Rhubarb Pests and Pest Control
Control weeds well before planting. Start cultivation early in the spring. Cultivation should be shallow to avoid injury to roots and can continue as late in the season as possible without damaging the plants.
Contact herbicides are registered for use but the crop must be well shielded.
Various types of mulch may be used between the plants and in the rows (most commonly straw).
Leaf Spots - Ramularia and Ascochyta (fungi)
These fungi cause circular, or angular spots, variable in size having beige centers surrounded by a red zone. When affected tissue dies, it may drop out, leaving large ragged holes in the foliage. Fungi overwinter in infected plant debris and in infected propagation stock.
Control: Remove and destroy leaves following the first heavy frost. During harvest, remove stems with spotted leaves first. Apply fungicide used for Botrytis control.
Botrytis Rot (fungus)
May cause a leaf, stem and crown rot of forced rhubarb. Disease intensifies where there is poor air circulation and high humidities.
Control: Practice strict sanitation. Apply recommended fungicide at first sign of disease and at 7 day intervals.
Root and Crown Rots (fungi & bacteria)
Characteristics: Plants become unthrifty. Leaves may turn yellow to red and collapse. The crowns, when sectioned, exhibit a brown-black decay. Large roots lack small feeder roots. Larger roots may have large brown-black lesions present.
Control: Purchase healthy propagation stock. Select well drained fields. Remove and destroy diseased plants.
Characteristics: Several viruses are known to occur in rhubarb. Reports from British Columbia and the U.K. indicate that turnip mosaic, arabis mosaic and cherry leaf roll virus are the most common. These viruses have wide host ranges and cause mottling and ring spotting of leaves. They may be introduced in infected planting stock.
Control: Obtain and plant healthy nursery stock. Avoid planting virus free crowns near virus contaminated crowns.
Potato Stem Borer
Characteristics: The potato stem borer is a caterpillar, which when fully grown is about 3.5 cm in length and pinkish-white in colour. The first stages of the insect attack only weeds, couch grass in particular. Later they move into plants with thicker stems, such as rhubarb. They may move from stem to stem, boring into the centre of the stalk. The adult moths lay their eggs on the stems of grasses in August. The eggs do not hatch until the following spring. Damage can be expected in June and early July. Serious infestation can lead to an unmarketable crop.
Control: This pest is not a problem when couch grass and other weeds are controlled in and around the rhubarb plantation. Weeds should be controlled to make the field less attractive for egg laying by the adult moth. Early spring burning of affected fields or field margins will effectively control this pest.
Tarnished plant bug
Characteristics: Adult tarnished plant bugs are light brown to reddish brown in colour and about 5-6 mm in length. They occur throughout the season. They are very active and quick moving. They can damage rhubarb by feeding on young leaves. They pierce the stalk with their mouthparts and cause wilting and distortion of the leaves. Tarnished plant bugs are mainly a pest of new plantings.
Control: Keep plantings and adjacent areas weed free. Avoid planting adjacent to legumes.
Characteristics: Slugs may be a problem in plantings with heavy soils, poor drainage and in weedy situations. Slugs fed at night, by rasping the surface of stems, leaving unsightly scars, which reduce the saleability of the stem.
Prevention: Provide good soil drainage. Keep weeds under control. Remove leaves and trash from the field when harvesting. Do not use manure and/or mulches in areas of field prone to slug damage.
Other Insect Pests
Black bean aphid Aphis fabae has caused problems on occasion. Large infestations may cause curling or wilting of leaves. There is also potential for the spread of virus by aphids.
Flea beetles can cause damage to new plantings by their feeding activity on the leaves. They are especially active during periods of hot dry weather.
Control: Provide good weed control. There are no products registered for either of these pests.