Catkins (the male part of the flower that produces pollen) are produced on wood that grew the previous year.  (They will occur at the tip of the one-year-old wood where the current twigs originate.)  Catkins buds are produced in late summer before they bloom the next year. 

Female flowers (the part that produces nuts) are produced on current season’s growth at the end of the twigs. Therefore, trees have to make all the year’s growth before the crop of nuts is set.  This is why it is so important to apply fertilizers approximately six weeks before trees bud. 

Trees in production should be fertilized to maintain a minimum annual terminal twig growth of six or more inches. Optimum growth is approximately six to eight inches.  Because nuts do not appear until trees have most of their annual growth, the pecan crop is rarely killed from late spring frosts.  Female flowers are pollinated by wind born pollen from the male catkins during the first two weeks of May. 

Reasons for Premature Dropping of Nuts

Natural Nut Drop:

Pecan trees will naturally drop nuts several times during a growing season:

1. Mid-May after pollination
2. Mid to late June
3. Late July to early August

If you observe a nut drop, it should be determined if it is from a natural shed or one of the following factors.

Disease:  Early scab infection of young nuts will cause nuts to drop.  Leaf disease such as scab, scorch, mildew, blotch, brown spot, and downy or vein spot also may cause nut shedding.

Insects:  The pecan nut casebearer probably causes more nut shedding than all other insects collectively.  However, insects such as black aphids, May beetles, shuckworms, stink bugs, and pecan weevils may cause dropping. 

Moisture and Plant Foods: Nuts may drop early due to lack of moisture and plant nutrients.  Variation in moisture available to trees can cause early nut drop, such as a period of high rain fall following a dry spell.  Moisture can be conserved by mulching, mowing grasses and weeds, and irrigation.

Weather:  Mechanical injury to leaves and nuts from hail and wind may cause prematuredropping.

Tree Condition:  Poor physical condition of trees may cause premature dropping of nuts.  This condition may be caused by inadequate fertilization for several years, continued drought for several years, or insect and disease damage. Trees may also be in poor condition if they are located in soil not adapted to high water table, or that is under-lined with solid rock.

Premature defoliation of any type (insect, disease, drought) will cause nut drop and low quality.  Every effort should be made to maintain the foliage of the tree.

Pollination: Too much rain during pollination season will cause poor pollination of female flowers, and those not pollinated will drop. Also, male pollen sometimes becomes mature and right for pollination before or after the female flower is receptive.