A review of leguminous fertility-building crops, with particular ...

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A review of leguminous fertility-building crops, Defra project OF0316 2. Rotational aspects Table 2.7. The relative importance of invertebrate pests in fertility-building and catch crops. (*** Major pest frequently capable of causing yield loss; ** Often present but only occasionally affects yield; * Sporadic, only rarely affects yield) Crop Pest Importance Comments Peas and beans (continued) Trefoils, vetches and other legumes Bryobia mites * Rarely of commercial importance Pea cyst nematode ** Localised, particularly east of England Stem nematode ** Both oat-onion and giant bean race important Pea moth * Has been bred on meadow vetchling and tufted vetch Bryobia mites * Will feed on a range of legumes Pea cyst nematodes * Will multiply on wild vetches Stem nematodes * Risk dependent on race present Stubble turnips Flea beetles *** Potential damage in dry springs (Phyllotreta spp.) and summer Cabbage stem flea beetle ** Turnip gall weevil * Negligible affect on yield Cabbage root fly ** Primarily risk from third generation flies Beet cyst nematode * Peach potato aphid * Potential virus transmission Mustard Turnip gall weevil * Beet cyst nematode * Mustard beetle * Sporadic pest, invades crops in spring 2.3.4. The potential for pest attack in crops following fertility-building crops The risk of carry over of pests from a fertility-building crop to subsequent cereal or other arable and horticultural crops is summarised in Tables 2.8 and 2.9, respectively. Further detail on specific interactions between the fertility-building crop and subsequent crop are provided in the following paragraphs. Carry over of pests from clover Slugs, leather jackets and wireworms and are the major pests which could pose a threat to any subsequent crop following a clover ley. Slug damage is reduced in well-consolidated seedbeds with a fine tilth, where there are fewer air spaces in the soil structure in which the slugs can move and feed. Consequently, avoidance of slug damage often depends on what success the farmer has in preparing a fine and firm seedbed. Cereal crops sown in the early autumn are generally less vulnerable to slug attack than later sowings. Early sowing results in rapid germination, less exposure to the risk of grain hollowing and the establishment of plants that are better able to outgrow slug damage than smaller and slower growing plants of later sowings (Port & Port, 1986). However, early Written by S Cuttle, M Shepherd & G Goodlass Page 38
A review of leguminous fertility-building crops, Defra project OF0316 2. Rotational aspects sowing can result in increased risk of BYDV infection so the relative importance and risk from each pest must be assessed on a local basis. The depth of sowing can also influence the amount of slug damage (Glen et al., 1990 & 1992). Seed sown at 22.5 cm was more vulnerable to attack than seed at 45 cm depth as slug activity is usually greatest near the soil surface. Deeper sowing thus made the seed less accessible to slugs feeding on or near the soil surface. However, excessively deep sowing (more than 5 cm) may have a detrimental effect by slowing crop emergence and establishment. Consolidation of the seed bed by rolling can reduce slug damage by causing larger soil aggregates to break down into finer particles, or by reducing the size of air spaces between soil particles (Stephenson, 1975; Davis, 1989). Provided that consolidation does not result in the seeds being made more accessible to slugs by decreasing the depth of burial, evidence suggests that consolidation can considerably reduce slug damage to wheat seeds (Glen, 1993). To minimise the risk of carry over of leatherjackets, early ploughing of the sward, before crane flies lay their eggs during August and September, is recommended. Ploughing will also tend to kill leatherjackets by mechanical damage and by increasing their chance of exposure to predators such as birds and small mammals. However, ploughing could increase the risk from wheat bulb fly if undertaken in July or early August. Improving the drainage of wet, low lying fields, which favour the survival of leatherjackets, would assist in reducing attack from this pest. Also, as with slugs, early sown crops are likely to withstand damage better than backward, late sown crops. There is little that can be done, by cultural means, to reduce the number of wireworms in old swards. Ploughing will help expose wireworms to predation by birds and small mammals. The time of ploughing is also important. Autumn ploughing for winter cereals does little to reduce the wireworm populations (Gair, 1982). However February or March ploughing, followed by a full fallow, causes a greater reduction in numbers than June or July ploughing followed by a partial (bastard) fallow. However, fallowing in July and August may increase the risk of wheat bulb attack in districts where this pest is established. If soil conditions allow, rolling is useful in cases of wireworm attack as it restricts the movement of the pests and encourages plants to grow away from damage. Peas and beans tend to be less susceptible to wireworm damage than most other crops. Both clover and oats can be attacked by stem nematode. The red clover race of stem nematode can attack kidney vetch, and strawberry and the white clover race only attacks alsike to any significant effect. The oat-onion race, if present, will potentially infest oats and alliaeceous vegetables such as onions and leeks. Carry over of pests from grass/legume leys The potential for carry over of slugs, leather jackets, wireworms and stem nematodes from mixed swards is very similar to that from clover and is described above. Additional pests are chafers, aphids and frit fly. Pests such as aphids and frit fly are a particular risk to cereal crops that follow a grass/clover ley. A natural reservoir of barley yellow dwarf virus (BYDV) exists in wild and cultivated grasses. Infestation of cereals following grass/clover leys can occur via the “green bridge” Written by S Cuttle, M Shepherd & G Goodlass Page 39
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