Tips on how to use this section
The symptoms of the most common problems are in the left column of the chart. In the right column are the probably causes of those symptoms. For those problems for which there is detailed information in a different part of Yardener’s Helper, the name of the problem is linked to a detailed file. For those problems for which there are no additional files, the discussion is found in the paragraphs below the chart.
| Solving Hollyhock Problems | |
|---|---|
| Symptoms | Probable Cause |
| Leaves and Petals Are Pale; Silvery | Thrips |
| Certain caterpillars cause hollyhock stems to break and leaves to wilt. Close examination shows small round holes in the stems, from which the stalk borers expel sawdust-like castings. | See Stalk Borers item below |
| Leaves Discolored; Webbed Over | Spider Mites |
| Holes In Leaves and Flowers | Japanese Beetles |
| Deformed or dwarfed flowers appear especially in late summer | See Tarnished Plant Bug item below |
| Ragged Holes in Leaves | Slugs and Snails |
| There are reddish or pale yellow areas on upper leaf surfaces and powdery orange spots of fruiting bodies on undersides directly beneath. | see Rust discussion below |
| Leaves Blotched | Anthracnose |
| Stem lesions are first dark brown and later ash-gray. As these spots girdle the stem the part above wilts, collapses, breaks off and dies. | See Stem Canker discussion below |
Stems Break Off; Leaves Wilt - Stalk Borers
Stalk borers are long, slender, brownish caterpillars. They have a dark brown or purple band around the middle and several conspicuous stripes running the length of their bodies. Adults are grayish-brown moths. These caterpillars cause hollyhock stems to break and leaves to wilt. Close examination shows small round holes in the stems, from which the borers expel sawdust-like castings. Control stalk borers by slitting each affected stem lengthwise, removing the borers, and binding the stems together. Practice clean cultivation and burn all weeds, stems and plant remains likely to harbor over-wintering eggs. For more information see the file on Controlling Borers
Deformed or Dwarfed Flowers - Tarnished Plant Bugs
Tarnished plant bugs are active greenish-brown bugs. Only 1/4 inch long, they are mottled with markings of yellow, brown, and black. Look for a distinctive black-tipped yellow triangle on each wing cover. They suck sap from young hollyhock shoots and especially buds, causing deformed or dwarfed flowers. Tarnished plant bugs appear in early spring, becoming more numerous toward the end of summer. Sprays must be used early in the morning when bugs are least active. Spray visible bugs with pyrethrum laced with rubbing alcohol once every 3 days. If the infestation is heavy, dust plant surfaces with sabadilla. The best way to control this pest is with a thorough fall and spring garden cleanup. For more information see the file on Controlling Plant Bugs
Powdery Spots On Leaves - Rust
Hollyhocks tend to be susceptible to rust diseases. They are caused by various fungi which produce reddish or pale yellow areas on upper leaf surfaces and powdery orange spots of fruiting bodies on undersides directly beneath. Rust is more prevalent in humid areas. It deforms infected stems, but does not harm hollyhock flowers. Remove any infected leaves as soon as possible. Remove and destroy all garden debris before plants start to grow in the spring. The first line of defense is to plant hollyhocks so that there is generous air circulation between them. Control weeds in and around the garden. Control insect pests which carry the disease with pyrethrum or rotenone. Prevent rusts with periodic sprays of wettable sulfur, ferbam or benomyl fungicides, starting several weeks before the disease normally appears. Avoid wetting hollyhocke foliage when watering. At season's end, cut plants back to the soil level to forestall reinfection. The hollyhock variety, 'Silver Puffs' is rust resistant. For more information see the file on Controlling Fungal Disease
Lesions On Stems; Foliage Wilted - Stem Canker
A fungal stem canker attacks hollyhocks at bloom time on rare occasions. Stem lesions are first dark brown and later ash-gray. As these spots girdle the stem the part above wilts, collapses, breaks off and dies. Remove and destroy infected plants or plant parts as soon as you notice them. (It's a good idea to go around the garden collecting all faded flowers.) Disinfect clippers and other tools after using them on cankered plants. In the fall gather and destroy all aboveground infected parts to reduce chances of the fungus over-wintering. Avoid wounding plants. Space plants farther apart to minimize splash-borne infection. If canker has been a problem and winters are not too severe, omit mulching entirely. Control weeds around the garden. Spraying with Bordeaux mixture may give some control. For more information see the file on Controlling Fungal Disease
