Rhubarb (Rheum)

Plant Health Problems
Diseases caused by Fungi:

Leaf spot, Ascochyta rhei.
These small, circular, brown spots are scattered over the surface of the leaf. The disease is caused by a fungus.

The leaf spot is common in Connecticut, but does not do enough damage to the plant to require special control measures.

Phytophthora root rot, Phytophthora cactorum.
The disease is caused by soilborne fungi which cause the crown and roots to rot. The disease appears in heavy wet soils.

Fungicide applications have not been shown to be effective. Control can be achieved by planting in well-drained soils.

Insect Problems:

The bean aphid and green peach aphid sometimes infest rhubarb. Control is not usually necessary. See Aphid fact sheet.

European corn borer.
This insect will sometimes tunnel in the stalks of rhubarb. Control is not generally necessary.

Rhubarb curculio, Lixus concavus.
The rhubarb curculio makes feeding and egg punctures in the stalks, and the sap exudes from the wounds as glistening drops of gum. The eggs laid in rhubarb do not hatch, but are killed by sap. This pest completes its life cycle in the stems of wild dock. The beetle is about half an inch in length, black, covered with yellow dust, and hibernates as an adult. It feeds upon the margins of the leaves besides puncturing the stalks. They are usually present in small numbers and can be handpicked and destroyed. Removal of their other host plants, such as dock and thistle, during July when the larvae are still in them may also reduce populations.

Stalk borer, Papaipema nebris.
The eggs of this caterpillar are laid in the fall by the moths on surrounding grasses and weeds. After hatching in the spring the borers feed on these plants and later may migrate into adjacent rhubarb where they cause injury. The caterpillars are very active. Their restless habit of frequently changing from one plant stem to another increases the damage. Keeping the borders of the vegetable garden well-mowed and controlling weeds may help deny these insects their breeding grounds.

Yellow woollybear, Spilosoma virginica.
This caterpillar sometimes feeds upon rhubarb but does not regularly require control.