Your easy-to-grow, colorful hollyhocks thriving in your home garden are under the threat of a potentially fatal fungal disease. Phymatotrichum root rot attacks hollyhocks and creates both cosmetic damage and severe injury. You can avoid damage to your home flower garden by paying close attention to the health of your hollyhocks and providing optimal care.
Healthy hollyhocks (Alcea rosea) kept vigorous in the garden have a greater likelihood of avoiding or dealing with root rot infection as opposed to neglected plants already in decline. Grow hollyhocks in locations that offer full sunlight, according to the University of Arkansas Cooperative Extension Service. Hollyhock flowers thrive in well-drained, fertile soil.
Hollyhocks are susceptible to phymatotrichum root rot, caused by the fungal pathogen Phymatotrichopsis omnivorum, according to the New Mexico State University Cooperative Extension System. Attacking only established hollyhock plants, this fungus is soil-borne, entering plants through their root systems during warmer months when fungi become active.
Phymatotrichum root rot of hollyhocks, also referred to as cotton root rot, is an aggressive disease that causes above-ground symptoms, including yellowed, wilted leaves. Due to the fast nature of this infection, the entire plant may die before above-ground symptoms become advanced; however, look for dead leaves that remain on the plant after death as a verification of phymatotrichum infection. Root rot takes hold of the root system, causing expedient decay and complete inhibition of water and nutrient uptake to the rest of the plant, leading to decline and plant death, according to the New Mexico State University Cooperative Extension Service.
Nearby susceptible plants often become infected as phymatotrichum root rot disease affects thousands of host plants. Avoid selecting susceptible plants if you suspect your soil is infected and, if replanting where a hollyhock died, do not replant with a susceptible variety. Other susceptible flowers to avoid include, but are not limited to, dahlias and peonies. Flowers known for their resistance, though not immunity, to root rot are calendulas, crocuses, geraniums, irises, pansies, snapdragons and sweet peas, according to the Oklahoma Cooperative Extension Service.
Once an infection occurs, there is no cure for root rot of hollyhocks. Prevention is the only medicine with phymatotrichum rot. Amend your soil with organic content as well as the addition of an organic mulch, like compost, in a 2-inch layer surrounding your hollyhocks and other potentially affected plants. Nutrients increase plant health and organic matter lowers the pH level, creating a more resistant environment to pathogens that favor alkaline soil, according to the New Mexico State University Cooperative Extension Service. Maintain healthy hollyhocks free of injury, avoid overhead irrigation, and remove and destroy affected plant parts. For severely affected hollyhocks, remove the entire plant, including the roots.