Thursday, November 22, 2007

Nursery - Drought and Christmas Tree Plantings

Chrismas tree plantings in Kent County suffered greatly this year because of the drought. The following is an article on the subject.

June through September proved to be very dry throughout most regions of the county. Drought or dry soil conditions result in root damage and death. Non-woody feeder roots, usually located in the top 15 inches of soil, are particularly sensitive and are the first ones affected. Without moisture, these roots shrivel and die. This is expecially severe in our sandy soils. In our heavier soils with high clay content (many Kent county christmas tree plantings are on heavier soils such as our "White Oak" ground), the soil pulls away from the roots as it dries which results in desiccation and killing of the fine roots. When these roots become nonfunctional, a water deficit develops since the roots cannot provide water to the top of the plant.

Effects of drought are particularly severe on seedlings or new transplants because their roots occupy the uppermost layers of soil where the most rapid drying occurs. In addition, recent transplants typically lose feeder roots during the transplant process. Contrary to popular opinion, it often takes woody transplants two years to become completely established in a new site. Therefore, seedling beds and new transplants should be given extra care and attention during periods of drought if possible.

Established trees are also affected by drought, especially those planted in marginal sites such as those in sandy soils or those that have been improperly planted. Drought can exacerbate even the most subtle of improper planting practices!

Symptoms are manifest in different ways depending upon species but are often not evident until some time after the event has occurred--even as much as one or two years later! Symptoms of early drought stress in conifers often appear at the top of the tree as a wilting and drooping of the needles and branches. If dry conditions persist, needles may appear pale and off-colored and can develop "scorch" symptoms or browning at the tips. On spruce, needles become chlorotic and drop. In the case of white pine, needles become discolored and can develop a permanent bend. With most conifers, severely affected needles of all ages will drop prematurely and tip dieback can occur.

Drought stress is especially noticeable in mid-summer on trees in sandy soils or where roots are located in the top layers of heavily compacted soils. Symptoms can develop in individual trees or in groups of trees which are growing under common soil conditions.

In addition to direct root damage, a significant secondary effect of drought is that it weakens trees and predisposes them to secondary invaders and opportunistic pests. For example, it has been reported that root rots and spider mites are more serious on trees under drought stress. Studies have shown that many drought-stressed trees are not as winter-hardy as healthy trees and often develop problems from winter injury. Drought-stressed trees are also more sensitive to air pollutants and pesticides to which they might be exposed.

While there is no cure for this problem, the effects of drought can be minimized by following some preventative measures. Water in periods of low soil moisture: trees require approximately one inch of water per week. This is best applied at one time as a slow, deep soaking to a depth of approximately 12-18 inches. The length of time required to "deep-water" will vary depending on soil type and water pressure: clay soils usually require more time than sandy soils. Frequent, light, surface watering will not help the tree and can actually cause harm by promoting growth of surface roots. A deep soaking just before the ground freezes in the fall will also help the winter hardiness of drought-stressed plants.

Select the appropriate site and follow good planting practices; drought-stress can magnify even the most subtle improper planting practices. Select native plants or match plant species to site conditions: drought-sensitive vs. drought-tolerant species. Prune any dead or weakened tissues to avoid secondary problems. Maintain tree vigor by following good cultural practices.

Modified from "Disease Problems in Connecticut Christmas Tree Plantations" By Dr. Sharon M. Douglas, Department of Plant Pathology and Ecology, The Connecticut Agricultural Experiment Station

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