Maize
Stunt of Maize
Spiroplasma kunkelii
Bacteria
In a Nutshell
- Wilting of leaves, yellowing of their margins.
- Reddening of tips.
- Severe stunted growth.
- Bushy appearance - short internodes, multiple ear shoots.
Can also be found in
Maize
Symptoms
Usually the first noticeable sign of an infection by S. kunkelii is the wilting of leaves and the yellowing of their margins. This is followed by the reddening of older leaves, starting from the tip and later extending to the rest of the tissue. Some 2-4 days after the appearance of these symptoms, small chlorotic spots appear at the base of young developing leaves. As they grow, these spots coalesce and turn into stripes that run along the veins, often up to the tip. Plants infected at early stages are severely stunted, with twisted and distorted leaves and very short internodes. Multiple ear shoots and new tillers may develop, sometimes as many as 6-7 on a single plant, giving it a bushy appearance. Ears are smaller than usual and do not fill properly, often with loose grains.
Recommendations
Organic Control
There is no direct biological treatment to control S. kunkelii. Some bioinsecticides containing parasitic fungi species such as Metarhizium anisopliae, Beauveria bassiana, Paecilomyces fumosoroseus and Verticillium lecanii can be used to control acute infestation of planthoppers.
Chemical Control
Always plan an integrated approach with preventive measures and biological treatments if available. There are no chemical treatment to control this disease. Insecticide treatments to reduce leafhopper populations are generally not recommended. Therefore, preventive measures are key to avoid the incidence of both leafhoppers and stunt of maize.
What caused it?
Symptoms will depend on the variety of maize and the altitude. They are caused by Spiroplasma kunkelii, a bacterial-like organism that only infects maize plants. A number of leafhoppers, e.g. Dalbulus maidis, D. eliminatus, Exitianus exitiosus, Graminella nigrifons and Stirellus bicolor may carry this pathogen during their overwintering period. When they emerge in early spring, they start to feed on plants and transmit the pathogen. Disease symptoms usually appear about 3 weeks after the maize plant is first infected. Not surprisingly, the disease is most severe during the summer season, when leafhopper populations are very high. However, it can also occur in maize planted in spring.
Preventive Measures
- Plant early to avoid peak populations of leafhoppers.
- Remove volunteer plants during the off-season.
- Use reflective plastic mulch to repel the adult leafhoppers.
- Control insecticide use as this can affect beneficial insects.
- Maintain a corn-free period over the winter months.
- Plan a crop rotation with non-susceptible crops (this will break the life cycle of the insect).
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