FAQs

Question:

I have noticed small holes in the bark of my apple, cherry, peach, plum and mulberry trees. It looks as if the trees have been shot with a shotgun. The stone fruits have gummy material coming out of the holes. What is the cause of these holes and how can I control it?

Answer

The holes you see are caused by shothole bores, (Scolytus rugulosus (Muller)). Shot hole bores are beetles that were introduced from Europe in 1878. They can be destructive pests of fruit and ornamental trees, and shrubs. Numerous small shot holes" are seen in the bark of twigs and branches. The gummy exudate from the stone fruit trees is their response to try and fend off the invaders. The adult beetle is 2.5 mm or less in length, brown-black, with a short stubby snout with chewing mouth parts. The thorax is shiny and elongated, the elytra, or wing covers are dull. Adults burrow through the bark and live between the bark and sapwood of the plant. Adult feeding excavates narrow galleries running parallel to the wood grain under the bark. Eggs are oval to round and pearly white in color. Females lay 50 eggs in niches along the gallery she has made. As the eggs hatch the larvae excavate slender mines or burrows, usually at right angles to the maternal gallery, occasionally crisscrossing over one another between the bark and sapwood. The larval burrows are filled with excrement and grow wider as the larvae grow. They become fully grown six to eight weeks later and construct pupal cells at the ends of the mines. Upon completion of pupation young adults burrow through the bark to the outside world, mate, and the cycle starts anew. The larvae of the last generation of the year complete development during late winter and early spring as temperatures rise. In Southern Arizona there are normally three generations per year."

Control

Healthy, vigorous, well-cared-for trees are less subject to attack by shothole borers. Plant maintenance through correct watering at the drip-line, proper fertilization, and pruning practices keep trees healthy. Affected branches should be pruned out burned to decrease insect populations. Plants receiving a regular spray program are not troubled by shothole borers.

Source

Orchard Pest Management. Elizabeth H. Beers, et al., Editors. 1993. Good Fruit Grower. Yakima, WA. Pages 186-187. Insect Pests of Farm, Garden, and Orchard. Ralph H. Davidson and William F. Lyon. 1987. John Wiley & Sons, Inc. New York. Pages 404-405.

Question:

I have a pear, apple, peach, nectarine, plum, apricot and cherry trees which have new leaves that are curling up around the edges and are deformed. Is this peach leaf curl?

Answer

Peach leaf curl is caused by a fungus and does not affect pear and apple trees. The problem at hand is caused by the western flower thrip or onion thrip. Thrips are small, 1/25-1/50th inch long or so, and lay their eggs in flower or leaf buds or on very young leaf tissue. They feed with their rasping sucking mouth parts and cause irreversible damage to the plant tissue, flowers and fruit. Five to 15 generations per year can be produced. To see if you have thrips hold a piece of white paper under the damaged leaves and tap them sharply. Thrips will fall on the paper and start to walk around. They rarely fly because they are weak flyers but will hop. There have been vast numbers of thrips this year because of the good winter rains we had which caused cool season weeds, mustard particularly, to thrive. Thrip populations build up to high levels on these weeds and when they die down, due to warm weather, the thrips migrate to fruit trees, roses and other perennial flowers.

Control

Thrips are hard to control once they are inside a bud because they are protected. Systemic pesticides do help with thrips on roses, peonies and other perennial flowers. Hang up blue or yellow sticky traps to catch adults as they move into an area. Diatomaceous earth applied to the underside of the leaves my also be helpful. As a last resort sprays of insecticidal soap, rubbing alcohol or other insecticides may be helpful. The best thing to do is control weeds where thrips are living in the early spring. Annually check weeds on your property to see if thrips are there. Us the method described above. Generally plants will out grow the damage caused by thrips by producing new leaves, but damaged leaves flowers and fruit will not be mended.

Source

Carr Anna et. al. Chemical-Free Yard and Gardening. 1991. Rodale Press, Inc., Emmaus, PA. pp. 242, 244.

Question:

I have a pear tree that has some bumps on the leaves. Over time the bumps turn into brown spots. Is this zinc deficiency?

Answer

No you do not have zinc deficiency. The damage you see is caused by mites, most likely the pearleaf blister mites (Phytoptus pyri Pagenstecher). This mite was introduced from Europe, probably before 1900. It is a pest of most pear growing areas of the world. Feeding by these mites causes damage on leaves and fruit. Blister mites overwinter as mature females at the base of buds or under outer bud scales. Adults are light to amber yellow in color and cylindrical, tapered sharply at the posterior end and resemble a short worm. In spring, when buds begin to swell, overwintering females penetrate deeper into bud and lay eggs on live tissues. Development from egg to adult requires 20 to 30 days during spring. Feeding of females and their offspring causes blisters on developing leaves. Blister are green or red at first but turn light brown to black as affected tissue dies. As the blisters form, leaf cells near the center of the blisters die and pull apart as surrounding cells enlarge, creating a hole. Blisters vary in size, with the largest about 1/8 inch in diameter. Mites do not live in the blisters on the fruit, but the fruit will be scarred. Mites of the first spring generation enter blisters through these holes and feed on soft leaf tissue inside. Several generations develop within the blisters during a growing season. Summer generations require only 10 to 12 days to develop. When blisters become crowded or leaves become heavily damaged, mites may migrate to growing terminals where their feeding produces new blisters. Fruit damage is caused by injury to buds before bloom. Severe damage to foliage can cause leaf drop and reduce shoot growth. Look at young leaves before bloom early in the spring just as leaves are unrolling. Noticeable light green to light red rough areas where mites have been feeding will be seen. This damage becomes more noticeable as the growing season progresses.

Control

Blister mites are not normally controlled by natural enemies. Predatory mites will feed on blister mites when they are exposed. Blister mites often attack weak, neglected or abandoned trees. If a pesticide is used to control blister mites the best timing is after harvest when mites migrate from leaf blisters to terminal and fruit buds. They are exposed on those sites until buds swell in the spring. Pre-bloom treatments can prevent fruit damage that occurs just before and during bloom.

Source

Orchard Pest Management. 1993. Edited by: Elizabeth H. Beers, et al. Good Fruit Grower Publications, Yakima, WA. Pages 151-153.

Question:

I have several twelve-year-old cherry and peach trees that have holes in the leaves. Also some of the cherries have a greyish spot forming on the fruit. I do not see any insects. What is causing the holes and what can I do about them?

Answer

It sounds as though your trees are affected by bacterial canker of stone fruit or Pseudomonas syringae. Other common names include gummosis, blossom blast, die back, spur blight, and twig blight. There are several different races of this bacteria. Symptoms may appear on some trees and not on others. These include canker development on twigs at the base of flower and leaf buds, and the base of spurs. Cankers normally spread upward, and the infected sunken areas are usually formed in late winter or early spring. Gum often exudes from the canker during the early part of the growing season. If the canker girdles a limb it will die in short order. However, the root system stays healthy and may even produce sucker growth. Dormant leaf and flower buds may be infected and are often killed, but some invaded buds develop normally but will collapse in early summer. Leaves and fruit produced by these buds wilt and dry out. In contrast, leaves and flowers of other infected buds will remain symptomless. Leaf infections especially on cherries appear as water-soaked spots that later become brown and dry. At a later stage shot holes may be seen on leaves sporadically and not always symptomatic of the disease.

Control

Make sure that the trees are pruned, watered and fertilized properly. There is some indication that during mild, wet winters bacteria populations can increase. Trees are particularly susceptible in sandy soils, water logged soils that drain poorly, and during prolonged drought periods. Careful watering is a must. Precautions should be taken while pruning not to spread the disease. Dipping pruners in 20% bleach solution after each pruning cut should help. Chemical control of bacterial canker is based on protective copper containing sprays applied in autumn and spring before flowering. In cherry and peach growing area there are strains of bacterial canker that are resistant to copper sprays.

Source

Compendium of Stone Fruit Diseases. 1995. Edited by Joseph M. Ogawa, et al. The American Phytopathological Society, St. Paul, MN. Pages 48-50.

Question:

My apple tree has branches that are dead or dying. Leaves are drying up and the bark is sunburned. What can I do to stop this?

Answer

What you are seeing are the symptoms of a problem in the root system of the apple tree. It could be a soil born fungus like phytophtera, but is more likely to be a ground dwelling insect pest called a wooly apple aphid, (Erisoma lanigerum). Also pears are injured by the wooly pear aphid, (Erisoma pyricola). These aphids are native to the eastern United States and Canada, but is a worldwide pest that attack elm, mountain ash, and some species of hawthorn trees as alternate hosts. A fluffy white wooly covering over most of the insect's posterior end of their blue black bodies and accounts for its name. This cottony looking substance can be seen in small masses on branches and shoots where injuries or pruning cuts have been made, as well as on roots.

The life cycle of these insects is rather complicated. Females lay eggs on the bark of host or alternate host trees in the late summer or fall. These eggs over winter and hatch in the spring as wingless parthenogenic, (development from an unfertilized egg), females produce ovoviviparous, (eggs hatch within the females body), stem mothers which establish colonies on the terminal leaves. These leaves soon become curled and stunted from feeding. By early summer winged forms appear and fly to other apple trees or hosts to establish new colonies. Repeated generations are produced during the summer. Some of the individuals may crawl to the roots where they continue to reproduce indefinitely. In the fall, winged individuals develop again and fly to hosts and give birth to sexual forms which eventually mate and lay over wintering eggs. Not all aphids leave the apple trees, some wingless forms remain all winter, both above and below ground, thus maintaining a continuous infestation year around. On the roots nodules are formed from the insects feeding. These nodules are rough and bumpy looking and restrict the flow of water and nutrients from the roots to the leaves. Small leaves form and eventually the bark becomes sunburned and dried out and limbs die over several growing seasons.

Control

When planting apple trees semi-dwarfing and dwarfing rootstocks with MM before the rootstock number should be used. Example: MM106 or MM111 are semi- dwarfing rootstocks which are resistant to the wooly apple aphid. The MM stands for Malling-Merton which are agricultural research stations in England which developed these rootstocks. Currently chemical control is the only means available to control wooly apple aphid. However, BioLogic Company, a bio-engineering firm has developed a parasitic nematode, (Steinernema carpocaposae), that has been 80% effective in controlling the ground dwelling form of this pest. They are not yet marketing the nematode. Chemical controls include dimethoate, (Cygon), a systemic insecticide. Other organic and chemical based insecticides that control aphids will control the above ground generations of this insect when they are in the tree, though the ground dwelling forms will not be affected.

Source

Insect Pests of Farm, Garden, and Orchard. R. H. Davidson and W. F. Lyon. 1979. 7th Ed. pp. 392-393. John Wiley and Sons, New York.

Question:

I have a Golden Delicious apple tree with irregular large spots on the leaves. In some places the spots are turning brown and dying. Some of these affected leaves are falling to the ground. What is causing this and what can be done to stop it in the future.

Answer

The apple tree is experiencing necrotic leaf blotch, also called leaf spot or leaf drop. Golden Delicious is particularly susceptible and this condition is restricted to this cultivar and others with its blood-line. This disorder is characterized by irregular necrotic blotches in mature leaves that develop rapidly, usually within 12 to 24 hours. The leaf first turns pail green and yellow, then darkens to a deep brown. The size of the affected area remains constant once visible symptoms appear. The size of the necrotic area is restricted by larger veins, which are not affected. Mature leaves, in the mid-shoot region, are usually affected first. Young vigorous trees appear less severely affected than older, more slowly growing trees. Leaf fall can be rapid once symptoms occur, sometimes within 4 to 7 days. Severity of the disease varies greatly from year to year. Variation can be great among trees in the same orchard or yard. Necrotic leaf blotch is a physiological disorder related to air temperature, light intensity, and soil moisture. It is most severe when a cool, rainy period of 4-5 days precedes several hot, sunny days. A hormonal imbalance is thought to be the cause, since symptoms are enhanced by gibberellin, (a plant hormone that is needed for cell enlargement); and inhibited by abscisic acid (another plant hormone that causes leaf and fruit fall).

Control

Zinc oxide, applied every two weeks from bud break until harvest is effective in reducing disease incidences. Also, healthy, vigorous trees produced by good watering, fertilizing, fruit thinning, and pruning practices contribute to decreased incidences of necrotic leaf blotch.

Source

Compendium of Apple and Pear Diseases. 1991. The American Phytopathological Society. Page 88.

Question:

There are small, sunken, brown spots on the Golden Delicious apples I picked. When I cut in these spots the tissue is brown and corky. What pest causes this problem? How can I control it?

Answer

The problem you are seeing is called bitter pit. This is not caused by a pest but rather a deficiency of calcium, causing cell walls to not form properly. Bitter pit is increased by nutrient imbalances, hot weather conditions, and orchard practices. The tendency for bitter pit to occur increases as the ratio of potassium and magnesium to calcium increases. Other factors include excessive tree vigor, light crop load, or excessive thinning.

Control

Bitter pit can be decreased by minimizing or avoiding excessive tree vigor, caused by over fertilization, harvesting only mature fruit, regular watering, and maintaining a proper fruit load. Foliar sprays of calcium can reduce bitter pit in fruit. Bitter pit can appear while the apples are still on the tree or during storage. Cool the fruit rapidly after harvest. Storage at low temperature and in high relative humidity conditions can also reduce the development of this disorder in stored fruit. The fruit is still good to eat but the bitter pit areas may impart a slight bitter taste.

Source

Compendium of Apple and Pear Diseases. 1991. A.L. Jones and H.S. Aldwinckle; Editors. APS Press, St. Paul, MN. Page 89.

Question:

I have apple, peach and plum trees were planted in 1963. They are being attacked by a boring insect that makes trails under the bark. What can I do to get rid of these insects?

Answer

There are several insects that will bore into and make galleries under the bark. These insects however for the most part attack only weak growing or old trees. The trees are nearly 34 years old and fall into the weak and old tree category. Generally fruit trees if cared for will live for 25 to 35 years. There are some exceptions like pear and apricot trees. I would not spend a lot of time on these trees that naturally declining anyway, other than taking them out and replacing them. I would plant some new fruit trees if you want to harvest fruit over the next few years.

Question:

How can I tell if my apples, pear, peach, cherry and apricot flowers suffered freeze damage from freezing temperatures?

Answer

Most of the fruit mentioned will freeze if in full bloom during temperatures from 23 to 28E F. To examine a flower or fruit remove one from the tree. Make a horizontal cut with a knife through the base of the flower just beneath where the flower petals are attached. If small fruits have already formed cut horizontally through them also. If the center of flower or fruitlet seed tissue, is brown in the center then the flower or seed(s) is/are dead. If the flower or seed tissue is green they are alive. If the seed(s) die then the hormonal stimulus that the seed(s) produce which signals fruit growth will not occur; therefore no fruit will be produced. Go around each tree and cut 10 or 20 flowers or fruitlets to determine the percent of survival. If only 5 to 10% of peach flowers survived there will be a crop. If only 10 to 20% of apple or pears survived you will have a full crop. If more survived you will probably have to thin the fruit in a few weeks to produce large fruit. If thinning is not done either by man or Mother Nature's freezes small, inferior fruit will be produced.