Short-stature corn requires new limit for fall armyworm control.

Producers of short-stature corn of the Delfín variety should begin controlling the fall armyworm When damage reaches 12,05% of the plants. A study conducted in the municipality of El Fuerte, Mexico, quantified linear losses of 32,515 kg/ha for each 1% of plants damaged by the pest.

The researchers evaluated seven treatments with different levels of artificial infestation of Spodoptera frugiperdabetween 0% and 25%. The DK-4050 hybrid was introduced as a regional control under natural infestation. The experiment used plots of 400 plants and manually infested each selected plant with two to three newly hatched caterpillars.

Assessments were conducted 20, 40, and 60 days after infestation. Damage levels increased with the percentage of infested plants. The severity of the attack also increased proportionally. Treatment T6, with 25% of plants infested, maintained the highest damage levels in all readings. The treatment without induced infestation recorded minimum values.

Production progressively decreased as damage increased. The highest productivity occurred in the treatment with minimal natural infestation (12.199,18 kg/ha). The lowest occurred with 24,33% of plants damaged (11.316,78 kg/ha), a reduction of 882,40 kg. The DK-4050 variety, under natural pressure of 11,42%, yielded 11.912,40 kg/ha, a performance similar to the treatment with 10% artificial infestation.

Based on the regional price of corn, at US$325/t, and the average cost of two insecticide applications, at US$127/ha, the researchers defined an economic loss equivalent to 391,6 kg/ha. Applying this value to the linear equation generated by the study, the economic limit was calculated at 12,05% of damaged plants. Above this level, insecticide application compensates for the cost of management.

The study indicates that Delfín maintains susceptibility until the beginning of grain formation, a longer period than observed in other hybrids. The authors recommend validating the economic threshold in other environments, sowing times, and natural levels of pest pressure.

Further information at doi.org/10.3390/insects16121219