Extension Educator, Horticulture
Is it better to burn out than rust out? Not for plants with fire blight or hollyhock rust
"It's better to burn out than rust out" might be a good mission in life, but if you are a plant neither is a particularly good goal if fire blight or hollyhock rust is bringing you down. This year apple, crabapple, pear and even ornamental callery pear are fighting a battle with the bacterial disease fire blight. Other plants in the rose family such as cotoneaster, hawthorn, quince, firethorn, and mountain-ash can also be infected.
As the name implies infected leaves appear scorched. Often leaves turn brown or black, but remain attached to stems. Branch tips typically bend down to resemble a shepherd's cane.
Fire blight infects leaves and flowers but also stems. It appears on stems as sunken, cracked areas called cankers that serve as a source of infection for continued spread. The bacteria multiply once temperatures reach 65 degrees F in the spring and infect plants through flowers and wounds.
Fire blight is a tough disease to control unless it is caught early. Prune out infected wood during an extended dry period and disinfect pruning tools after every cut with bleach or antibacterial sprays. It is easy to spread the disease on pruning tools if they are not disinfected after every cut. Since the bacterium may have extended down the stem ahead of the canker, wood should be removed 8-10 inches below the edge of the visible canker. If the disease has been allowed to progress, this may require major pruning. Always look for fire blight resistant apples, pears and crabapples when selecting new plants.
Rusting out is also an issue this year. Hollyhocks are tough plants, but hollyhock rust is 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.
Good sanitation can control rust. The first rusted leaves 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 let a few flower stalks ripen before removal so plants can reseed.
If sanitation does not control the disease, a fungicide may be applied in spring as new growth starts. It's too late for this year. Several sprays will be necessary to keep new leaves protected against infection.
Each garden season brings successes, but also plant problems. UI Extension is here to help. Check in the phone book for your local county UI Extension office or go to our website http://web.extension.illinois.edu/state to find the one nearest you.
UI Plant Clinic is also an option as it provides plant and insect identification, diagnosis of disease, insect, weed and chemical injury, nematode assays, and help with nutrient-related problems, as well as recommendations involving these diagnoses for home gardeners as well as commercial growers. The Plant Clinic is located southeast of the Assembly Hall at 1401 West St. Mary's Road, Urbana, IL 61801. Visit http://plantclinic.cropsci.illinois.edu or call 217-333-0519 for proper ways to submit samples.