Dr. Margret McGrath, Cornell University
Dr. Sally Miller, Ohio State University
This clip is from the Late Blight Control in Your Organic Farm Webinar
The scouting is the foundation of integrated pest management in that we always need good information as to whether a pathogen is present or an insect is present in order to make those management decisions. So what we will be asking in scouting is: is the disease present, how much of the disease is present, that is incidence and the severity, so that's how many plants are affected and for the affected plants, how bad is the disease and what is the pattern of the disease, is it in hot spots, along the edges or is it random throughout the field.
Lets talk about the basics of scouting. First we need to very early in the season look for late blight carryover from the previous year. We talked about the potatoes that might be carriers over the winter in cull piles or that weren’t harvested and they might sprout up volunteer potatoes. So volunteers need to be destroyed. Volunteer tomatoes also need to be taken out. If in the case of tomatoes the seedlings should be inspected very carefully and essentially it's always good idea to not plant tomato seedlings that do not look healthy. Sometimes that's difficult because they have to be held a little while but if they look like they've got disease symptoms, it's really better not to plant them.
So begin scouting as soon as green tissue emerges for potatoes so as soon as the potatoes start coming up it's time to start scouting particularly if the weather conditions are favorable to late blight. For tomatoes this should be soon after transplanting. We can focus on areas of the field because of what we know about late blight. Where the moisture and humidity are highest and where the cover of fungicides might be poor, for example, around the edges of the field. Scout as early in the morning as possible because then you are most likely to see that sporulation, that ring around the edge of the lesion. And that's a very good way to confirm what you've got there. Check the leaves, dig down into the canopy and look for those stem lesions and perhaps some infection on the fruits or the leaves. Now when the conditions are cool and rainy, that is when you should be out there more often and intensifying the scouting.
Finally I would just like to say scouting is again very important to do but we don't want scouting to be a means of spreading disease from one field to another so hands should be washed very carefully, boots should be washed off every care taken to not get clothing in contact with plants. That is really critical to do that to prevent the movement of pathogen from one field to another.