Maple decline affects primarily sugar maple, Norway maple, and red maple in the Northeast and Midwest. The problem is not a new one; stagheaded maples were described as early as 1917 in Massachusetts. At that time, dieback was attributed mainly to drought and poor conditions for tree growth afforded by the urban environment. These same conditions exist today, and reports of the incidence and severity of maple decline have increased markedly in recent years.
In urban sites, principle stress factors in maple decline include drought, de-icing salts, and/ or road and sidewalk construction. These stresses also facilitate invasion by secondary organisms, including root rots, decays and twig blights, which greatly reduce chances of recovery from the original stress(es). When a healthy tree is stressed repeatedly, the stress alters the tree's internal chemistry to allow repeated attack by secondary organisms, and the tree declines and ultimately dies.
- Reduced twig growth. A general rule of thumb is that if the annual increase in twig length averages less than 5 cm., the tree may be in trouble.
- Reduced foliage growth. Sparse, light-green or scorched foliage signals that the tree may be declining.
- Early fall coloration. Maples normally begin showing fall color after the first frost or in mid to late September. When fall color develops earlier than normal, in late July or early August, the maple is definitely suffering from decline.
- Dead branches in upper canopy. Small dead branches seen in tree tops in late spring or early summer are indicative of decline. Over time, larger, more visible branches and limbs will die. The more numerous the dead twigs or branches are, the more severe the die-back decline conditions.
- Poor root conditions. If roots can be examined, look for reduced occurrence of small feeder rootlets; dead, brittle roots; and decaying buttress roots.
The success of treatment to declining maples depends primarily on early detection of maple decline, the health of the tree prior to treatment, and its ability to respond to treatment.
Treatment for declining urban maples includes: watering, fertilizing, pruning dead branches, and reducing salt-laden spring water runoff over the roots.
Watering trees every week or two during dry weather is recommended. Trees should be watered slowly to soak the entire soil area under the tree canopy to a depth of 12 or more inches.
Fertilizing is best done with a slow-release fertilizer to minimize soil salts and safeguard the sensitive absorbing roots. Davey recommends Arbor Green injected into the root area to a depth of 12 inches. Proper fertilization will help stimulate new roots and improve the health and vigor of trees.
Dead branches should be pruned as well, to stimulate renewed vigorous shoot growth. Pruning, in addition to fertilization, helps revitalize declining trees and helps the tree ward off secondary organisms.
Road salt impact can be reduced by placing a barrier (curb, berm, ditch, etc.) to catch or divert the spring runoff water which often contains copious amounts of salt. If soil and foliar analyses have been run and high sodium or chloride concentrations were found, then leaching the soil with fresh water or applying gypsum to improve soil structure may be useful.