Pest & Disease Control for Walnut Trees
Every tree has the future potential for disease and insect damage. Factors such as location and weather will play a part in which issues your tree encounters. If available, disease-resistant trees are the best option for easy care; and for all trees, proper maintenance (such as watering, fertilizing, pruning, spraying, weeding, and fall cleanup) can help keep most insects and diseases at bay.
NOTE: This is part 7 in a series of 11 articles. For a complete background on how to grow walnut trees, we recommend starting from the beginning.
Dieback
Causes a slow death, branch by branch. The bark changes from normal greenish-brown to reddish-brown and finally gray in color.
Natural Control
- Pruning out infected branches promptly. If the disease reaches the trunk, the whole tree needs to be removed.
Other Control Options
- Consult County Extension Agent
Walnut Bunch
“Witches Brooming”
- Tufting brooms a profuse development of branches appears on stem, branches and tips. A cause and control is not known. Try pruning out the brooms. Be sure to sterilize shears between each cut.
Control
- Consult County Extension Agent
Scale
Tan to gray 1/16” hard, scaly shell covers developing young. This usually on bark of twigs and branches but may also be on the nuts. Sap feeding weakens the tree.
Natural Control
- Bonide® Citrus, Fruit & Nut Orchard Spray
- Rub off with burlap.
Aphids
They are the size of a pinhead and vary in color depending on the species. Cluster on stems and under leaves, sucking plant juices. Leaves then curl, thicken, yellow and die. Produce large amounts of a liquid waste called “honeydew”. Aphid sticky residue becomes a growth media for sooty mold.
Natural Control
- Bonide® Citrus, Fruit & Nut Orchard Spray
Caterpillars
Many kinds can damage walnuts.
Natural Control
- Bonide® Citrus, Fruit & Nut Orchard Spray
- Bonide® Thuricide Bacillus Thuringiensis (BT)
Codling Moth
The adult is moth gray with brown patches on the wings. The worms are about 1” long. The nuts have holes from side to core.
Control
- Consult County Extension Agent
Anthracnose
Causes irregular purplish or reddish-brown spots on leaves and these spots may merge to form irregular shaped blotches. Although significant defoliation may occur after cool, wet spring weather, this disease is usually not serious to the health of the tree.
Chemical Control
- Bonide® Fung-onil™ Fungicide
Bark Beetle
Young twigs wilt because of boring done by a dark brown beetle, 1/5” long. The larvae bore into sapwood, which can girdle branches. Remove and burn severely infected trees, peel bark from stump.
Control
- Consult County Extension Agent
Cigar Case Bearer
Leaves are mined, turn brown and fall. Mining is done by larvae that is 1/5” long with a black head. The adult is a moth with brown wings, fringed hairs along edge. The larvae over-winter on twigs and branches in cigar shaped cases 1/8” long.
Control
- Consult County Extension Agent
Walnut Blight
Black, dead spots on young nuts, green shoots and leaves. Many nuts fall early but some will reach full size with husk, shell and kernel black and ruined.
Natural Control
- Bonide® Citrus, Fruit & Nut Orchard Spray
Gall Aphids
Hollow green galls turn black in July. On leaves, stems and small twigs. Insides are lined with living young. Galls are ‘pea sized’ to ½“.
Control
- Consult County Extension Agent
Mites
Pinpoint in size with many different colors. Found on underside of leaves. Sap feeding causes bronzing of leaves. Severe infestations have some silken webbing.
Natural Control
- Bonide® Citrus, Fruit & Nut Orchard Spray
Omnivorous Leafroller
Adult is bell shaped, blackish gray snout-like mouthparts, forewings dark rusty brown with tan tips. Over winters in larval stage in mummified berries, in weeds and other trash. Moths emerge in spring and lay egg masses on leaves. Eggs hatch in 5 days and larvae tie two young leaves together to form nest in which they feed. Does not roll leaves. Later nests can be found in flower clusters and in bunches. Damage is not only from feeding on leaves, flowers and berries, but feeding sites allows rot organisms to enter fruit.
+Natural Control +
- Bonide® Thuricide® Baccillus Thuringiensis (BT)
Fall Webworm
Damage the leaves by both feeding and web building. Webworms over-winter within cocoons located in protected places, such as crevices in bark or under debris and fences. Adult moths emerge in summer. They have a wingspan of about 1 1/4” and vary from pure satiny white to white thickly spotted with small dark brown dots. Females lay white masses of 400-500 eggs on the undersides of the leaves. The caterpillars hatch in 10 days and all from the same egg mass live together as a colony. They spin webs that enclose the leaves, usually at the end of a branch, to feed upon them. After they have defoliated a branch, they extend their nest to include additional foliage. ?When caterpillars are mature, they leave the nest to seek a place to spin gray cocoons. The mature caterpillars are about 1 1/4” long with a broad dark brown stripe along the back, and yellowish sides thickly peppered with small blackish dots. Each segment is crossed by a row of tubercles with long light brown hairs.
Natural Control
- Bonide® Captain Jack’s™ Deadbug Brew
- Bonide® Thuricide® Bacillus Thuringiensis (BT)
Husk Flies
Over winter as pupae in the ground and midsummer adult fly emerges, nearly as large as the common housefly. The bodies of the fly are yellowish-brown and have a dark color pattern on the wings. They feed on the husks of nuts. Female lays its eggs in the husk and the larvae feed on the green husk of nuts.
Natural Control
- Bonide® Captain Jack’s™ Deadbug Brew
Fruit Tree Leafroller
Moth is brown with irregular yellowish to brown bands across the wings and is about ½ inch long. Larva is about 7/8 inch long, head and back may be amber to light brown or black with rest of its body light green. They feed on opening buds and new leaves and will roll up a leave, webbing them together, for protection.
Natural Control
- Bonide® Captain Jack’s™ Deadbug Brew
