While unattractive, tree health is not usually affected. However, yearly infestations of oak leaf blister can weaken a tree, making it more susceptible to other problems. Maintain good tree health. In fall, rake up fallen leaves and dispose of them.
Moist spring weather also contributed to the appearance of rose rust. This fungal disease causes orange pustules to form on leaf undersides. Leaf surfaces initially have orange-colored spots superficially resembling drops of paint. As the pustules enlarge, spots turn brown. Infected leaves may drop.
When a rose has the leaf symptoms, also look for black crusty growths on canes (which are overwintering fungal structures) and remove the canes. If not done already, prune roses to increase air circulation within the leaf canopy.
Moisture management is essential to minimize this disease, so water early in the day to dry leaves quickly. In the fall, clean up leaf debris from around infected plants
A few fungicides are available for rose rust management but must be applied when conditions are conducive to the development of the disease: moderate temperatures and wet leaves. Products available for rust management include potassium bicarbonate, mycobutanil, propiconazole and sulfur. Fortunately, hot dry weather stops disease development.
