Leaves browning or turning color early: what the sources say it may indicate

This page reports what the named sources say. It does not say whether any tree is stressed, diseased or healthy. The sources list several possible causes for the same look, and none says a photo or a glance at the leaves settles which one applies.

Water, sun and wind

The Utah State University Extension page Leaf Scorch describes scorch as a general plant reaction to several environmental conditions, listing drought, underwatering, strong sun and heat, wind, compacted soil and nutrient deficiencies. It says scorch shows as dead leaf margins or dead areas between veins, is most severe on ash, maple, pine, horse chestnut, elm and poplar, and that severe scorch can kill leaves. It gives the primary cause as a lack of water in the root zone together with wind and sunlight.

The Utah State page Drought Underwatering says drought stress shows as leaf wilt, folding or rolling, scorch, yellowing, premature leaf drop or death and overall decline, and that some of these look like salt damage because salt reduces a plant's ability to take up water.

The Missouri Botanical Garden page Drought and Water Stress says woody plants under drought stress can show yellow, wilting leaves that colour early in the fall, along with scorched or burnt leaf edges. It adds that symptoms of drought may look like overwatering or like some pest and disease problems, and that most established woody plants recover when watered. It also says a plant that has dropped most of its leaves may still be alive, and describes scraping a twig to look for a green layer.

A bacterial cause

The NC State Extension publication Scorch Diseases on Shade Trees describes scorch caused by bacteria that live in the water-carrying cells of a tree. It reports the disease on elm, red maple, mulberry, sycamore, pin oak and southern and northern red oak, and says leafhoppers can carry the bacteria between plants. It says leaf symptoms first appear in late July and early August as brown or red colour around the leaf margin, may first be noticed as early fall colour on one section of an otherwise green tree, and grow more severe each year. It says severe dieback and decline come before death of the whole tree in 3 to 4 years, and refers to a proper diagnosis being made first.

Source	Causes it lists for the look
Missouri Botanical Garden	Drought and water stress, with symptoms that can look like overwatering, pests or disease.
NC State Extension	A bacterial scorch disease carried by leafhoppers, on named shade trees.
Utah State University Extension	Drought, underwatering, sun and heat, wind, compacted soil and nutrient deficiencies.

Who looks at it

None of the four pages names a way for an owner to tell these causes apart from the leaves alone. The guide on leaf scorch and the guide on drought describe the terms arborists use. The guide on whether a tree is dying reports who the sources say assesses trees.

Who to call

ISA Find an Arborist: the ISA directory for an arborist who can examine a tree
Consulting arborists by country: the credentials and registers consulting arborists hold in each country
NC State Extension, county centers: the local Cooperative Extension centers in North Carolina, which the NC State scorch publication names as the place to get help; other states have their own extension offices