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The Homeowners Column
Hollyhock Rust – the ugly story
Extension Educator, Horticulture
A view of orange "ditch lilies" and Easter egg colored hollyhocks is the consummate picture of summer on the farm. Many a childhood memory includes a view of colorful spires of bell-shaped hollyhock flowers rising above the sight and smell of chicken pens and cowpies. Their less appealing name of "outhouse flower" reflects their history in highlighting the urgent location of the outhouse.
Hollyhocks with their hoop skirt flowers reminiscent of ladies waiting in line for a summer cotillion have come off the farm with the growing interest in cottage gardens. At 5-9 feet tall they can be used as a towering background plant in a flower border, or along a fence or wall.
Hollyhocks (Alcea rosea) are tough plants, but they do have some insect and disease problems. Hollyhock rust is the most common and widespread disease and has been particularly prevalent this year.
Rust is a fungus that first appears on the undersides of lower leaves as lemon-yellow to orange pustules that darken with age. The top of the leaf shows bright yellow to orange spots with reddish centers. Spots may quickly come together to destroy large portions of the leaf. With severe infection pustules may also appear on the stem of the plant.
The same fungus can also infect several related plants in the mallow family (Malvaceae). We may not care that the common weed, roundleaf mallow (Malva rotundifolia), can get rust disease but it can act as a temporary site for the rust spores to reside before infecting hollyhock. Rust spores are carried by the wind and water, and can infect hollyhocks quite a distance away.
Minor rust infections will not harm the plant. However with severe infection, the disease may cause wilting and leaf drop and you will wish it would die to relieve its and your misery.
As with management of any insect or disease problem, several strategies should be implemented in conjunction to deal with hollyhock rust:
Good sanitation is crucial in controlling rust. The first rusted leaves that appear in the spring should be picked off and destroyed. As soon as flowering is over, infected plants should be cut back to the soil line. All infected leaves and stalks should be removed and destroyed by burying in a compost pile or unused part of the garden. However be sure to let a few flower stalks ripen before removal so plants can reseed.
Remove and destroy any mallow weeds growing nearby.
Add mulch around hollyhocks in spring to hinder overwintering of spores in plant debris.
Proper location can be important to reduce the chance of infection. An ideal site has adequate sunlight, good soil drainage, and sufficient air circulation.
Water plants early in the day, so leaves dry quickly.
Consider purchasing more resistant hollyhock species such as the Alcea rugosa and Alcea ficifolia.
If sanitation does not control the disease, a fungicide (chlorothalonil) can be applied in spring as new growth starts and before infection occurs. Several sprays will be necessary to keep new leaves protected against infection.
For more information check out UI Extension's Home, Yard and Garden Newsletter http://hyg.ipm.illinois.edu
Spider mites, Japanese beetles (and yes, they have already emerged in southern Illinois) and leaf feeding caterpillars can also plague hollyhocks. However most problems except for Japanese beetles cause the leaves to look lousy, but the flowers still look charming. Or just plant hollyhocks far enough away or behind shorter plants to hide their sickening leaves.
Garden Walks – UI Extension Master Gardeners Champaign County in Champaign/Urbana Saturday June 23, PH: 217.333.7672; UI Extension Master Gardeners Vermilion County in Danville Sunday June 24, PH: 217.442.8615; and Village Gardeners of St. Joseph Sunday July 8. Check out area garden centers for tickets.