Fruit tree pruning ranks high on most home gardeners' “to do” list during the winter months. While deciduous fruit trees may be pruned at other times of the year, most gardeners do their annual heavy pruning during the trees' dormant period. Deciduous fruit trees need some annual pruning to remain vigorous and productive.

If you do not prune your trees enough, they will become too tall to harvest, even with a tall ladder.  If you have an unpruned fruit tree in your garden, you know that most of the fruit grows in the top. Yearly pruning is necessary to keep the tree at a reasonable height, for instance, no more than 10 or 12 feet high. If your tree is already overgrown, you may want to reduce its height gradually, say over a two-year period.

The main objectives of pruning mature fruit trees are to reduce the number and increase the size of the potential crop, to develop new fruit wood, to remove interfering and broken branches, and to contain tree height and spread for convenient harvest. Most fruit trees, when not pruned, produce more fruit than they can size and mature properly. You can prevent such overproduction with yearly pruning.

If you do not prune your fruit trees for several years, not only will they grow too tall, but they also become brushy and weak and stop producing satisfactory fruit wood. Some new fruit wood is necessary each year for most trees to keep producing good crops. Which wood becomes fruitful, and at what time, depends on the species of tree. For example, peach and nectarine trees bloom and bear fruit only on one-year old shoots (branches that grew the previous year). Therefore, they require heavy pruning each year to develop adequate fruit wood for the following year's crop. Other fruit tree species, such as apples, apricots, cherries, pears and plums bear fruit on growth called “spurs.” The number of years the spurs are able to bear fruit depends upon the species; for example, plum spurs may be fruitful for 5 to 8 years; the spurs of apples, pears and cherries may be fruitful for up to 10 years. Assuming that your tree has spurs that will bear fruit for 5 years, heavy enough pruning to produce about one-fifth new spurs each year is necessary to keep your tree bearing properly.

Persimmons, many figs, quinces and pomegranates bear fruit on current season's growth.  When you prune these trees, remove old and weak branches, leaving some younger branches to produce new growth and fruit the coming year. Overcrowding and lack of sunlight will cause branches to die, so you need to thin out some branches to allow light infiltration into the tree so that the fruit wood stays healthy.

Nut trees such as almonds and walnuts do not need as much pruning for height control as fruit trees. You harvest nuts by knocking them down with a long pole, rather than by hand picking, so the trees can be much taller.

Fruit Tree Resources

Fruit Trees: Training and Pruning UC ANR Publication

The California Backyard Orchard For more details about training and pruning deciduous fruit trees.

Citrus and Avocado Trees Require Little Pruning For information on pruning citrus and avocado trees.

Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.

 

Soil solarization is a simple technique that you can use in your home garden to reduce or eliminate many soil-inhabiting pests. Solarization works by heating up the soil in the presence of moisture to temperatures that are high enough to kill many fungi, nematodes, weeds and weed seeds.

In order to solarize your soil, you must leave a clear plastic tarp on the soil surface for 4 to 6 weeks during the hottest part of the year, which of course is now. Black or colored tarps will not allow the soil to get hot enough, so you must use transparent plastic. Polyethylene plastic 1 mil thick is the most efficient and economical, but you must handle it carefully because it rips and punctures easily.

Before laying the plastic down, clean up all weeds, debris and large clods, then level and prepare the soil as for planting.  The closer the tarp to the soil, the hotter the soil becomes. Air pockets caused by clods or debris will decrease the effectiveness of the treatment. A smooth, bare soil surface is best.

You must also wet the soil before covering it with the tarp. The moisture causes organisms to be more sensitive to heat and also allows the heat to penetrate deeper into the soil. It's best to wet the soil thoroughly before laying the tarp.

While some pests may be killed within a few days, 4 to 6 weeks of treatment in full sun during the summer is needed to kill most pests with solarization. The highest soil temperatures will occur when the days are long and hot, and when the sky is clear and there is no wind.

Many disease organisms are effectively controlled with solarization, including the fungi that cause Verticillium wilt, Fusarium wilt and damping off of seedlings. Many annual weeds are also controlled, but perennial weeds such as Bermudagrass, field bindweed, johnsongrass, and yellow nutsedge are suppressed but not completely controlled by the procedure. Nematode populations are also reduced, but the heat may not penetrate deep enough to destroy those below the top foot of soil.  Nematodes should be controlled well enough for shallow-rooted crops.

Once the solarization is completed and you've removed the tarp, take care not to disturb the soil very much. Turning the soil can bring up living weed seeds and diseases that were too deep to be destroyed by the heat.

Read the publication Soil Solarization for Gardens & Landscapes for more information.

The University of California Cooperative Extension (UCCE) Master Gardeners of Stanislaus County are teaching a free Managing Pests in Your Vegetable Garden class on Thursday, July 18, 2019 from 6:00-7:30 p.m. at the Agriculture Center on 3800 Cornucopia Way in Modesto at Harvest Hall, Rooms D&E.

Join us for a free class about common pests that plague warm-season vegetable gardens. Learn how to identify insects, diseases, and weeds and how to control them using less-toxic methods.

This family-friendly class is open to everyone. Participants will receive free seeds (while supplies last). Our instructor for the class is Ed Perry, Environmental Horticulture Advisor (emeritus) for Stanislaus County. This class is free, but please visit http://ucanr.edu/vegpests2019 or call Anne Schellman at (209) 525-6862 to sign up. Space is limited, so please reserve your seat today.

If you haven't already, please “like” us on Facebook and Twitter @UCMGStanislaus so you never miss an announcement for a class or workshop.

 

Home gardeners often become concerned when their fruit trees begin dropping fruit prematurely. In some cases, fruit drop is nature's way of reducing a heavy fruit load. In other cases, premature fruit drop may be caused by pests and diseases, adverse weather conditions or poor cultural practices.

Apples may have a couple of periods when fruit drop occurs. The first is often after the flower petals fall off and may last two to three weeks. The very small dropping  fruits are the ones that were not pollinated, so will not develop further. Many fruit species need to be pollinated by bees. Lack of pollination may be the result of cold or wet weather during the bloom period, or by a lack of honey bees. Also, if there is freezing weather just before the flower buds open, more fruit drop may occur.

Other adverse weather conditions may also contribute to fruit drop. For example, persimmons may drop if the weather turns suddenly hot in spring, just as the small fruits begin to develop. Trees not receiving adequate irrigation water would be more prone to dropping fruit. 

Pests and diseases may contribute to the problem of premature fruit drop. Cool wet weather during the bloom period of walnuts often  results in infections of walnut blight, a bacterial disease that damages catkins, leaves, and newly-pollinated nuts. Infected nuts may drop prematurely. Premature ripening and fruit drop often occurs in apples and pears that are infested with codling moth larvae. 

In apples and pears, a second drop occurs once the fruits are about the size of marbles, usually in May or June. This is commonly referred to as “June drop.” Fruit drop at this time of year is thought to occur as a result of competition between fruits for available resources. 

Some fruit tree species, such as plums, may experience a mid-summer fruit drop. Proper  fruit thinning can help to prevent this. How much to thin depends upon the tree species.  With peaches and nectarines, it's important to make room on the branches for each fruit to grow to 2 ½ to 3 inches in diameter. Thin by pulling off ¾ to 1-inch long fruit in April and May, leaving one fruit every 6 inches. This results in more fruit on the ground than on the tree, but it's important to produce large, flavorful fruit and to minimize limb breakage.

Thin apricots when the fruit is about ¾ inch in diameter, leaving 1 apricot every 3 inches.  Thin plums when the fruit is ¾-inch-long, leaving 1 plum every 4 to 6 inches.  Thin apples after the usual May or June drop. Leave 1 apple every 6 inches or allow only 1 apple to remain per  spur. Asian pears should be thinned to leave only 1 fruit per spur.

When mature fruit begins to drop, it's a sign that the fruit is ready for harvest.

Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County.