| Rust, Puccinia heterospora, is a fungal disease that
infects leaves and stems of hollyhock. Lower leaves
show the condition first, and the disease progresses
upward during the growing season. The extent and
severity depend on weather conditions.
Symptoms and Diagnosis
First symptoms appear on the leaves as individual,
yellow, circular spots about one-eighth inch in size
that enlarge to one-quarter inch or more in diameter.
On the underside of the leaves, swellings or blisters
soon emerge within these spots. At this stage, the
symptoms resemble insect or mite galls found on
many other plants; however, such galls are rare on
hollyhock. The swellings continue to develop and in
a few more days, they release masses of reddishbrown
spores, covering the entire undersurface of the leaf.
You can easily identify the disease in the field by the
round pustules that are covered by loosely attached
red spores. Leaves that are heavily infected
eventually turn gray or tan and die. Rust spots may
also occur on the stems and leaf petioles and
occasionally on green flower parts.
Life Cycle
The reddish spores are easily spread by splashing
water, rain, and wind. The fungus overwinters in
plant debris and possibly in overwintering, living
plant tissue. Symptoms will appear very early the
following spring when weather conditions are
favorable.
Hollyhock rust is not extremely common throughout
the state. Fortunately, we can usually enjoy colorful
hollyhocks in spite of the disease, though the foliage
may become unattractive in wet years.
Integrated Pest Management Strategies
1. Use disease-free plants.Start plants from seeds
and place them some distance from infected stock.
2. Improve air circulation. Space plants out in a dry
sunny location so that moisture is quickly
evaporated from the foliage.
3. Keep plants healthy. Maintain the plants in a
vigorous growing condition through a good
fertility program. Irrigate during dry periods but
keep the foliage dry, if possible.
4.Remove infested material. Remove old plant
material and bury, burn, or compost it at the end
of the flowering season. Picking off the first
infected leaves as they appear may also be
helpful. However, this practice alone often is not
successful in controlling rust.
5. Control weeds. Destroy common mallow weeds
in the vicinity as they may be hosts to the rust
disease and a source of hollyhock infection.
6. Use fungicides if necessary. Consider using
fungicides to supplement cultural control
methods. Direct the applications primarily at the
lower surface of the leaves and treat at
approximately 7 to 10 day intervals. Reapply if
rainfall exceeds 1/2 inch during the period.
Pesticides registered for use include chlorothalonil
(Daconil), sulfur, mancozeb, and maneb. All are
protective fungicides and prevent rather than
eradicate the fungus. Start
using a fungicide prior to the first sign of
disease development. | 
