Rhubarb (Rheum rhabarbarum) is a robust, long-lived perennial, but its vigor can be quickly compromised by environmental stresses, pathogens, or pests. Identifying the exact problem—whether related to soil, fungus, or insects—is the first step toward effective recovery and restoring the plant’s health. By analyzing the symptoms, you can pinpoint the issue and apply the precise remedies needed to ensure a plentiful harvest.
Cultural and Environmental Causes
Rhubarb requires consistently moist soil but absolutely cannot tolerate standing water, making drainage one of the most frequent non-living culprits. Poorly draining, heavy soil creates an anaerobic environment where roots cannot breathe, leading to water stress. If leaves wilt despite wet soil, it signals root suffocation or rot, fixable by amending the soil with organic matter to improve porosity. Conversely, the plant suffers during extended dry spells, especially when temperatures rise above 90°F. Wilting is the plant’s signal to conserve water and indicates a need for deep watering.
Bolting is another stressor, where the plant sends up a tall central flower stalk to set seed. This process uses a significant amount of energy that would otherwise be directed to producing thick, edible stems, and can be a sign of heat stress or that the plant needs division. Cutting the flower stalk at the base as soon as it appears redirects energy back into the crown for stem production.
Pathogen-Based Diseases
Crown Rot is the most devastating biological issue, caused by fungal and bacterial pathogens attacking the plant’s base. Symptoms include wilting and yellowing leaves, even when the soil is moist, followed by the collapse of the stalks. When cut open, the crown shows mushy, brown, or black decay, sometimes with a foul odor. This rot is almost exclusively caused by excessive moisture around the crown, often from overwatering, poor drainage, or planting the crown too deeply.
Fungal leaf spot diseases, such as Ascochyta and Ramularia, are less destructive but can reduce photosynthesis. The infection thrives in prolonged periods of leaf wetness and high humidity. While the stalks remain safe to eat, removing the affected leaves is the primary control measure.
Ascochyta Leaf Spot
Ascochyta leaf spot presents as small, yellow-green spots that develop white centers with reddish margins. These spots eventually fall out, leaving a tattered appearance or holes.
Ramularia Leaf Spot
Ramularia leaf spot starts as small red dots that expand into circular, whitish-tan lesions with purplish halos.
Insect and Pest Damage
The Rhubarb Curculio (Lixus concavus) is a large snout beetle, about a half-inch long, often covered in a yellowish powder. This beetle causes damage by feeding and laying eggs, which results in characteristic notches and shallow depressions on the stalks and leaves. The most visible symptom of its activity is the exudation of a glistening, gummy sap from these wounds, which can create entry points for disease pathogens.
Slugs and snails are also common pests, easily identified by the ragged, irregular holes they chew in the leaves, especially on new growth. Their damage is often accompanied by the tell-tale shiny, silvery trails they leave behind as they move across the plant and soil surface. While Curculio eggs laid in rhubarb stalks are often killed by the plant’s rapid growth, the beetle itself is managed through non-chemical means like hand-picking. Slugs and snails can be controlled by simple barriers or traps, as insecticides are generally not recommended for use on edible crops.
Recovery and Preventative Measures
If Crown Rot was the problem, the only solution is to immediately dig up and destroy all decayed plant material, then improve the soil drainage before replanting or establishing a new bed. For leaf spot issues, meticulous sanitation is necessary, which involves removing and disposing of all infected leaves and plant debris from the garden. Preventative measures focus on cultural practices that maintain vigor and discourage pathogens.
Ensure the rhubarb crown is planted just at or slightly above the soil surface, never buried, to prevent water from pooling around the growth buds. Dividing mature rhubarb plants every four to five years prevents overcrowding, which improves air circulation and reduces the likelihood of fungal diseases taking hold. Proper harvesting involves twisting and pulling the stalk away from the crown rather than cutting, as a clean cut can introduce a pathway for rot-causing organisms.