Question: I have a very large black walnut tree in my yard. This year the tree has no walnuts on it. My question is this: Is there a way to keep my tree from producing walnuts every year? Last year we had a bumper crop of walnuts, 12 large wheelbarrows full, that I had to haul off into the woods out back. Not having any walnuts to have to shovel/rake up this year is a blessing to me. R.B.
Answer: Florel is used to reduce or eliminate fruit (nuts) on trees. The product is most often used on fruit trees but is labeled for use on ornamental/landscape trees (although walnut is not specifically listed). The active ingredient in Florel is ethephon which is a synthetic form of the plant hormone ethylene. When sprayed on the flowers during mid to full bloom, the hormone prevents fruit development. There are a couple of problems using Florel. First, it is difficult to get complete spray coverage in the upper canopy, where the flowers are located, of full sized trees. Good coverage is required for the product to be effective. Secondly, black walnut flowers are fairly small and inconspicuous so it may be challenging to know exactly when to spray trees. Correct timing is essential for the product to work.
Black walnuts, like many trees, are alternate year bearing – one year they have a large crop and the next few nuts/fruits. Production in 2013 was unusually high for many trees and shrubs because of the drought stress in 2012. The odds of another mega crop, like 2013, are fairly low. My recommendation is don’t waste your effort and money spraying to prevent walnuts. Enjoy the lean years and tolerate the large years.
Question: One of my red oak trees that is about 15 years old has not shed last falls’ leaves. It normally holds its fall leaves until the following spring but then they eventually drop. This year the new leaves came but the old ones have not dropped. Wondering if you can shed some light on this for me. M.C.
Answer: Young or juvenile oak trees typically hold onto their leaves through the winter. Usually the old leaves are pushed off by bud expansion in spring but it sounds like that didn’t happen this year. I think it is one of those unusual phenomena that may be related to the environmental conditions. I don’t think there is any need for concern.
Barb Larson is horticulture educator for Kenosha County University of Wisconsin Extension. Barb has a Master’s of Science in horticulture from the University of Wisconsin-Madison. If you have a plant or gardening question, email Larson at firstname.lastname@example.org or call her at 262-857-1942.