WEED CONTROL IN ONION WITH POSTEMERGENCE HERBICIDES

Transcription

1 WEED CONTROL IN ONION WITH POSTEMERGENCE HERBICIDES Corey V. Ransom, Charles A. Rice, and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 2004 Introduction Weed control is essential for the production of marketable onions. Weed control in onions is difficult compared to many crops because of the lack of a complete crop canopy and limited herbicide options. Chateau (flumioxazin), formerly called Valor, and Nortron (ethofumesate) are two experimental herbicides that have been evaluated for use in onions in past research trials. Trials were conducted this year to determine the benefits of using these experimental herbicides in postemergence herbicide combinations and compare their performance to registered herbicide combinations. Methods General Procedures Trials were conducted at the Malheur Experiment Station to evaluate experimental and registered herbicides for weed control and onion tolerance. Trials were conducted under furrow irrigation. On March 25, onions (cv. 'Vaquero', Nunhems, Parma, ID) were planted at 3.7-inch spacing in double rows on 22-inch beds. Plots were 4 rows wide and 27 ft long and arranged in a randomized complete block design with four replications. Lorsban was applied in a 6-inch band over each double row at 3.7 oz/1,000 ft of row. Onions were sidedressed with 175 lb nitrogen (N), 30 lb phosphorus (P), 35 lb sulfate, 38 lb sulfur (S), 2 lb Zinc (Zn), 3 lb manganese (Mn), and 1 lb boron (B)/acre on June 3. Registered insecticides and fungicides were applied for thrips and downy mildew control. Herbicide treatments were applied with a CO 2 -pressurized backpack sprayer. Preemergence applications and postemergence grass herbicides were applied at 20 gal/acre at 30 psi and postemergence treatments were applied at 40 gal/acre at 30 psi. All plots were treated with a preemergence application of Roundup (glyphosate) at 0.75 lb ai/acre plus Prow l (pendimethalin) at 1.0 lb ai/acre on April 5 and a postemergence application of Poast (sethoxydim) at 0.19 lb ai/acre plus crop oil concentrate (COC) (1.0% v/v) on June 16. Postemergence treatments were applied to two-leaf onions on May 6, two- to three-leaf onions on May 14, and to five-leaf onions on June 2. In the Chateau application timing trial, a separate application of Chateau was made to three-leaf onions on May 18. Weed control and onion injury were evaluated throughout the season. Onions were harvested September 16 and 17 and graded by size on October

2 Data were analyzed using analysis of variance and means were separated using a protected least significant difference (LSD) at the 5 percent level (0.05). Comparison of Postemergence Chateau or Combinations Chateau and (oxyflurofen) were applied in combinations with (bromoxynil) to evaluate weed control and onion tolerance.,, and Chateau were evaluated at two rates. Comparisons of or Chateau with included several combinations of herbicides and rates. Additional treatments included a split application of Chateau applied to two-leaf and again to three-leaf onions, and a comparison of plus Chateau treatments following preemergence applications of Roundup, Prowl, and Dacthal (DCPA). Application Timings for Chateau Chateau was applied at two rates in combination with to two-leaf or three-leaf onions. Chateau treatments were compared to plus. Additional treatments included Chateau in a separate application 4 days after the application at the three-leaf application timing. Addition of Nortron to Postemergence Treatments This trial was conducted to determine if the addition of Nortron to postemergence herbicide applications would improve weed control. Each treatment was applied with or without Nortron added to the two-leaf and three-leaf applications at either or 0.5 lb ai/acre. One treatment evaluated Outlook (dimethenamid-p) added to the two-leaf application and Nortron added to the three-leaf application. Results and Discussion Preemergence herbicides worked fairly well due to rainfall in April. Adequate rainfall also ensured that weeds were actively growing when postemergence treatments were applied. Comparison of Postemergence Chateau or Combinations Because the preemergence application of Prowl was so effective, there were no differences in weed control between any of the postemergence herbicide treatments (Table 1). Control of all species was 85 percent or greater. There were also no differences in onion injury among treatments. This is surprising as there were large differences in the herbicide rates applied for different treatments. There were a few differences in onion yields, with higher yields resulting from treatments with additional soil-active herbicides applied or with higher rates (Table 2). Application Timings for Chateau Treatment with Chateau combined with when applied either to two-leaf or threeleaf onions did not cause greater injury than combinations of plus (Table 3). When Chateau was applied alone 4 days after was applied to three-leaf onions, injury increased significantly. By July 21 there were no differences in onion injury 55

3 among treatments. The injury caused by the delayed application of Chateau was probably related to wet cool weather that occurred after the application and prior to the Chateau application. Pigweed (redroot pigweed and Powell amaranth), common lambsquarters, hairy nightshade, and barnyardgrass control was not different among herbicide treatments and was 88 percent control or greater. Kochia control was significantly greater with treatments that contained Chateau tank-mixed with and applied at either the two-leaf or three-leaf timing compared to plus. Treatments where Chateau was applied alone following the application to threeleaf onions did not control weeds better than plus. There were few significant differences in onion yields between herbicide treatments, with marketable yields ranging from 1,107 to 1,459 cwt/acre. Addition of Nortron to Postemergence Treatments Onion injury was not different among treatments on either evaluation date (Table 5). Pigweed, hairy nightshade, and barnyardgrass control was similar among herbicide treatments and was 89 percent or higher. The addition of Nortron at either rate to significantly increased common lambsquarters control, but control was similar to that provided by plus. There was no improvement in common lambsquarters control when Nortron was added to plus. Kochia control was less when was applied alone compared to treatments containing plus Nortron or or both. A few of the treatments containing Nortron produced more supercolossal onions than did alone, but yields were similar to the other herbicide treatments (Table 6). Nortron is useful for improving weed control in onion but in this trial did not provide greater benefits than the currently registered herbicides. 56

4 Table 1. Onion injury and weed control from or Chateau combinations with, Malheur Experiment Station, Oregon State University, Ontario, OR, Treatment Rate Timing* Pigweed Injury Weed control Common lambsquarters Hairy nightshade Kochia Barnyardgrass lb ai/acre Leaf % Untreated

5 Table 1 (continued). Onion injury and weed control from or Chateau combinations with, Malheur Experiment Station, Oregon State University, Ontario, OR, Injury Weed control Common Hairy Barnyardgrass Treatment Rate Timing* Pigweed lambsquarters nightshade Kochia lb ai/acre Leaf % LSD (P = 0.05) NS NS NS NS NS NS NS *Preemergence () treatments were applied on April 5, two-leaf () on May 6, three-leaf () on May 14, and five-leaf () on June 2. Weed-control ratings were taken September 2. Pigweed is a combination of redroot pigweed and Powell amaranth.

6 Table 2. Onion yield in response to or Chateau combinations with, Malheur Experiment Station, Oregon State University, Ontario, OR, Onion yield Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable lb ai/acre Leaf cwt/acre Untreated , , , , , , , , ,041 3

7 Table 2 (continued). Onion yield in response to or Chateau combinations with, Malheur Experiment Station, Oregon State University, Ontario, OR, Onion yield Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable lb ai/acre Leaf cwt/acre , , , , ,222 LSD (P = 0.05) *Preemergence () treatment applied on April 5, two-leaf () on May 6, three-leaf () on May 14, and five-leaf () on June 2. Onions were harvested on September 16 and 17.

8 Table 3. Weed control and onion injury in response to Chateau application timings, Malheur Experiment Station, Oregon State University, Ontario, OR, Injury Weed control Treatment Rate Common Hairy Barnyard- Timing* Pigweed lambsquarters nightshade Kochia grass lb ai/acre Leaf % Untreated Chateau (S) Chateau (S) LSD (P = 0.05) NS NS NS NS 15 NS *Preemergence () treatments were applied on April 5, two-leaf () on May 6, three-leaf () on May 14, three-leaf separate ( (S)) on May 18, and five-leaf () on June 2. Weed control ratings were taken September 2. Pigweed is a combination of redroot pigweed and Powell amaranth.

9 Table 4. Onion yield in response to Chateau application timings, Malheur Experiment Station, Oregon State University, Ontario, OR, Onion yield Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable lb ai/acre Leaf cwt/acre Untreated ,117 + Chateau Chateau (S) (S) , , , , , ,145 LSD (P = 0.05) *Preemergence () treatments were applied on April 5, two-leaf () on May 6, three-leaf () on May 14, three-leaf separate ( (S)) on May 18, and five-leaf () on June 2. Onions were harvested on September 16 and 17.

10 Table 5. Onion injury and weed control in response to the addition of Nortron to postemergence applications of and, Malheur Experiment Station, Oregon State University, Ontario, OR, Weed control Injury Common Hairy Barnyard- Treatment Rate Timing* Pigweed lambsquarters nightshade Kochia grass lb ai/acre Leaf % Untreated Nortron + Nortron + Nortron + Nortron + Nortron + Nortron + Outlook + Nortron + Nortron + Nortron LSD (P = 0.05) NS NS NS 7 NS 13 NS *Preemergence () treatments were applied on April 5, two-leaf () on May 6, three-leaf () on May 14, and five-leaf () on June 2. Weed control ratings were taken September 2. Pigweed is a combination of redroot pigweed and Powell amaranth. 7

11 Table 6. Onion yield in response to the addition of Nortron to postemergence applications of and, Malheur Experiment Station, Oregon State University, Ontario, OR, Onion yield Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable lb ai/acre Leaf cwt/acre Untreated Nortron + Nortron + Nortron + Nortron + Nortron + Nortron + Outlook + Nortron + Nortron + Nortron , , , , , ,219 LSD (P = 0.05) *Preemergence () treatment applied on April 5, two-leaf () on May 14, three-leaf () on May 18, and five-leaf () on June 2. Onions were harvested on September 16 and 17.