As written in this blog a year ago, Cape Ann Beech trees are under assault by Beech Leef Disease (BLD). Bartlett Tree Research Laboratories has been at the forefront of research to study BLD, caused by a nematode that attacks the leaves. These nematodes cause dark bands between the leaf veins. However, this year the symptoms are severe, and include stunted leaf development, curling, yellowing and browning of leaves, tips of branches and entire branches dying and pre-mature leaf drop.
As of last year, there was no proven treatment, but as recently as March 2024, results from experimental treatment trials were published in the Journal of Environmental Horticulture.
Fungicide Spray Treatment
The trials showed that foliar treatment of the fungicide fluopyram, when applied at the right time, kills over 90% of live nematodes. According to Dr. David Burke, VP for Science and Conservation at Holden Forests & Gardens, "effective fluopyram application needs to occur when the nematodes are migrating out of the leaves and into the buds to overwinter, which occurs in late summer when the leaves are wet, such as after a heavy rain. This treatment won’t improve leaf symptoms in the current year, but would affect the following year’s leaf out." Because Fluopyram is a harsh chemical, it may kill all the fungi in the application area, so its use should be considered with caution and should be applied only by a professional. According the U. Mass Extension Fruit Program, Fluopyram is rated as only slightly toxic to non-toxic to honeybees.
Soil Drench
A milder option that is promising uses potassium fertilizer to reduce the symptoms of BLD. It is not known exactly how it works, but Holden Forests & Gardens recommends applying PolyPhosphite 30®, 0-0-27 to reduce nematode numbers and alleviate the symptoms of beech leaf disease. Friends of Manchester Trees has begun applying phosphite soil soaks on four of our public Beech trees. The treatment should be performed at least twice each summer, between May and October.
PolyPhosphite 30 is a specific brand that’s only available for professional/commercial use, but alternatives are available for homeowners. It’s a potassium fertilizer; the 27 refers to its concentration of 27% soluble potash (K2O). To search for alternatives, look for products called “potassium polyphosphite” (note the “i” in phosphite; phosphate with an “a” is a common fertilizer and may autocorrect), “soluble potash,” or “muriate of potash.” The exact concentration of the product shouldn’t matter (the label will say “0-0-X”); you will need to follow the directions to prepare the solution for use (e.g. for a 27% solution like PolyPhosphite 30, you would use at least 1 gallon of water for every 2.5 oz of fertilizer concentrate, per the label). Note also that products you find may be labeled as “foliar” liquid fertilizer but its effectiveness against BLD is as a soil drench. Do not spray on leaves. After diluting your solution according to the label, apply 1 quart per inch of stem diameter (measured at 4.5 feet, or DBH), drenching the soil around the base of your tree. Read all labels carefully before use and follow all recommended safety protocols. Rubber gloves or latex gloves are recommended while handling this or any chemical.
Selective Pruning to Reduce BLD
Since the nematodes migrate from the leaves to the tree buds in the fall, using water as a transport, strategic pruning is recommended to reduce moisture in the tree canopy. There is no way to prevent beech leaf disease from spreading to your trees, but keeping the tree dry and healthy may help.
What if I have a healthy Beech Tree?
Your tree may be naturally resistant to BLD, and researchers want to know about that! To report a healthy American beech, you should reach out to the Forest Health Coordinator, Rachel Kappler, at Holden Forest (rkappler@holdenfg.org).
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