Evaluation of Nematicides for Management of Plant-Parasitic Nematodes in Sugarcane

Plant-parasitic nematodes (PPN) are an understudied threat in sugarcane production. Previous survey work showed that Tylenchorhynchus (stunt nematode), Pratylenchus (lesion nematode), Mesocriconema (ring nematode), and Helicotylenchus (spiral nematode) are the primary PPN genera found in sugarcane fields in Louisiana. This study evaluated the impact of nematodes on sugarcane growth and the effect of nematicides on nematode population densities. Greenhouse studies were conducted using soil collected from multiple sugarcane fields with moderate PPN infestation levels to determine the nematode impact on sugarcane growth and nematicide efficacy. Field soil collected from each site was subjected to four treatments: an untreated and sterilized control, ethoprop (Mocap 15G), and fluensulfone (Nimitz). After three months in a greenhouse, PPNs were extracted from soil and roots to quantify nematode population densities. Plant growth was evaluated by measuring shoot height, number of tillers, and total biomass. Sterilized soil significantly increased sugarcane growth suggesting that PPNs likely negatively influenced sugarcane production in Louisiana. Both nematicides showed the potential to suppress PPNs on sugarcane. A field experiment evaluated the efficacy of nematicide formulation and application frequency on nematode population development and sugar yield in a newly planted sugarcane field. The trial consisted of six treatments: (1) untreated control, (2) ethoprop applied once, (3) fluensulfone applied once, (4) fluensulfone applied twice, (5) cyclobutrifluram once, and (6) cyclobutrifluram twice. During the cropping cycle, PPN soil population densities increased with crop age. Cyclobutrifluram reduced lesion nematode densities in soil and roots regardless of application frequency, while stunt nematode populations were reduced only with two applications of fluensulfone or cyclobutrifluram. No differences were observed in sugar yield and cane tonnage. Additional greenhouse experiments were designed to evaluate the efficacy of the three nematicides under more controlled environmental vii conditions. The greenhouse experiment did not show the potential effectiveness of fluensulfone and cyclobutrifluram observed in the field trial. In conclusion, the efficacy of nematicides in this study varied depending on nematode genera and application frequency. No significant yield differences were observed during the plant-cane year however, differences may become apparent in the following years as nematode population densities increase in untreated soil over time.