Early Tree Nut Drop

Boxed Black Walnuts Under Tree
Boxed Black Walnuts Under Tree. Photo by Steve Nix, Licensed to About.com

Sometimes nut-bearing trees such as hickory, walnut, and pecan drop their fruit before full maturity. At times, it can be a natural shedding of a portion of the nut crop. Other causes can be more problematic, including adverse weather conditions, poor tree health, inadequate pollination, insects, and disease.

How Nut Trees Set Fruit

Most nut-bearing trees have male pollinators and female flowers, both called catkins.

Female flowers produce nuts during the current season's growth and have to survive through that year's growth before the crop of nuts is set. Not all flowers on a tree will produce a nut each year; in fact, they may alternate years. 

There can be several natural nut drops between mid-May's pollination through the end of August's fruit set, and they can be minimized by proper tree fertilization. For example, if a tree wasn't adequately pollinated or didn't have enough potassium to set good fruit, there will be nuts that may be malformed with few seeds inside (fruits on the tree grow but embryos inside don't develop). The tree will drop this fruit early because it's not biologically sufficient for the tree's reproduction. The tree will concentrate its energy on growing fruits that are going to set good seeds.

A Tree's Physical Condition

Poor tree health can cause premature dropping of nuts. A tree's health is often compromised because of inadequate nutrient uptake, which is most evident during drought.

Insect and disease infestations increase during these times of tree stress and can further degrade a tree's condition, especially if trees are growing in poor soil. Any early defoliation will cause nut drop and low-quality fruit.

Water and fertilize your tree adequately to make sure it has the proper nutrients to set and grow its fruits.

Weather Influence on a Tree's Nut Crop

Excessive rain or frost during late spring/early summer pollination will cause inadequate pollination of female flowers. Those poorly pollinated flowers may produce a nut that will drop early or no nut at all. Sometimes, male pollen can mature either before or after the female flower is receptive, and this condition is usually weather related.

An extended drought during nut growth may also result in the dropping of tree nuts, particularly if the plant is in sandy soil that dries out quickly. That's a "resource competition" drop, or a so-called "June drop," as the tree is concentrating its energy on the amount of nuts it can support. 

As well, mechanical injury to leaves, flowers, and nuts from hail and wind may cause premature dropping.

Insects and Diseases of Nut Trees

Early pecan scab infection of young nuts will cause nuts to drop and is a major cause of pecan crop failure. Black walnut is highly vulnerable to anthracnose, and the disease is of much concern in commercial orchards. Leaf diseases in nut trees such as scab, scorch, mildew, blotch, brown spot, and downy or vein spot also may cause nut shedding.

The pecan nut casebearer probably causes more nut shedding than all other insects combined in pecan orchards.

Codling moth causes significant premature nut drop in black walnut groves. Other insects such as black aphids, walnut caterpillar, shuckworms, stink bugs, and pecan weevils may cause early nut dropping.

Avoid using pesticides during flowering, however, as chemicals can kill the beneficial insects and result in inadequate pollination.

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Your Citation
Nix, Steve. "Early Tree Nut Drop." ThoughtCo, Mar. 7, 2018, thoughtco.com/early-tree-nut-drop-1342911. Nix, Steve. (2018, March 7). Early Tree Nut Drop. Retrieved from https://www.thoughtco.com/early-tree-nut-drop-1342911 Nix, Steve. "Early Tree Nut Drop." ThoughtCo. https://www.thoughtco.com/early-tree-nut-drop-1342911 (accessed March 17, 2018).