Large plot evaluation of insecticidal control of the Mexican rice borer (Eoreuma loftini) in Louisiana, 2020

The Mexican rice borer (MRB), Eoreuma loftini, is the most destructive insect attacking sugarcane in Texas and is increasing in economic importance in Louisiana. The MRB has been expanding eastward and northward into Louisiana sugarcane production regions since 2008 and damaging infestations have been reported with increasing frequency in recent years. Insecticidal control of MRB has been evaluated in Texas sugarcane, and farmers there are spraying to control the pest after having abandoned the practice for the past 30 years. Sugarcane in Louisiana is routinely scouted for the presence of sugarcane borer (SCB), Diatraea saccharalis, infestations from late-May through early-September. Fields are sprayed if infestations exceed economic thresholds. Prevathon (chlorantraniliprole, FMC, Philadelphia, PA) has become the most widely used insecticide due to its effective and long-lasting control of the sugarcane borer. It is unknown if the chemical control strategies used for SCB will also be effective against MRB. A trial was conducted in cooperation with a commercial farmer in Vermilion Parish. The trial evaluated Prevathon at the high (20 fl oz/acre) and low (14 fl oz) labeled rates applied with a ground sprayer. A field of L 01-299 was scouted on 26 Jun 2020, and MRB infestations were determined to be 6% of stalks with larvae in the leaf sheaths, above the recommended threshold to trigger an insecticide application. The treatments were randomized to approximately 5-acre plots (20 rows, 1,900 ft long) arranged in a randomized block design with three replications. The application was made on 29 Jun 2020, with a ground sprayer with a 5-row boom delivering 20 gallons per acre. No adjuvants were included. Control was assessed on 22 Oct 2020, by taking 15 stalk samples from the front and back of each plot and recording the number of bored internodes and total internodes. Percentage bored internodes were analyzed with a generalized linear mixed model (SAS Proc Glimmix) with treatment included as a fixed effect and rep*treatment as random effects using a binomial distribution. Means were separated with Tukey’s honestly significan difference (HSD) test.

Both treatments reduced the level of MRB injury relative to the untreated check, but did not differ from each other (Table 1) (This research was supported in part by industry gifts of pesticides and/or research funding).

Louisiana, 2020.