I have revceived many calls this week on leaf fall from Green Ash trees. We are seeing whole leave as well as leaflets littering the ground.

We have had a very mild winter, relatively dry spring, although soil moisture is rated adequate to surplus. It has been slightly cool in evenings. Although there is not much disfiguration showing on the leaves, I wonder if this is just a different form of Ash anthracnose than I am used to seeing.

There is no sign of insects, have been no high winds or late season frosts (today is the last average frost for the area), abnormal rainfall or drought. Not all trees are affected, but about 20% are showing something.

Bob Underwood

Reply to post by Bob Underwood, on May 27, 2000 at 12:42:03:

I've seen similar leaf drop on F. pennsylvanica in the mid Atlantic region also. Univ. of Delaware found it to be a type of anthracnose (don't recall the species- this was about 12 years ago) that affected the petioles more than the blades. The broken tips of the petiole or rachis were black.

Reply to post by Bob Underwood, on May 27, 2000 at 12:42:03:

Bob,

This response is a tangent... really a soils and physiology topic. But among the things you observed or ruled out in addressing the leaf drop problem was soil moisture. This seems very intuitive.... not enough moisture and leaves fall.

A recent (and ongoing as we speak) experience raises a question. The current case involves a large Quercus alba which suffered almost 90% root loss in February. It has leafed out completely... started bud break mid-April. About on schedule as compared to other similar or older age-class Q.a. in the locale. The three 90+ degree days we had in early May pushed the leaves very quickly to near full expansion. We have not lost a leaf yet. We had a severe drought last Summer, though there are some perrenial springs in the area of this tree.

So, the question is - in a very general way - when do the new leaves start to really require replacement moisture from soil. Is there some seasonal rule of thumb? A number of degree days? That's somewhat rhetorical.... the point being the trees seem to be able to maintain leaf turgor with "on-board" moisture for quite a while.

I'd guess you're somewhat later than we are in seasonal terms in sunny ND. (Why not Minot? Freezin's the reason. Do they still have those t-shirts?) So your trees might be less far along in that timeline to soil moisture need.