Diagnosing Apple Tree Leaf Discoloration

Erwinia amylovora

Distinctive “shepherd’s crook on apple (Penn State Department of Plant Pathology & Environmental Microbiology Archives, Penn State University, Bugwood.org)

Symptoms

• Young shoots wilt and droop, forming a distinctive “shepherd’s crook.” 
• Leaves on infected shoots turn brown as if scorched by fire.
• Fruit may turn dark and shriveled and persist on the branch.
• Slightly sunken bark cankers may appear on branches and stems.

Fireblight symptom on fruit (Bruce Watt, University of Maine, Bugwood.org)

Management and other important facts

• Plant less susceptible apple and crabapple cultivars.
• Mark infected twigs with ribbon or paint during the growing season.
• Prune all marked twigs and cankered branches in late winter at least 8-12 inches below the infection.
• May also use “ugly stub” method of pruning.
• Avoid excessive application of fertilizer that may promote overly lush growth.
• If fireblight is a yearly problem on a high value apple tree, apply a copper spray just as the leaf buds are starting to swell in spring; do not apply after ½-inch of green, leafy tissue is visible because the copper spray may burn the leaf tissue

Authors:  Esther McGinnis and Kasia Kinzer

Note the irregular yellow botches that may be more pronounced in the leaf margins (Esther McGinnis, NDSU)

Symptoms

• Leaves have a blotchy pattern of yellowing during the summer
• This disorder only appears in young ‘Honeycrisp’ apple trees that are not producing much fruit yet
• The appearance is more random than iron chlorosis

Leaf mottling has an irregular pattern and may resemble leafhopper damage (Esther McGinnis, NDSU)

Management and other important facts

• This disorder is genetic and occurs primarily in juvenile ‘Honeycrisp’ apple trees
• The mottling is caused by the accumulation of large starch granules in the leaves that reduce photosynthesis
• No treatment is necessary and the symptoms will abate as the tree matures and produces more apples

Author: Esther McGinnis

Hosts

Freeman maples, silver maple, river birch, Swedish columnar aspen

River birch leaf with interveinal chlorosis (Esther McGinnis, NDSU)

Symptoms

• Leaves turn yellow-green or bright yellow but veins remain green (interveinal chlorosis)
• In severe cases, leaf margins may turn brown and appear scorched
• Symptoms first appear on newest leaves at branch tips
• Over time, twigs and branches may die back from the crown
• Eventually, the tree may die if the iron deficiency persists for years

Branch dieback on silver maple (Joseph Zeleznik, NDSU Extension)

Management and other important facts

• This abiotic disorder is caused by an iron deficiency that is associated with alkaline soils, cool temperatures, and wet soils; these conditions render the normally abundant iron in North Dakota soils as unusable by the plant
• Foliar sprays of chelated iron may provide quick green-up of the foliage but this treatment is temporary and trees do not always respond
• Iron chelate products may be applied to the soil or injected into trees for longer lasting relief
• Broadcasting soil acidifiers such as elemental sulfur or iron sulfate onto the soil surface may lower the soil pH; gradually converting the iron in the soil into a usable form by the plant
• Replace iron-deficient trees with individuals that are better adapted to alkaline soils

Authors:  Esther McGinnis and Kasia Kinzer

Symptoms

• Look for browning around the margins of the leaves.
• Eventually the entire leaf may turn brown and wilt.
• Damage will be worst on branch ends.

Leaf scorch on an elm leaf; symptoms would be similar on apple leaves (Esther McGinnis, NDSU)

Management and other important facts

• Leaf scorch is caused by drought or the interruption in the flow of water to the branches and leaves.
• Supplemental irrigation may ameliorate the effects of drought.

Author: Esther McGinnis