Gummosis of Fruit Trees
Gummosis is a term that refers to the presence of amber-colored sap oozing from the trunk or branches of a tree. It is important to understand that the term “gummosis” is a symptom, not a cause of a tree ailment. Anything that stresses the tree can be a causal factor. It is necessary to determine the cause of the stress in order to mitigate future damage to the tree.
Gummosis has a variety of causes:
Environmental stress: Compacted soils, poorly drained soils, light sandy soils, use of weed and feed or other herbicides nearby, and winter injury can all contribute to the cause of gummosis, as can lack of irrigation under the canopy.
Correct any environmental stresses that you can. Avoid planting in heavy soils or light sandy soils that do not hold moisture. Irrigate under the canopy as needed. Do not plant fruit trees in poor, thin soil.
Mechanical injury: Damage to trunk from mowers and string trimmers, deer rubs, improper pruning cuts, or pruning in fall and winter when disease is active can contribute to the cause of gummosis. The injury to the tree provides an opening for disease to enter the tree.
Unfortunately, once the damage is done, there is little that can be done to correct the damage. Trees do not regenerate vascular tissue once it has been destroyed. It is important to keep the tree as healthy as possible through proper pruning, fertilization, and watering practices. These practices may extend the life of the tree.
Disease: Pseudomonas bacterial canker affects weakened trees. Entry is usually through injury sites or pruning cuts. Bacteria may also enter the tree through borer holes. Symptoms vary, but typically appear in the spring when infected twigs die. Cankers (sunken tissue) may occur on larger branches and trunks. Gummosis has a distinctive sour-smelling odor when it is caused by bacteria. Sap will be clear with no sawdust or frass. There may be an increase in formation of water sprouts (shoots growing from the base of the trunk). Bacterial Canker can also cause leaf spots that begin as a dark purple lesion, then a “shot hole” condition when the center drops out.
Prevention is the best course of action. Trees that are 2-8 years old and stressed are the most susceptible. Avoid poorly drained soils, mechanical injury, improper pruning practices. Do not prune in fall or winter. Pruning closer to the time the tree “leafs-out” in late winter to early spring is the preferred timing for pruning.
Applying bactericidal chemicals is not recommended or effective for prevention or treatment of this disease.
Maintain tree health with proper fertilization and watering and avoid pruning between October and January. Sterilize pruners with a 10% bleach solution after pruning each tree.
Remove severely affected branches or entire trees to prevent spread.
Insects: Borer insects, such as the Peach Tree Borer and the Lesser Peach Tree Borer, lay eggs on tree bark and the larvae bore into the trunk. Peach Tree Borers are seldom a problem with healthy trees, but are attracted to damaged areas of the tree caused by poor cultural practices.
Peach Tree Borers are the larvae of a “clear wing moth” that has translucent wings and resemble wasps. Eggs are deposited in March to May, and again in August to September on the trunk of peach trees near the soil line. The larvae hatch and bore into the cambium layer, just below the tree’s bark, where they feed on vascular tissue. Young trees are especially vulnerable during establishment. Weakened trees are also more prone to damage, as are trees with mechanical damage, disease organisms or previous borer activity. Borers are “secondary invaders”. They target trees already weakened by other factors. The sap oozing from the trunk will contain sawdust and frass (excrement) in trees infested by borers. Sap with no sawdust is likely caused by disease organisms.
Peach Tree Borers are usually more damaging than the Lesser Peach Tree Borer, as they lay their eggs at the base of the trunk at or near ground level. The larva bore into the cambium layer beneath the bark and feed. If much of the vascular system is destroyed at the base of the the tree, the supply of water and nutrients to the entire tree will be affected.
Probe small holes in the trunk near the soil line with a thin wire to crush the larvae.
Spray trunks with Permethrin when larvae are hatching in April and May and again in mid-August to September to prevent the larvae from boring into the bark. Spray three times at two-week intervals if infestation is heavy.
Spinosad may also be sprayed on the tree trunks as larvae hatch and sprayed directly into the borer holes. Repeat every week from mid-August to late September.
Spray with Dormant Oil in late February before the buds swell. Spray when the temperatures are between 45°F and 85°F and the humidity is low. Under these “fast-drying” conditions, the oil will suffocate overwintering insects.
DO NOT USE MOTH BALLS AS SOME SITES RECOMMEND.
Keep trees as healthy as possible by watering adequately and avoiding mechanical damage.
Lesser Peach Tree Borers: Like other borers, Lesser Peach Tree Borers are attracted to unhealthy trees which are usually the result of poor cultural practices. Careless pruning techniques and improper timing provide many sites for the borers to enter the tree. Unlike Peach Tree Borers, the Lesser Peach Tree Borers will feed in the scaffold branches of the tree instead of the lower trunk of the tree. (They may also be found at the base of the tree, but it is not common) Masses of gum exuding from the branches will be mixed with sawdust and frass. Adults are a clear winged moth and appear from March to May, and may have a second generation in late summer to early fall. Larvae hatch from eggs deposited on the bark and bore under the bark into the cambium. Larvae overwinter while feeding under the bark, then pupate and emerge the following spring as adults.
Probe into small holes in the trunk with a stiff wire to crush the larvae.
Prevent mechanical damage and careless pruning techniques. Prevent broken branches by thinning fruit to avoid overloaded limbs.
Water and fertilize trees appropriately to keep them as healthy as possible.
Spray trunks and branches with Spinosad or Permethrin in April and May and again in August and September.
Remove severely damaged limbs or trees.
Spray with Dormant Oil in late February before the buds swell. Spray when temperatures are between 45°F and 85°F and humidity is low. Under these “fast-drying” conditions the oil will suffocate overwintering insects.
Varietal Tendencies: Genetic Dwarf peach trees are prone to gummosis symptoms when the trees are young. This may occur when the roots uptake more water than the top requires. Control the moisture you give the to tree if possible and do not plant in heavy soils.