Fusarium in cereals - occurrence, symptoms and management
Fusarium are seedborne and soilborne fungi that colonise host plants such as cereals, maize and potatoes worldwide. The term Fusarium covers many different Fusarium species.
Fusarium graminearum (Gibberella zea) is of primary importance for cereal cultivation in Germany and is a species that results in seedling blight, foot rot and head blight, particularly in wheat. Economic damage results primarily from fusarium head blight due to the high amounts of toxic mycotoxins formed. Agronomic prevention is a vital strategy when avoiding fusarium. Potential issues with feed and foodstuffs due to increased mycotoxin levels should be mitigated in advance as much as possible.
The Fusarium fungus belongs to the Ascomycota genus (tubular fungi, of the scientific classification Pezizomycotina). These tubular fungi, including moulds and ergot, make up the largest and most species-rich group of true fungi. The tubular fungi’s classification is based on the fruiting body type. Fusarium belongs to Pyrenomycetes due to its bottle-shaped and open fruiting bodies (perithecia).
Fusarium species of varying significance
Fusarium fungi include more than 150 different species. The most significant in our local climes is Fusarium graminearum, formerly Gibberella zea, which occurs on maize and certain cereals, particularly wheat. The disease can cause seedling blight, foot rot and head blight. In cases of early and fierce infection, yield losses occur due to shrivelled grain formation. When ears are infected, the fungi form metabolic products in the grain which are toxic to humans and animals. Mycotoxin formation, in particular, deoxynivalenol (DON), nivalenol and zearalenone, causes the greatest economic damage as the necessary limits for crops intended for human consumption and as feed are often exceeded by the harvested crop. DON is also conducive to plant infection.
Fusarium culmorum produces a similar result. Since this genus does not form spores, however, and only occurs as a stage of conidia, its damage potential is usually lower. This fungus should not be ignored, however, as it can severely affect site-specific plants, particularly their roots and stems due to its persistent conidia.
Fusarium poae and Fusarium avenaceum are Fusarium species that do not produce toxins meaning they are less significant. In addition to cereals, crops such as potatoes, tomatoes and cucumbers can also act as host plants. The various Fusarium oxysporum (wilt pathogen) species are most common among these.
Occurrence and development of Fusarium
Fusarium pathogens are widespread and survive in the soil for many years. They are involved in organic substance decomposition. They can be found on the remains of dead maize and grain, and sugar beet. They favour maize stubble, however they can also survive on seeds.
Fusarium of the Graminearum species form a filamentous mycelium and tubular fruiting bodies (perithecia). The fruiting bodies contain asci (sporangia) in which eight ascospores are formed by meiosis. Plants are infected by the ascospores, which have been actively ejected from the asci. Spores are then carried on the wind to the ears. Fusarium pathogens also use the wind to access host plants located in areas where the disease is less present.
Outbreaks of Fusarium
Outbreaks of Fusarium are mainly weather dependent. Frequent rainfall or persistent high humidity combined with warm temperatures promotes occurrence. In the early stages of ear emergence, temperatures down to 16 degrees are favourable. Wheat is generally most susceptible to Fusarium during flowering. When temperatures of 25 degrees prevail for several days with similarly high humidity, outbreaks are highly likely, particularly when maize was the previous crop.
Fusarium graminearum spores land on plant flowers and infect individual ears. Spores immediately begin to form mycotoxins on the surface of the ears. The fungus also enters plants through the natural stomata. It grows along pathways to reach other spikelets and destroys water and nutrient supply.
Mycotoxin formation also inhibits protein synthesis, weakening the immune system and reducing the plant's resistance.
Fusarium infections are often, but not always, visible thanks to the pink fungal mycelium apparent on the ears. The affected areas lose their colour and become bleached. Ears become partially blighted, dusty and white. Depending on when the infection occurs and the period of colonisation, total ear infestation may occur. During the later stages, ears may also become infected with black fungus.
Management of Fusarium
To manage Fusarium, the general goal should be to minimise the risk of infection from the outset. This will mitigate any potential problems with feed and foodstuff production resulting from the increased mycotoxin levels.
The infection potential rises according to the previous crop, therefore crop rotations should be adapted accordingly. Rapeseed is the most problem-free crop to precede wheat. By contrast, maize is conducive to infection and should therefore not be sown before wheat.
Tillage also reduces the risk of infection. Intensive tillage can significantly reduce the risk. Cultivation without tillage increases the risk of infection, especially after cereals and sugar beet and particularly after maize. Non-inversion tillage is also an option. To reduce the risk of Fusarium, it is vital that the stubble is worked and intensively ploughed after harvesting. This is the only way to deprive the pathogens of their nutrition.
Varietal resistance offers another key tool when managing Fusarium. Resistant varieties are less susceptible to Fusarium and reduce the formation of mycotoxin. This can reduce mycotoxin levels by up to 25 per cent.
If conditions are unfavourable, a fungicide treatment may be necessary. Management of ear blight is only possible during flowering between BBCH 61 and 65. This can be done with a strobilurin- and carboxamide-free azole-based fungicide according to various sources.
The goal is to improve quality and reduce yield losses and mycotoxin levels. DON levels can be reduced by 50 to 70 per cent with flower treatment. This level of reduction cannot always be achieved in particularly susceptible varieties or in cultivation after a previous crop of maize.
Delaying harvesting should be avoided at all costs - the longer a grain grows, the more mycotoxins are formed. Conversely, earlier harvesting can help reduce toxic levels.
Great results with GRAINGUARD
Plants infected with Fusarium suffer from impaired water and nutrient absorption and protein synthesis can be inhibited as a result of mycotoxins. This weakens the immune system and reduces the plant's resistance.
The GRAINGUARD seed treatment addresses and strengthens those processes and properties that Fusarium affects. GRAINGUARD ingredients are specially selected to increase plant vitality, leading to stress-stable growth.
GRAINGUARD lays the necessary foundations in the first nine growth stages thanks to its specific active ingredients. For example, the organic acids contained in the seed ensure increased germination rates and seed vigour. Other substances improve field emergence.
Humic substances and selected plant extracts influence root formation, and as a rule, plants develop a larger root mass. The advantage of this is that plants are more able to tap into the soil, including the stocks of water and nutrients located there. They benefit from this increase in nutrients, and this forms the ideal foundation for plant growth. The immune system also benefits, and the plant's defences are fundamentally strengthened. With all these benefits, plants are much more resistant to pests and do better thanks to GRAINGUARD - not just during the early growth stages, but over their entire life cycle.
Read more about GRAINGUARD.