Sugarcane borer resistance in sugarcane as affected by silicon applications in potting medium

The sugarcane borer, Diatraea saccharalis (F.)(Lepidoptera: Crambidae) is the most important insect pest of sugarcane (interspecific hybrids of Saccharum) in the Americas, and the key insect pest of sugarcane in Louisiana. Although the release of borer resistant varieties is sporadic in Louisiana, planting them, when available, is an important tactic in the season-long control of this pest. One approach to ameliorate yield losses associated with planting susceptible sugarcane varieties would be to increase silicon (Si) content in the sugarcane plant. Increasing the level of Si in the host plant has been shown to increase resistance to several species of stem borers. We conducted a greenhouse experiment to determine the response of sugarcane to calcium silicate amendment using the sugarcane borer susceptible variety HoCP 96-540 and the borer resistant variety L 99-226. Four levels of Si were evaluated at equivalent rates of 0, 1, 2, and 4 Mg Si ha-1. Resistance was measured by counting the number of internodes bored by sugarcane borer larvae, the cumulative length of borer tunneling, the number of inoculations required to establish a larva, and the weight of individual larva recovered. All measurements were taken after 14 days of feeding. We did not detect any significant differences in plant Si content among the different amendment levels. However, we did see a significant difference among the main effects of variety and silicate for number of internodes bored, and for the main effect of silicate for the number of inoculations required to establish a larva. Silicon reduced bored internodes in the susceptible variety HoCP 540 by 45%, and 40% in the resistant variety L 99-226. Also, after supplementing with Si, an additional inoculation was required to establish larvae, e.g. from 2 to 3 inoculations. No significant differences were detected for the other response variables measured; however, there were consistent trends in these data. In general, larvae recovered after 14 days of feeding on the plants supplemented with Si weighed 130% less than those feeding on plants not supplemented with Si. The addition of Si reduced tunneling within the stalk by approximately 25%. This study indicates that supplementing sugarcane fields with Si will increase resistance to the sugarcane borer and that further field studies are warranted.