Lesser cornstalk borer
· Wheat · Sorghum · Maize · Peanut
Caterpillars of Elasmopalpus lignosellus can feed on maize leaves but the bulk of the damage is done when they tunnel into the base of stalks and stems, usually during the late seedling stage. hey eat the stems' inner tissues which is replaced by abundant larval frass visible around the entry points. This group of symptoms is commonly known as dead heart. Plants are usually deformed, and show a stunted growth with few ears. Impaired water and nutrient transport leads to wilting and whithering of the plants, as well as lodging or death in some cases. Lesser cornstalk borers are adapted for hot, dry conditions, and are more damaging following unusually warm, dry weather.
The moths vary in color depending on regional and environmental factors. The males' forewings are brownish-yellow with scattered dark spots that are tighly-packed near the margins, where a broad darker brown band is found. The females' front wings are charcoal black, with reddish or purplish scales. The hindwings of both sexes are transparent with a silvery tinge. Females lay greenish eggs below the dry soil surface, or at the base of stems. The larvae are thin and hairy, with striated alternate purple and whitish bands encircling the body. They wiggle violently when disturbed. They dwell in tubes or tunnels made of silken webbing just below the surface of the soil and come out to feed on roots and plant tissues. Dry years or well-drained sandy soils are particularly beneficial for the pest. Irrigating the crop at 80% of field capacity actually helps to control the population.
There are many predatory enemies, but the larvae's well protected habitat inside the stems and stalks makes an effective control difficult. In some cases, the parasitoid braconid wasps Orgilus elasmopalpi and Chelonus elasmopalpi can change the dynamics of the population. The use of bio-insecticides based on the nuclear polyhedrosis virus (NPV), the fungi Aspergillus flavus and Beauveria bassiana or the bacterium Bacillus thuringiensis can help to control the infestation.
Granular or liquid formulations can be used in the furrows to kill the larvae. Most effective in maize are treatments with products containing carbosulfan, carbofuran, tiodicar and furatiocarb. Spraying the leaves with chlorpyriphos, carbofuran and tiodicarb also helps to control the infestation.
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