[From the UC IPM blog Pests in the Urban Landscape] 

Citrus trees need care throughout the year, including cultural practices to keep trees healthy and pest management. During the fall season, several pests can attack citrus trees in many California regions. 

Brown Rot

Monitor for this disease by checking for damaged fruit on your tree, as well as fruit in storage. Sometimes affected fruit develops a pungent odor and can ruin fruit held in storage. See the UC IPM web page on Brown Rot to learn more.

Citrus Leafminer

If you see what look like small “tunnels” on your citrus tree leaves, your tree might have citrus leafminer. The adult stage of this pest is a small, light colored moth; the larval stage feeds and develops inside the leaves of young citrus and other closely related plants.

Citrus leafminer rarely causes problems for mature trees, however, it can seriously damage very young trees. Read the UC IPM Pest Notes: Citrus Leafminer for recommendations for prevention or management.

Snails and Slugs

Snails and slugs are attracted to citrus trees and can feed on foliage and fruit. A good sign that these pests are the perpetrators of tree damage are the silvery trails of slime along the ground or on tree leaves, or even see the snails or slugs themselves. For management tips, read the UC IPM Pest Notes: Snails and Slugs.

Asian Citrus Psyllid and Huanglongbing

You may have heard of the Asian citrus psyllid (ACP) and the deadly disease huanglongbing (also called citrus greening) that has been featured in the news. This disease doesn't pose a threat to humans or animals, but is deadly to citrus trees. Once a tree develops huanglongbing, there is no cure, so for this disease prevention is key.

Stopping this serious citrus pest will require everyone's help. To learn more about the psyllid and the disease, as well as what you can do, visit the UC IPM Pest Notes: Asian Citrus Psyllid and Huanglongbing Disease.

UC IPM Web Site

For information on managing other citrus pests in the garden, see the UC IPM webpage on Pests in Gardens and Landscapes: Citrus.

Citrus trees can be planted any time after the danger of frost has passed, which in our area is usually around mid-to-late March. It's a good idea to plant citrus early – try to have your trees in the ground by May – because a sudden hot spell may damage trees that are not well established. Citrus trees planted during the cool spring months will be better able to withstand the cold weather of their first winter than trees planted later in the year. Your favorite nursery or garden center should have a good supply of new citrus trees right about now.

Citrus trees grow best in loam or sandy loam soil, but you can grow them in most soils that have good drainage. If your soil drains poorly, you might try planting in a raised bed or on a mound. Plant your trees in an area that receives full sun, and allow enough room for the tree's mature size.  I don't recommend planting in a lawn area because it's difficult to irrigate both the citrus and the lawn correctly. Also, the grass tends to absorb many of the nutrients needed by the tree.

In the nursery, citrus varieties are budded onto suitable rootstocks and grown for one or two years. Trees are sold in containers. Choose a one or two year old tree, but avoid older trees that have been held in containers so long that they're root bound.

Dig the planting hole just deep enough to plant the tree at the same level that it was in the nursery. The diameter of the hole should be about 6 inches larger than the root ball. If the hole is too deep, the tree will settle too much after planting.  Trees that settle too deep are likely to be killed by crown rot, a fungus disease that frequently develops where the soil covers the bark of the tree.

You can place balled and burlap-wrapped trees in the planting holes without removing the cloth sacking that covers the roots. Plant them a little higher than they were in the nursery, allowing about 3 inches for settling. Try to have the uppermost roots branch out at about ground level after the trees have settled.

You should handle trees in containers in much the same way. Carefully remove the container and place the tree in the hole at the correct depth. Be careful not to break the ball of soil surrounding the root system. After you have the tree properly placed, fill the hole three-fourths full of soil and tamp the soil around the root ball. Then finish filling the hole. Be sure to form a basin around the tree and irrigate thoroughly.

Do not put any fertilizer in the hole when planting your tree because it may damage the roots. It's safer to apply fertilizer to the surface of the soil after you've planted. If you use manure, use it lightly because roots may be damaged by salts which manures contain.

Citrus trees do very poorly in dry soil, so be sure to pay close attention to irrigation, especially during the first summer.

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.

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.

 

We recently wrote the blog post “Wait! Don't Prune Apricot and Cherry Trees Just Yet,” to caution gardeners against pruning these trees in winter. Now we'd like to discuss when and how to prune avocado and citrus trees. 

Avocados

Most avocado trees need little or no pruning. Whenever possible, allow them to develop naturally. Avocado leaves produce and store food for the tree. If this food supply is reduced by pruning, fruit production will also be reduced. Usually, removing dead or weak branches is the only pruning you need to do. Avoid pruning in late summer and early fall, as this stimulates new shoot growth that is susceptible to frost injury. In general, remove as few green branches and leaves as possible.

If you need to remove lower branches, prune them out completely, or cut them back to an upright growing shoot. Prune only after your tree has developed enough upper foliage to prevent sunburn damage on the lower limbs or trunk.

Sometimes a young tree grows tall without branching, grows sideways, or grows a top that is unbalanced. Correct these conditions by cutting the unruly limb or trunk back to a strong lower branch, or by staking the tree. Keep in mind that avocado trees grow naturally in an irregular way and will develop a better structure if they are not pruned at all. If you want to control the height, it's best to do so while the tree is young.

To prevent tall, upright growth, pinch back the terminal bud of the upright shoots on the young tree. Repeat this after each growth flush during the first few years. Your tree will spread out to the sides and develop a more compact form. If you reduce the size of an older tree by heading back large branches in the top of the tree, be sure to thin out the new growth which follows. Otherwise, the tree will soon grow back to its original height.

Citrus

If necessary, light pruning can be done in citrus trees any time of year. However, the best time to prune citrus is in early spring, after danger of frost has passed and before the start of spring growth. 

Nearly the same rules for avocado trees apply to pruning citrus trees. The foliage of a citrus tree is an important food (carbohydrate) storage area. Pruning removes foliage and stored foods and causes the tree to produce a flush of vegetative growth instead of fruit. For the most part, prune out only dead or broken limbs. 

Citrus trees normally produce vigorous shoots from the base of the tree called suckers, which you should remove as they grow. Vigorous shoots that grow from branches are called watersprouts. Remove watersprouts if they are not well placed but leave them whenever possible. Young trees need no pruning for the first two or three years after planting, except to remove suckers. As the tree grows older, prune lightly only to remove branches which are too closely spaced or entangled. Do not remove low-hanging branches, as they bear fruit within easy reach and shade the trunk and soil. The ideal citrus tree has a skirt of foliage that extends almost to the ground. Left alone, citrus trees normally develop an even, round-headed shape as they mature.  

Lemons usually need a bit more pruning than other types of citrus. Cut back some of the more vigorous shoots on young trees. Lightly thin the branches of mature lemon trees each year to improve the size and quality of the fruit.

 

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