By Alberta Agriculture and Rural Development
Apr. 28, 2014 - When it comes to controlling ergot, the best control is prevention. Affecting all cereal crops except oats, ergot produces mycotoxins that are extremely toxic to humans and livestock.
"Although not significantly impacting yield, the low tolerance level for affected grain can cause grain rejection or downgrading at the elevator," says Neil Whatley, crop specialist with Alberta Agriculture and Rural Development. "Forage grasses and roadside grasses are also susceptible to this fungal disease. Since no seed treatments, pesticides or resistant varieties are available as control measures, prevention is the only way to manage this disease."
Ergot appears as dark, hardened resting bodies (sclerotia) in harvested grain that either fall to the ground or become harvested with the grain. Prolonged wet soils in spring and early summer promote germination of disease spores from over-wintering sclerotia in the soil. During the early part of the growing season, the disease cycle has two stages – the primary and the secondary stage.
Primary infection occurs when wind blows spores from germinating sclerotia to the tiny florets of flowering cereal crops or field edge grasses. The ergot fungus then produces another spore type in infected florets that results in a mass of spores and a sugary, sticky substance. Secondary infection happens when these spores stick to insects or are splashed by rain drops that in turn spread these spores to the florets of nearby cereal or grass heads. Prolonged wet, cloudy and cool weather not only extends the infection window but can also favour an increase of insect populations like aphids, midge and leaf hoppers that contribute to spore transfer. Sclerotia eventually develop in place of the kernels in infected florets.
"The most effective preventive measures are crop rotation and mowing field edges," says Whatley. "Since ergot bodies only remain viable for one to two years in the soil, rotation out of cereals for two years limits infection; especially do not plant a cereal crop on rye or triticale stubble. Since they can be a major infection source, field edge grasses should be mowed prior to their flowering period and nearby forage grasses should be cut or grazed before they flower in the heading stage."
Since open cereal flowers are susceptible to ergot infection, anything that extends the overall flowering period or prevents uniform crop maturity in a field enhances the risk of ergot by increasing the window of time during which infection can occur. As such, ensuring a uniform crop stand is important and can be enhanced by:
- Using a high seed germination percentage
- Avoiding seeding into cold soil
- Seeding shallow and at an even depth
- Maintaining a balanced fertilizer program
- Preventing herbicide injury to the crop including avoidance of late herbicide applications
- Using a higher seeding rate to prevent tillering
Deficiencies in copper and boron can lead to reduced pollen viability which may also extend the flowering period. Wheat and barley are normally closed flower self-pollinators; however, a reduction in pollen viability causes these normally closed flowers to open to access pollen from adjacent plants, heightening the possibility of infection. Therefore, amendments of copper and boron may help, but only if soil tests indicate a deficiency in these micronutrients.
"If a field does end up having a significant amount of ergot in cereal heads at harvest time, delaying swathing/harvesting can allow the wind to blow ergot bodies from infected crop heads prior to harvesting," notes Whatley. "If the headlands are more infected from field edge grasses, harvest and bin grain from the headlands separately.
"The early part of this growing season may not have prolonged, cool and moist weather, which increases ergot infection; however, since there are numerous viable sclerotia currently present in the soil from last year, it is important to consider preventive control methods to avoid an infestation in 2014."