Diseases of Broadleaf Trees

Diseases of Broadleaf Trees

Author(s): Mark Harrell, Laurie Stepanek, Rachel Allison
Photo of a flowering crabapple tree

Broadleaf trees are a critical part of our urban and rural landscapes. If trees are subjected to adverse conditions, an array of issues may arise, including disease. Use this guide to help discover common diseases that affect broadleaf trees in Nebraska. 

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Anthracnose

Identification

  • On sycamore, ash, maple, oak, and walnut
  • Worse in years with wet springs
  • Leaf spots and blotches appear in the spring (later for walnut), often following leaf veins
  • Leaves drop early
  • Dead shoots may appear on sycamore and oak

Control

  • For ash, maple and walnut, controls are usually not needed. Trees typically recover
  • For sycamore and oak, a control may be desired if shoot death is severe
  • Spray foliage at budbreak with chlorothalonil (Daconil, Fung-onil), thiophanate-methyl (3336, Fungo) or copper fungicide (Camelot, Bordeaux mixture)* and repeat 2-3 times every 7-14 days
  • Improve tree health by mulching and watering about 1 inch per week. Avoid overwatering

Cankers

Identification

  • On cottonwood, honeylocust, willow, elm and many other broadleaf trees
  • Dead areas of bark appear, often around pruning cuts or where branches are attached

Control

  • Chemical controls are not effective
  • Improve tree health by mulching and watering
  • Avoid winter pruning or other injuries that weaken the tree or create wounds through which canker fungi can enter

Verticillium wilt

Identification

  • On maples and other broadleaf trees
  • Branches die
  • Wood has dark green to dark brown streaks or mottled areas

Control

  • Chemical controls are not effective
  • Remove the tree or parts of the tree as they die
  • DO NOT use chips made from branches or trees killed by Verticillium wilt because of the high risk of spreading the fungal pathogen through the chips
  • Plant trees known to be resistant
  • Improve tree health by mulching and watering about 1 inch per week. Avoid overwatering

Bur oak decline

Identification

  • On bur oak
  • In areas that were once native forests but are now parks, residential areas or other developed landscapes or near roads or field edges
  • Branches generally die back from the ends
  • Trees become more susceptible to insects and diseases and may die

Control

  • Improve tree health by mulching with wood or bark chips and watering about 1 inch per week. Avoid overwatering

Apple scab

Identification

  • On crabapple and apple
  • Dark spots appear in leaves, often with feathery margins and along leaf veins
  • Leaves turn yellow and drop from the tree

Control

  • Spray with chlorothalonil (Daconil, Fung-onil, Ortho Garden Disease Control), thiophanatemethyl (3336, Fungo), myclobutanil (Immunox, Eagle), mancozeb (Dithane, Fore, Protect), or propiconazole (Banner Maxx, Infuse)* at 7 to 14 -day intervals from prebloom (April) through rainy periods
  • Some chemicals cannot be used on trees grown for fruit production

Cedar-apple rust

Identification

  • On crabapple, apple, juniper, and redcedar
  • Orange spots appear on the upper leaf surface
  • Raised spots appear on the lower leaf surface
  • Ball-shaped growths (galls) or orange gelatinous masses appear on juniper and redcedar

Control

  • Spray with chlorothalonil (Daconil, Fung-onil, Ortho Garden Disease Control), thiophanatemethyl (3336, Fungo), myclobutanil (Immunox, Eagle), mancozeb (Dithane, Fore, Protect), or propiconazole (Banner Maxx, Infuse)* as flower buds break, at petal drop and 3 or 4 additional times at 7 to 10-day intervals
  • Some chemicals cannot be used on trees grown for fruit production

Ash rust

Identification

  • On all common ash species
  • Swollen areas with many circular orange spots on leaves, petioles and green twigs

Control

  • Spray with myclobutanil (Immunox, Eagle) at budbreak and repeat 2 to 3 times at 10 to 14-day intervals

Fire blight

Identification

  • Mostly on apple, crabapple, pear, and mountain-ash
  • Shoots and leaves droop and turn dark

Control

  • Prune out dead branches 8-12 inches down from diseased tissue
  • Sterilize pruning tools after each cut with a 70% alcohol solution
  • Spray with streptomycin (Agri-Mycin)* at pink stage (3 to 4 days before blossoms open— usually mid-April) and every 5 to 7 days until petal drop

Dutch elm disease

Identification

  • On American elm
  • Leaves turn yellow, then brown
  • Branches die, then the whole tree dies
  • Brown to black streaks appear in the wood

Control

  • Trunk inject with thiabendazole (Arbotect) or propiconazole (Alamo)* before or as symptoms begin appearing (if 5% or less of the crown is affected).

Oak wilt

Identification

  • Mostly on red and bur oak
  • Red oaks often die within 2 to 6 weeks
  • Bur oaks decline and may die, especially if stressed by changes in site conditions
  • Leaves turn brown
  • Branches die, then the whole tree dies
  • Brown to black streaks appear in the wood

Control

  • For red oak, trunk inject with propiconazole (Alamo)* as soon as symptoms begin appearing or before
  • For bur oak, improve tree health by mulching with wood or bark chips, watering about 1 inch per week, avoiding overwatering and by trunk injecting with propiconazole (Alamo),* if advised, to quicken the recovery

Tubakia leaf spot

Identification
• Mostly on bur oak
• Brown blotches on leaves, often along veins
• Affected leaves may drop from the tree
• Young shoots may die
• Symptoms are more extensive in lower branches than in higher branches

Control
• Control is rarely needed
• If needed, spray with mancozeb (Dithane, Fore) or propiconazole (Banner Maxx, Infuse)* at budbreak (April) and repeat 2 times at 10 to 14- day intervals

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Tree issues