STUDIES ON THE CEREAL ECOSYSTEM
185
changes in crop husbandry must have been counterproductive. Some
of the underlying reasons appear to be biological problems of intensification, and recently new attempts have been made to alleviate the
simplification which this entails by mixing varieties, by the use of
break crops and by improved hygiene, but none of the systems has been
carried out for long enough to permit any long-term predictions.
It seems that ecologists cannot really help from their experience in
other ecosystems except to follow Southwood (1972) and advise
“proceed with caution”. One ecological concept in need of urgent
quantitative attention is the Elton concept (e.g. Elton, 1966) that
complex ecological systems are more stable. May (1971) has concluded
from valuable studies of mathematical models that the issues can only
be sorted out by real ecological data. Way (1973) has considered the
general validity of the Elton concept and concludes that it has little or
no value in applied ecology and especially in problems of biological
control. Our work supports Elton and we have generally felt that there
is considerable virtue in complex trophic connections; other things
being equal, fewer pesticides are required. Several instabilities have
resulted from the recent simplification of the cereal ecosystem even
though it is still very complex, and it is apparent that cereal aphids,
grass weeds and the pathogenic fungi have reduced the ecological
stability of the system. New pesticides are being rapidly introduced to
control these and to reassert stability even before the long-term
effectiveness of the first generation of pesticides is assured.
Long-term methods of controlling cereal leaf diseases have yet to be
developed; even the production of disease-resistant varieties may
bring new problems. For example, leaf blotch on barley became
prominent with the introduction of mildew-resistant varieties, about
ten years ago (Home, 1969). Thus the control of one foliar disease may
be a factor in promoting the spread of another. The pattern of physiological races and the development of other new races of foliar diseases
may be altered by the introduction of chemicals to control disease.
Noble et al. (1966) noted that the organo-mercury compound which
on oats had previously controlled leaf spot, Helrninthosporium avenue
Eidam., was now ineffective. Schroeder and Prowidenti (1969) also
reported that a race of powdery mildew resistant t o the systemic
fungicide, benlate, had already developed on cucumber plants.
There will of course be problems associated with any change. On the
one hand, those varieties of wheat with the greatest tillering capacity
were those best able to tolerate and recover from wheat bulb fly
attack (Lupton and Bingham, 1967) but on the other, the same
varieties also favoured the survival of this pest (Raw, 1967). The
same principle appears to apply to the frit fly, 0. frit L. (Vickerman,
185
changes in crop husbandry must have been counterproductive. Some
of the underlying reasons appear to be biological problems of intensification, and recently new attempts have been made to alleviate the
simplification which this entails by mixing varieties, by the use of
break crops and by improved hygiene, but none of the systems has been
carried out for long enough to permit any long-term predictions.
It seems that ecologists cannot really help from their experience in
other ecosystems except to follow Southwood (1972) and advise
“proceed with caution”. One ecological concept in need of urgent
quantitative attention is the Elton concept (e.g. Elton, 1966) that
complex ecological systems are more stable. May (1971) has concluded
from valuable studies of mathematical models that the issues can only
be sorted out by real ecological data. Way (1973) has considered the
general validity of the Elton concept and concludes that it has little or
no value in applied ecology and especially in problems of biological
control. Our work supports Elton and we have generally felt that there
is considerable virtue in complex trophic connections; other things
being equal, fewer pesticides are required. Several instabilities have
resulted from the recent simplification of the cereal ecosystem even
though it is still very complex, and it is apparent that cereal aphids,
grass weeds and the pathogenic fungi have reduced the ecological
stability of the system. New pesticides are being rapidly introduced to
control these and to reassert stability even before the long-term
effectiveness of the first generation of pesticides is assured.
Long-term methods of controlling cereal leaf diseases have yet to be
developed; even the production of disease-resistant varieties may
bring new problems. For example, leaf blotch on barley became
prominent with the introduction of mildew-resistant varieties, about
ten years ago (Home, 1969). Thus the control of one foliar disease may
be a factor in promoting the spread of another. The pattern of physiological races and the development of other new races of foliar diseases
may be altered by the introduction of chemicals to control disease.
Noble et al. (1966) noted that the organo-mercury compound which
on oats had previously controlled leaf spot, Helrninthosporium avenue
Eidam., was now ineffective. Schroeder and Prowidenti (1969) also
reported that a race of powdery mildew resistant t o the systemic
fungicide, benlate, had already developed on cucumber plants.
There will of course be problems associated with any change. On the
one hand, those varieties of wheat with the greatest tillering capacity
were those best able to tolerate and recover from wheat bulb fly
attack (Lupton and Bingham, 1967) but on the other, the same
varieties also favoured the survival of this pest (Raw, 1967). The
same principle appears to apply to the frit fly, 0. frit L. (Vickerman,