Identifying & Treating Hollyhock Diseases And Pests

Hollyhocks can grow to 8 feet or more in height and produce large flowers in shades of purple, pink and yellow. A major problem with hollyhocks is a fungal disease called rust which can survive on infected plant parts from year to year. Other pests such as weevils, caterpillars and slugs can damage or kill your hollyhocks.

Rust

You can help to prevent initial rust infection by giving the plants good ventilation. Water the soil around the plants rather than the plants themselves because the rust spores can attach easier to damp or wet leaves.

The first sign of a rust infection is reddish brown spots on the underside of leaves near the bottom of the plant. The top side of the leaf can show a larger orange or yellow spot, sometimes with a red center. The more spots there are, the more chlorophyll is destroyed and misplaced.

Halt the development and spread of rust by removing infected leaves as soon as you identify them. Do not use the leaves or any infected plant material for compost. Regularly treat this persistent infection with topical fungicides according to the manufacturer’s instructions. At the end of the season, remove all hollyhock growth down to the base and destroy it.

Weevils

Hollyhock weevils are tiny insects that multiply rapidly. The insect drills into the plant stem and flower buds for food. Weevils that are around when the seeds have developed will drill through the seed pods to get at the seeds and destroy them. Unless massively infected, a plant can survive a weevil attack—though the flowers, if they survive, will be damaged. An insecticidal soap can be effective against weevils, but a specific pesticide is the only real solution.

Cut Worms

Cut worms will eat the leaves between the veins, turning them into skeletons. They can also do serious damage to new growing stems, often causing collapse.

Mature hollyhocks are not very attractive to cutworms, but you do need to protect any new growth. Because cutworms travel across the surface of the soil, you can erect a fine mesh fence to keep them off new plants. A long strip of material about 12 inches high and set into the soil at the bottom will be an effective barrier.

Slugs and Caterpillars

Slugs and caterpillars will attack hollyhocks, but if the numbers are small the plant will be able to cope with minor damage. Kill slugs with a simple application of table salt. Unless you can identify the caterpillar as being from an unwanted creature, it is best to leave them alone or move them to a less important plant.