Fifty Useful Things to Know About Leafspot Diseases of Trees

A leafspot is an infected area of limited size on a leaf.

The size of a leafspot may be limited by defensive reactions of the tree.

Or the size may be limited by toxic wasteproducts by the disease organism.

Leaf spots often are fairly circular, but may have irregular shapes.

Leafspot disease infections may be caused by bacteria, fungi, viruses.

Most leafspot infections occur in spring as buds open and leaves enlarge.

Fungal leafspot infections are spread mostly by airborne spores.

Wet weather—also sprinklers!—favor fungal & bacterial leafspot infections.

Spacing plants or thinning foliage—quicker drying, makes for less leafspot.

Many preventive fungicides can reduce leafspot disease infection rates.

When tree-owners notice leafspots it's usually too late to spray that year.

Fungicides are usually put on as buds swell & open and as leaves enlarge.

Leaf expansion leaves unprotected areas between the particles of fungicide.

So sprays often are repeated twice at 7-to-10 (or 10-to-14) day intervals.

Spray registrations change so often that the user must check each time!

Spray materials must be registered for that (a) host tree and (b) disease.

The USER must ask at each purchase: is THIS PACKAGE labeled for this use?

Leafspot diseases rarely threaten a large or strong tree's life.

We usually don't recommend efforts to control most leafspot infections.

Leafspot control is important, however, if the tree is weak or for sale.

Leafspot control is important if the propertysite appearance is valuable.

A leafspot where the fungus itself is visible is "tar spot" of maple.

Leafspot fungi can include the rusts, like ash rust or pine needle rust.

Leafspot-causing bacteria can be carried by insects or splashed by rain.

Leafspot diseases can be confused with "felt" mite patches of "erineum."

In erineum, the patches are enlarged leaf cells on the lower side of leaf.

Leafspot diseases can be confused with airpollution or spray injury.

In air-pollution injury of pine, spots are the same point on all needles.

In spot-type spray injury, spots range from very tiny to very large.

Leafspot diseases can be confused with "shock" symptoms by some viruses.

Many tiny spots on leaves are caused by sucking insects, like leafhoppers.

All 8 of the preceding lines, no fungus or bacterium is present.

Pine-needle-scale insects can be confused with pine-needle-rust leafspot.

But pine needle scales are flat/streamlined while the rust is humped.

Spraying for leafspot diseases is worthless if it rains before sprays dry.

No spray now registered can remove or halt established leafspot infections.

Some leafspot diseases (like Entomosporiumon hawthorn) make leaves fall.

Other leafspot diseases leave the leaves attached to the tree.

Defoliation in late spring or early fall does little harm to the tree.

Defoliation in mid-summer (e.g. hawthorn leafspot) weakens trees a lot.

Well nourished, properly watered trees endure leafspot infection weakening.

The Horse-chestnut "Leaf Blotch" is caused by Gu?gnardia aesculi.

The Horse-chestnut "Leaf Blotch" fungus rarely crosses lateral leaf veins.

So Horse-chestnut "Leaf Blotch" has spots with some straight edges.

The Elm "Pepper-and-Salt Leafspot" is caused by an Anthracnose fungus.

The Elm "Pepper-and-Salt Leafspot" is caused by Gnomonia ulmea.

The Maple "Tar Spot" disease is caused by Rhytisma acerinum.

The Oak "Leaf Blister" disease is caused by Taphrina coerulescens.

Oak "Leaf Blister" was controlled by every fungicide that was tried.

Oak "Leaf Blister" contains NO fluid…the leaf merely bends upward there.