Examination of Pre-emergence Control of Johnsongrass in Sugarcane Seedlings

Abstract

Sugarcane is susceptible to many diseases and insect pests; therefore, to maintain high sugar yield new varieties must be developed. Producing new varieties contributes to the overall crop success through enhanced yield, insect and/or disease resistance, cold tolerance, and ratooning ability. However, unlike conventional sugarcane, which is vegetatively propagated, new sugarcane varieties are produced from true seed. These seedlings are more susceptible to herbicidal injury and weed competition than conventional sugarcane. For sugarcane seedlings to succeed, weeds must be controlled therefore, the most effective herbicide program with regards to seedling safety must be implemented. The objectives of this research were to determine the safety of several preemergence (PRE) herbicides on sugarcane seedling crosses and to evaluate their efficacy in controlling seedling johnsongrass. Field studies were conducted at the LSU AgCenter’s Sugar Research Station in 2019 and 2020 to evaluate crop injury, seedling mortality, and yield of ten sugarcane crosses against seven PRE herbicide treatments applied directly after seedlings were transplanted into the field. Of the seven herbicide treatments evaluated, three of the treatments contained the active ingredient S-metolachlor which was labeled for use in sugarcane production in 2018. Results revealed that metribuzin (1.68 kg ha-1) was the only treatment that significantly increased sugarcane seedling mortality at 90 days after the transplanting procedure. Supplementary experiments were conducted in 2020 at the LSU AgCenter’s Sugar Research Station to test the efficacy of these treatments in controlling seedling johnsongrass. Plots were overseeded with johnsongrass seed and were shallowly tilled prior to herbicide application. Johnsongrass emergence was counted 7, 14, and 28 days after treatment (DAT), and johnsongrass dry weight was measured 28 DAT. Results showed that pendimethalin and metribuzin provided the best control of johnsongrass seedlings, and control with S-metolachlor was not as sufficient. Based on the results of these studies, pendimethalin at 2.32 kg ha-1 is a sound option for controlling seedling johnsongrass without compromising the survival of newly established sugarcane.