Pest & Disease Control for Flowering 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. 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 10 articles. For a complete background on how to grow flowering trees, we recommend starting from the beginning.

Aphids

They are the size of a pinhead and vary in color depending on the species. Clusters 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’s sticky residue becomes a growth media for sooty mol
also during 1/2” green kills newly hatched except Rosy Apple Aphid.

Natural Control

Birch, Oak

  • Safer® Brand Insect Killing Soap

Shade

  • Monterey Horticultural Oil

Ornamentals

  • Monterey Fruit Tree Spray Plus

Chemical Control

Elm, Oak, Birch

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Ornamentals

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Bagworms

Bagworms are the larvae of moths. Brown bags up to 2 inches long and composed of bits of dead foliage, twigs and silk are often seen attached to twigs and inside is a dark brown or black caterpillar. Adult female moth is wingless and the male has wings. Severe infestations can defoliate an entire plant often killing evergreens such as arborvitae and cedar but may only slow the growth of a deciduous plant.

Natural Control

  • Remove and destroy all bags.

Shade

  • Natural Guard® Caterpillar Killer Spray w/BT

Chemical Control

Elm, Oak, Birch

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Ornamentals

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Leafrollers

Pale yellow or ‘dirty’ green worms. Leaves are rolled and webbed together where insects feed. Eventually becomes ‘skeletonized’.
Spray is seldom necessary. When detected the caterpillar stage might be complete and spray will be of no benefit. Unless the tree is very small, it will not die.

Chemical Control

Elm, Oak, Birch

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Ornamentals

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Locust

Large (up to 1½ inches long) dark bodied insects with wings. Young insects hatch and enter the soil, where they burrow to the roots. Immature locust suck sap from roots and adults may suck sap from young twigs. Female lays eggs in the sapwood of twigs, causing the leaves on damaged twigs to turn brown. Twigs may break and fall to the ground eventually.

Chemical Control

Ornamentals

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Elm, Oak, Birch

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Mealybugs

Adults are 1/4” long, flat, oval shaped with a white waxy covering. Yellow to orange eggs are laid within an egg sac. Crawlers are yellow to brown in color. Over winters as an egg or very immature young in or near a white, cottony egg sac, under loose bark or in branch crotches, mostly found on north side. Damage is by contamination of fruit clusters with egg sacs, larvae, adults and honeydew, which promotes growth of black sooty mold.

Natural Control

Birch, Oak

  • Safer® Brand Insect Killing Soap

Ornamentals

  • Monterey Fruit Tree Spray Plus

Shade

  • Monterey Horticultural Oil

Chemical Control

Elm, Oak, Birch

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Ornamentals

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Spider Mites

Pinpoint size, many different colors. Found on undersides of leaves. Severe infestations have some silken webbing. Sap feeding causes bronzing of leaves

Natural Control

Birch, Oak

  • Safer® Brand Insect Killing Soap

Shade

  • Monterey Horticultural Oil

Ornamentals

  • Monterey Fruit Tree Spray Plus
  • Remove and destroy heavily infested plant parts.
  • Light infestations wash off with a strong stream of water from your garden hose.

Chemical Control

Elm, Oak, Birch

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Whitefly

Adults are tiny, white winged insects found mainly on the underside of leaves. Nymph emerge as white, flat, oval shapes. Larvae are the size of a pinhead. Suck plant juices from leaves causing them to turn yellow, appear to dry or fall off plants.

Natural Control

Birch, Oak

  • Safer® Brand Insect Killing Soap

Shade

  • Monterey Horticultural Oil (larvae)

Ornamentals

  • Monterey Fruit Tree Spray Plus

Chemical Control

Elm, Oak, Birch

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Tent Caterpillar

Hairy caterpillars that enclose large areas in webbing and feed on enclosed leaves. Remove web with rake and burn. Caterpillars are pulled out with webs.

Natural Control

Birch, Oak

  • Safer® Brand Insect Killing Soap
  • Prune out and destroy webs when first noticed.
  • Remove and destroy egg masses.

Shade

  • Natural Guard® Caterpillar Killer Spray w/BT

Ornamentals

  • Monterey Fruit Tree Spray Plus

Chemical Control

Elm, Oak, Birch

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Ornamentals

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Japanese Beetle

Adult is a metallic green beetle. It skeletonizes leaves. Larvae are a grub, which feeds on turf roots. Check turf product labels for timing of control of grubs. This is more of this problem is east of the Mississippi river.

Chemical Control

Elm, Oak, Birch

  • GardenTech® Sevin® Bug Killer

Ornamentals

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Elm Leaf Beetles

Adult beetles feed on the leaves leaving small holes.
Larvae usually feed on the underside of leaves and eventually the leaves will dry up and die. Adult beetles are olive green with black stripes along the margin and center of back. Larvae are black when hatched and after feeding become a dull yellow or green.

Chemical Control

Elm

  • GardenTech® Sevin® Bug Killer

Elm Spanworms

Adult moths are a powdery white with a wingspan of 1-1½ inches. Larvae are about 2 inches long and coloring can be from dull or slate black to light green. They feed on the underside of leaves, causing a shot hole effect.

Natural Control

Shade

  • Natural Guard® Caterpillar Killer Spray w/BT

Chemical Control

Elm

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Ornamentals

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)
  • Prune small twigs that are infested with eggs.

Fall Webworms

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

Shade

  • Natural Guard® Caterpillar Killer Spray w/BT

Chemical Control

Elm, Honeysuckle

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)
  • Prune out and destroy webs.

Elm

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Oakworms

Adult moths are yellowish red, with a single white dot on each of the forewings. They lay eggs on the underside of leaves. Larvae are about 2 inches long and have a long, curved horn and feed on the foliage, skeltonizing leaves.

Chemical Control

Oak

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Ornamentals

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Thrips

Tiny, slender, fringed wing insects ranging from 1/25 to 1/8” long. Nymphs are pale yellow and highly active and adults are usually black or yellow-brown, but may have red, black or white markings. Feed on large variety of plants by puncturing them and sucking up the contents.

Natural Control

Birch, Oak

  • Safer® Brand Insect Killing Soap

Ornamentals

  • Monterey Fruit Tree Spray Plus

Chemical Control

Elm, Oak, Birch

  • GardenTech® Sevin® Concentrate Bug Killer (not for use on large trees)

Ornamentals

  • GardenTech® Sevin® Concentrate Bug Killer (exposed) (not for use on large trees)

Leaf Spot

Appears as black or brown spots on underside of leaves. Often the center falls out leaving a hole with a red halo. Leaves may turn yellow and fall.

Natural Control

Hawthorn, Maples

  • Monterey Liquid Copper Fungicide

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Tools & Supplies for Flowering Trees