Problems of Larch

Surface Roots Appear At Base Of Tree
The European Larch is vulnerable to compacted soils and will produce surface roots in that environment. For solutions see the file Dealing With Surface Roots

Larch Fails to Thrive
Too Much Shade - Larches, like most trees, need many hours of sun per day to thrive. Take care that neighboring plantings have not grown to block the exposure of young larch trees to the sun.

Needles Curled and Distorted
Aphids - Woolly larch aphids are soft-bodied, pear-shaped sucking insects, about the size of the head of a pin. They cluster on tree foliage and suck cell fluids, retarding or distorting tree growth. Needles may turn yellow or brown or sometimes curl and pucker.

Leaves Browned in Spring
Larch Casebearer. - One of the most serious pests of larches, this small black-headed caterpillar enters larch needles through a hole that it chews in the end or middle of the needle. It then tunnels, or mines, into the needle as it feeds during the late summer. In the fall it cuts the needle in half, forming a 1/4 inch long case that hangs from the twigs in which it over winters. To kill over wintering pests, spray the visible egg cases with lime sulfur or dormant oil to kill them before leaves emerge.

Needles Notched, Stripped
Larch Sawfly - These sawflies are larvae of small, wasp-like flies. They are worms that are 3/4 to 1 inch long, olive-green and covered with brown spines. They hatch from eggs laid in cuts in larch twigs in late spring and feed on larch needles, causing them to fall to the ground and rapidly stripping twigs bare. Heavy infestations will defoliate a tree.

Needles Consumed, Visible Tawny Egg Masses
Gypsy Moth Caterpillar - Larvae of the gypsy moth sometimes mass on larch foliage and devour it, defoliating the tree. The tree may die after repeated defoliations. Newly hatched caterpillars are about 1/16 inch long, and grow to about 2 1/2 inches. When mature they have 5 pairs of blue spots and 6 pairs of red spots along the back. Adult male moths have a wingspan of 1-1/2 inches, are light tan to dark brown, with blackish wavy bands across the forewings. The female moths are larger, nearly white, with 2 1/2 inch wings. They do not fly. They do lay masses of eggs, from 400 to 500, covered with velvety, buff-colored hairs which become caterpillars.

Branches and Stems Girdled, Resin Visible
Canker - Several kinds of fungi cause canker disease in larches. Typically cankers, or swellings, develop on branches and stems of trees. Stimulated by spores that enter the bark through injuries and destroy the inner tissue, these cankers develop gradually, leaking resin and causing severe distortion of the tree. Eventually affected limbs die. A specific form of canker that attacks European larches spawns ΒΌ-inch hairy, white cup-shaped fruiting bodies that develop in the cankered tissue. Control of canker is very difficult. Prune away infected stems and branches promptly. Burn them or put them in the trash to avoid spreading the disease. Limit further outbreaks by maintaining tree vigor. Water, feed and protect trees as recommended above. Japanese larches are resistant to canker.

Needles Yellowed, Undersides Show Fungus
Rust - Several kinds of fungi cause rust on larch needles. One rust develops on nearby willows and then affects larches, another rust requires poplars as its alternate hosts. These fungi affect the tender young needles at the tips of branches. Their undersides become coated with pale yellow pustules and they turn yellow then brown and die. If the affected larch tree is the valued ornamental tree in the landscape, remove the alternate host of the rust to interrupt the life cycle of the fungi. Be absolutely sure that the problem is rust before cutting down the suspected host tree.