Two springs ago I found five "nests" looking like tightly woven...
Two springs ago I found five "nests" looking like tightly woven spiderweb on my ornamental 20 foot crab apple tree. Now it looks like the photos of apple scab disease and about half of the leaves turned yellow and fell off a month ago. We did have a wet year, so what do you think happened? Do you suggest I try to revive the tree to its beautiful (I haven't done any spray or fertilizer at all) state or is it too late for this tree?
Sibley County Minnesota
Fungicides only prevent apple scab they do not treat it once the crab is infected. Apple crab spores are released very early in the growing season so fungicide sprays must begin when the first green leaf tips emerge in spring. Sprays should be repeated until petal drop for crab apple. Rake and destroy the infected leaves before the first snowfall to eliminate locations where the fungus can survive to re-infect your tree the next spring.
There are two caterpillars that make webs on crabapple trees.
Eastern Tent Caterpillar or Malacosoma americanum creates a protective web or "tent" that is found in the fork of the branches.
Fall Webworm or Hyphantria cunea create a web that covers the ends of branches.
You may find more information about these caterpillars at this site.http://www.extension.umn.edu/garden/diagnose/plant/deciduous/crabapple/branchwebbing.html