Pest & Disease Control for Plum Trees

Every fruit 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 11 articles. For a complete background on how to grow plum trees, we recommend starting from the beginning.

Crown Gall

Trees appear stunted and slow growing; leaves may be reduced in size, little or no fruit. If tree is dead, inspect roots for hard, woody ‘tumors’. Note: many things can cause stunted trees.

Control

  • Consult County Extension Agent

Bacterial Canker

Appears on branches and trunk as gummy cankers and water-soaked areas. Fruit develops dark, deeply sunken areas, causing them to be more likely to get ‘Brown Rot’. Cool, wet weather after blooming favors development.

Control

  • Consult County Extension Agent

Black Knot

Appears as hard black knobby growths on twigs and branches. Will eventually girdle and kill branches.

Natural Control

  • Prune out and burn.

Scale

Usually on bark of young twigs and branches, encrusted with small (1/16”) hard, circular, scaly raised bumps with yellow centers, may also be on fruit. Sap feeding weakens the tree.

Natural Control

  • Monterey Horticultural Oil
  • Monterey Fruit Tree Spray Plus

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

Tarnished Plant Bug

Yellow-brown winged insect may have black spot or red stripes. Injects toxins into the buds and shoots causing ‘dwarfed’ shoots and sunken areas (cat facing) on fruit.

Natural Control

  • Monterey Fruit Tree Spray Plus

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

Leafroller

Pale yellow or ‘dirty’ green worms. Leaves are rolled and webbed together where insects feed. Eventually becomes skeletonized.

Natural Control

  • Hi-Yield® Vegetable & Ornamental Insect Control

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

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 sticky residue becomes a growth media for sooty mold.

Natural Control

  • Monterey Fruit Tree Spray Plus

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

Brown Rot

Fruit turns brownish with lighter spots. Quickly becomes soft, rotten and unusable.

Natural Control

  • Monterey Fruit Tree Spray Plus
  • Fall clean up of all fruit and debris.

Chemical Control

  • Ferti-lome® Broad Spectrum Landscape & Garden Fungicide
  • Hi-Yield® Captan 50W Fungicide

Bacterial Leaf Spot

Appears on the undersides of leaves as black or brown spots. Often the center falls out leaving a hole with a red halo. The leaves may turn yellow and fall. Fruits also get spots, sunken areas & cracks.

Control

  • Consult County Extension Agent

Green Fruitworm

Bluish-gray moth. Larvae are 1’ long, usually green or brown with white sports and body stripes. Feeds on young leaves and young fruits. Disfigures the fruit.

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

Plum Curculio

Adult is brownish-gray 1/5” long, hard-shelled beetle with long snout and 4 humps on back. Cuts a crescent shaped hole under the fruit skins and lays eggs. Worms hatch and tunnel into fruit. Premature dropping of fruit can occur.

Natural Control

  • Post harvest clean up.

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

Oriental Fruit Moth

Gray moth, 1/2” long. Larvae are white with a brown head, 1/2” long. Larvae burrow into twigs and fruits.

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

Cherry Fruit Fly

This fly is very similar to Apple Maggot. Adult similar to housefly but smaller, larvae are yellowish-white worms. Eggs lay under fruit skins, larvae tunnel making railroad pattern. Small pinpoint sting marks visible on fruit.

Natural Control

  • Hi-Yield® Vegetable & Ornamental Insect Control

Mites

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

Natural Control

  • Monterey Fruit Tree Spray Plus
  • Monterey Horticultural Oil

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

Rose Chafer

Beetle has ½“ long, tan wings with reddish-brown edges. Long, thin hairy legs. Skeletonizes leaves and flowers. Present in large quantities in June & July. Worst on sandy sites near grassy areas.

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

Borers

Appears as a thick, gummy substance (sap) leaking from round holes on the trunk or in a crotch of the tree. Worms with brown heads and cream-colored bodies tunnel thru trunks that will kill the tree.

Natural Control

  • Hi-Yield® Vegetable & Ornamental Insect Control
  • Use a fine wire to try and mash or dig them out.

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

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 a problem east of the Mississippi river.

Natural Control

  • Hi-Yield® Vegetable & Ornamental Insect Control
  • Traps

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

Powdery Mildew

Whitish-gray powdery mold or felt like patches on buds, young leaves and twigs. Leaves may crinkle and curl upward. New shoots are stunted. Over winters in fallen leaves.

Natural Control

  • Monterey Fruit Tree Spray Plus

Leafhopper

Various colors and similar to aphids this small, active, slender-winged insects are usually found on the underside of leaves. Retard growth, leaves become whitened, stippled or mottled. Tips may wither and die. This insect carries virus of certain very harmful plant diseases.

Natural Control

  • Monterey Fruit Tree Spray Plus

Chemical Control

  • GardenTech® Sevin® Concentrate Bug Killer

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

  • Monterey Fruit Tree Spray Plus
  • Hi-Yield® Vegetable & Ornamental Insect Control

Coryneum Blight

Small reddish-purple spots appear on young leaves then enlarge and eventually dropping out of the leaf blade leaving a “shot hole.” It appears on fruit, usually in clustered as light brown spots or lesions with dark purple margins.

Natural Control

  • Monterey Fruit Tree Spray Plus

Chemical Control

  • Ferti-lome® Broad Spectrum Landscape & Garden Fungicide

Scab

Spots on young leaves are velvety and olive green turns black; leaves wither, curl and drop. Fruit also has spots, is deformed, knotty, cracked and drops.

Chemical Control

  • Ferti-lome® Broad Spectrum Landscape & Garden Fungicide

Leaf Curl

Leaves become thickened, puckered and twisted with a reddish-purple color along puckered areas. Turn yellow and drop, may completely defoliate and causes weakening of tree. Any remaining dead leaves should be removed in the fall and all debris removed from the area.

Chemical Control

  • Ferti-lome® Broad Spectrum Landscape & Garden Fungicide

Blotch

Fungus disease that is spread by rain in spring and early summer and can appear as early as 2-3 weeks after petal fall. Patches of dark green to black, circular or irregular in shape, may merge together to cover a large area of the fruit surface. Sometimes it can be rubbed or washed off, but may leave a brown discoloration on fruit. Little damage is done to the flesh.

Natural Control

  • Prune for air and light, clean up fallen leaves and fruit.

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Tools & Supplies for Plum Trees