Temperate Vegetables (1+1)

DISEASES & PESTS

Leaf Spots : (Ramularia and Ascochyta spp)

• These fungi cause circular or angular spots, variable in size having big centers surrounded by a red zone.
• When affected tissue dies, it may drop out, leaving large ragged holes in the foliage.
• These fungi overwinter in infected plant debris and propagation stock.

Control measures

• Remove and destroy leaves following the first heavy frost.
• During harvest, remove stems with spotted leaves first.

Botrytis rot : (Botryis cinerea)

• The fungus may cause a leaf, stem and crown rot of forced rhubarb.
• Disease intensifies where there is poor air circulation and high humidity.

Control measures

• Follow strict sanitation.
• Apply recommended fungicides like copper oxychloride @ 0.3per cent at first appearance of disease and repeat at 7 days interval.

Root and crown rots: (Pythium and Phytophthora spp)

• 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.

Control measures

• Purchase healthy propagation stock.
• Select well drained fields.
• Remove and destroy the diseased plants.

VIRAL DISEASES

• Several viruses are known to occur in rhubarb but turnip mosaic, arabis mosaic and cherry leaf roll virus are the most common.
• These viruses have wide host range and cause mottling and ring spotting of leaves.
• They may be introduced through infected planting stock.

Control measures

• Obtain and plant healthy nursery stock.
• Avoid planting virus free crowns near virus contaminated crowns.

PESTS
Potato stem borer: (Hydraecia micacea)

• The first stage of the insect attacks only weeds and 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 measures

• This pest is not a serious 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.
• In early spring burning of affected fields or field margins will effectively control this pest.

Tarnished plant bug: (Lygus lineolaris)

• Adults are very active and quick moving.
• They damage rhubarb by piercing their mouth parts in leaves and stalks thus causing wilting and distortion of leaves.
• This bug is a pest of new plantings.

Control measures

• Keep plantings and adjacent areas weed free.
• Avoid planting adjacent to legumes.
• If attack is severe, apply dimethoate (0.03 %) or oxy-demeton methyl (0.025 %).

Slugs

• Slugs may be a problem in plantings with heavy soils, poor drainage and in weedy situations.
• Slugs feed at night by rasping the surface of stems, leaving unsightly scars, which reduce the salability of the stem.

Control measures

• 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.

Black bean aphid: (Aphis fabae)

• Heavy population of this pest causes curling or wilting of leaves.
• There is also potential for the spread of virus by this aphid.

Control measures

• Spray malathion (0.05%) or oxy-demeton methyl (0.025 %).

Flea Beetle:

• These can cause damage to new plantings by their feeding activity on the leaves.
• They are especially active during hot dry weather.

Control measures

• Remove weed hosts, follow the phytosanitary measures and spray carbaryl (0.1%).
• Repeat spray if attack persists.