Beech leaf disease treatment

Beech leaf disease treatment – June 2, 2022

Beech leaf disease is a new disease and there has not been time for extensive research. In Ohio, researchers have encouraging results treating American beech saplings (<4 inch diameter trees) with a phosphite product twice a year for five years. There are several Phosphite products available including Agri-Fos,Fosphite, Fungi-Phite, Lexx-a-phos, and Prophyt. This article refers to PolyPhosphite 30 fertilizer since this was used in the research in Ohio. PolyPhosphite 30 is a potassium fertilizer, 0-0-27. You do not need to be a certified pesticide applicator to apply it and there are no reentry restrictions for the general public, but the fertilizer is harmful if swallowed and can cause serious eye and respiratory irritation. The Material Safety Data Sheet for PolyPhosphite 30 can be viewed at

Treatments are made during the growing season about one month a part – from May to August. PolyPhosphite 30 can be applied to beech trees as a soil drench or injected into the soil with soil injection equipment.

The amount of product depends on the size of the tree.
Apply 2 oz of PolyPhosphite 30 per one inch DBH (diameter at breast height). (For instructions on determining DBH see this website:

PolyPhosphite 30 must be diluted in water. Use 14 oz of water/2 oz PolyPhosphite 30.  For example: a 6-inch diameter tree would receive 12 oz PolyPhosphite 30 diluted into 84 oz of water. This treatment should be done twice during the growing season.

MANY PEOPLE HAVE MENTIONED THAT THEY HAVE NOT BEEN ABLE TO LOCATE POLYPHOSPHITE 30. There are many other phosphite products available. Most of the other phosphite products are sold as fungicides. You must follow the pesticide label for soil drench applications for whatever product is applied.

To apply as a soil drench, dig a shallow trench around the base of the tree and pour the solution into the trench. The picture below is with a blue chemical, not PolyPhosphite 30, which is a clear liquid.

Dig shallow trench at base of tree.                                Pour into trench (PolyPhosphite 30 isn’t blue).

RI DEM information available here:

Heather Faubert
URI Plant Protection Clinic