- Author: Ed Perry
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.
- Author: Ed Perry
Aphids are a common garden pest in spring and are attracted to new, succulent plant growth. This year, heavy aphid infestations can already be found on roses and fruit trees.
Aphids often first show up along the edges of the garden. Many species infest the undersides of leaves first, so turn leaves over while looking for aphids. On some plant species, especially plum and apple trees, aphid feeding causes the leaves to curl. Once this happens, it's harder to obtain control because the curled leaves protect the pests from natural enemies or sprays.
When you find aphids, check for evidence of natural enemies like lady beetles, lacewings, syrphid fly larvae, and the mummified skins of parasitized aphids. Learn to recognize aphid “mummies,” as they indicate the presence of tiny parasitic wasps that lay eggs inside the aphids. The wasp larva hatches and feeds inside the aphid, killing it. The skin of dead aphids turns crusty and golden brown or black, a form called a mummy. Not long after, the adult wasp chews an exit hole and emerges from the aphid's body. During warm weather, parasitic wasps may have several generations and cause a rapid decline in aphid populations.
There are fungus diseases that infect aphids, especially when it's warm and humid. Entire populations of aphids may be killed when conditions are right. While aphids thrive under mild temperatures, populations of many species are reduced by hot summer weather conditions. If you have any of these natural controls at work, the aphid population may crash rapidly.
You may be able to control aphids in your trees by controlling ants. If large numbers of ants are seen climbing up and down tree trunks, it may mean an aphid infestation. Ants are attracted to the honeydew produced by the aphids. If you plan to use pesticides for ant control, first seek out and treat the ants' nests in the ground near the tree. Or, place sticky barriers around the tree trunk to keep the ants from reaching the aphids. Unprotected by the ants, the aphids may then be attacked by natural enemies.
You can help prevent aphid infestations, especially in vegetables, by removing weeds where aphids may be building up. Also, check transplants for aphids and remove them before planting. If you notice a few curled leaves on your fruit trees, the best control may be to simply prune out and dispose of the infested shoots and leaves.
- Author: Ed Perry
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.
- Author: Ed Perry
Did you know that fallen leaves can become a valuable garden resource? You can turn these leaves into compost. Although low in essential plant nutrients like nitrogen, the leaves still contain small amounts of all the nutrients plants need and are a valuable source of soil-improving organic matter.
Get started by chopping the leaves into smaller pieces before adding them to the pile. You can use a chipper or a shredder if you have one. Otherwise, run over them with a lawn mower and then mix them into your compost pile. If you have a lot of leaves, you can store them after shredding in garbage bags or containers, then occasionally layer them into your compost pile over the winter to add air to the pile.
Sometimes certain green materials, like grass clippings, become matted in the compost pile. When this happens oxygen is excluded, and the composting process may stop. Adding leaves helps keep the grass clippings fluffed up and aerated.
If you're new to composting, keep in mind that the decomposition process works best if you mix equal volumes of carbon-rich, naturally dry plant material (dead leaves, dried grass, straw, and woody prunings) with nitrogen-rich green plant material (grass clippings, wilted flowers, green prunings, weeds and fruit and vegetable waste). This mixture allows a “carbon to nitrogen” ratio of 30 to 1, which is ideal for efficient compost production. You can produce compost slowly or quickly. Here are two methods:
The Slow Method
Build a pile of organic materials and let it stand for a year, when the compost will finally be ready for use. The advantage of this method is that it takes relatively little effort. However, some nutrients may be leached due to exposure to rainfall, and low composting temperatures may not kill some weed seeds and disease-producing organisms. For more information on this method, download the leaflet Composting is Good for Your Garden and the Environment.
Rapid Composting Method
This process produces compost in as little as 2 to 3 weeks but requires more effort. It allows you to produce large amounts of compost quickly. For more details about this method, you can download the leaflet Compost in a Hurry.
Many local nurseries and the Modesto Junior College offer hands-on composting classes. In the future, our UCCE Master Gardeners plan to offer composting classes. Keep in touch with us by signing up for our blog and following us on Facebook and Twitter @UCMGStanislaus to hear about upcoming classes and workshops.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County.
- Author: Ed Perry
Many gardeners are interested in knowing how winter temperatures affect garden pests. The hope is that following a cold winter–such as this year–fewer pests will survive to plague the garden. Unfortunately, both insect pests and plant diseases have ways of surviving our harshest winters. However, there are some things that you can do to lessen potential pest problems, mostly by eliminating the places where pests and disease may overwinter.
Although a few pests can migrate great distances, many come from sources within your garden or nearby areas, surviving on weeds, in crop debris, as pupae in soil, or as seeds, spores or eggs. You can also unknowingly bring some pests into your garden on infested transplants or contaminated soil or equipment.
Good common-sense sanitation practices will help to eliminate overwintering garden pests. In your fruit trees, be sure to remove and destroy old fruit “mummies” hanging in trees and pick up and destroy any fallen nuts. Old fruits and nuts often contain pests such as codling moths. It's also very important to get rid of pruned branches, especially those from your fruit trees, that might be infested with disease or borers. Bark beetles may emerge from infested branches in late winter or early spring, so be sure to dispose of prunings as soon as possible. Don't forget to treat your fruit trees, especially peach and nectarine trees, with fungicide sprays to prevent spring diseases such as peach leaf curl; oil sprays applied now will also help to control overwintering insect and mite pests on deciduous trees.
Also, remove any weeds around your garden well before planting any new crops. Not only do weeds produce seeds that may find their way into your garden, but they are also likely to harbor numerous migrating pests. For instance, cutworms, earwigs, stink bugs, thrips and certain viruses carried by aphids and leafhoppers are all pests associated with weedy areas. If you wait until your garden is planted before destroying these weeds, the pests will move into your crops. Waiting for the weeds to dry out naturally will also encourage pest migrations. Besides, it's easier to control weeds when they're seedlings, rather than waiting until they've matured and set seeds.
Good sanitation also means making sure the planting stock you're using is free of pests. Check transplants or other greenhouse stock for aphids, diseases, nematodes and other pests. Use certified seed or stock if available. Make sure any organic soil amendments you use are free of weed seeds and pathogens, and don't move soil infested with nematodes, Bermudagrass stems, or nutsedge tubers to other parts of your garden. If you're not sure whether the soil is infested with pests, it's best to not take the chance. Also, clean equipment before moving it from infested areas.
Always be sure plant debris, particularly residue from previous vegetable crops, is completely decayed or removed before planting a new crop. A good way to destroy most crop and weed residues around your garden is by composting. Composting destroys most of the pests that may be harbored in the residues.
You can download a free copy of Composting is Good for Your Garden and the Environment to learn more.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County.