Impact of nitrogen fertilization on Mexican rice borer (Lepidoptera: Crambidae) injury in bioenergy sorghum

The Mexican rice borer, Eoreuma loftini (Dyar), is a significant pest of sugarcane, rice, sorghum, and corn, but also threatens initiatives to expand production of bioenergy crops in the Gulf Coast region. A study was conducted in 2013 and 2014 in Jefferson County, Texas to evaluate the effect of nitrogen fertilization on E. loftini injury to three varieties of sorghum with potential for biofuel production (ES 5200, ES 5140, and M81E). Each year, four rates of nitrogen (0, 40, 80, 120 lbs N/Acre) were subjected to each sorghum variety in a replicated small-plot field experiment under natural E. loftini infestations. In 2013, differences were detected in the percentage of bored internodes across nitrogen rates, with injury increasing from 2.9 to 8.4% bored internodes across all varieties when nitrogen rates were increased from 0 to 120 lbs N/Acre. E. loftini adult emergence was substantially higher in plots with 120 lbs N/Acre for both ES 5200 and ES 5140, however this trend was not evident in M81E. Fresh weight per stalk was significantly greater at higher nitrogen rates, increasing 1.6-fold when nitrogen rates were increased from 0 to120 lbs N/Acre.  This research suggests that the level of nitrogen fertilization impacts both injury and yield losses attributed to E. loftini in bioenergy sorghum.