One of the frustrating things about disease issues on ornamentals such as hollyhocks and peach trees is that by the time the symptoms of the disease show up, the opportunity to control that disease is gone. Two diseases that qualify for this problem are hollyhock rust and peach leaf curl.
Hollyhocks are growing like weeds at this point. Because of the wonderfully wet spring and the high humidity that we are used to having, rust will often develop on Hollyhock. This disease is spread by wind and splashing rain from plant debris which has been left overwinter. This may be either old hollyhock stems or other plant debris nearby. As leaves emerge they are infected. This appears as numerous yellow spots on the upper leaf surface with orange-brown raised areas under the underside of the leaf.
It is important to break the disease cycle early or it will continue to get worse resulting in the death of the plant. Remove any leaves that have symptoms of the disease and destroy them. Water in the morning in a way that keeps leaves from becoming wet. Fungicides such as Chlorothalonil, sulfur and horticulture oil can be used as directed on the label to prevent infection or further spread once infection is noticed. If sulfur or horticulture oil is used, do not apply when the temperature will exceed 85°F or the leaves may burn. If the infection is severe enough you may need to cut the stem back and begin again.
In the fall, cut all hollyhock flower stalks back to the ground and destroy this tissue. Remove any leaf or stem debris that is left in the bed and destroy this as well.
The next disease affects peach trees. This disease is called leaf curl, one of many problems that may affect peaches. Leaf curl becomes very apparent once the leaves have formed as the leaves are distorted, curled and discolored. Depending on the severity of the disease it may only affect a few leaves or it may affect the majority. The disease usually does not cause the death of the peach tree itself unless it has been present for many years and has affected the majority of the leaves.
Because the leaves form incorrectly they are not capable of photosynthesis as are leaves which form a normal, smooth surface. This is the cause of the discoloration in the leaves. The food energy produced by photosynthesis is absent and the tree is not as healthy.
The combination of fewer food stores and weaker growth will ultimately lead to other infections and insect damage which will eventually kill the tree. For this reason it is important to keep leaf curl at a minimum.
Peach leaf curl is spread as leaves emerge in spring when cool, wet weather is present. These leaves emerge through a film of overwintered infection that settled as a film on the stems in the fall of the previous year. When managing the disease, treat with a fungicide after the leaves fall or in early winter. A second application can be applied as flower buds swell but before green leaf tips show. Use copper (MCE) or Chlorothalonil as the label directs for control. These can be combined with horticulture oil and sprayed together for scale control during the late dormant season.
As you can see, in both cases the disease infections occur before it is noticed. Use sanitation in both cases to lower disease pressure. If the disease is present now then mark your calendar to spray peaches in fall and winter and work to reduce pressure on hollyhocks now and as the leaves emerge in spring.
The Extension office is open Monday - Friday, located in Kennett, Missouri at 233 North Main Street. For horticulture questions contact the horticulture specialist at 573-686-8064. MU is an equal opportunity/ADA institution.