Rhubarb is a popular perennial vegetable known for its long, edible stalks. Despite its hardiness, this plant can be susceptible to damage from specific pests that target its leaves, stalks, or crown. Identifying these threats and implementing timely controls is the most effective way to ensure a healthy, productive harvest. This guide focuses on the most common pest challenges and provides actionable management steps.
Identifying the Rhubarb Curculio
The Rhubarb Curculio (Lixus concavus) is the most destructive pest specific to the plant. This large snout beetle measures about one-half to three-quarters of an inch long and has a distinctive downward-curving snout. Young adults appear dark with a dusty coating of yellow or orange powder, which rubs off to reveal a brownish-black body underneath.
The damage caused by the adult Curculio is characterized by feeding and egg-laying punctures, usually appearing as shallow, circular depressions on the stalks and sometimes the leaf edges. The plant responds to this injury by exuding a sticky, gummy sap that collects around the wounds, a tell-tale sign of this pest. While the beetles deposit eggs in rhubarb stalks, the rapidly growing plant tissue crushes the eggs, preventing them from developing into larvae.
The Curculio larvae do not develop in rhubarb but rely on weedy hosts growing nearby, such as dock, thistle, and sunflower. The primary control method is mechanical: handpicking the adult beetles from the plants as soon as they become active in late spring. Since these beetles are slow-moving and drop off when disturbed, holding a container beneath them aids in collection and destruction. Chemical controls are not effective, making physical removal and destruction of affected stalks the main strategy.
Controlling Common Leaf and Sap Feeders
Beyond the Curculio, rhubarb foliage is commonly targeted by smaller pests, including aphids, slugs, and snails. These pests damage the leaves, which can weaken the plant and reduce its ability to photosynthesize. Inspecting the undersides of the large leaves is important for early detection.
Aphids, such as the Black Bean Aphid, cluster on the undersides of leaves and on flower stalks, using piercing mouthparts to suck out plant sap. A heavy infestation can cause leaves to wilt or curl, and the pests excrete a sticky, sugary substance known as honeydew. A strong, targeted spray of water from a garden hose can often dislodge small aphid populations. For more persistent issues, an application of insecticidal soap can be effective, working by disrupting the cell membranes of the soft-bodied insects.
Slugs and snails thrive in moist environments and cause damage by chewing ragged holes in the leaves and sometimes leaving silvery slime trails on the stalks. Management focuses on creating barriers and trapping the pests. Barriers made of copper tape, which reacts with the pests’ slime to create a mild electric shock, or sharp, abrasive materials like diatomaceous earth can deter them from reaching the plant crown. Simple traps, such as shallow containers filled with beer or yeast-and-sugar water, can also be sunk into the soil to lure and drown the mollusks.
Preventative Cultural Practices
Proactive garden management is the best long-term defense against rhubarb pests, reducing the conditions that allow infestations. Maintaining plant vigor through proper soil health and nutrition helps the rhubarb resist and recover from damage. Applying a balanced fertilizer in early spring and amending the soil with compost supports robust growth.
Garden sanitation plays a significant role in interrupting pest life cycles, particularly for the Curculio. The adult beetles spend the winter months in leaf litter and other debris near the plant crown. Removing and destroying all old leaves and stalks in the fall eliminates these overwintering sites, reducing the number of pests that emerge in the spring.
Controlling weeds is also paramount, especially the removal of dock weed, which is the preferred breeding host for the Rhubarb Curculio larvae. Eliminating these weedy hosts from the area prevents the beetle’s life cycle from completing near the rhubarb patch. Proper watering is another important cultural practice; watering in the morning rather than the evening allows the soil surface to dry before nightfall, making the environment less appealing to slugs and snails.