Scab– A common fungal disease that infects both leaves and fruit of apples and crabapples in Iowa.

• Infected leaves have olive-green to brown spots.
• Overall tree color is usually yellow/ chlorotic with brown spots
• Leaf loss weakens the tree when it occurs many years in a row.
• Planting disease-resistant crabapple varieties is the best way to manage scab.
  • Coralburst
  • Royal Raindrops
  • Starlite
• Apple trees are likely to get apple scab, spraying is recommended.  Resistant varieties include:
  • Honeycrisp
  • Legacy
• Proper pruning will help prevent scab, as more air flow is present
• Fungicides can be used to manage apple scab. Proper timing of sprays is needed for fungicides to control disease.  Fungicides are not a cure, only a preventative measure
  • Needs to be sprayed during bud break, they periodically after
  • Retail offerings
    • Broad Spectrum (Chlorothalynyl)- concentrate
    • Fungonil (Chlorothalynyl)- ready to use.

Canker– Cytospora canker is a common disease on spruce trees that are stressed by drought, winter injury or other factors. Cytospora canker is most common on Colorado blue spruce, but can affect all spruce trees grown in NW Iowa.

• Cankers kill random branches throughout the tree canopy.
• The disease is common on large mature trees.
• Cankers are located close to the trunk of the tree on dead or dying branches.
• A thick layer of hard, dry, bluish-white resin will coat the area of the branch over the canker.
• Keep trees healthy,  water in drought,  use correct spacing, fertilize
• Treatment:  There is no cure for trees infected with Canker
  • Prune out and destroy infected branches during dry weather.
  • Plant Norway or white spruce instead of Colorado blue spruce.

Needle cast– Rhizosphaera needle cast is a fungal disease of spruce trees that causes needles to turn brown and fall off.

• Trees stressed from drought, poor planting practices or other factors are more likely to suffer from Rhizosphaera needle cast.
• In spring or early summer, new needles at the branch tips are green, and the older needles turn brown to purple.
• Use a magnifying glass to look closely at both green and discolored needles. Tiny black bumps can be seen arranged in neat rows on infected needles.
• Discolored needles fall off in late summer to fall.
• Damage typically starts on the lower branches and moves up the tree.
• If the majority of needles are infected for 3 to 4 years in a row, the branch will die.
• Do not plant straight Colorado blue spruce.  Select a more disease resistant spruce varieties:
  • Fat Albert
  • Hoopsi
  • Other spruce varieties such as Black Hills or Norway
• Trees can be protected from needle cast with properly timed fungicide applications.
  • Proper timing of sprays is needed for fungicides to control disease.  Fungicides are not a cure, only a preventative measure
  • Needs to be sprayed when new needles are 50% emerged,  then again 4 weeks later.
  • Retail offerings
    • Broad Spectrum (Chlorothalynyl)- concentrate
    • Fungonil (Chlorothalynyl)- ready to use.