Spots, powder and speckles on tree leaves: which ones matter
Why tree leaves get black spots, brown blotches, white powder or pale stippling, how to tell tar spot, mildew and lace bugs apart, and when to rake or call.
On this page
Spots and blotches: the leaf spot fungiBrown along the veins: anthracnoseRaised black spots on maples: tar spotWhite powder: powdery mildewPale speckles and black specks: lace bugsThe few that matterWhat to do about spotted leavesWhere to startCommon questionsSourcesMost spots, powder and speckles on the leaves of a native tree or shrub do it no lasting harm. Leaf spot fungi, anthracnose, tar spot and powdery mildew mark the leaves in a wet or humid year and are a minor stress on the tree. They matter when they cost a tree much or all of its leaves two to four years in a row. A few diseases kill, among them dogwood anthracnose, bur oak blight and beech leaf disease. Raking up the spotted tree’s own leaves in fall, thinning the crown and watering at the roots do more than a spray.
What the leaf shows, and on which side, points to the cause:
| What you see | What it usually is | Does it matter |
|---|---|---|
| Round or angular spots, tan to black | A leaf spot fungus | Rarely |
| Brown blotches along the veins after a cool, wet spring | Anthracnose | Seldom |
| Raised black spots like tar, on maples | Tar spot | No |
| White to gray powder | Powdery mildew | Seldom; early on a dogwood |
| Fine white stippling above, black specks beneath | Lace bugs | On small shrubs in sun |
| Purple-edged spots on a dogwood, dead leaves hanging on | Dogwood anthracnose | Yes, it kills |
| Dark bands between the side veins of beech leaves | Beech leaf disease | Yes |
| Bumps, pouches or velvety patches | Galls of wasps or mites | Seldom |
Spots and blotches: the leaf spot fungi
Almost every tree and shrub can get a leaf spot disease, most of them caused by fungi. The spots may be round or angular, raised or sunken. They run from yellow and orange-red to tan, brown or black. They show first on the lower and inner branches, where the leaves stay shaded and humid. The fungi winter in fallen leaves and need a leaf wet, or very humid air, for 12 to 24 hours to infect, so a rainy year brings far more spots.
Bacterial leaf spots often start small and dark with a yellow halo, and their centers may fall out to leave shot holes. Bright yellow to orange spots on a serviceberry, hawthorn or crabapple are usually a rust, and cedar rusts have a page of their own.
Brown along the veins: anthracnose
Anthracnose is a group of fungus diseases that strike leaves as they open. After a cool, wet spring, with daily average temperatures of about 50 to 57 degrees at bud break, tan, brown or black blotches spread along the veins or leaf edges. The damage is worst on the lower branches, and badly hit leaves fall soon after. Most trees push out new leaves by midsummer, and even a severe year does not kill a shade tree.
Oak anthracnose can damage a swamp white oak but is seldom fatal. Sycamore, which we do not grow, can lose its buds and all its young leaves, and still leafs out again by summer. The browns of a dry summer are another matter, and drought and an established tree tells them from anthracnose and from leaf blotch on buckeyes.
Raised black spots on maples: tar spot
Tar spot starts as yellowish spots about an eighth of an inch across, which may grow to three quarters of an inch over the summer. Black crusts like blobs of tar then form on them. On silver maple each crust is often single, large and raised, while Norway maple carries clusters of small ones. A big crust’s surface winds in lines like a fingerprint. We grow neither, but tar spot shows up on black maple too.
A less common kind, speckled tar spot, crowds tiny black specks onto a tan patch. However black the spots, the tree is not in danger:
“For most maples and other susceptible trees and shrubs, tar spot is not a serious disease. […] Tar spot does not kill trees or shrubs, nor does it typically even cause serious defoliation.” (University of Wisconsin-Madison Division of Extension, Tar Spot of Trees and Shrubs)
White powder: powdery mildew
Powdery mildew coats leaves, green stems and buds in white to gray powder. A plant looks dusted with baby powder or hung with cobwebs. It is worst on young leaves and shoots, and on shaded or crowded plants where the air barely moves. Unlike most leaf fungi it thrives in humid air but not on wet leaves.
On shade trees it usually comes so late in the season that it does no real harm. Nannyberry whitens late in summer in still, shady spots, which looks poor and does little harm. On ninebark a gray film in humid summers is the one blemish, and spacing answers it. On a flowering dogwood, mildew that starts early in the season can be severe.
Pale speckles and black specks: lace bugs
Fine white stippling on top of a leaf, with black specks beneath, is the work of lace bugs, insects an eighth to three sixteenths of an inch long with lacy wings. They suck out the leaf’s cells from the underside and leave their black eggs and black specks of excrement there. The pale spots merge until the leaf looks bleached, and it may yellow and drop early. Spider mites stipple leaves too, but leave no black specks.
Large trees need no treatment, since the feeding does not hurt their health. The harm falls on broadleaf evergreen shrubs in full sun, where a heavy infestation can kill a small shrub. Mountain laurel shows the trade: lace bugs stipple its leaves in hot full sun, and leaf spot follows still, damp shade, so a half-shaded, airy site dodges both. Parasitic wasps and predatory beetles feed on lace bugs, so where they are at work, do not spray.
Leaves that yellow without spots or speckles have other causes, which yellow leaves in summer sorts out.
The few that matter
Heavy leaf loss two to four years in a row slows a tree and invites pests and other diseases. Three diseases call for action sooner:
- Dogwood anthracnose. Tan spots with purple edges start on the lower leaves in spring and climb the tree. Blighted leaves hang on the twigs, sunken cankers girdle shoots and branches, and sprouts crowd the lower trunk. Cankers that girdle the trunk kill the tree. It is worst at high elevations and in cool, moist, shady places. Spot anthracnose, small tan spots with reddish-purple borders on the flower bracts, often does little lasting harm.
- Bur oak blight. Known as BOB, it strikes bur oak alone. From July the leaves die along the veins and brown in wedges, low in the crown first and higher year by year. A tree stripped several years running can die.
- Beech leaf disease. Dark bands between the side veins of American beech leaves mark a nematode that winters in the buds. Saplings can die within a few years, while big trees thin out more slowly.
Iowa State University Extension, in a state where bur oak blight has been seen since about 2005, expects more frequent rain to make it worse:
“As long as the rains keep coming, BOB will probably continue to intensify on upland sites across much of Iowa, and we could lose a number of stately bur oak.” (Iowa State University Extension and Outreach, Bur Oak Blight)
What to do about spotted leaves
What helps, from fall cleanup to the rare spray:
- Rake up the spotted tree’s own leaves in fall, before the first snow, since the fungi winter in them. Bury them, or compost them only in a turned pile that heats to about 140 degrees, hotter than most home piles get.
- Leave the rest. Many leaf spot fungi infect only trees of one family, so other leaves can stay as leaf litter that feeds the roots.
- Open the crown and give plants room. Prune for light and air, in winter for mildew, and space new plants by their mature size.
- Water at the base. A soaker or drip hose keeps the leaves dry, where a sprinkler wets them for the hours the fungi need.
- Skip the fertilizer unless a soil test calls for it, since the soft new shoots it pushes out are the ones mildew likes best.
- Keep fungicide for the rare tree. It only protects leaves not yet infected, so it goes on from bud break, and a big tree needs an arborist’s high-pressure sprayer.
Raking does little against bur oak blight, whose fungus winters on the stalks of dead leaves still hanging on the tree. On a dogwood with anthracnose, cut out cankered twigs and sprouts in dry summer weather and pick off the dead leaves that hang on. Air movement and morning sun that dries the leaves do more for a flowering dogwood than any spray.
Where to start
Look at both sides of a spotted leaf first:
- Spots, tar spots or powder on a tree that leafs out each spring: rake its leaves in fall and leave it be.
- Stippling with black specks beneath, on a shrub in full sun: plant the next one in part shade.
- Blighted dogwood leaves that hang on, brown wedges on a bur oak, or banded beech leaves: have a certified arborist look at the tree.
- Still unsure: Blue Whale Trees answers questions about a tree you already have through its support page. Say which tree it is and when the spots appeared, and photos of both sides of a leaf can follow by email once we reply.
Common questions
Should I rake up leaves with tar spot?
You can leave them, since tar spot does a maple no lasting harm. Raking that maple’s leaves each fall and burying or hot-composting them can cut next year’s spots or end them.
Will leaf spot kill my tree?
Rarely, since most leaf spots take a small share of the leaves and are a minor stress. The risk comes from losing much or all of the leaves several years in a row, and from a few killers such as dogwood anthracnose and bur oak blight.
Should I spray a fungicide on a tree with leaf spots?
Rarely, because a fungicide only protects leaves not yet infected and is usually wasted once the spots show. It earns its cost on a tree stripped several years in a row, sprayed from bud break by an arborist.
What is the white powder on my oak leaves?
Powdery mildew, a fungus that whitens leaves and young shoots in humid weather, worst in shade and still air. On a big tree it mostly comes late in the season, when the leaves are nearly done for the year, so it needs no treatment.
Sources
(8 references)
- Leaf spot diseases of trees and shrubs: University of Minnesota Extension, with its page Powdery mildew on trees and shrubs (Rebecca Koetter and Michelle Grabowski, reviewed 2026): leaf spots as a minor stress, moderate to complete leaf loss two to four years in a row as the point to act, the shapes and colors of spots, the lower and inner branches first, 12 to 24 hours of wet leaves, fungi wintering in fallen leaves, bacterial spots with yellow halos and shot holes, yellow to orange rust spots, raking before the first snow, spacing, pruning for light and air, watering at the base, no fertilizer without a soil test, fungicides as protective and for an arborist with high-pressure gear, host-specific fungi, and powdery mildew’s look, its humid but not wet weather, its worst places, its harmlessness to a tree, winter pruning and fertilizer’s soft shoots.
- Anthracnose of Shade Trees: The Morton Arboretum: anthracnose as a group of fungi on newly emerging leaves, cool, wet springs at daily means of 50 to 57 degrees, blotches along the veins and margins, the lower branches, early leaf fall, new leaves by midsummer, no tree death even in a severe year, sycamore’s dead buds and lost leaves, fungi wintering in fallen leaves, and sprays as ineffective once injury shows.
- Anthracnose On Shade Trees: Penn State Extension (Gary W. Moorman, updated November 4, 2026): cool weather of 50 to 55 degrees at bud break, sprays begun at bud break, and spraying not recommended for a tree without severe or frequent leaf loss.
- Tar Spot of Trees and Shrubs: University of Wisconsin-Madison Division of Extension, Wisconsin Horticulture, from the UW Plant Disease Diagnostics Clinic (Brian Hudelson, revised March 2, 2024): the first yellowish spots of an eighth of an inch, growth to three quarters of an inch, black crusts like tar, single raised spots with fingerprint lines on silver maple and clusters on Norway maple, speckled tar spot as less common, fungi wintering in leaf litter and infecting in spring, the quotation, and leaves gathered each fall and buried or hot composted at about 140 degrees.
- Bur Oak Blight: Iowa State University Extension and Outreach, Yard and Garden, with its page Powdery Mildew- Ornamental Plants: bur oak blight on bur oak alone, seen in Iowa since about 2005 and worsening with more frequent rain, leaves dying along the veins and browning in wedges from July, the lower crown first, death after years of defoliation, a fungus that winters on leaf stalks still on the tree so that raking does little, the quotation, and powdery mildew late on shade trees, a fungus of its own for each kind of plant, and home compost piles too cool to kill it.
- Dogwood Diseases and Insect Pests in South Carolina: Clemson Cooperative Extension, Home and Garden Information Center (HGIC 2003, updated August 11, 2026): dogwood anthracnose’s tan spots with purple edges from the lower canopy up, blighted leaves that stay on the twigs, cankers, sprouts on the lower trunk and death of the tree, its high and cool, moist, shady sites, cutting out cankers and sprouts and removing hanging leaves in dry summer weather, spot anthracnose’s small tan spots with reddish-purple borders on the bracts and its little lasting harm, and powdery mildew on dogwood as severe when it starts early.
- Lace Bugs on Trees and Shrubs: University of Maryland Extension (updated October 17, 2024): lace bugs about three sixteenths of an inch long, white stippling that merges and yellows, black eggs and fecal spots under the leaf, early leaf drop, no treatment needed on large trees, broadleaf evergreens in full sun hurt most, small shrubs killed, and predatory beetles as a reason not to spray.
- Azalea Lace Bug: NC State Extension (James Baker, revised June 21, 2023): lace bugs about an eighth of an inch long, sucked-out cells and bleached leaves, mountain laurel among the hosts, the bug specks that tell lace bug damage from spider mite damage, and the parasitic wasps that attack the eggs.
