It is also the most devastating because infection of the large scaffold limbs and trunk eventually kills the tree. Scab, cedar-apple rust and powdery mildew, on the other hand, usually don't directly kill trees, but instead render them aesthetically unattractive. Repeated infection, however, makes them more prone to winter injury and general decline. Cedar-Apple Rust Figure 1. Spores released from these tendrils in May and June are blown to crabapples where they primarily infect leaves, although occasionally fruits and twigs become infected.
Infected leaves develop orange spots surrounded by a reddish-brown band on the upper surface.
The spores produced by the tubular structures complete the cycle by infecting the juniper host, which, in Nebraska, is usually eastern redcedar. Other juniper species, such as Rocky Mountain juniper, are also susceptible. Fire Blight Figure 2. Fire blight is the oldest, most serious bacterial disease of crabapple, pear and apple trees. The disease is indigenous to North America and probably occurred on native American plants and then spread to susceptible cultivated apples, pears and woody ornamentals planted by early settlers.