Malheur Experiment Station Information for Sustainable Agriculture

PRELIMINARY EVALUATION OF ACTIVATED CARBON TO DETOXIFY

PRE-EMERGENCE APPLIED HERBICIDES IN DRY BULB ONION

Joel Felix and Joey Ishida
Malheur Experiment Station
Oregon State University
Ontario, OR, 2008

Introduction

Onion sensitivity to soil-residual herbicides, especially early in the growth stage, has limited the use of pre-emergence (PRE) applications of Dual Magnum^® and Outlook^® to control yellow nutsedge. Until selective PRE herbicides that can be applied to direct-seeded onions become available, other innovative means of using these products have to be investigated. One such approach is the use of activated charcoal to protect onion seedlings from PRE-applied herbicides as they emerge.

Activated carbon is a proven powerful herbicide adsorbent (Elmore and Woods 1980, Toth and Milham 1975) and is successfully used in western Oregon to protect grass seed from PRE-applied herbicides (Hulting 2007, Young 2003). Even though application of carbon within the furrow seems like a viable approach, Toth et al. (1987) and Morgan and Morgan (1992) showed that the best placement for carbon was on the soil surface immediately above the seed row. If a narrow band of carbon is applied directly over the onion seed row, smaller amounts would be required per acre and the benefits of using PRE herbicides on direct-seeded onions would far outweigh the cost of charcoal (about $100/acre). Weeds emerging in the charcoal-treated bands would be controlled with postemergence (POST) herbicides. Most importantly, the production of yellow nutsedge tubers per unit area would be reduced significantly if use of activated charcoal proves to be useful. The objective of this study was to evaluate the potential use of activated charcoal to protect emerging onion seedlings from PRE applications of Outlook and Dual Magnum herbicides under field conditions.

Material and Methods

The study was conducted in 2008 in a field about 2 miles from the Malheur Experiment Station, Ontario, Oregon. The field was disked twice during fall 2007 to create a smooth seedbed as practiced by onion growers in the area. After fertilization, 22-inch-wide beds were created to facilitate furrow irrigation. The study was a randomized complete block design with 4 replications and individual plots were 7.33 ft wide (4 rows) by 15.0 ft long.

Onion seeds ('Vaquero') were planted on April 1, 2008 in double rows spaced 3.7 inches apart on 22-inch beds. Immediately after planting, Lorsban^® 15G at 3.7 oz/1,000 ft of row was applied as a preventive measure against onion maggot. A narrow band of charcoal slurry was hand sprayed directly over the onion row on April 16, 2008, using a CO₂-pressurized backpack sprayer equipped with four Teejet 8008EVS nozzles and calibrated to deliver 25 gal/acre. Outlook, Dual Magnum, and Nortron^® herbicides at 21 fl oz/acre, 1.33 pt/acre, and 32 fl oz/acre, respectively, were broadcast over respective plots immediately after charcoal application. The soil was fertilized on June 16, 2008 with a compound fertilizer to supply 180, 20, and 3 lb/acre of nitrogen, potassium, and zinc, respectively, based on the soil analysis. Except for the untreated control, all plots were sprayed again with Dual Magnum at 1.33 pt/acre on June 26, after hand pulling all emerged broadleaf and grass weeds. Plots were sprayed for thrips control using Success^® (8 oz/acre) plus Aza-Direct^® (16 oz/acre) plus Ad-wet non-ionic surfactant (1 qt/acre) starting June 25, 2008. The trial was furrow irrigated on a schedule to maintain moisture at a level suitable for onion production. Visual observations for onion injury and weed control were based on a 0 percent for no injury or weed control to 100 percent for total crop kill or excellent weed control. Onions were harvested at maturity from 10 ft of the 2 center rows. Dry bulb onions were transported to the shed and eventually graded into different marketable categories. The data were subjected to analysis of variance and means separated using least significance difference (LSD, P = 0.05).

Results and Discussion

Visual evaluations on July 14, 2008 indicated very low onion injury ranging from 0 to 9 percent (Table 1). Injury was mainly characterized by sparse emergence and generally weak seedlings. However, it is important to note that seeding was done late for the area and the excessive dry conditions in the field before the irrigation commenced may have contributed to poor emergence. A timely planted study in 2009 will provide better assessment of this practice. Yellow nutsedge control on July 14 ranged from 30 to 80 percent with Dual Magnum and Outlook providing the best control (Table 1). Control for other weeds including pigweed species, kochia, and common lambsquarters was excellent and only needed a single hand weeding on June 26, 2008 to clean up the field. Visual evaluations on August 19 (125 days after treatment) indicated yellow nutsedge control as high as 70 to 95 percent, and again Dual Magnum and Outlook provided the best results.

Onions were hand harvested from the 2 center rows on August 18, 2008, which was 16 days earlier than direct-seeded onions. Harvested onion bulbs were stored in the shed until grading on September 4, 2008. Total marketable onion yield was similar for Outlook-, Dual Magnum-, and Nortron-treated plots (Table 2). The study will be repeated in 2009 at two sites; the charcoal slurry will be applied more uniformly by attaching a special sprayer on the onion planter to apply carbon at the time of planting. If this practice proves to be a viable option for applying Dual Magnum and Outlook in dry bulb onions, growers will potentially be able to control yellow nutsedge because these products provide appreciable weed control when applied before emergence.

References

Elmore C. L., and J. Woods. 1980. Screening of pre-plant incorporated herbicide in plug-planted and direct-seeded tomatoes. Pages 93-94 in Western Society of Weed Science 1980 Research Progress Reports, Salt Lake City, UT.

Hulting, A. 2007. Grass seed crops. Page 113 in E. Peachey (ed.). 2008 Pacific Northwest Weed Management Handbook, Extension Services of Oregon State Univ., Washington State Univ., and Univ. of Idaho.

Morgan W. C., and A. S. Morgan. 1992. Potential use of activated carbon as a protectant against pre-emergence herbicides in direct seeded processing tomatoes. Weed Research 32:87-94.

Toth J., and P. J. Milham. 1975. Activated carbon and ash-carbon effects on the adsorption and phytotoxicity of diuron. Weed Research 15:171-176.

Toth J., P. J. Milham, G. R. Hillier, and C. J.Kaldor. 1987. Use of activated carbon to protect tomato against metribuzin. Weed Research 27:367-373.

Young, W.C., III. 2003. Grass seed production in Oregon. http://cropandsoil.oregonstate.edu/seed-ext/Pub/or_prod.html

Table 1. Weed control and dry bulb onion response to pre-emergence application of Dual Magnum, Outlook, and Nortron with activated carbon (44 lb/acre) at Malheur Experiment Station, Oregon State University, Ontario, OR, 2008.

^aMeans within a column followed by same letter do not significantly differ (LSD, P = 0.05).

^bDAT = Days after treatment application.

Table 2. Dry bulb onion yield in response to pre-emergence application of Dual Magnum, Outlook, and Nortron with activated carbon (44 lb/acre) at Malheur Experiment Station, Oregon State University, Ontario, OR, 2008.

^aMeans within a column followed by same letter do not significantly differ (LSD, P = 0.05).

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Last updated  Wednesday July 1, 2009 .