The most serious of the diseases attributable to Fusarium species is ear blight, caused predominantly by the pathogens Fusarium graminearum and F. culmorum. This disease causes significant yield losses through lower thousand-seed-weights and numbers of kernels per ear. The disease also leads to a reduction of seed quality, diminishing the baking quality of, for example, wheat.
Dangerous mycotoxins
Moreover, F. graminearum and F. culmorum produce toxic metabolites in the form of mycotoxins, for example deoxynivalenol (DON). These substances are highly toxic to people and animals, even at low concentrations.
Spread of the pathogens
Fusarium pathogens overwinter as conidia and ascospores on moribund plant residues such as straw and stubble. The conidiospores are then spread by rain-splash from leaf to leaf, progressively up the stem; ascospores, which develop in fruiting bodies, are spread by wind.
Ears become bleached
Infection of ears has serious consequences. The cereal plants are most vulnerable to infection during the flowering period. The pathogen can penetrate into the tissues of flowers during this phase: if infection is particularly heavy, large amounts of mycelium can develop, which can eventually block the vascular bundles within the rachis. This prevents nutrients from reaching developing seeds situated at the tops of the ears. The result: partial or complete whiteheads.
Plant debris encourages infection
The sequence of crops in the rotation and the soil-cultivation methods used both have a significant influence on the development of infection potential. For example, short rotations (especially those involving maize) and direct seeding of cereals into stubble both favour the incidence of whiteheads. Any plant debris remaining behind after minimum cultivation strongly increases the likelihood of infection.
Soil cultivation is important
This means that besides limiting the frequency of maize and cereal crops in the rotation, the farmer can reduce the risk of infection by turning the soil thoroughly, or by at least chopping the plant residues left after harvest, and spreading them evenly in the field.
Effective fungicides are available
However, it isn’t always possible to prevent infection entirely. Warm - the optimum is about 20oC, depending on the Fusarium species - and damp weather encourages the development of these species. The critical phase is the period between flowering and ripening of cereal plants. But even during this phase, using the appropriate fungicide can keep the pathogen effectively under control.
Folicur and Proline
FolicurŽ (tebuconazole) and ProlineŽ (prothioconazole) have proven their excellent efficacy in numerous field trials. Their strength is expressed not only in terms of decreased infection frequency and disease severity, but also through increased yield and quality, and lower levels of contamination with mycotoxins.
Timing is critical
The characteristic epidemiological behaviour of the pathogen means that the time-window for applying fungicides is very small – so the timing of applications must be judged very carefully. Experience has shown that treatments should be applied between three days before, and three days after, flowering.
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