Fruit Thinning Adds Quality Asserts LSU AgCenter Horticulturist

John R. Pyzner  |  4/22/2005 12:44:52 AM

News You Can Use For March 2005

Fruit thinning is an important step in consistently producing good quality fruit, according to LSU AgCenter horticulturist Dr. John Pyzner.

Fruit trees will often set more fruit than is needed for a full crop. Pyzner says several undesirable things can happen when excess fruit is left on trees. Weight of extra fruit can cause tree limbs to break. Excessive fruit often will result in small fruit with poor flavor. Excessive fruit also can result in alternate bearing in which a tree will produce little or no fruit in the year following a large fruit crop.

The horticulturist says fruit thinning is generally most effective when it is done shortly after fruit set, although fruit thinning a couple of weeks prior to harvest can sometimes result in larger fruit and less limb breakage. Thinning will reduce the amount of fruit being produced, but this can be offset by improved fruit quality and size, which can bring higher prices. The importance of fruit thinning varies with different types of fruits.

"Fruit thinning is very important on peach trees," Pyzner says, explaining, "Peach trees frequently set an excessive number of fruit, since a 10 percent bloom set will often produce a full crop. A very heavy fruit crop can result in poor quality fruit and damaged trees.

Fruit thinning should begin as soon as frost danger is over. An exception to this rule is after mild winters when trees may not have had adequate chilling to come out of dormancy properly. A sign of this condition is delayed and non-uniform leaf emergence. There will often be a tuft of leaves near the tip of a stem and no leaves for 10 to 20 inches below the tips.

Another sign of inadequate chilling is flowers blooming for several weeks instead of a few days. Thinning should be delayed several weeks if inadequate chilling is suspected, because the flowers are often deformed, and many of them will not produce fruit or the fruit that develops will often not grow properly.

Most fruit thinning is done by hand, which is very time consuming. Using sticks to break up fruit clusters and shakers to shake fruit off the trees are less time-consuming methods; however, they do not result in consistent thinning.

Fruit are generally thinned to 6-inch intervals on twigs. Early peach varieties are usually thinned to 10 inches because of the short time available for the fruit to mature. When thinning, look at the number of fruit remaining on the tree and not at the ground. Looking at the ground will prevent you from removing enough fruit.

Thinning is also a good time to remove damaged fruit. A properly thinned mature peach tree will usually have 500 to 700 fruit remaining.

Pyzner points out that it takes fewer large peaches to make a bushel; therefore, the yield can remain good on thinned trees. A peach tree producing 2-inch diameter fruit that takes 293 peaches to make a bushel will produce 3.4 bushels with 1,000 fruit. A peach tree producing 2 1/2-inch diameter fruit that takes 159 peaches to make a bushel will produce 4.4 bushels with 700 fruit. A peach tree producing 3-inch diameter fruit that takes 98 peaches to make a bushel will produce 5.1 bushels with 500 fruit.

Japanese plums, which include most plums grown in Louisiana, tend to overbear like peaches. Fruit on these plums should be spaced 4 to 6 inches apart, and the fruit cluster should be broken up. Native plums do not need thinning unless heavily loaded.

Apples frequently require thinning. There is usually a naturally occurring fruit drop in June. If excessive fruit remain, the apples can be thinned to 6 inches to 8 inches along the limbs. Thinning to one apple per fruiting spur can aid disease control.

Pears are usually thinned only when very heavy crops are set and the trees might be damaged. Thinning is usually done a few weeks before harvest.

Oriental persimmons are seldom fruit thinned unless a heavy crop threatens to damage limbs. Sometimes persimmons will fail to produce a fruit crop the year following a heavy crop. Fruit thinning during heavy crop years appears to reduce alternate bearing.

Grapes, muscadines, citrus, figs, blackberries and blueberries are not fruit thinned. Grapes and muscadines are frequently pruned in the winter. This reduces the number of buds available to produce fruit clusters. Pruning is a form of fruit thinning that results in improved fruit quality and also controls the size of the vines.

For related topics, look for Gardening and Get It Growing links in the Feature section of the LSU AgCenter Web site: www.lsuagcenter.com.

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On the Internet: LSU AgCenter: http://www.lsuagcenter.com/
On the Internet: www.louisianalawnandgarden.org
Source: John Pyzner (318) 644-5865, or Jpyzner@agcenter.lsu.edu

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