Ergot
Ergot (claviceps purpurea) affects many
cereals and grasses. Rye and triticale are more susceptible than wheat and
barley.
Cool damp weather in
late spring and early summer favours ergot germination as well as prolonging
the flowering period of cereals and grasses thus increasing the risk of
infection.
Ergot
is more of a problem when florets stay open for a lengthy time. This may be an
effect of variety but may also be due to poor nutrition of the crop. Nutrients,
which can affect ear fertility, include Boron and Copper, both of these
elements are becoming more deficient in soils as they are removed by crops or
by leaching and not replaced.
Research
in Canada, Australia and Kenya has shown that copper deficient cereals are more
susceptible to ergot. Work in the US and Canada has shown that the presence of
Ergot is strongly correlated with soils which are low in copper, or with
management practices that cause copper deficiencies.
Copper
deficiency is associated with low protein levels in cereals and ripening may be
delayed. Genotypes with high protein concentrations in the grain have been
shown to respond more sensitively to copper deficiency than genotypes with low
grain protein concentrations (Nambiar 1976)
Copper
is also implicated in the production of polyphenol oxidases, which are involved
in the balance of phytohormones, the lignification of cells and in defence
responses to viral and fungal infection.
Copper
deficient plants have thin cell walls with little lignin thus making entry of
disease easier. Copper deficient plants have been shown to be more susceptible
to Take-all, mildew and possibly septoria.
The
formation of flowers and fruit may be more seriously affected than growth since
the synthesis of compounds needed for these organs is inhibited at an early
stage. Pollen may become sterile and ovaries may be reduced in size.
High
phosphate levels inhibit uptake of copper if soils are low. Heavy dressings of
potash, high pH soils and high humus levels all reduce uptake High N levels
delay the translocation of copper from older leaves to the growing point i.e.
the ear thus enhancing copper deficiency.
HGCA reported that 5% of land in England and Wales and 30% of land in
Scotland was deficient in Copper. Results from soil analyses suggest that these
figures are now much higher.
Copper
deficiencies can also result in later maturity of the crop.
Boron
applications have also been shown to reduce the incidence of ergot in barley.
Boron is known to affect the number of flowers produced, the retention of
flowers, pollen germination, pollen tube growth and seed and fruit development.
For normal growth and maturity there must be a steady supply of boron to the
meristems. Anything that interrupts this steady supply will cause a malfunction
of the meristem Low or deficient levels of boron may cause flowers to fail to
pollinate by inhibiting anthesis thus exposing them to ergot spores. Since
boron is poorly translocated within the plant a continuous supply or repeated
applications gives best results.
Boron
can leach from soils, particularly when rainfall is heavy! And research has
shown that as levels of N and K fertilisers are increased more boron is
required. Although cereals are regarded as not requiring boron, they can remove
as much boron per acre as 20t/acre crop of cabbages.
Wet
growing conditions induce shallow rooting in the topsoil layers €“ this is where
copper and boron are most deficient.Any herbicides/growth regulators, which affect rooting, may also affect
nutrient uptake.
Programme
Research
in Canada has shown that applying Cu to the soil can reduce levels of ergot.
Plants
generally respond best when nutrients are available throughout the growing
season, the best way to achieve this constant availability is by applying
granular B and Cu to the soil. This also eliminates the risk of scorching the
growing crop.
Copper
oxysulphate granules (15%Cu,) and boron granules (10% B) may be broadcast on
the soil at rates of 5-10kg for B and 10-20kg/ha for Cu(depending on soil levels) in autumn in
order to start correcting the soil deficiency.
Otherwise
where copper is known to be low apply a spray as soon as conditions allow.
Further applications at the late tillering stage and early boot are likely to
benefit the crop. Applications after the early boot stage can be detrimental.
Where
B is deficient apply B at these growth stages