Summer Fruit Drop


During the summer period many fruit trees experience summer fruit drop. This occurs on almost all trees. It occurs approximately 80 days after flowering.

Growers will tend to fertilize the trees before the summer fruit drop period in order to get more new shoot growth. They realize that additional shoot growth will tend to reduce summer fruit drop problems. The effectiveness of this practice will depend upon the climate conditions and the amount of new shoot growth that is promoted by the fertilization.

Even though the above practices are implemented, (even where irrigation is available) the summer fruit drop is still present. The amount of fruit drop will depend upon the climate conditions as well as the variety of the tree crops that are being treated.


When any fruit (such as a nut fruit) passes from liquid or fluid stage and begins forming the embryo which becomes the seed, the seed embryo does not properly form and the nut will abort from the tree. This is not true only for nut trees. It is true for other type trees, such as avocados, mangoes, citrus coffee, and any other seeded fruit.

This is an ongoing problem. The economic severity of this problem will depend upon climatic factors. During this period the inside of fruit seed passes from its liquid stage into the solid embryo stage of fruit.

During the flowering period of the tree, the strength of the pollination occurs in each flower. The cell division and cell differentiation within that young fruit will determine whether it is maintained by the tree or experiences post flower abortion or post flower drop. This will normally result in the formation or lack of formation of the seed embryos. If pollination is not strong, many of these early fruit that drop have no seed embryos or a deformed seed embryo.

The fruits that the tree maintains will continue to develop and pass through two different phases. The first phase is the accumulation if liquids that will cause the initiation of a seed embryo formation.

When the milky stage or liquid stage of the seed accumulates enough of a single hormone then it will start to form the seed embryo. This is very specific. Only one hormone is needed inside the fruit in order to establish the seed embryo. All other hormones must be reduced to a very low level in order to have the perfect seed embryo form. Hormones in the fruit during this period that normally occurs approximately 8 weeks after flowering, is called auxin. All other hormones such a gibberellic acid, abscisic acid, and cytokinin at this stage or formation should be reduced. This research has been done on nut trees. There is really no difference between nut trees and any other tree that has fruit.

Farmers should not be discouraged from fertilizing previous to the summer nut drop problem. It will not, however, be really effective due to the varying climatic conditions and the conditions of the trees that are being treated.

Although the timing of the formation of the seed embryo can vary amongst different tree varieties, normally a period of 8 weeks after flowering will cover many of our tree varieties when summer fruit drop occurs.


Apply 1.5 to 2.0 pints per acre of Bio-Forge as a foliar application approximately 2 weeks before the summer nut drop season is common. Bio-Forge has the ability to up regulate auxin and auxin transport into the fruit during this change from the liquid state into the seed embryo state.

The use of Bio-Forge will greatly reduce the sumer fruit drop on any tree. The timing, however, is very important. It must be applied approximately 2 weeks before the liquid stage begins the development of the seed embryo stage inside the fruit.

When considering citrus, the seed in the citrus fruit will determine the time of summer fruit drop. The seed inside the citrus fruit will also pass from a liquid stage into an embryonic or solid stage. It is during this transition period that citrus will experience summer drop.

J/PEP - Summer fruit drop 032707 bc