Trees need special care during drought

News Release Distributed 08/17/11

SHREVEPORT, La. – Just because a tree has turned brown or dropped leaves during a drought does not mean it is dead.

“Before you cut, make sure the tree is dead,” LSU AgCenter forester Hallie Dozier said. “If it is alive, irrigate and protect the root zone.”

LSU AgCenter horticulture agent Denyse Cummins concurs with not cutting down trees that have defoliated. “It happens in very dry summers, and it’s looking like fall in some areas right now,” Cummins said.

Drought in Louisiana has lowered the soil water content to the point where plants, including trees, cannot extract enough water to support normal growth and maintenance, Dozier said.

Trees under drought conditions lose the ability to grow normally, Dozier explained. Stressed trees essentially shift their energy and resources to survival rather than growth. Taking actions that redirect the tree’s energy to heal or grow hampers its efforts to survive.

Trees will shift some of their energy to closing stomates on its leaves to help retain water, but that shuts down normal growth. They also shunt energy to grow more roots to capture limited water resources in the soil, and they tap into their food reserves – or stored starches – needed for future growth.

As conditions get dryer, roots cease growth and function, leading to death. This may save the tree energy in the short term, but it severely restricts the tree’s ability to recover and resume growth once water again becomes available.

Finally, the tree starts shedding fruits, leaves and branches. This is when most tree owners notice that the tree is under stress – long after drought stress-related changes have begun.

During a drought, irrigation is necessary, Dozier said. “Water the tree deeply and slowly, roughly 10 gallons per inch of tree diameter at breast height.”

To water deeply, lay a soaker hose in the critical root zone – between trunk and edge of canopy or the “drip line” of the tree. “But do not wrap the hose against the trunk or directly water the trunk,” Dozier said. “Turn the hose on low and let it run slowly.”

Dozier offers the following tips for irrigating trees:

– Check your flow rates after a few hours. If water is running off the surface, turn the hose lower. Slow water application allows you to water the tree roots without loss to runoff or evaporation.

– If your tree is mulched, push mulch aside so water reaches the soil. Avoid disturbing the soil because doing so may disrupt root tissue and hamper the tree’s ability to absorb moisture.

– Similarly, avoid digging or otherwise disturbing the soil during drought. “Limit mower, vehicular and pedestrian traffic under the tree during periods of extended drought,” Dozier said.

Trees may need two or three days to be watered deeply, depending on soil conditions and tree size. Large trees should be irrigated every two to four weeks during drought. Smaller trees and new plantings may take less time to irrigate, but they need watering at least once a week. Be sure your irrigation plan complies with local water restrictions, if any.

“The LSU AgCenter does not recommend pruning of live branches during drought unless necessary to correct immediate structural or safety issues,” Dozier said. She added that leaves are a tree’s food manufacturing center, and pruning basically removes some of a tree’s ability to make its own food.

From the tree’s standpoint, pruning is “wounding,” and removing live branches forces the tree to direct energy to closing the wound against pathogens and insects. “When the tree is under drought stress, it needs to use all of its resources just to survive,” she said.

“Sometimes it is necessary to prune a tree, and we do so to create and maintain strong structure of the tree, increasing the tree’s chances of survival, and to reduce potential hazards,” Dozier said.

But removing live branches can retard the tree’s recovery from stresses such as root damage, wind and drought. Because of this, pruning should be done only for reasons that improve or maintain its health and safety, Dozier explained.

“If you have potential hazards such as dead wood or diseased limbs, you can prune anytime during the year. Otherwise, wait until the dormant season to prune live branches,” Dozier said, “especially during times of stress, such as high heat or drought.

“Trees under extreme drought may take several years to recover completely after rains resume,” Dozier said. Avoid unnecessary pruning and soil disturbance for a few growing seasons after the drought ends.

“When water is plentiful, young trees may benefit from fertilizers that help them put on growth,” Dozier said. Larger trees rarely need fertilizing unless soil tests show a lack of necessary nutrients in the soil.

Fertilizers are salts and may harm a drought-stressed tree by pulling water away from the roots. Hold off fertilizing trees until water is plentiful, and then fertilize only when there is a lack of nutrients in the soil or rapid growth is desired, Dozier said.

“If the branch or the whole tree dies, you need professional help,” Dozier said. “Always hire licensed workers.”

Louisiana has a state license that requires testing, continuing education and proof of insurance. “Do not hire anyone without first confirming that they are licensed by the State,” she said.

To check, call the Louisiana Department of Agriculture and Forestry at 225-952-8100. By hiring someone who is not licensed, you are putting yourself at risk for poor work and liability in the event that something goes wrong, Dozier said.

Mary Ann Van Osdell

8/17/2011 9:44:27 PM
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