|Shrefler, James - OKLAHOMA STAE UNIV.|
Submitted to: Horticulture Industries Show
Publication Type: Proceedings
Publication Acceptance Date: February 9, 2003
Publication Date: March 1, 2003
Citation: Webber III, C.L., Shrefler, J., 2003. Weed control options for transplanted onions. Proceedings of the 22nd Annual Horticultural Industry Show. p. 112-115. Interpretive Summary: Oklahoma and Arkansas sweet onion producers need additional options for controlling weeds within the crop row that mechanical cultivation can not eliminate when removing the weeds between rows. The objective of this field research was to determine the effect of 21 weed control treatments on weed control and onion yields for spring transplanted onions (Hybrid Yellow Granex PRR) in southeast Oklahoma. The research investigated both organic [Corn Gluten Meal (CGM)] and inorganic (pendimethalin and oxyfluorfen) herbicides applied on March 15, 2002, the day after transplanting. Herbicide applications included 3 application rates for each herbicide (pendimethalin, oxyfluorfen, and CGM), 3 tank mixes with pendimethalin and oxyfluorfen, and a series of weedy-check and weed-free treatments to serve as experimental controls for comparisons. Heavy weed pressure, combined with decreasing weed control across the season, produced low broadleaf and total (broadleaf and grass) weed control at harvest. Pendimethalin applications, either alone or with oxyfluorfen, produced greater percent grass control and marketable yields than oxyfluorfen or CGM. As the grass weeds were controlled by pendimethalin, the broadleaf weeds compensated by increasing their growth. The yield advantage for pendimethalin was probably the result of early season weed control that was not totally apparent at harvest. The success or failure of these specific weed control treatments will need to be further evaluated during a second year of the experiment.
Technical Abstract: As interest in sweet onion production has grown in Oklahoma and Arkansas, so has the realization that uncontrolled weeds can result in a total loss of marketable onion production. Although mechanical weed control can successfully control weeds between rows, producers need reliable methods for controlling the weeds within the crop row between the onions. Field research was conducted in southeast Oklahoma (Lane, OK) to determine the efficacy of inorganic and organic herbicides for use on spring transplanted onions. Twenty-one weed control treatments, including both inorganic (pendimethalin and oxyfluorfen) and organic (Corn Gluten Meal) herbicides, were applied on March 15, 2002, the day after transplanting, to `Hybrid Yellow Granex PRR' onions planted in two rows, 36 inches apart, on raised beds. The herbicide treatments included pendimethalin applications at 0.56 lb ai/a, 1.12 lb ai/a, and 1.68 lb ai/a, oxyfluorfen at 0.89 lb ai/a, 0.178 lb ai/a, and 0.266 lb ai/a, and tank mixes with the herbicides pendimethalin and oxyfluorfen at each rate. Corn Gluten Meal (CGM) was applied by hand, spreading the dry material at 4 rates (2 lb/100 ft2, 4 lb/100 ft2, 6 lb/100 ft2, and 8 lb/100 ft2). The experiment also included a series of weedy-checks and weed-free treatments to serve as experimental controls. The experiment had very high weed pressure with multiple species of broadleaf and grass weeds. Treatments receiving pendimethalin (pendimethalin or pendimethalin + oxyfluorfen) resulted in a greater percent grass control and an increase in marketable onion yields compared to the weedy-check. Select weed control treatments did shift the weed composition compared to the percent grass and broadleaf cover within the weedy-check. As the grass weeds were controlled by pendimethalin, the broadleaf weeds compensated by increasing their growth. The yield advantage for pendimethalin was probably the result of early season weed control that was not apparent at harvest. The success or failure of these specific weed control treatments will need to be further evaluated during a second year of the experiment.