DISEASES & PESTS
DISEASES & PESTS
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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.
- 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.
- 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.
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Last modified: Monday, 11 June 2012, 12:38 AM