Is your tree on death’s door? Here’s how to tell

Healthy trees grow lots of branches and leaves — their canopy — as thickly as they can, to gather all the sunlight they need. Dreamstime/TNS

Worried about a sad-looking tree in your yard?

Climate change, invasive species and even international trade are taking a serious toll on California trees. An estimated 150 million trees died during the drought that started in December 2011, according to Smithsonian Magazine, and the stressed trees that survived became more vulnerable to attack by a host of newcomer pests, said Philippe Rolshausen, subtropical tree specialist for the Cooperative Extension office at UC Riverside.

“There are lots of invasive pests everywhere because of global warming and the movement of plant materials in general,” he said.

Identifying specific tree diseases or pests usually requires an expert, but Rolshausen said three indicators suggest your tree needs help: yellowing leaves, a thinned-out canopy and branch die-back.

If you’re willing to wait, researchers or master gardeners in the state’s county Cooperative Extension offices can help you diagnose a sick tree for free, Rolshausen said.

Professional consulting arborists usually can respond more quickly but charge $200 to $400 for a consultation, said Darren Butler, a Los Angeles-based consulting arborist, horticulturist, landscape designer and cocreator of the GardenZeus.com. When you consider how healthy, mature trees boost property values, that’s a relatively small fee to pay, he said, but people often wait until it’s too late to ask for help. Search for trained arborists through the American Society of Consulting Arborists or the International Society of Arboriculture.

Yellow leaves

A few yellow leaves aren’t an issue, but if whole parts of your tree have brown or yellow leaves, that’s a sign it needs more nutrients, Rolshausen said. If you don’t fertilize your tree every year or two, it will eventually run out of nutrients, but a sudden big jolt of fertilizer could stress the tree even more, he warned. The best approach is gradual, adding compost and mulch around the drip line of the tree — that is, the place where water drips off the outer branches — so the trees can absorb the nutrients slowly.

Homeowners unwittingly remove the best fertilizer and mulch for trees — their own fallen leaves, Butler said.

“The tree spent so much effort gathering nutrients for those leaves, to remove that leaf litter is devastating to the tree,” Butler said. “Mulch is very, very important for trees, as long as it’s not right up against the trunk. You should have bare soil around the tree for a distance about three times the diameter of the trunk so roots can breathe.”

Mineral deficiencies or pollutants such as salt or even dog urine also can cause problems, especially if your dogs have been peeing around the same tree for years, Butler said.

One option is to send samples of your soil and tree tissue to a diagnostic lab to determine what if any deficiencies they have, Rolshausen said. UC Riverside plant pathologist Marcella Grebus created a list of diagnostic labs around the state, but be sure to call them first to learn how they want samples collected and packaged.

Thinned-out canopies and branch die-back

Healthy trees grow lots of branches and leaves — their canopy — as thickly as they can, to gather all the sunlight they need, Butler said. “Trees feed themselves through their leaves, so when you’re standing under a tree, you shouldn’t see a lot of blue sky. If you see a lot of blue sky, that’s an indication of a problem,” he said.

Another sign of trouble: bare branches sticking out of the canopy,

More likely, Rolshausen said, thinning canopy is the result of a soil-born disease such as phytophthora, aka root rot, that’s caused by excessive water.

“Homeowners have a tendency to over-irrigate a tree that’s not doing well, but soil-borne diseases actually thrive in wet soils, so that’s making things even worse,” he said. “Trees don’t like standing water on their root systems because they can’t breathe.”

Sprinklers that constantly hit tree trunks are another contributing factor, Butler said. People tend to plant lawns around trees, then water everything the same way. That’s detrimental to the trees, which need sporadic deep watering instead of the frequent shallow watering most people give their lawns.

“If you see green moss or algae on a tree in Southern California, it’s usually a sign that the tree is being hit by irrigation water,” Butler said. “Trees are not equipped to deal with sprinklers hitting their trunks all the time and it will probably make the tree sick.”

Sprinkler sprays can actually spread the disease to other trees, Rolshausen said; drip irrigation is better for trees. Water slowly and deeply along the drip line of the tree, then make sure the soil dries completely before you water again.

Tribune Wire

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