Common Hollyhock Pests and How to Manage Them

Hollyhocks attract a predictable cast of insects and diseases that can turn a towering flower spike into a tattered mess by midsummer. Rust fungus is the single most common and damaging problem, but Japanese beetles, hollyhock weevils, aphids, spider mites, slugs, and sawfly larvae all take their share. Most of these pests can be managed without heavy chemical intervention if you understand what you are dealing with and time your responses well.

Hollyhock Rust

If you grow hollyhocks long enough, you will encounter rust. The disease shows up as small orange, yellow, or brown pustules on the undersides of leaves, eventually spreading to stems and the upper leaf surfaces. Leaves yellow, curl, and drop, often from the bottom of the plant upward. In bad years the lower half of the stalk is completely bare by bloom time. The fungus responsible is most commonly Puccinia malvacearum, though a closely related species, P. heterogenea, also infects hollyhocks and can be difficult to distinguish without molecular analysis. At least four other rust species can infect hollyhocks as well, though they are less frequently encountered.¹

Rust spores overwinter on old plant debris and spread by wind and splashing water. The disease thrives in humid conditions with moderate temperatures and crowded plantings where air circulation is poor. Because the spores travel easily, a neighbor’s infected hollyhocks can re-infect your garden even after you have cleaned up your own plants.

Managing rust starts with sanitation. Remove and dispose of infected leaves as soon as you see pustules, and cut stalks to ground level in the fall rather than leaving them standing through winter. Do not compost infected material. Water at the base of the plant, not overhead, and space hollyhocks far enough apart that air moves freely around the foliage. If you grow hollyhocks as biennials or short-lived perennials, starting fresh plants from seed every year or two keeps the disease cycle from building up in one spot.

When cultural controls are not enough, fungicide sprays can provide meaningful protection. Research on ornamental perennial crops has found that products containing pyraclostrobin combined with boscalid, triticonazole with pyraclostrobin, mefentrifluconazole, or myclobutanil are effective against rust, though the researchers stress that spraying works best when integrated with sanitation and environmental management rather than relied on alone.² Timing matters: fungicides are preventive, not curative. Once you see pustules, the infection in that leaf is already established. The goal is to protect new growth from incoming spores, so spraying before symptoms appear or at their very first sign gives the best results.

Japanese Beetles

Japanese beetles are among the most destructive foliage feeders on hollyhocks. The metallic green-and-copper adults emerge in early to midsummer and feed in groups, skeletonizing leaves by chewing the tissue between the veins. A plant can go from lush to lace-like in a matter of days when a large population is present. Hollyhocks seem to be particularly attractive to Japanese beetles, and a heavily infested plant can draw beetles from surrounding areas, compounding the damage.

For small gardens, hand-picking is surprisingly effective. The beetles are sluggish in the early morning and easy to knock into a bucket of soapy water. Japanese beetle traps are widely sold but often make the problem worse by luring beetles from a wide radius into your yard; most entomologists advise against them unless placed well away from the plants you are trying to protect.

If hand-picking is impractical, neem oil or spinosad-based sprays can reduce feeding damage. Both break down relatively quickly in sunlight and are less harmful to beneficial insects than broad-spectrum synthetics, though spinosad is still toxic to bees when wet, so spray in the evening after pollinators have finished foraging. For long-term population reduction, treating your lawn with milky spore disease or beneficial nematodes targets the grubs that develop into adult beetles. This is a slow strategy that takes a season or two to build up in the soil, but it reduces the local beetle population over time.

The Hollyhock Weevil

The hollyhock weevil is a small gray-brown snout beetle, only a few millimeters long, that feeds almost exclusively on plants in the mallow family. Adults chew small, round holes in leaves and flower buds. The real damage, though, is reproductive: females bore into developing seed pods and lay eggs inside, and the larvae consume the seeds as they develop. If you have ever opened a hollyhock seed capsule and found it full of frass and grubs instead of seeds, you have met this pest.

Weevils are hard to spot because they are small and drop to the ground when disturbed. Inspect buds and flowers in the morning, and look for the telltale round feeding holes in foliage. Removing and destroying infested seed pods before the larvae mature is one of the most effective controls, since it breaks the breeding cycle. If you do not plan to save seed, cutting off spent flower heads promptly also helps. In severe infestations, pyrethrin-based sprays can knock back adult populations, but timing matters: spray when adults are actively feeding on buds, before they have laid eggs inside seed pods.

Aphids

Aphids cluster on hollyhock stems, leaf undersides, and developing flower buds, sucking sap and excreting honeydew that attracts sooty mold. A moderate aphid population on a mature hollyhock is more cosmetic nuisance than existential threat, but heavy infestations weaken plants, distort new growth, and can transmit viral diseases.

A strong stream of water from the hose dislodges aphids effectively and is the simplest first step. Repeat every few days as needed. Lady beetles, lacewings, and parasitic wasps all prey on aphids, and encouraging these beneficial insects by planting diverse flowering plants nearby often provides meaningful natural control. Insecticidal soap sprayed directly on aphid colonies kills on contact without leaving persistent residues. Avoid broad-spectrum insecticides for aphids; they wipe out the natural predators that keep aphid populations in check, often causing a worse rebound infestation a few weeks later.

Spider Mites

Spider mites are tiny arachnids that thrive in hot, dry weather. They feed by piercing leaf cells and sucking out the contents, leaving behind a fine stippling of pale dots on the upper leaf surface. In heavy infestations, fine webbing becomes visible on the undersides of leaves and between stems. Hollyhocks growing in full sun against a south-facing wall, where reflected heat and low humidity create ideal mite conditions, are especially vulnerable.

Like aphids, spider mites are best managed by encouraging natural predators and avoiding pesticides that eliminate those predators. Predatory mites, particularly species in the genus Phytoseiulus, are voracious spider mite feeders and can be purchased for release in gardens. Regular overhead watering or misting the foliage disrupts mite colonies, since they prefer dry conditions. Horticultural oil or insecticidal soap sprays applied to the undersides of leaves can reduce populations, but coverage needs to be thorough because these products work only on contact.

One pattern worth knowing: over-fertilizing with nitrogen can make spider mite problems worse. High nitrogen levels increase the nutritional quality of leaf tissue for mites, encouraging faster reproduction. Feeding hollyhocks moderately rather than heavily, and using balanced fertilizers instead of high-nitrogen formulas, can reduce your mite pressure over the course of a season.

Slugs and Snails

Slugs and snails are a particular problem for hollyhock seedlings and young plants, where they can chew through tender leaves overnight. Mature plants are less vulnerable but still sustain ragged holes in lower leaves. Damage is worst in damp climates, shady beds, and mulched areas where slugs shelter during the day.

Iron phosphate baits are effective and safe around pets and wildlife. Scatter them around the base of plants in the evening, when slugs become active. Copper tape around raised beds or individual pots creates a mild deterrent, though its effectiveness drops over time as it oxidizes. Beer traps work but tend to catch slugs only from a short radius and need frequent refreshing. For gardeners who prefer no products at all, going out with a flashlight after dark and hand-removing slugs remains the most reliable method. Reducing daytime hiding spots by clearing debris and pulling mulch a few inches back from hollyhock stems also helps.

Sawfly Larvae

Hollyhock sawfly larvae look like small caterpillars but are actually the larval stage of a wasp-like insect. They feed gregariously, often in rows along the leaf margin, and can strip a plant’s lower foliage quickly. Because they are not true caterpillars, products based on Bacillus thuringiensis (Bt), which target caterpillars specifically, do not work on sawfly larvae. Spinosad is effective, as is hand-picking when populations are small. Inspect the undersides of lower leaves in late spring and early summer, when larvae are most active.

Powdery Mildew

Though not an insect pest, powdery mildew deserves mention because it often shows up alongside rust and causes confusion. It appears as a white or grayish powdery coating on leaves, stems, and buds, distinct from rust’s colored pustules. Powdery mildew favors warm days with cool, humid nights and poor air circulation. Like rust, it responds well to improved spacing and airflow. Potassium bicarbonate sprays and sulfur-based fungicides provide some control, and the same fungicide products effective against rust also tend to work against powdery mildew on ornamental perennials.²

Cultural Practices That Prevent Multiple Problems at Once

Many hollyhock pest and disease problems share root causes, which means a handful of cultural habits address several issues simultaneously. Good air circulation, achieved by spacing plants at least 18 inches apart and avoiding planting tight against walls or fences, reduces rust and powdery mildew while also making the foliage less hospitable to spider mites. Watering at the base of the plant keeps leaves dry, discouraging fungal diseases, while occasional overhead rinsing during dry spells disrupts mite and aphid colonies. Cleaning up dead foliage in fall removes overwintering sites for rust spores, sawfly pupae, and slug eggs.

Choosing resistant or tolerant varieties helps as well. Some hollyhock cultivars, particularly those bred from Alcea rugosa or crosses with it, show better rust tolerance than the common Alcea rosea types. No variety is completely immune, but starting with a tolerant cultivar and combining it with good cultural practices reduces the amount of intervention you need during the growing season.

Growing hollyhocks as biennials rather than trying to keep them going as perennials is another underappreciated strategy. Rust and weevil populations build up on established clumps over successive years. Starting new plants from seed every year or two, and rotating their location in the garden, keeps these problems from compounding.

Choosing Pesticides Without Harming Pollinators

Hollyhocks are pollinator magnets. Bumblebees, honeybees, and hoverflies work the large open flowers heavily, which means any pesticide you apply to hollyhocks has a high chance of reaching beneficial insects. This is especially true of systemic insecticides applied to the soil, which are taken up by the plant and distributed to every tissue including pollen and nectar. Research on ornamental flowers treated with the systemic neonicotinoid imidacloprid found that the insecticide accumulated in flower tissue at concentrations high enough to reduce survival of several species of lady beetles and butterfly larvae.³ A second application months later more than doubled the residue levels in flowers, meaning repeated use builds the problem rather than diminishing it.

Even foliar-applied insecticides and fungicides leave residues in pollen and nectar, though at much lower concentrations than systemics. Research measuring pesticide residues in flowers found that concentrations in pollen and nectar were far lower than in foliage sprayed days earlier, and individual residue levels from a single flower visit fell below acute toxicity thresholds for honeybees. However, bees make many flower visits per foraging trip, and the researchers noted that cumulative exposure from multiple visits could still pose a risk.⁴

The practical upshot for hollyhock growers: avoid systemic neonicotinoids entirely on flowering plants that pollinators visit. When you do need to spray, use contact-based products like insecticidal soap, horticultural oil, or spinosad, and apply them in the evening when bees are not active. Target your sprays to the specific pest rather than blanket-spraying the entire plant. Directing insecticidal soap at an aphid colony on one stem is far less disruptive to the garden ecosystem than drenching every leaf with a broad-spectrum product.

When to Accept Some Damage

Hollyhocks are tough, fast-growing plants that tolerate more cosmetic damage than most gardeners expect. A moderate level of Japanese beetle feeding, a few aphids on the stems, or some rust on the lower leaves does not threaten the plant’s survival or prevent it from flowering. The impulse to keep every leaf pristine often leads to more intervention than the plant actually needs, and heavy pesticide use on a flower that attracts so many beneficial insects creates its own set of problems.

A more relaxed threshold for acceptable damage often works better in practice. Remove badly infected rust leaves, hand-pick the beetles you can reach, hose off the aphids, and let the plant do the rest. Hollyhocks self-seed readily, and next year’s volunteers will fill gaps left by plants that had a rough season. For gardeners willing to grow them as cheerful, semi-wild cottage plants rather than flawless specimens, hollyhocks reward that approach with less work and more flowers over time.