Amanda Gevens, UW-Extension Plant Pathologist
Department of Plant Pathology
UW-Madison College of Agricultural and Life Sciences
Total time – 3:05
0:11 – Current situation for late blight
0:23 – Why is late blight a concern in Wisconsin
0:55 – How is late blight transferred to crops
1:38 – Late blight symptoms
2:13 – What to do if late blight is suspected
2:33 – What if late blight is confirmed
2:55 – Lead out
Lorre Kolb: Late blight in tomatoes and potatoes. We’re visiting today with Amanda Gevens, Extension vegetable crops plant pathologist, University of Wisconsin-Madison/Extension, in the College of Agricultural and Life Sciences, and I’m Lorre Kolb. Amanda, what’s the situation with late blight this year?
Amanda Gevens: Late blight, that potentially can affect both tomato and potato crops here in the state and really globally, has not yet been found here in the state.
Lorre Kolb: Why is late blight a concern in Wisconsin?
Amanda Gevens: Late blight can be a very concerning disease, particularly to potato growers here. In this state we have over 62,000 acres of commercial potatoes in Wisconsin and so for economic reasons we are always watchful of this particular disease because it can be very severe in the crop and costly. The risk to tomatoes in our state is also high. While we don’t have a significant commercial acreage, we do have many tomato plantings around the state in home gardens as well as in direct markets and farm stand markets across the state.
Lorre Kolb: If late blight is found in plants, how is it transferred to larger crops?
Amanda Gevens: The pathogen that causes late blight is typically introduced in a production season through just a few means. And one is on infected seed potatoes. So the planting of potatoes from a crop that was infected last year can introduce inoculum into that planting. And then when the weather is right, so when we’ve had very moist weather conditions and moderate temperatures, that disease can initiate. The other source of introduction is on infected transplants, in particular tomato transplants that are raised in other regions of the U.S. that may have late blight. And then we can also receive inoculum or spores by wind.
Lorre Kolb: And what are indicators of late blight?
Amanda Gevens: Most typically we speak of symptoms of what we call water soaking or what looks sort of oily or greasy looking wet area or lesion on a plant. Typically it’s seen first on leaves and petioles or stems of tomatoes and potatoes. And then that lesion can get a bit dry looking and look brown and dead. But it will often have with it this white fuzzy growth and that is the pathogen producing new spores. And we can see that both on the foliage as well as on tomato fruits and the infection can make its way down to potato tubers as well as the season progresses.
Lorre Kolb: And what should someone do if they suspect late blight?
Amanda Gevens: We have numerous online resources through my program – through UW Vegetable Pathology, as well as a national website which is USABlight. And we also offer free diagnostics here in our plant disease diagnostics clinic and my program, the UW Vegetable Plant Pathology Research and Extension program offers free diagnostics as well.
Lorre Kolb: And what if late blight is confirmed?
Amanda Gevens: Late blight is a regulated disease in the state of Wisconsin due to the potential negative economic impact in potatoes. Typically the first reports or those first detections will be managed quite aggressively – it’s asked that those plants be destroyed or disposed of to limit further spread.
Lorre Kolb: We’ve been visiting today with Amanda Gevens, Extension vegetable crops plant pathologist, University of Wisconsin-Madison/Extension, in the College of Agricultural and Life Sciences, and I’m Lorre Kolb.