Nut drop in English Walnuts
The nuts on my english walnut trees have dropped off before ripening the last two seasons. Nuts appear to be fine, the husk is green and no sign of husk fly or blight they just drop in early August. Any suggestions? These are not on grafted rootstock, trees are at least 40 years old. I am not sure of the variety since they were on the property when we purchased it.
Clackamas County Oregon
Thanks for your question about English walnut trees dropping nuts before ripening. Walnuts are ripe when the drying green hulls start to split, usually after rain beginning in late August through late November. You noted no evidence of husk fly nor Walnut Blight, the bacterium xanthomonas arboricola. In addition to premature nut fall, Walnut Blight presents first with reddish brown stem spots and young infected leaves turning dark brown or black and then dying. The Anthracnose fungus, ophiognomonia leptostyla, also causes premature nut drop with similar stem and leaf symptoms as the blight. Codling moths are rarely an Oregon walnut problem, but an early infestation arrests nut development and may result in heavy nut drop. As you stated the nuts appear fine with green husks, so we can likely rule out blight, anthracnose and codling moth. English walnuts are good nut bearing shade trees in western Oregon but are vulnerable to early fall and winter freezes as well as spring frosts. Their roots grow rather shallow, so walnuts are adverse to weed competition and appreciate deep irrigation rather than frequent short watering. Also lack of essential nutrients can cause impaired blossom formation resulting in poor nut production. A soil test would reveal any nutrient issues. Locally H&L Western Agricultural Labs is located on 10220 SW Nimbus Bldg. K-9, Beaverton Or. Their email address is http://www.al-labs-west.com. Their phone is 503-968-9229. They require 2 soil samples and have varying price packages depending upon what analysis is needed and prices vary accordingly. You might also find useful the following
Oregon State Extension catalogs: EM 8907 - Growing Walnuts in Oregon and EC 631 Managing Diseases and Insects in Home Orchards. Both are available at: https://catalog.extension.oregonstate.edu/topic/gardening/fruits-and-nuts