FRUIT BLOOM DROP
AND
FRUIT AND NUT CARE
by Jerry Parsons, Ph.D.
Horticulture Specialist, Texas Agricultural Extension Service in San Antonio

Gardening is in full swing now. Just as vegetables need our full attention at this time of the year so do the fruit trees. Fruit trees have already bloomed. Bloom deterioration and petal fall signals a time for fruit thinning. If you or a hail storm haven't thinned your fruit, do it as soon as possible. (Plums generally are not thinned.) A good rule of thumb to follow is to thin fruit until they are 6 inches apart on the branch making sure that no two fruit are side by side. Or, in the case of fruit produced in clusters on spurs, such as apples and pears, remove all but one fruit. A fruit will grow larger if it can be produced under optimum growing conditions for a longer period of time.

Many growers are complaining of fruit drop or lack of any fruit set at all. Some fruit drop is normal but excessive amounts of drop may have been caused by either lack of chill and/or pollination.

As a general rule, fruit trees bear fruit when they become old enough to blossom freely, provided other conditions are favorable. Pollination, cultural practices and environment greatly influence the plant's ability to bear. Any of these factors alone or in combination can prevent fruit set or cause flowers not to develop and fruit to drop prematurely. Obviously growers do not have any control over most of these factors.

Even though many trees blossom freely, some still may either fail to set fruit or they will shed most of their fruit prematurely if adequate pollination does not occur. Some fruit trees have "perfect flowering" blossoms with both male and female parts. When this type of tree bears fruit as a result of pollination from their own blossoms the tree is said to be "self-fruitful". Unfortunately many fruits with perfect (male and female parts in same flower) flowers do not set fruit if only their pollen is available, i.e., the female flower part requires pollination from another flower. If such pollination is required, then the flower and fruit type is said to be "self-unfruitful". Apples and pears are good examples of this type of pollination type. Remember that fruit trees that are classified as "self-unfruitful" may produce some fruit if an alternate source of pollination is not available but maximum fruit set will only occur if the proper pollinators are available.

In some fruit varieties, the pollen-producing or staminate (male) blossoms that never produce fruit are borne on separate plants from the pistillate (female) or fruit-producing blossoms. In cases such as this it is necessary to have at least one plant with male flowers to serve as a pollinator. Plants with only staminate flowers will normally pollinate a number of plants with female blossoms. Kiwi and pistachio are examples.

Examples of self-pollinating fruit are apricot, avocado, blackberry, citrus, fig, most domestic grapes, jujube, nectarine, peach, pomegranate, quince and strawberry. Those fruit which benefit from cross-pollination include apple, Japanese persimmon, pear, pecan, plum (some varieties such as Bruce) and walnut.

Blackberries typically produce an abundant crop. Soon blackberry growers will be eating themselves sick. Many novice producers are asking what to do with the large canes which are growing through the middle of the canes which have the blooms. Blackberries bloom and produce berries on last year's canes. Once last year's canes have produced berries they will die and all such canes should be removed. This means that those large, new canes will produce next year's crop. If the planting of blackberries is young (1 or 2 years old), these large, "prima" canes can be tipped to encourage branching. More branching means more berry production surface for next year's crop, since next year's crop will be born on this year's growth. However, in older plantings these prima canes become nothing but obstacles to harvest. Early removal of the prima canes to expedite harvest is recommended since most of these canes are severely damaged when old canes are removed at the end of harvest. Many commercial berry producers shred the entire planting at the end of the harvest period. With proper watering and fertilization, sufficient new growth will occur before fall to insure a full crop the following year. Old canes can be more easily removed from a new planting.

Pecans also deserve special attention now. A pre-pollination spray of zinc should produce large, healthy leaves. This spray should be applied 3 weeks after bud break.

Last, but certainly not least, are the pear problems. "What causes the blooms of my pear tree to die? Why do I have black, dead limbs on my pear tree?" These questions signal spring's arrival! With spring blooms comes the pear horror named fire blight. Appropriately named, the bacteria infection causes limbs and blooms of trees to look as if they have been scorched by fire. It is now too late to correct or prevent the problem. Some varieties are resistant--not immune but resistant. These include Kieffer, Orient, Fan-Stil and Monterrey. Unfortunately the best tasting pears such as Bartlett and Le Conte are the most susceptible.

As you can see, fruit trees do need constant care and attention. Also, remember that too many fruit are not good either for the tree or the fruit.

THINNING FRUIT

Most of us especially enjoy the blooms of spring. But to a peach producer the joy of spring blooms signals an approaching fruit thinning task.

Homeowners also should realize the importance of this necessary evil of relieving peach trees of their "overload." Even though you pruned the poor creature unmercifully this winter, the tree still has too many peaches on it to size them properly. Eight percent of blossom set equals a full crop of quality peaches. This means that 92 percent has to go!

How does one properly thin the fruit of a peach tree? With determination, will power, vim, and vigor. Be determined that you will remove the unnecessary 92 percent of that fruit. Have the will power to stay with the gruesome task until the job is finished. And exert plenty of vim and vigor so that you will have the job finished before your spouse comes home and has you committed for ruining the first decent peach crop that you have ever had!

You must be strong! You must make a decision at this point. The decision is whether to have a lot of small, worthless peaches or a few, high-quality fruit. Too many fruit on a tree will result in damaged trees and pit-and-skin peaches. Remember that it takes 191 peaches of a 1-3/4 inch diameter to make a half bushel, while it only takes 79 peaches of a 2-1/2 inch diameter size to make the same half bushel.

Thinning is the hardest of all tasks for the novice fruit grower. The idea of removing all of those "baby" peaches is more than most of us can stand. But too many "babies", especially 92 percent too many, would be bad on any "mommy". These "babies" can break the "mommy's" arms (limbs) and weaken the tree to the point of death.

Peaches should be thinned when the fruit is still as small as a dime. Some say that the best effects of thinning will be realized if thinning is accomplished at bloom time. This is especially true with earlier-ripening types such as June Gold. The longer the fruit has to mature under the ideally thinned situation, the larger it will get --less nutrient competition equals larger fruit. But I don't expect that we have many homeowner peach growers with enough fortitude to remove the beautiful blooms. I will be happy if you thin the fruit at a dime-size stage!

Fruit should be thinned until all small peaches are at least 3 to 6 inches apart on the branch and there are no partner (side-by-side) fruit. This small fruit can be removed by hand plucking or limb beating. Commercial producers use a rubber hose on the end of a broom handle. The rubber hose will not injure the limb upon impact.

When you complete this task, the ground will be covered with small peaches, and you probably will say ugly things about this columnist. I felt the same way upon completion of my first thinning assignment. I couldn't see any peaches left on the tree and knew that I had destroyed the entire crop. That season, when the peaches ripened, the limbs were broken by large luscious fruit --I had not thinned enough! Since most of us are too squeamish and reserved when it comes to the task of fruit thinning, nature usually gives us a helping hand and finishes the job we started. A "natural" fruit thinning will soon occur.

The shedding of unripened fruit from fruit trees is often very alarming to the backyard gardener. About the time one begins to count the fruit and breathes a sigh of relief, the young fruit, for no apparent reason, begins to fall. This wave of fruit drop is referred to as the "June drop." Even though "June drop" occurs in June in the northern states, its occurrences in Texas is usually in April or May.

Actually, such shedding of fruit is a natural process and with most fruit species, little if anything can be done to prevent its occurrence. This is not to say that there are certain cultural practices, which when neglected, can contribute to fruit drop. This type of fruit drop may occur in April or May. The exact time depends upon latitude and upon species and varieties. The "June drop," may be highly beneficial: it properly thins the fruit early, in time to promote the largest influence on size. Trees of some species, such as peaches and plums, rarely drop enough fruit and hand thinning is necessary.

The ability of fruit to hold on the tree is directly related to its ability to produce a specific hormone in its seeds. Some fruit species produce fruit with little or no seed. The persimmon and the common fig produce no seeds and their ability to hold on the tree is greatly influenced by such external factors as moisture availability, nutrient supplies, and insect and disease damage. In species like the apple and pear, that have more than one seed per fruit cavity, the fruit with the most developing seed tends to be the least apt to fall. Usually a young fruit on a weak branch or on a branch having weak or injured leaves near it is more apt to fall than the fruit with the same number of seeds but on a stronger branch. If the supply of nitrogen is low, more fruit may fall in the "June drop" than if the nitrogen supply is adequate. In the absence of an annual fertilizing, one can expect more fruit to drop.

The water supply may also influence the number of young fruit to fall. A water deficit may not be as critical as too much water. In soils that are poorly drained, the roots of the fruit tree are often injured due to low oxygen supplies in the soil. In such cases, the roots do not absorb water rapidly enough because of a limited root system to replace the water lost from the leaves during dry, hot days. Likewise, the soil may be so shallow that the root system is too small to absorb water as fast as the leaf surface loses it. When there is a severe water deficit, leaves of some species draw water away from the fruit. This creates a water deficit in the fruit. Such a deficit seems to be a strong influence towards fruit drop.