Ammonium Nonanoate Broadcast Application Over Onions.

Ammonium nonanoate occurs in nature and is primarily formed from biodegradation of higher fatty acids.  Racer (40% ammonium nonaoate) is a potential contact herbicide for weed control in organic crop production. Field research was conducted in southeast Oklahoma (Atoka County, Lane, OK) to determine the effect of broadcast over-the-top applications of Racer on weed control efficacy, crop injury, and yields.  Intermediate day, sweet onion cvs. ‘Candy’ and ‘Cimarron’ were transplanted into 2 rows per 6 ft-wide by 10 ft-long raised beds.  The experiment included 8 weed control treatments (3 application rates at 2 hand-weeding levels, plus an untreated weedy-check and an untreated weed-free) with 4 replications.  Nutsedge (Cyperus esculentus L.) and grass weeds were removed from all plots, including the weedy-check, to investigate the impact of ammonium nonanoate on the broadleaf weeds.  Racer was applied as an over-the-top broadcast application at three rates, 7.5, 10, and 15% v/v, at  44 days after transplanting using a tractor mounted CO₂ sprayer equipped with four extended range, stainless steel, 0.30 gallons/min nozzles on 20-inch spacings at a spraying height of 19 inches at 35 gpa.  The two weed control treatments within each application rate involved no hand-weeding, where the uncontrolled weeds were allowed to grow, or a season-long hand-weeding, where all weeds were removed. Broadcast applications of Racer at 7.5 and 10% produced poor (45% or less) broadleaf weed control, while Racer at 15% provided good (≥80%) weed control.  Onion injury increased as Racer application rate increased with no visual injury by 18 days after treatment.  Although, crop injury and lack of weed control from Racer did reduced crop yields, Racer at the lowest rate produced a yield advantage compared to the untreated weedy-check.  If the Racer’s application method can be modified to reduce crop injury, the higher application rate has potential to make significant impact on broadleaf weed control in spring-transplanted onions.