Brown leaves in summer probably signal scorched plants

Sometimes, in the height of summer, the tips of leaves on trees and plants turn brown and crispy. This condition is rarely caused by an insect or disease, according to Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle.

“The plants are just scorched,” she said.

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Scorch occurs when plants can’t move water up from their roots fast enough to replenish the water they lose through the tiny holes in their leaves. Without enough water, the leaves start to dry out.

They dry first at the leaf tips, because the veins that lead to the tips are the end of the water supply line. Then the entire leaf can turn brown and wither as its tissue dies. The majority of scorched leaves will usually be on the side of the plant most exposed to sun and wind.

On evergreens such as fir, arborvitae and yew, the scorch starts at the tips of the needles and moves toward their base. “It’s very similar to the damage we see in winter when evergreens are dried out by sidewalk salt,” Yiesla said.

“Leaf scorch is a condition, not a cause,” she said. It’s most often seen in July or August after a spell of hot, dry weather.

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The best prevention is to make sure there’s always moisture in the soil for plants’ roots to absorb. However, even if the soil is moist, other factors can cause or worsen leaf scorch, Yiesla said.

For example, if some of a tree’s roots have been severed by digging, it may not have enough working roots left to draw up sufficient water. If the soil is compacted, roots may not function well. Plants that have recently been transplanted, such as young trees, may not have developed enough roots to keep themselves supplied.

Many herbicides lead to browning of the leaves. Weed-killing sprays may drift onto desirable plants, causing leaf scorch and often killing the plant.

Some diseases, such as verticillium wilt and Dutch elm disease, interfere with the flow of water within a tree’s trunk and branches, cutting off the water supply to the leaves and leading to leaf scorch. Damage caused by some insects, such as emerald ash borer, has the same effect.

“If a plant shows scorched leaves, the first thing to do is water it deeply,” Yiesla said.

After you water, spread mulch to help prevent the moisture from evaporating from the soil. If the area already is covered with mulch, it’s still important to water thoroughly, so the water soaks down into the soil beneath the mulch.

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Avoid applying fertilizer in hot, dry weather because it may cause plants to develop new, tender leaves that are especially vulnerable to drying out. Fertilizer applied to dry soil also can damage roots, Yiesla said.

If you still see leaves drying out when you know the soil is moist, check for damage to the roots or to the trunk of a tree. Try to remember if you or a neighbor has sprayed an herbicide recently. If a tree shows leaf scorch without any obvious explanation, call in a certified professional arborist to look for a cause.

For tree and plant advice, contact the Arboretum’s Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).

Beth Botts is a staff writer at the Morton Arboretum in Lisle (www.mortonarb.org).

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Source: https://gardencourte.com
Categories: Outdoor