How to Prevent Fruit on a Black Walnut Tree


The black walnut tree is grown not only for hardwood to be made into lumber, but also to provide shade and edible walnuts. The tree has few competitors because the roots produce a toxin known as juglone in the roots of the plant as well as the buds and nut husks. Because the shells of black walnuts are thick and hard and the husks are filled with juglone, some walnut tree growers prefer to block the fruit of walnut trees.

Step 1

Select a chemical growth inhibitor containing ethephon.

Step 2

Time the application of the chemical for a point just before the walnuts set on the tree.

Step 3

Put on protective clothing including breathing protection, eyewear, long pants, long sleeves and gloves.

Step 4

Mix the chemical at a ratio of 1 tsp. per 6 oz. of water.

Step 5

Pour the chemical mix into the holding chamber of a pressurized spray applicator.

Step 6

Prime the pressure of the applicator by grasping the pump handle and moving it up and down until you have built up sufficient pressure in the applicator.

Step 7

Carry the applicator wand with one hand and the holding tank with the other. Turn on the wand by squeezing the trigger to emit a fine spray mist from the tip.

Step 8

Pass the wand over the walnut tree using slow, even strokes.

Step 9

Shower immediately after using the chemical so you do not absorb it into your body through skin contact.

Tips and Warnings

  • Apply the chemical within four hours of mixing. Only mix the amount you plan to use, as the chemical will lose its effectiveness after four hours.

Things You'll Need

  • Chemical growth inhibitor containing ethephon
  • Chemical spray applicator
  • Protective eyewear
  • Breathing protection
  • Long pants
  • Long-sleeved clothing
  • Gloves
  • Ladder


  • University of California: Ethephon sprays
  • Ohio State University: Black Walnut Toxicity to Plants, Humans and Horses
  • Purdue University: Black Walnut Toxicity

Who Can Help

  • Monterey Lawn and Garden: Florel Brand Fruit Eliminator
Keywords: black walnut tree, preventing nut set, ethephon chemical inhibitor

About this Author

Tracy S. Morris has been a freelance writer since 2000. She has published two novels and numerous online articles. Her work has appeared in national magazines and newspapers, including "Ferrets," "CatFancy," "Lexington Herald Leader" and "The Tulsa World."