Archive | April 10, 2014

Oozing Gel: Peach Tree Borer or Cytospora Canker?

“My peach trees are oozing gel. What is wrong with them? Thanks, Gary”


Hi Gary,

Thank you for your question.  Oozing gel could be one of two things.  If the gel has fine sawdust on it, you have Peach Tree Borer.  If not, the other problem the tree could have is cytospora canker.

Peach Tree Borer

The peach tree borer (also called the peach crown borer) is the most destructive insect pest of peach, cherry, plum and other stone fruits (Prunus spp.). The insect feeds under the bark of the tree, where it cuts deep gouges. When abundant, peach tree borers seriously weaken and even kill trees.

The entire life cycle of the peach tree borer requires one year to complete. The immature (larva) stage produces tree damage. Upon hatching from the eggs, young larvae immediately tunnel into the sapwood of the tree, usually through cracks and wounds in the bark. Larvae continue to feed and develop until the onset of cold weather. Most activity occurs a few inches below ground on the trunk and larger roots. The Insects spend the winter as partially grown larvae below ground under the bark.

With the return of warmer weather in early spring, the larvae again feed on the tree. Injury is most extensive at this time because the maturing Insects feed more. The larvae finish feeding and change to the pupal stage in late May through early July. Pupation occurs in a cell made of silk, gum and chewed wood fragments located just below the soil surface.

The pupal stage lasts almost one month. Adult borers then emerge. They often pull out the pupal skin in the process. This skin may be seen at the base of the tree. Adults are a kind of clearwing moth that fly during the day and superficially resemble wasps. Adult activity may begin as early as mid-June but primarily occurs during July and August. After mating, the female moth lays up to 400 eggs on the bark of the lower trunk and in soil cracks near the tree base. Eggs generally hatch in about 10 days.

External evidence of peach tree borer tunneling is a wet spot on the bark or the presence of oozing, gummy sap. The sap is clear or translucent and often dark from the sawdust-like excrement of the insect. Most injuries occur along the lower trunk beneath the soil line. Lower branches rarely receive injuries.

Peach tree borer can be difficult to control because insecticides cannot reach the damaging larvae after they move under the bark. The most effective controls are preventive insecticide applications at the vulnerable egg and early larval stages, while the insect is on the tree bark.

Egg laying occurs during the middle of the growing season. It may begin July 1 and continue into September. In general, peak egg laying occurs from mid-July to mid-August.

As a general guideline, apply preventive trunk sprays the first or second week in July and again in August if flights continue. Better determination of egg-laying occurrence is possible using pheromone (sex attractant) traps that capture adult Insects. Pheromone traps are available through some garden supply catalogs.

Peach tree borer is controlled in commercial orchards by insecticides that contain permethrin (Pounce, Ambush) or esfenvalerate (Asana). Insecticides containing these active ingredients (permethrin, esfenvalerate) are recently becoming available in some garden centers. Perhaps more widely available is carbaryl (Sevin). Some formulations of this insecticide allow use on fruit-bearing trees.

Paradichlorobenzene (PDB) moth crystals, used as a fumigant, may help control infestations of peach tree borer within a tree. After clearing away leaves and other debris from around the tree base, place the crystals in a band 1 to 2 inches from the base of the tree trunk. Cover the crystals with enough soil to create a 5- to 10-inch packed mound around the plant. The crystals release a gas at temperatures above 60 degrees F. The gas penetrates the trunk to kill peach tree borer larvae. Applications of PDB crystals are best made in late September or early fall but also can be applied in late spring.

PDB can injure plants. To avoid plant injury, follow these precautions:

1.    Do not allow the crystals to touch the tree bark.

2.    Adjust the amount of crystals used by tree size. Use 1/4 ounce on a first-year tree, 1/2 ounce on a 2-year-old tree, 3/4 ounce on a 3- to 5-year-old tree, and 1 to 2 ounces on a large, well-established tree.

3.    Remove the soil mound three weeks after the application.

With some effort, many larvae can be dug out of the tree or killed by puncturing them with a strong, thin wire. Be careful with these methods because they may cause more mechanical injury to the tree than the borer itself.

Maintaining tree vigor through proper tree care (water, fertilization, pruning, etc.) can greatly affect how well the tree can tolerate borer injury. Avoid any unnecessary wounding around the lower trunk; this area is often attacked. Extra care of already damaged trees is particularly important.

The use of insect parasitic/predator nematodes has given inconsistent control of peach tree borer larvae. If they are used, it is suggested that they be applied in a large volume of water to adequately moisten the soil. Also, use them only if soil temperatures are at least 50 degrees. insect parasitic nematodes are available through many nursery catalogs and some local nurseries.

Cytospora canker

Cytospora canker is a destructive disease of tree fruits. Although most common on stone fruits, the disease can be encountered on apple. Also known as peach canker, perennial canker, and Valsa canker in some areas, the disease occurs wherever stone fruits are grown. The disease is general in occurrence in peach, nectarine, prune, plum, and sweet cherry orchards. Cytospora canker is associated with winter-injured or mechanically wounded twigs, trunks, and scaffold branches.

Cytospora canker is caused by either of two fungi species, Cytospora leucostoma or Cytospora cincta. These two fungi are very similar morphologically and can be definitively separated only by microscopic examination of the sexual fruiting structures. These structures, called perithecia, are not frequently found.

The Cytospora fungi are vigorous wound invaders that grow throughout the bark and cambium and to a lesser extent into the structural wood of the tree. Common infection sites are bark that has been killed or injured by low winter temperatures or sunburn, pruning cuts, or insect damage. Winter injury is frequently an important predisposing factor to infection. Once established in dead or weakened tissue, the Cytospora fungi will invade adjacent healthy tissue, causing dieback and stem cankers.

As cankers enlarge, the fungus produces pinhead-sized, black, pimplelike, spore-producing structures, called pycnidia. These structures produce millions of spores, called conidia. During wet weather, spores ooze out of the spore-producing structures in reddish to orange colored gelatinous masses. Spores are carried to other infection sites (that is, wounds on the same or nearby trees) by splashing and windblown rain, insects, or people. These spores are not adapted to wind dispersal. Spores germinate at wound sites, resulting in infection and eventual cankering. Spore-producing structures ultimately form in the new cankers, producing more spores for subsequent infections. The spore-producing structures generally form 4 to 6 weeks after a cankered branch dies. The fungus overwinters in diseased tissue of living hosts and in stem debris on the ground.

If cankers are allowed to remain for several years, a second spore-producing structure, the perithecium, develops in the diseased tissue and produces ascospores. Ascospores are wind-disseminated; infection can result if moisture is present when ascospores are blown against wounded host tissue.

Infection can occur anytime during the year, except during very hot and dry, or cold weather. In Idaho, most infections occur during spring and early summer when temperatures are mild and moisture from rainfall is high.

Usually, the first symptoms of infection are dead twigs and dieback. Leaves above stem infections droop and discolor through shades of green to various shades of brown, and often remain attached, sometimes through the winter. These “flags” are caused by stem invasions and girdling or near-girdling cankers immediately below the flag.

Cankers are dark and depressed areas of dead bark and wood on main leaders and branches. Canker margins are sharp and distinct on the bark and discolored wood. Cankers are frequently perennial and may assume a zoneate appearance. Young cankers usually exude gum at the margin and may have a sour, sap odor. The surface of the cankers may develop raised pinhead-sized pycnidia in the bark. The spore-forming structures are rarely produced on cherry stems. After rainy weather, tendrils of dried reddish-orange ooze are sometimes visible coming from pycnidia.

Small at first, cankers slowly enlarge elliptically; sometimes they streak rapidly up and down the stem without girdling it immediately.

There is currently no cure for infected trees. Prevention and sanitation practices are the best management approaches. Use the following three steps concurrently.

1. Minimize injuries. Winter injuries are the most common infection sites. Painting tree trunks white before winter has reduced Cytospora infections. Take other measures to reduce winter injury and maintain good tree vigor.

2. Remove and destroy infected wood. Prune out infected branches, flags, cankers, and maintain good orchard sanitation. Cytospora has been isolated from apparently healthy tissue on cankered branches. Make pruning cuts at least one foot below the infected area.

3. Prune correctly. Make cuts that leave a raised collar of tissue at the branch junction rather than flush cuts or cuts that leave a stub. Pruning in the spring when wounds heal most rapidly has effectively reduced disease incidence in some areas.

Do not establish new orchards close to badly diseased orchards. Treetop or other hedgerow pruning and overhead irrigation favor the disease. Maintain trees in good vigor, but with maximum hardiness. Trees under water stress or grown in potassium-deficient soil are susceptible to infection. Weakened trees easily become victims of the Cytospora fungi.

I hope this information helps you out.  If you have any other questions, please feel free to ask.


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