Herbicides and Plant Physiology. Andrew H. Cobb. Читать онлайн. Newlib. NEWLIB.NET

Автор: Andrew H. Cobb
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Биология
Год издания: 0
isbn: 9781119157700
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to the crop, e.g. wild oats (Avena fatua) in cereal crops. Similar problems are encountered in the contamination of oilseed rape seed with seeds of weed species such as cleavers (Galium aparine). Where a proportion of the seed is saved for planting in subsequent seasons, this can cause a large increase in weed infestation. Contamination by poisonous seeds, such as darnel (Lolium temulentum) and corncockle (Agrostemma githago) in flour‐forming cereals is also unacceptable and once led to vastly increased costs of crop cleaning. Such cleaning, however, has meant that these weeds are now probably extinct in agroecosystems in the UK. A further example that still causes major problems is black nightshade fruit (Solanum nigrum) in pea crops (Hill, 1977). In this case, the poisonous weed berry is of similar size and shape to the crop and so must be eradicated. Although grazing animals avoid poisonous species in pasture (e.g. common ragwort, Senecio jacobea), they may be difficult to avoid in hay and silage, and some species, notably the wild onion (Allium vineale), can cause unacceptable flavours in milk and meat.

       1.4.4 Weeds as reservoirs for pests and diseases

      Source: Hill, T.A. (1977) The Biology of Weeds. London: Edward Arnold.

Pathogen or pest Weed Crop
1.Fungi
Claviceps purpurea (ergot) Black‐grass (Alopecurus myosuroides) Wheat
Gaeumannomyces graminis (take‐all) Couch (Elytrigia repens) Cereals
Plasmodiophora brassicae (clubroot) Many crucifers Brassicas
2.Viruses
Tobacco ringspot Dandelion (Taraxacum officinale) Tobacco
Cucumber mosaic Chickweed (Stellaria media) Many crops
3. Nematodes
Ditylenchus dipsaci (eelworm) Chickweed (Stellaria media) Many crops
Spurrey (Spergula arvensis)
4. Insects
Aphis fabae (black bean aphid) Fat hen (Chenopodium album) Broad and field beans

      In 1994 and 1995 there were several severe outbreaks of the disease brown rot in potato in several European countries, especially in The Netherlands, which was possibly exported to other countries via infected seed potatoes. This extremely virulent pathogen (Pseudomonas solanacearum, syn. Burkholderia solanacearum, syn. Ralstonia solanacearum) causes a vascular ring rot in the developing tuber and causes a major loss of yield. Although often considered a soil‐borne organism, it was not found to persist for long periods in the soil following the harvest of infected crops. However, it was found to survive in the aquatic roots of infected woody nightshade (Solanum dulcamara) growing at the edge of irrigation channels. Thus, it may be the case that the pathogen overwinters in this wild host and is leaching into watercourses used to irrigate the crop, thus spreading the disease. This perennial plant is now being eradicated from potato‐growing areas. Several other species could also act as alternative hosts to the pathogen, including Solanum nigrum and Tusilago farfara, but further work is needed to confirm this.

      Knowledge of the biology of a weed species is essential to the design of management strategies for that weed. An understanding of the life cycle of a species can be exploited in order to identify vulnerable times when weed management and control might prove more successful.

       1.5.1 Growth strategies

      Ruderals are the most successful