Tomato late blight spreads in Wisconsin
Extension Plant Pathologist
Department of Plant Pathology
UW-Madison College of Agricultural and Life Sciences
Coping with tomato late blight
Time – 3:03 minutes
0:16 – Potential to lose tomato crop
0:51 – What tomato late blight looks like
2:04 – Step to prevent late blight
2:35 – Post harvest threat
2:53 – Lead out
Late blight makes it appearance in Wisconsin. We’re visiting today with Amanda Gevens, Department of Plant Pathology, University of Wisconsin-Extension in the College of Agricultural and Life Sciences, Madison, Wisconsin and I’m Sevie Kenyon.
Sevie Kenyon: Amanda, what’s the primary concern at this point with late blight?
Amanda Gevens: The primary concern in the tomato crop for home gardeners, small farms both conventional and organic, is late season planted fruit infections. At this point in the season, we have quite lovely plants. All season with a dry, hot summer tomatoes were quite happy and got tall and were beautiful looking but now we have the risk of those beautiful green fruit on plants becoming infected with late blight and really wiping out a significant portion of this late season harvest. So that’s our concern in the tomato crop.
Sevie Kenyon: Amanda can you give us an idea of what the symptoms look like?
Amanda Gevens: Yes, on tomato, symptoms that you would be looking for are approximately dime-size brown to dark brown lesions on leaves and on stems. And these lesions may look dry if the weather is dry. If it’s a bit wetter you may see these lesions looking a bit oily or greasy is how it is typically described. If you flip the leaves over often you will see a white fuzzy growth that is in a ring or a halo around that lesion. And that is the pathogen producing new spores that will be further spread aerially. On tomato fruit the symptoms are quite distinctive. If gardeners have seen it once, they can usually detect it again for the rest of their lives. On fruit you will see a dark brown, almost a copper color to dark brown firm lesion. So it’s hard, not a soft rot or a sunken rot but that brown spot will often have lines or rings in it. As the pathogen grows each day, you’ll see sort of a next wave or flush of growth. So often times you do see rings within that brown firm lesion on a fruit.
Sevie Kenyon: And are there steps people can take to stop it or prevent it?
Amanda Gevens: In my program here we have been looking at some organic fungicides for control of late blight. And the one thing we find consistent across all materials is if you don’t get it out until after an infection has occurred, almost none of them work very well. But if you get those control measures, those fungicides, out in advance of first infection, you can limit infection and then limit overall disease on those plants and have a harvestable, healthy crop.
Sevie Kenyon: How should growers handle their crop post-harvest?
Amanda Gevens: Late blight can develop post-harvest. A careful, critical eye almost on a daily basis is then required. You don’t want late blight infected fruit being sent out. And it’s not recommended that those infected fruits be consumed or processed, in a canning process even.
Sevie Kenyon: We’ve been visiting with Amanda Gevens, Department of Plant Pathology, University of Wisconsin-Extension in the College of Agricultural and Life Sciences, Madison, Wisconsin and I’m Sevie Kenyon.