My Late Blight Experience in the Red River Valley
by David Hankey, Potato Grower, Grafton, ND
Late blight is a very fast moving disease. One really has to go with protectants early in the season. That is the first and most important point which I want to make. Early application is the cheapest and the best method, to stop late blight before it ever starts.
The minute late blight is found in a field; it better be treated immediately. There is no time to wait since late blight can take a field down in a week. If the conditions are persistent, a second treatment will be necessary. We can really look at what has happened in the RRV during the 1990s. Every time someone has had a problem, something was not done right. Recommendations were not followed. Either protectants were not sprayed early enough or time was wasted and treatment delayed, hoping that the weather conditions would change, or a second treatment was skipped. The next thing that happens is that late blight breaks out and growers have to make some hard decisions.
Varietal differences can play a factor. For example, we have seen a big difference in susceptibility between Frito Lay variety 1533 which was by far the most susceptible variety, and Snowden and Russet Burbank which are not very susceptible.
From the growers' perception, the first thing is to be able to identify late blight. The very first time that I saw it was real interesting. I walked the fields and walked the fields, and could not figure out if what I saw was late blight. Then, all of a sudden, it was all over the place and I knew that was what it was. I didn't need an expert to tell me; it just explodes. If you have anything questionable, test it the minute you find it.
Here is another experience that I would like to share. I sprayed everything with Ridomil prepacks twice in 1993, sprayed protectants five and six times, and I was relatively sure the fields didn't have late blight. There was nothing more that could be done. Late in the season while walking the fields, I found some misses that I didn't know were there. They were just left and harvested last. Even when you think that you have all the bases covered, you still have to walk your fields and walk them close. Special attention was given to samples from lots going into storage. One person was assigned just to test samples, looking for late blight on tubers. Even if you think there is only two or three percent infection, it can amount to more. You really have to know what is going in storage.
How did potatoes get checked as they were going into storage? Every truck load coming from the field had someone taking 25 to 50 lb samples which were washed and inspected. It is not fool proof. Part of the reason for vine desiccation two to three weeks before harvest is to prevent any new infections, so by the time tubers are harvested the infection should show up.
In dealing with late blight, another factor to be prepared for is the cost. The best strategy is to alert the banker that there may be extra cost per acre to combat late blight. This will give the bankers time to have it approved and you won't waist time waiting. Late blight can really add to your cost and you had better be ready for it. Although we spray primarily with ground rigs, an emergency situation may occur where aerial spraying is needed.
To sum it up, you have to go in early and scout your fields. If the field has late blight, you had better be prepared to spend the money because it will be a lot more expensive if you have a problem.
A Farmer's Check List on Late Blight:
1. Learn to Identify
2. Walk the Fields
3. Test Anything Questionable
4. Sample at Harvest
5. Insure Crop (if possible)
6. Prepare Banker of Cost
7. Be Ready to Apply Fungicides