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Parched trees in P-town

Enough water needed to keep away fungus, harmful beetles

Deep-root watering ensures that trees receive enough moisture even during a drought. (Contributed photo)

People and pets aren't the only things wilting in the summer heat. High temps are tough on many plants.

Flowers dramatically droop when thirsty but trees often don't show the effects of too little water until too late.

"A tree will get stressed by a certain event or years of drought but a lot of times, it won't show up for five to 10 years," said Joe Berg, an arborist with the Davey Tree Expert Co. who has worked in Pleasanton for 12 years.

Roots will die out during a drought allowing fungal diseases in the root system, he explained.

"It's tough for a tree, going from one heavy stress to another heavy stress," Berg said. "Typically when they die, it is not just one thing that happens. There will be drought, then fungal disease, then bark beetles come in."

"Many houses I go to, the trees are in obvious signs of decline and it is too late," he noted. "When you get to the point where the tree shows signs of distress, a lot of times it is too late."

The place to start, Berg pointed out, is planting the right trees for Pleasanton in the first place.

"Plant one that is more drought-tolerant and you are going to win," he said. "Plant more native species that have adapted to our climate."

Many non-native birch trees and redwoods have been planted in the Tri-Valley, he said, and they make attractive landscaping.

"But pine trees end up getting attacked by bark beetles -- they bore into the tree and disconnect the vascular system," Berg said.

Trees send out "drought signals," which attract the beetles, and the trees cannot produce enough sap to defend themselves.

Arborists often spray or inject trees to prevent damage by bark beetles.

"If homeowners buy their own insecticides, they really have to make sure they are wearing the proper protective equipment," Berg said.

Well-maintained trees increase property values by as much as 15% while an attractive landscape can boost values up to 30%, Davey Tree estimates. Trees also, of course, reduce pollutants in the air and prevent erosion.

When people ask for recommendations about what trees to plant, Berg said he tells them: "Look around the neighborhood and see what is doing well."

Pleasanton soil varies, even from yard to yard.

"This is not a natural soil column that has been undisturbed for eons," Berg said. "We have had bulldozers run through, disturbance and compaction. A low spot in a yard may have been compacted more -- or may have more clay in it."

This makes it difficult for trees to get proper amounts of water.

"Drainage is one of the biggest factors in tree mortality," Berg said. "The tough thing with the drought is that too much water and not enough water look very similar."

Proper watering is key to trees' survival. Young trees need water to establish deep root systems, according to California Urban Forests Council, and mature trees require more water when growing near "heat traps" such as driveways and foundations.

The council recommends watering young trees twice a week and mature trees once a week, about five gallons of water, directly with a hose or a five-gallon bucket. Berg said deep watering is even better.

"Landscape irrigation is great but it doesn't penetrate nearly as deep as what trees need," Berg said. "You'd be lucky to get down six inches, and tree roots are down three to four feet."

Watering probes are available, he said, that hook onto a hose.

Professional deep-root watering services bring a tanker and inject 200 gallons of water at high pressure.

"You want to get water down to where roots of the tree are," Berg said. "You need to get a deep root soak. Water is a big, big deal."

Proper mulching is also important. An arborist might do "vertical mulching," drilling holes into the oil and backfilling them with beneficial, porous materials.

"Mulching trees keeps the roots cool and soaks up water so it doesn't leave the planting area," Berg said. "It improves soil structure and increases the microbial activity, with worms and insects, giving it a natural soil profile like in a forest."

Fertilizing is important for urban soil because it is often depleted of nitrogen, he added.

"Proper TLC is the most important thing," Berg said.

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