In the most severe cases, maize eyespot can reduce yields by 80%, but in a more typical infection yield loss would be up to 25% – still a very considerable penalty.
Infections at this time of year need more careful consideration; the disease lifecycle happens rapidly given the right conditions, making earlier infections the ones to approach more cautiously.
Simon Trenary, an agronomist with Countrywide, explains what to look for and how to deal with it.
Eyespot produces fungal stroma, or resting bodies, which over-winter in maize debris and then germinate the following spring to produce conidia. These conidia are then dispersed by both wind and rain, to infect new crops meaning that infections can be moved beyond last season’s fields to nearby crops.
The fungus is specific to maize, is a foliar leaf spot and is not related to the cereal eyespot pathogen.
The fungal stroma germinate as soon as the temperature reaches 10C in the spring, with maize plants being at their most susceptible when temperatures are 10-12C and leaves are wet for seven hours continuously.
Cold, wet seasons tend to lead to relatively high levels of infection, which is perhaps why the disease is rearing its head again this year.
How do you identify it?
The disease begins with small yellow lesions within a brown margin, or “halo” – with the paler parts of the leaf spot being translucent, when held up to the light.
When the conditions remain cold, wet and/or windy, these spots multiply and grow, eventually joining up with one other to cover the whole of the leaf – ultimately killing it.
Once green leaf area has been lost, grain fill will cease and yield loss will be incurred; feed quality will be reduced.
Is there any need to take action?
Eyespot tends to be a regional disease, so if you haven’t got it – and there are crops that are disease free at the moment – or infection levels are very low, just keep an eye on your crops.
The disease tends to be very sporadic in nature and often builds from quite small patches within fields, so be aware that you will need to get right into the crop to check for infections.
Do keep an eye on your crops though; eyespot can appear rapidly in fields, going from disease-free to a serious infection in two to three weeks.
Remember, when the crop gets stripped of green leaves, the plant will have little or no ability to fill its cobs.
How do I deal with a crop at this stage of the season, if it is infected?
If the disease begins to become established at a relatively early stage of the season – with harvest still eight weeks or more away – you may need to consider applying a fungicide.
Any damage that is inflicted by a self-propelled sprayer – mostly restricted to the headlands, is likely to be less damaging to overall yield than allowing the crop to be defoliated; you’ll need to weigh this up on a field-by-field basis.
What can I do for next season?
Cultural control is the key weapon against eyespot. Burying the trash as early as possible after harvest will minimise levels of infection.
Deep ploughing offers the highest levels of control, preventing sporulation and leading to stromas rotting