Agenda - Parks and Recreation Commission - 10/14/1993

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I First, cut part wa), lhrough the branch al A; then cut il off at B. Make U~e final cul at C. Live branch branch collar Figure 78. Prune bronche~ at the branch collect. mulch, A tree-care specialist may recommend other alternatives, includ- ing soil iniections of air or pressurized water, to improve soil aeration. FERTILIZER lniured trees may need additional nutrients to replace damaged root systems. Fertilizers containing phosphorous and nitrogen can help stressed plants recover since these nutrients promote root a~d plant growth. Avoid excessive nitrogen; increased stem and foliage growth can cause stress, especially during hot, dry weather or if tile tree has been stressed due to construction activities. Because of this problem, many experts recom- mend waiting two years after damage has occurred before fertilizing the trees. Specific guidelines for selecting and applying fertilizer are described in Tree Fertilization (Minnesota Extension Service publication AG-FO-2421). PRUNING AND WOUND REPAIR Careful pruning and wound repair are important treatments for damaged trees. Prune broken or dead branches cleanly at the branch collar (Figure 18). To test whether a branch is dead, bend several twigs. Twigs on live branches tend to be pliable, while twigs on dead branches tend to break. Buds also can be used to evaluate branch condition. Live buds appear full and normal in color while dead ones appear shriveled or dry. Pruning is commonly recom- mended for large trees that have suffered root damage. Opinions differ over the merits of this practice. Assuming that the tree has adequate water and is not in severe decline, some experts believe that retaining maximum leaf cover is important for root regeneration and only dead limbs should be removed.. Others argue that pruning selected live limbs is neces- sary to compensate for lost roots. Generally, it is best to follow the recommendation of your tree-care specialist. When properly done in modera- tion by a skilled professional, pruning may reduce v,,ind resistance and limb failure and improve tree health and appearance. Except in extreme cases (e.g., overhead powerlines), DO NOT let anyone cut off all of the top branches to the same height ("top- ping"). The treatment of trunk wounds depends on tile extent of damage. If thc bark has been completely removed around thc entire trunk, thc tree wi]] l~ot survive and M~ould be removed. If onh' a patch of bark I~as been removed leaving a ~ew splinters, use a si~arp knife to c]eanlv cut off the loose bark t~ a place on ti~c slem where il is tirnflv attached. DO NOT make tl~e wound any larger Ihan necessary. You do not need to use pruning painl or dressing to cover exposed wounds or pruned limbs. Excep~ for special cases involving disease control, these products do little more than improve appeara nee. OAK WILT Oak wilt is a }ethat fungal disease normally spread through rc~-grafts between adjoining oak trees. The disease also may be spread overland by picnic beetles. In Minnesota, construction activities that injure roots, break branches, or otherwise open a wound on an oak between May 1 and Jul,,,, ~ provide the beetles easy access to transmit the fungus. (Some studies have found the occurrence of oak wilt to be four times more ]ike}v within 160 feet of a construction site.) Immediately cover all open wounds with any latex paint during this period. If you suspect oak wilt, contact your city forester or private tree-care specialist. If you have oaks on your site, obtain a copy of Oak Wil! in ~im~esota (Minnesota Extension Service publication NR-MI-3174) for additional information on identifying the disease and protecting your trees. OTHER INSECT AND DISEASE PROBLEMS Insects are attracted by distinctive chemicals that are released by plants recovering from injuries. Examples of insect pests that can sense a tree under stress include the pine bark beetle, bronze birch borer, two-lined chestnut borer, picnic beetle (transports oak wilt fungus) and some scale insects. These insects can kill a plant by their feeding or boring or by transmitting disease.