Diagnosing spots on tree leaves

By Joseph O'Brien, USDA Forest Service, Bugwood.org (Forestry images website) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

Oak wilt symptoms. Photo by Joseph O’Brien, USDA Forest Service, Bugwood.org (Forestry images website) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

Brian Hudelson, UW-Extension Plant Disease Diagnostician
Plant Diagnostic Lab
Department of Plant Pathology
UW-Madison College of Agricultural and Life Sciences
(608) 262-2863

Brian Hudelson talks about what types of tree leaf diseases to be aware of in the state and what to do about these diseases. 

3:08 Total Time

0:14 – What tree leaf diseases might we see
0:47 – What to do about the diseases
1:16 – Plant diseases seen in fruit trees
1:58 – Diseases that might threaten forests in the state
2:20 – Describe oak wilt and what to do about it
2:49 – How to remedy oak wilt
2:58 – Lead out



Sevie Kenyon: Trying to figure out what those spots on your tree leaves are, we’re visiting today with Brian Hudelson UW-Madison Extension Plant Pathologist, Plant Disease Diagnostic Lab in the College of Agricultural and Life Sciences, and I’m Sevie Kenyon. Brian, tell us a little bit about what kind of tree leaf diseases we might see this year.

Brian Hudelson: What I am really worried about, at this point, is a group of diseases called the Anthracnose diseases and we see these on oaks and maples and ash trees. If you start to see kind of blotchy brown dead areas on leaves that’s probably what you’re dealing with. Another disease we see a lot of is something called Tar Spot; it’s been a real problem on Norway maples, which is an introduced maple here in Wisconsin. If you happen to have crab apples, Apple Scab is also another very common leaf disease that we see.

Sevie Kenyon: And Brian, should people do anything about these diseases if they see them?

Brain Hudelson: Most of the time not, they tend to be pretty cosmetic. Certainly there are fungicide treatments if you want to go that route. My usual recommendation for things like Anthracnose and Tar Spot is really good Fall clean up. With apple scab it can get a bit a little bit diceier, often times the tree will bloom profusely. If you are really worries about it sometimes I recommend remove your current crab apple and replace it with a newer variety that has some resistance.

Sevie Kenyon: Are there some plant diseases people should look out for with their apple trees, pear trees, those kinds of fruit trees?

Brain Hudelson: The Apple Scab, again, is one that we see on apples and pears as well, and that can be a situation where you may want to get into a routine fungicide spray treatment if you’ve had a chronic problem with defoliation. Some of the commercial apple varieties are quiet susceptible to scab and for homeowners we have a really nice publication that’s available through our learning store website. It’s our UW-Extension publications unit, if you go onto that website and just do a search on apples, you’ll find one about apple pests in the home garden and there’s a really nice table on that particular publication.

Sevie Kenyon: Are there diseases that might threaten our entire forest system here in the state, ever?

Brain Hudelson: Well, certainly one of the big ones that we are looking at is Oak Wilt, which is a disease that occurs on oaks, it causes tree death. Usually it’s introduced into an area by sap beetles that visit trees that have been wounded in some way and that one can cause a fair amount of damage.

Sevie Kenyon: Perhaps you could describe that Oak Wilt and what people might do about it?

Brain Hudelson: Yeah that one’s a little bit difficult to diagnose. If you start to see an oak tree where you have a sectional die back so it usually starts with a single branch and then a group of branches and then eventually the entire tree will die. If you see those sorts of symptoms my recommendation would be to get a sample into my clinic for verification and there are some other diseases, and also insect pests, that can cause somewhat similar symptoms, so we really need to verify whether it is Oak Wilt.

Sevie Kenyon: Are there things that can be done about those situations?

Brain Hudelson: Unfortunately with Oak Wilt, its tree removal but you have to be very careful about how you do that particularly when you have an Oak Grove.

Sevie Kenyon: We’ve been visiting with Brian Hudelson, Plant Diagnostic Lab Department of Plant Pathology University of Wisconsin-Madison in the College of Agricultural and Life Sciences, and I’m Sevie Kenyon


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