Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, August 18, 1994 TAG: 9408190056
SECTION: CURRENT PAGE: NRV-10 EDITION: NEW RIVER VALLEY
SOURCE:
DATELINE: LENGTH: Medium
Injecting fungicides into American elms to combat Dutch elm disease is perhaps the best known use of this procedure. These materials are systemic and move rapidly throughout the plant. However, as most chemicals are preventive rather than therapeutic, they must be injected prior to infection.
Miscalculation of the rate can result in overdosing, which could kill or damage the tree. However, if the right material is properly applied at the correct time, it can, indeed, forestall death due to fungus.
Other tree diseases (live oak wilt, x-disease of Prunus, elm phloem necrosis and bacterial-associated leaf scorch) are treated by injection, but it is still an uncommon procedure. Experimental work is being done on immunization or injection of plants to enhance their natural immune systems.
The injection or implantation of fertilizer into a tree generally is reserved for correcting minor nutrient deficiencies, such as iron chlorosis or manganese russeting, and it is the least common method of tree fertilization. Either a liquid may be injected, or a capsule may be implanted in the tree. While this method generally relieves visible symptoms, this relief is temporary and does not correct the underlying problem. Excesses of certain nutrients through overuse of certain lawn fertilizers and extremes in pH can create micronutrient deficiencies even when the element is in the soil. For long-term relief, the actual deficiency problem must be corrected.
A few insecticides have been applied experimentally via injection to control certain insects (borers and gypsy moths). Injection application of insecticides has not received the attention that injection application of other chemicals has, probably due to the existence of effective insect spray control methods.
Utility companies inject growth regulator or growth retardant chemicals into trees to retard sprout growth on trees under and around power lines. Injection generally is combined with pruning to prevent damage to power lines that could interrupt electrical service. Some of the compounds also have proved effective when applied as bark paints, foliar sprays and soil drenches. In other forestry and vegetation management situations, various herbicides have been injected to kill or control tree growth.
Regardless of the material being used, injection application requires special equipment and training, can be very time-consuming, and results in an injury either to the tree trunk or to the root flare (the expanded area at the base of a tree). While the first two disadvantages may be justifiable from an economic perspective under certain conditions, the last may be harder to justify for any reason. Anytime a material is injected or implanted into a tree, a wound is created. Some species of trees have the ability to compartmentalize or wall off the wounded area so that little injury results, but many trees do not compartmentalize or close wounds well, so the injection sites may provide entry for disease organisms and insects.
When injection applications are used, the injection holes should be small and very shallow - no deeper than the current season's growth. They are best made at the base of the tree, not higher on the trunk or into the roots. If roots must be injected, the injection should be in the mid-root flare area. They should never be made above, below, or into old injection sites. Damaged, stressed, or diseased trees should never be injected, nor should nonliving or decayed tissue.
The holes should be checked after one growing season, and if they have not closed, no further injections should be made into the tree. Large holes can lead to cracks, cankers, cambial dieback, wetwood, and discolored and decayed wood. While this may not directly kill the tree, it can seriously injure and weaken it.
Injection generally is best done in spring when wound closure is fastest and when fewer fungal spores may be present. The best environmental conditions for injection include soil temperatures of 50 degrees, air temperatures at least 75 degrees, low humidity and ample sunlight (midday is good). Injection probes must be securely seated to prevent leakage and bark blowout.
In general, injection and implantation of chemicals into trees should be used only as a last resort, after other methods have failed to alleviate a problem or are too costly. These methods should be used only by people who know the proper application method and who strive to minimize tree injury when making an injection.
Joe Hunnings is the Virginia Cooperative Extension agent for agriculture in the Montgomery County Extension Office in Christiansburg. If you have questions, call him at 382-5790.
by CNB