if LB is present at a low level in the field but not if there is a raging infestation. Catching LB early and timely fungicide applications are key in controlling this very destructive disease which under overcast and moist conditions will progress very rapidly. If you have questions or think you may have LB, please let one of the ENYCHP educators know. Stay tuned…we will keep you updated on this outbreak. -TR