Maize
Maize Bushy Stunt Phytoplasma
Phytoplasma asteris
Bacteria
In a Nutshell
- Leaf margins show chlorosis and older leaves show red discoloration.
- Plants are stunted with an abnormally number of shoots that give them a bushy appearance.
Can also be found in
Maize
Symptoms
Severity of symptoms depends on the variety of maize plant and the stage of infection. Usually, a yellowing of the margins of whorl leaves and a red coloration of older leaves are the first signs of an infection by P. asteris in maize. These symptoms intensify as the disease progresses, and eventually the margins of leaves frequently acquire a torn or tattered appearance. The plant displays a bushy appearance as lots of additional ear shoots and tillers appear. Shortening of the internodes and stunting become apparent. Male inflorescences are often either not formed or are barren. Plants have either no ears or a proliferation of ears, which produce little or no grains.
Recommendations
Organic Control
Bioinsecticides based on the parasitic fungi Metarhizium anisopliae, Beauveria bassiana, Paecilomyces fumosoroseus and Verticillium lecanii may be used to control the population of leafhoppers. Parasitic insect species such as Anagrus atomus may also be used for this purpose. Beneficial insects such as ladybugs and lacewing are voracious predators of both the egg and larval stage.
Chemical Control
Always consider an integrated approach with preventive measures and biological treatments if available. Use contact insecticides to keep leafhopper populations under control. This can greatly reduce the incidence of the disease when maize plants are young. However, in most maize-growing regions, this practice is often not economically feasible.
What caused it?
The symptoms are caused by the bacterium Phytoplasma asteris, a pathogen of maize that is spread naturally by several leafhoppers, among others Macrosteles quadrilineatus. It is also transmitted via infected plant material (seedlings or grafts), but not by seeds. These leafhoppers can also pass on the pathogens to a number of host plants, among others the parasitic "dodder" (Cuscuta spp.). High temperatures contribute to a worsening of the symptoms, while cool weather usually results in no or little effect. Early infections are also much worse in terms of symptoms and the consequences on yields.
Preventive Measures
- Use resistant or tolerant varieties, if available.
- Make sure to use healthy plant material from certified sources for planting only.
- Do not plant maize all year round.
- Avoid to plant maize under irrigation during the dry season.
- Monitor the field regularly for signs of the disease.
- Remove infected plants as soon as symptoms are visible.
- Practice a thorough control of weeds in and around the field.
- Keep fields fallow for several weeks or a few months to break the cycle of the insect vectors.
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