Rhubarb is one of the hardier edible plants you can grow, but it still attracts a handful of pests that can weaken harvests or disfigure stalks. The most distinctive is the rhubarb curculio, a large weevil that gouges oval pits into stalks, though slugs, aphids, and a few less common insects also show up regularly. Knowing which pest you’re dealing with matters because the response for each one is different, and many rhubarb problems don’t require chemicals at all.
The Rhubarb Curculio
If you’ve ever noticed gummy sap oozing from small, shallow depressions on your rhubarb stalks, you’ve likely met the rhubarb curculio (sometimes called the rhubarb weevil). It’s a robust, dark-colored snout beetle roughly half an inch long, and it’s the signature pest of rhubarb in North America. Adults notch the edges of leaves and stalks as they feed and also create shallow, round or oval pits in the stalks where they lay eggs. Those feeding and egg-laying wounds often go unnoticed until the telltale gummy sap appears, sometimes followed by dark streaks as decay sets into the damaged tissue.1Virginia Cooperative Extension. Rhubarb Curculio – Section: Damage / Life History
Here’s an oddity of this pest’s biology that works in rhubarb’s favor: eggs laid inside rhubarb stalks don’t actually develop. The plant tissue grows so rapidly that the eggs get crushed before they can hatch. The curculio’s larvae only survive when eggs are deposited in other host plants like wild dock, thistle, and sunflower, where they hatch in about a week to ten days.1Virginia Cooperative Extension. Rhubarb Curculio – Section: Damage / Life History That means the real nursery for the next generation of curculios isn’t your rhubarb patch at all. It’s the weedy plants nearby.
This fact makes cultural control straightforward and effective. Removing and destroying any dock, thistle, and sunflower growing near your rhubarb during midsummer eliminates the habitat where curculio larvae are actively developing.2Virginia Cooperative Extension. Rhubarb Curculio – Section: Cultural Control If you keep a reasonably clean perimeter around your rhubarb bed, you cut the pest’s life cycle without spraying anything. Hand-picking adults off the plants in early morning, when they tend to be sluggish, also reduces numbers. Because curculio damage is mostly cosmetic to the plant itself and doesn’t compromise the edibility of the stalks once you trim away the wounded spots, many growers tolerate low populations and focus on weed management.
Slugs and Snails
Rhubarb’s big, broad leaves are an open invitation for slugs and snails, especially in damp climates or during wet springs. You’ll recognize slug damage by the irregular, ragged holes chewed through the leaves, often with silvery slime trails visible on and around the plant. The leaves themselves aren’t harvested for eating, but heavy slug feeding weakens the plant over time by reducing its ability to photosynthesize and feed the crown.
Young rhubarb divisions and newly emerging shoots in spring are most vulnerable. A slug can chew through a tender emerging stalk overnight, which is more damaging than leaf holes on an established plant. Slug management in rhubarb beds usually relies on a few practical steps:
- Reduce hiding spots: Clear mulch, boards, and debris from around the base of plants where slugs shelter during the day.
- Water in the morning: Evening watering leaves the soil surface damp overnight, which is when slugs are most active. Morning watering gives the surface time to dry.
- Beer traps or iron phosphate baits: Shallow containers of beer sunk into the soil attract and drown slugs. Iron phosphate pellets are a low-toxicity option that breaks down into soil nutrients.
- Copper barriers: Copper tape or strips around raised beds can deter slugs, which avoid contact with copper.
Slug control is an ongoing effort rather than a one-time fix. In persistently wet regions, it may be the most labor-intensive pest issue rhubarb growers face, even though it’s rarely serious enough to kill a well-established clump.
Aphids on Rhubarb
Several species of aphid colonize rhubarb, and they tend to cluster on the undersides of leaves and along the stems, especially in late spring and early summer. You’ll often notice them before you notice any damage because they congregate in visible colonies, sometimes accompanied by ants farming them for honeydew. The leaves may curl, yellow, or develop a sticky coating from the honeydew the aphids excrete, and sooty mold can grow on that residue.
In most home gardens, aphid populations on rhubarb stay manageable without intervention. Ladybugs, lacewings, hoverfly larvae, and parasitic wasps all prey on aphids, and a healthy garden ecosystem usually keeps numbers in check. If populations spike, a strong jet of water from a hose knocks aphids off the plant and disrupts the colony. Insecticidal soap, sprayed directly on the aphids, is effective for heavier infestations. The key with aphids is patience: unless the plant is visibly wilting or the colonies are enormous, the predators often catch up within a couple of weeks.
One thing to watch for with aphid-infested rhubarb is virus transmission. Aphids can carry and spread plant viruses, and rhubarb is susceptible to several mosaic-type viruses that cause mottled, distorted leaves and reduced vigor over time. There’s no cure for a virus-infected plant, so keeping aphid populations down is as much about long-term plant health as it is about cosmetic damage to this season’s leaves.
Spider Mites
Spider mites are tiny arachnids, barely visible without magnification, that pierce plant cells and suck out their contents. On rhubarb, you’ll notice their presence as a fine stippling or bronzing on the upper leaf surface, and in severe cases, fine webbing on the undersides of leaves. Hot, dry conditions favor spider mite outbreaks, so they tend to be more of a problem in midsummer than in the cool, damp conditions rhubarb prefers.
Because rhubarb is a food crop, chemical options for mite control must meet food-safety standards. Acequinocyl is one miticide that has been evaluated for use on rhubarb and found acceptable with regard to consumer exposure, with maximum residue levels formally established for the crop.3Europe PMC / EFSA Journal. Modification of the existing maximum residue levels for acequinocyl in celeries, Florence fennel and rhubarb For most home growers, though, spider mites on rhubarb rarely reach the level where a miticide is justified. Spraying the undersides of leaves with water, encouraging predatory mites, and avoiding drought stress usually keep them under control. If your rhubarb is in a particularly hot, exposed location and mites are a recurring issue, the best long-term fix may be improving the site with afternoon shade or better irrigation.
Stalk Borers
The common stalk borer is a caterpillar that tunnels into the stems of a wide range of garden plants, rhubarb included. It’s the larval stage of a nondescript brown moth, and the caterpillar itself is striped with a distinctive dark band around its midsection when young. You’ll know a stalk borer is at work when individual rhubarb stalks suddenly wilt, often with no external damage visible. Splitting the stalk open reveals a hollow tunnel and sometimes the caterpillar itself.
Stalk borers typically move into rhubarb from surrounding grassy or weedy areas, where the moths lay their eggs on stems in the fall. The caterpillars hatch in spring, bore into nearby plant stems, and migrate from plant to plant as they outgrow each host. Keeping grass and weeds trimmed around the rhubarb patch in fall and early spring reduces the number of borers that find their way in. Once a caterpillar is inside a stalk, there’s no practical spray that will reach it. Your options are to remove and destroy the affected stalk or, if you’re motivated, slit it open and extract the larva by hand. Plants almost always survive stalk borer damage because only one or two stalks are typically affected per plant.
Flea Beetles and Leaf-Chewing Beetles
Small, shiny flea beetles occasionally show up on rhubarb leaves, leaving behind a scattering of tiny round holes that give the foliage a shotgun-pellet appearance. The damage is almost always cosmetic and minor on rhubarb, partly because the leaves are so large that even moderate flea beetle feeding barely dents the plant’s photosynthetic capacity, and partly because rhubarb’s oxalic acid content makes it less palatable than many other garden plants.
Japanese beetles and other larger leaf-chewing beetles can also feed on rhubarb leaves, skeletonizing them by eating the tissue between the veins. Again, this is rarely a crisis for rhubarb unless populations are very high. Hand-picking larger beetles into a bucket of soapy water is the simplest control. Floating row covers can keep beetles off entirely, though covering a large, established rhubarb clump isn’t always practical. If flea beetle damage is persistent year after year, it may indicate a soil-health issue, since flea beetles tend to hit stressed plants harder than vigorous ones.
Diseases That Mimic Pest Damage
Not every damaged rhubarb stalk is the work of an insect. Several diseases produce symptoms that gardeners initially blame on pests, and misidentifying the cause leads to the wrong response.
Crown rot is the most serious. It’s caused by fungal or bacterial pathogens that attack the base of the plant, turning the crown soft and mushy. Affected stalks collapse and the bases may smell sour. No amount of insecticide will help because no insect is involved. Crown rot is almost always a drainage problem: rhubarb crowns sitting in waterlogged soil are vulnerable. Improving drainage, dividing overcrowded clumps, and avoiding heavy mulch that holds moisture against the crown are the real fixes. Badly infected plants sometimes need to be removed entirely and replaced in a new location.
Leaf spots, caused by various fungi, produce brown or tan patches on the leaves that can look like feeding damage at first glance. The giveaway is that fungal spots tend to have defined edges or concentric rings, while insect damage is more irregular. Leaf spot diseases are mostly cosmetic on rhubarb and rarely warrant treatment. Removing and disposing of badly affected leaves reduces spore load. Fungal problems tend to flare in humid, crowded conditions, so spacing plants for good airflow makes a noticeable difference.
Rhubarb that develops mottled, distorted, or unusually narrow leaves may be suffering from a viral infection, often spread by aphids as mentioned earlier. Viral infections are chronic, progressively weaken the plant, and cannot be cured. If you suspect a virus, the standard advice is to remove and destroy the affected plant to prevent spread to neighboring rhubarb. Starting fresh with certified virus-free divisions is the only real solution.
Why Rhubarb Gets Off Easier Than Most Crops
Compared to nearly any other edible plant in a home garden, rhubarb’s pest list is short. There are a few reasons for this. The high oxalic acid concentration in the leaves makes the foliage unpalatable or outright toxic to many herbivores. Rhubarb is a perennial with an established root system, so it can tolerate feeding damage that would set back an annual vegetable. And because the harvested part is the stalk rather than the fruit or seed, pests that target flowers or developing fruit are irrelevant.
This resilience can encourage neglect, which is where most rhubarb pest problems actually originate. A clump that hasn’t been divided in a decade, sitting in increasingly compacted soil with weeds growing through it, is far more likely to attract curculios, suffer crown rot, or host slugs than a well-maintained planting. The single most effective pest-management strategy for rhubarb is mundane: divide the clump every five to eight years, keep the area weeded, and make sure the soil drains well. Pest problems in rhubarb are almost always a secondary symptom of a tired, overcrowded planting rather than a standalone crisis.
When Chemical Controls Make Sense
For most home rhubarb patches, chemical pesticides are unnecessary and arguably counterproductive, since they can harm the predatory insects that keep aphids and mites in check. The situations where a targeted pesticide might be warranted are narrow:
- Severe mite outbreaks: If spider mites are defoliating the plant in a hot, dry summer and cultural controls aren’t keeping up, a miticide labeled for use on rhubarb can break the cycle.
- Commercial production: Growers selling rhubarb at scale may face economic thresholds where pest damage affects marketability. In these settings, integrated pest management programs that combine scouting, thresholds, and targeted sprays are standard practice.
- Unusual infestations: Occasionally, a pest that isn’t normally a problem on rhubarb shows up in large numbers due to local conditions. If hand-picking and cultural methods can’t keep up, a targeted insecticide may be justified for a single season.
Any pesticide used on rhubarb must be labeled for that crop. Because rhubarb stalks are eaten raw or lightly cooked, residue limits matter. Regulatory bodies evaluate specific active ingredients for safety on rhubarb, and only products with established tolerances should be used.3Europe PMC / EFSA Journal. Modification of the existing maximum residue levels for acequinocyl in celeries, Florence fennel and rhubarb Always check the label for pre-harvest intervals, the number of days you must wait between the last application and harvest.
Companion Planting and Physical Barriers
Rhubarb’s strong-smelling foliage may itself act as a mild deterrent to some pests on neighboring plants, which is one reason it has a long history as a companion plant in kitchen gardens. Whether planting garlic, onions, or strong-scented herbs near rhubarb provides measurable pest reduction on the rhubarb itself is more folklore than settled science. Still, diverse plantings around rhubarb support the beneficial insect populations that control aphids and mites, so there’s an indirect benefit even if the companion plant isn’t directly repelling anything.
Physical barriers can be surprisingly effective for specific problems. Copper tape deters slugs. Floating row covers exclude flea beetles and curculio adults in spring. A thick layer of coarse gravel or crusite around the base of each clump discourages slugs and also helps with drainage, attacking two problems at once. These low-tech approaches fit rhubarb well because the plant is large enough and long-lived enough that a one-time investment in barriers pays off over many seasons.
For gardeners dealing with persistent curculio pressure, the most impactful physical intervention remains the simplest: walk the rhubarb bed in early morning when the beetles are cool and sluggish, pick them off by hand, and drop them into soapy water. Combined with clearing nearby dock and thistle, this approach can reduce curculio numbers to near zero within a season or two without any spray at all.2Virginia Cooperative Extension. Rhubarb Curculio – Section: Cultural Control