Cereals processing technology

It is now well recognised that in many areas of southern and eastern England
populations of blackgrass (Alopecurus myosuroides) have developed that are
resistant to the most commonly used herbicides for grass weed control.
Resistance has been mainly associated with continuous, or near continuous
winter cereal cropping, often established by non-ploughing techniques and
regular use of a narrow range of herbicides to control grass weeds. In general
grass weeds are more expensive and more difficult to control than broad-leaved
weeds.
2.6 Disease control
Cereal production methods 23
Cereals are prone to a range of diseases caused by micro-organisms,
predominantly fungi, which can attack the roots, stems, foliage and/or the ear,
causing substantial losses of yield and frequently having a detrimental effect on
grain quality. The presence of disease in an otherwise healthy crop is first
recognised in the field by the appearance of well defined symptoms resulting
from earlier activity on the part of the pathogen. If the disease is allowed to
progress then the pathogen itself becomes more obvious, but often more difficult
to control at this stage of its development.
Disease control has traditionally been based on cultural practices aimed at
improving the ability of the crop to resist infection or attempting to interfere
with the life cycle of the pathogen. Exploiting genetic resistance through careful
selection of varieties remains an important disease control strategy but over the
last thirty years fungicides have become an integral part of cereal production
systems in the UK.
Conditions have been identified from numerous field trials that promote the
establishment and development of pathogens on cereal crops. For winter sown
cereals, early sowing and a high soil nitrogen status in the autumn promote lush
soft tissue which can become very prone to a number of the leaf infecting
diseases such as mildew (Erysiphe graminis) and brown and yellow rust
(Puccinia spp.) with mild autumn weather. The frequency with which cereal
crops are grown in the rotation can also be a major determinant of crop
susceptibility to a range of pathogens. The most important disease in this respect
is undoubtedly take-all (Gaeumannomyces graminis) which is particularly
serious in winter wheat in second and successive crops. Until the recent
introduction of seed-based fungicides, the inclusion of a break crop of a different
species was the only practical way of keeping this disease under control.
Considerable genetic resistance to the major cereal diseases is to be found in
wheat and barley, with the exception of take-all. Selection of resistant varieties
is often the simplest and cheapest way of controlling diseases. Unfortunately
other criteria may have an overriding influence on the selection process, for
example, quality requirements or yield of grain. The emergence of new races of
pathogens may also result in an established variety losing its ability to provide
an accepted level of resistance against specific pathogens.