We have come to associate the Labor Day weekend as the end of the summer and the beginning of fall, yet the autumnal equinox does not occur until around the 21st of September. In the southeast, the seasonal signs of fall don’t typically show until a month or so after that. So what’s going on with the trees around here? As one drives around Atlanta and beyond, intermittent splotches of brilliant fall color can be observed among the trees. In other places, leaf drop litters lawns to the point that thoughts of raking leaves are provoked- good thoughts for some folks, possible dread for others! Remembering last summer, an uncommonly moist and mild one, the Cherry trees around town were completely bare by Labor Day. Does the onset of fall have a hair trigger?
Fall color is revealed as chlorophyll in the leaves begins to break down. Since this chemical is the one that allows the plant to turn water and carbon dioxide into simple sugars and oxygen in the presence of sunlight, its demise in the leaves means that food production in the tree is dwindling. The colors that we see- reds, yellows, oranges, and browns were there in the leaf the whole season- they were simply masked by the green pigment. The triggering mechanism for this change in leaves is complex and not fully understood, but it is evident that temperature and the changing angle of sunlight are contributing factors. As the autumn season progresses, another chemical seals off the place where the leaf petiole attaches to the stem, and the leaf falls off the tree to be recycled into mulch and fertilizer for subsequent seasons. This phenomenon, called leaf abscission, is an adaptation of many temperate-zone plants (deciduous trees) to prevent excessive drying out by cold winter winds.
The fact that all of this is happening months too soon is indicative of stress in the trees. This year, Atlanta has seen over 2½ months of daytime temperatures in excess of 90 degrees F. While the record is over 3 months of such extremes in the hottest years, this summer has been far hotter than the last three. Additionally, rainfall has been less than normal- 4 inches less than our 30-year average. While this may not seem like a lot, the combination of high temperatures and reduced rainfall place considerable stress on trees. Consider a large Maple tree, for example: the tensile pull of water initiated by leaves and extending all the way down the twigs, branches, and trunks to the roots can cause a loss of as much as 52 gallons of water per day! While most established trees can tolerate a period of time lacking rainfall or supplemental watering, sooner or later a stress response will ensue, be it wilting, marginal burn on the leaves (a textbook sign of stress), premature leaf drop, or premature fall color.
Maple trees are very often the first trees to exhibit the stress symptoms described here. Several examples are shown, all taken right around the Labor Day holiday. By all indications, some photosynthesis is likely taking place, but premature shut-down of the plant is also evident. Carbohydrates in the plants can be transformed into starches which can be stored in stems and roots, something that takes place especially this time of the year with the dormant season approaching. By not meeting the tree’s potential for the accumulation of starch, the resulting deficit and stress can predispose it to other problems. Borer infestations, root and stem dieback, scale infestations, and fungal attack are but a few of the potential problems that could plague a stressed tree.
The chances that any of these problems will occur can be greatly diminished by reducing the stress the on the tree.
The first management strategy is providing water. The benchmark for optimal water in Georgia is 1 inch per week. If Mother Nature does not provide, we should supplement to make up the deficit. Let’s say, for example, that the thunderstorm last night dumped ½ inch of rain on our property (we know this because we checked our rain gauge). This means that for the rest of this week, assuming we don’t have another storm, we need to provide an additional half inch of water. One inch of water per 1000 sq. ft. is equivalent to 660 gallons per 1000 sq. ft. Therefore, applying 330 gallons of irrigation water per 1000 sq. ft. will allow us to make up the deficit. Again, we will utilize our rain gauge to approximate the correct application. Trees should receive 5 gallons of water per inch of trunk diameter per week. That means your beautiful 6” DBH (diameter at breast height) Japanese Maple tree will need 30 gallons of water this week, barring any rain. Mistakes most made by well-meaning folks include watering by frequency instead of amount (this is the way we are conditioned to water by those that provide and regulate it), not calibrating their watering to know how much they are applying in a given period of time, and not adding in rainfall as a portion of the water application.
Deep penetration of water into the root zone can be accomplished by longer, slower applications of water on consecutive days. In addition, de-compaction of the soil can improve the pore space to allow water applications to percolate more deeply and prevent water from running off and away from the root zone. Downey Trees provides soil fracturing and de-compaction utilizing a pneumatic air tool and compressed air to open up the soil for improved movement of water and oxygen. Another effective way to improve the health of the tree is by enhancing the health of the soil. Our products for soil web management include organic beneficial fungi, humates (carbon compounds that promote a living, active soil structure), and low-analysis fertilizers to provide direct macro and micro-nutrients to the tree’s root zone.
Downey Trees, Inc. will design a specific program for the important trees on your property that utilizes these management tools and others to reduce the stresses imposed by a harsh urban environment. Call us soon for a free review of your trees- before the stress of an early fall shows its colors too soon!