Age-Specific Susceptibility of Sugarcane Internodes to Attack by the Mexican Rice Borer (Lepidoptera: Pyralidae)

Abstract

The time required for sugarcane (Saccharum spp.) to grow one internode was estimated to be 10 d. In 1983, the largest increase in bored internodes occurred in 100d-old internodes. The percentage bored internodes (cumulative with internode age) increased with internode age until internodes were 70-80 d old, then remained constant near 55% bored internodes. In 1984, the percentage bored internodes increased from 7% in 100d-oldinternodes to 24% in 70-d-old internodes and remained constant. Using nonlinear regression, the estimated age at which internodes were no longer susceptible to Mexican rice borer was 72.3 and 70.0 d in 1983 and 1984, respectively. Internodes were most prone to attack by the Mexican rice borer during the first 70 d after initial formation. Discussion of possible reasons for the susceptibility of internodes ≤ 70 d old is provided. Results reinforced the strategy of making pest management decisions based on estimates of Mexican rice borer larval densities in leaf sheaths and internode age distribution. Leaf sheath infestation threshold levels should be increased 70 d after formation of the first 10 internodes.