Rhubarb crops are affected by a number of weeds, insects, diseases and other pests.
Regular, shallow cultivation is all that is usually required to control weeds, but some hand-weeding may be necessary. No herbicides are registered in Queensland for weed control in rhubarb.
There are relatively few insect pests of rhubarb. Broad mites cause a bronzing effect on young leaves, inducing slow and weak growth. Stem borers enter the tip of the stem and burrow downwards, leading to stem collapse.
The most serious disease of rhubarb in Queensland is crown rot, caused by the fungus Phytophthora nicotianae var. parasitica. The crown, roots and stem are affected by a rot that causes the whole plant to eventually collapse. This disease can be prevented by ensuring that internal and surface soil drainage is adequate. A registered fungicide dip can also be used to treat crowns after division and prior to planting. Diseased crowns should not be used for propagation.
Downy mildew, caused by the fungus Peronospora jaapiana, may occur during very wet weather where a downy growth may be visible on the undersurfaces of affected leaves. Large, light-brown spots up to 3 cm across develop, and then later dry out to a papery texture. Affected plants should be heavily harvested and sprayed with a registered fungicide.
Rust (Puccinia rhei-undulate) causes small, raised, rust-coloured pustules on the leaves and stalks. No fungicides are registered in Queensland for the control of this disease in rhubarb.
Leaf spot (Ascochyta rhei) is characterised by round, light-tan spots on leaves and sometimes on stems. Small black dots develop within these spots. No fungicides are registered in Queensland for the control of this disease in rhubarb.
Root knot and cyst nematodes have been recorded on rhubarb in Queensland, but are not considered to be serious problems. Snails may cause occasional damage.