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Corey V. Ransom, Charles A. Rice, and Joey K. Ishida
Malheur Experiment Station
Oregon State University
Ontario, OR
Introduction
Weed control in potatoes is essential for production of high-yielding marketable tubers. Herbicide options in potato production are often limited. Several herbicides currently registered for use in other crops show promise for use in potatoes. Spartan (sulfentrazone) and Valor (flumioxazin) are protoporphyrinogen oxidase (PPO) inhibitors that disrupt the enzyme system necessary for the production of chlorophyll. These herbicides represent a mode of action that is not currently used in potatoes and offer more effective hairy nightshade control than current herbicide programs. Outlook (dimethenamid-P) is similar to Dual (metolachlor) but controls a larger spectrum of weeds. Trials were conducted to evaluate new herbicides for weed control in potatoes.
Materials and Methods
General
Four trials were conducted at the Malheur Experiment Station to evaluate new herbicides for weed control efficacy and crop tolerance in potatoes. Potatoes were planted April 11 and 12 in an Owyhee silt loam soil with pH 7.5, 0.9 percent organic matter content, and a cation exchange capacity of 14. 'Russet Burbank' seed pieces were planted every 9 inches in 36-inch-wide rows. Potato seed pieces were treated with the fungicide/insecticide formulation Tops-MZ plus Gaucho at seed cutting. Experimental plots were four rows wide and 30 ft long. Plots were sidedressed with fertilizer (90 lb N, 4 lb Zn, 4 lb Mn, 1 lb B, 44 lb elemental S/acre) and beds were reshaped with a Lilliston cultivator on April 18. Preemergence herbicides were applied and incorporated with sprinkler irrigation on May 2. Postemergence treatments were applied on May 22 and 30. Treatments were broadcast applied with a CO2-pressurized backpack sprayer delivering 20 gal/acre at 30 psi. Plots were sprinkler irrigated 14 times during the growing season according to crop requirements. Plots were treated with Ridomil Gold plus Bravo at 2 lbs product/acre on June 4, Dithane on June 15 and July 1 to prevent late blight, and with liquid sulfur on June 20 and August 14 to control powdery mildew. Potato injury and weed control were evaluated throughout the growing season. Tuber yields were taken by harvesting the center two rows of each plot. Weed biomass samples were taken from 5 ft of row within each plot on August 26. Plots were harvested on September 9-12. Potatoes were graded for yield and size on September 17-24.
Weed Control with Valor and Spartan Rates
Weed control with preemergence applications of Valor at rates of 0.063, 0.078, 0.094, and 0.125 lb ai/acre and Spartan at rates of 0.125, 0.141, and 0.188 lb ai/acre were compared to Sencor (0.5 lb ai/acre) plus Dual Magnum (1.0 lb ai/acre) and Matrix (0.008 lb ai/acre) plus Dual Magnum (1.0 lb ai/acre). Treatments were replicated four times.
Weed Control with Valor and Spartan Combinations
Preemergence treatments of Valor and Spartan were applied alone and in combination with Outlook (0.656 lb ai/acre), Dual Magnum (1.0 lb ai/acre), Prowl (1.0 lb ai/acre), and Eptam (3.0 lb ai/acre). Treatment rates for Valor and Spartan were 0.094 and 0.141 lb ai/acre, respectively. Valor and Spartan treatments were compared to Outlook, Dual Magnum, Prowl, and Eptam alone, and to a tank mixture of Sencor plus Dual Magnum. Treatments were replicated four times.
Weed Control with Outlook Combinations
Outlook at 0.656 lb ai/acre was applied preemergence with several herbicides including Prowl (1.0 lb ai/acre), Prowl H2O (1.0 lb ai/acre), Sencor (0.5 lb ai/acre), Matrix (0.0156 lb ai/acre), and Prowl plus Sencor. Outlook treatments were compared to combinations of Dual Magnum (1.0 lb ai/acre) plus Prowl, Sencor, or Matrix, Prowl plus Sencor, and Prowl plus Eptam plus Sencor. Treatments were replicated three times.
Matrix Combinations with New Herbicides for Weed Control in Potato
Preemergence applications of Matrix at 0.024 lb ai/acre were applied alone and in combination with Outlook (0.656 lb ai/acre), Valor (0.094 lb ai/acre), Spartan (0.094 lb ai/acre), Sencor (0.5 lb ai/acre), and Dual Magnum (1.0 lb ai/acre). Matrix plus methylated seed oil (MSO) (1.0% v/v) were applied postemergence following preemergence applications of Outlook, Valor, and Spartan. Postemergence Matrix applications were inadvertently applied at one-third (0.008 lb ai/acre) of the desired rate on May 22, therefore a second application of 0.016 lb ai/acre was applied on May 30 to achieve the intended rate of 0.024 lb ai/acre. Treatments were replicated three times.
Results and Discussion
Weed Control with Valor and Spartan Rates
Control of pigweed species (i.e., Powell amaranth and redroot pigweed) and common lambsquarters with Spartan treatments, Sencor plus Dual Magnum, and Matrix plus Dual Magnum was greater than with all Valor treatments on June 5 (34 days after treatment [DAT]) and August 26 (116 DAT) (Table 1). Valor at 0.063 to 0.125 lb ai/acre provided hairy nightshade control ranging from 56 to 89 percent on June 5 compared to 100 percent control with all Spartan rates. However, on August 26 hairy nightshade control was similar with all Spartan rates and Valor at 0.125 lb ai/acre (93-99 percent). Valor at 0.125 lb ai/acre, Sencor plus Dual Magnum, and Matrix plus Dual Magnum provided similar hairy nightshade control on June 5. However, by August 26 hairy nightshade control was greater with Valor at 0.063, 0.094, and 0.125 (81-93 percent) than from either Sencor plus Dual Magnum or Matrix plus Dual Magnum( 66-67 percent). Barnyardgrass control on June 5 was significantly less with Valor at 0.063 and 0.078 lb ai/acre than from all other treatments. Total weed biomass was significantly greater with Valor treatments. In general, weed control increased with increasing Valor rates while weed control with Spartan was similar among rates.
Based on weed biomass samples, there was a strong correlation between weed control and marketable potato yield (Fig. 1). Total marketable potato yields ranged from 161 to 435 cwt/acre. Potato yields were significantly less with Valor treatments compared to all other treatments (Table 2). Marketable potato yields with Spartan treatments were similar to Sencor plus Dual Magnum and Matrix plus Dual Magnum.
Weed Control with Valor and Spartan Combinations
Outlook and Spartan were the only single-product treatments that provided Powell amaranth and redroot pigweed, hairy nightshade, and common lambsquarters control similar to tank-mix treatments on June 5 (34 DAT) (Table 3). On June 5, control of these weeds with Outlook was not significantly improved by the addition of Valor or Spartan. Similarly, weed control was not improved when Outlook, Dual Magnum, Prowl, or Eptam were applied with Spartan compared to Spartan alone. However, hairy nightshade control was significantly greater on August 26 (116 DAT) when Valor or Spartan were tank-mixed with Outlook, compared to Outlook alone. Prowl alone and Prowl plus Valor provided poor weed control on both evaluation dates. All treatments with either Valor or Spartan provided similar hairy nightshade control on August 26 (69-100 percent). When Outlook and Eptam were applied with Valor, barnyardgrass and hairy nightshade control were greater on June 5 and control of pigweed species and common lambsquarters were greater on June 5 and August 26 compared to Valor alone. Dual Magnum plus Valor provided greater pigweed, hairy nightshade, barnyardgrass, and common lambsquarters control on June 5 and greater pigweed control on August 26 compared to Valor alone. Outlook provided greater control of common lambsquarters than Dual Magnum, Prowl, Eptam, or Valor. Total weed biomass production was significantly less than the untreated check with Outlook alone and all tank-mix treatments except Valor plus Prowl. Hairy nightshade control was greater with all treatments including Spartan and the combination of Valor plus Outlook compared to Sencor plus Dual Magnum.
Weed biomass samples indicated a strong correlation between weed control and marketable potato yield (Fig. 2). Total marketable potato yields ranged from 165 to 479 cwt/acre (Table 4). Marketable yields increased when Outlook, Dual Magnum, or Eptam were applied with Valor compared to Valor alone. The addition of a tank-mix partner to Spartan did not provide greater U.S. No. 1 or total marketable potato yields over those obtained with Spartan alone.
Weed Control with Outlook Combinations
Pigweed control was excellent (93 to 100 percent) with all treatments except Dual Magnum plus Prowl, which provided 63 and 52 percent control on June 5 (34 DAT) and August 26 (116 DAT), respectively (Table 5). Hairy nightshade control with Outlook plus Prowl H2O was less on June 5 than from Outlook plus Sencor and Outlook plus Prowl plus Sencor. On August 26, Outlook plus Prowl provided significantly less hairy nightshade control than Outlook plus Sencor. All herbicide treatments provided greater common lambsquarters control than Dual Magnum plus Prowl on June 5 and August 26. On both evaluation dates, Outlook alone provided less common lambsquarters control than treatments including Sencor. Total weed biomass was greatest in plots treated with Dual Magnum plus Prowl and was not different from the untreated control.
U.S. No. 1 and total marketable potato yields were less with Dual Magnum plus Prowl than with all other treatments (Table 6). Marketable potato yields with Outlook plus Sencor, Outlook plus Prowl plus Sencor, and Prowl plus Sencor were greater than with Outlook alone. All Outlook treatment combinations provided similar U.S. No. 1, U.S. No. 2, total marketable, and total yields.
Matrix Combinations with New Herbicides for Weed Control in Potato
All treatments except Valor alone provided greater than 94 and 89 percent pigweed control on June 5 (34 DAT) and August 26 (116 DAT), respectively (Table 7). The combination of Matrix plus Valor provided 78 and 65 percent greater pigweed control compared to Valor alone on June 5 and August 26, respectively. Matrix plus Valor provided less hairy nightshade control compared with all other Matrix combinations on June 5. The combination of Matrix plus Sencor provided greater late-season (August 26) hairy nightshade and common lambsquarters control than either herbicide alone. Outlook applied with Matrix improved late-season hairy nightshade control by 69 percent over Matrix alone. Valor applied with Matrix improved late-season hairy nightshade control by 54 percent over Matrix alone. Matrix plus Valor controlled pigweed, barnyardgrass, and common lambsquarters better than Valor alone. Spartan applied with Matrix increased common lambsquarters control by 10 percent on June 5 and late-season hairy nightshade control by 59 percent compared to Matrix alone. Weed control was not different when Matrix (0.024 lb ai/acre) was applied preemergence with either Outlook or Spartan or when Matrix (0.008 followed by 0.016 lb ai/acre) was applied in sequential postemergence applications following preemergence applications of Outlook or Spartan. Preemergence Valor followed by sequential postemergence applications of Matrix provided greater hairy nightshade control on June 5 compared to the preemergence combination of Matrix plus Valor. Late-season common lambsquarters control was greater with the preemergence combination of Matrix plus Valor compared to the split PRE/POST treatment of Valor followed by Matrix. Total weed biomass production was less than the untreated control with all preemergence Matrix combinations, the PRE/POST treatment combinations of Outlook or Spartan followed by Matrix, and Outlook alone.
Total marketable potato yields in herbicide-treated plots ranged from 219 to 452 cwt/acre. U.S. No. 1 and total marketable potato yields were significantly greater than the untreated control with all herbicide treatments except Valor alone (Table 8). Total marketable potato yield with Matrix plus Valor was 212 cwt/acre greater than from Valor alone.
Table 1. Valor and Spartan rates for weed control in potato, Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.
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Weed control‡ | |||||||||
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Pigweed spp.† | Hairy
nightshade |
Barnyardgrass | Common
lambsquarters |
Total
weed
biomass |
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Treatment* |
Rate | 6-05 | 8-26 | 6-05 | 8-26 | 6-05 | 8-26 | 6-05 | 8-26 | 8-26 |
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lb ai/acre | ------------------------------------------- % ------------------------------------------- | g/m2 | |||||||
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Untreated check |
-- | 0 | 0 | 0 d | 0 | 0 | 0 | 0 f | 0 | 908 |
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Valor |
0.063 | 30 | 36 | 60 c | 81 | 39 | 78 | 28 e | 41 | 748 |
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Valor |
0.078 | 40 | 30 | 56 c | 74 | 43 | 61 | 46 d | 38 | 692 |
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Valor |
0.094 | 46 | 38 | 68 c | 85 | 81 | 85 | 63 c | 62 | 666 |
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Valor |
0.125 | 61 | 56 | 89 b | 93 | 85 | 86 | 62 cd | 63 | 709 |
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Spartan |
0.125 | 100 | 95 | 100 a | 92 | 88 | 88 | 100 a | 97 | 6 |
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Spartan |
0.141 | 100 | 99 | 100 a | 99 | 95 | 88 | 100 a | 98 | 29 |
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Spartan |
0.188 | 100 | 96 | 100 a | 95 | 98 | 91 | 100 a | 100 | 20 |
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Sencor + Dual Magnum |
0.5 + 1.0 | 100 | 96 | 89 b | 67 | 100 | 100 | 98 ab | 98 | 6 |
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Matrix + Dual Magnum |
0.008 + 1.0 | 100 | 99 | 87 b | 66 | 100 | 99 | 95 b | 96 | 25 |
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LSD (0.05) |
19 | 21 | -- | 15 | 34 | 23 | -- | 21 | 232 | |
*Herbicide treatments were applied preemergence on
May 2, 2002.
†Pigweed species predominantly Powell amaranth mixed with
some redroot pigweed.
‡In columns where letter designations occur the ANOVA was
performed on arcsine square root percent transformed data. Mean
separations are applied to non-transformed data.
Table 2. Valor and Spartan rates for weed control in potato, Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.
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Potato yield | ||||||||
| U.S. No. 1 | Total
No. 2 |
Total
marketable |
Total
yield |
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Treatment* |
Rate | 4-6 oz | 6-12 oz | >12 oz | Total | % | |||
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lb ai/acre | -------------------- cwt/acre -------------------- | % | ------------- cwt/acre ------------- | |||||
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Untreated check |
-- | 93 | 57 | 4 | 154 | 96 | 8 | 161 | 161 |
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Valor |
0.063 | 95 | 72 | 6 | 172 | 94 | 11 | 183 | 184 |
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Valor |
0.078 | 104 | 79 | 9 | 191 | 95 | 12 | 203 | 203 |
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Valor |
0.094 | 90 | 77 | 12 | 178 | 89 | 23 | 201 | 202 |
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Valor |
0.125 | 97 | 88 | 18 | 203 | 91 | 22 | 225 | 226 |
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Spartan |
0.125 | 111 | 186 | 78 | 375 | 85 | 60 | 435 | 440 |
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Spartan |
0.141 | 111 | 182 | 56 | 349 | 85 | 61 | 410 | 413 |
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Spartan |
0.188 | 115 | 208 | 57 | 380 | 85 | 63 | 443 | 446 |
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Sencor + Dual Magnum |
0.5 + 1.0 | 129 | 185 | 48 | 362 | 87 | 47 | 409 | 415 |
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Matrix + Dual Magnum |
0.008 + 1.0 | 128 | 184 | 57 | 369 | 87 | 56 | 425 | 427 |
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LSD (0.05) |
22 | 38 | 24 | 47 | 5 | 19 | 57 | 57 | |
*Herbicide treatments were applied preemergence on May 2, 2002.
Figure 1. Response of marketable potato yields to total weed biomass (dry-weight basis). Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.
Table 3. Valor and Spartan combinations for weed control in potato, Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.
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Weed control | Total
weed biomass |
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Pigweed spp.† | Hairy
nightshade |
Barnyardgrass | Common
lambsquarters |
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Treatment* |
Rate | 6-05 | 8-26 | 6-05 | 8-26 | 6-05 | 8-26‡ | 6-05 | 8-26 | 8-26 |
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lb ai/acre | ----------------------------------------------- % ----------------------------------------------- | g/m2 | |||||||
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Untreated check |
-- | 0 | 0 | 0 | 0 | 0 | 0 d | 0 | 0 | 807 |
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Outlook |
0.656 | 92 | 89 | 81 | 33 | 100 | 92 ab | 88 | 89 | 190 |
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Dual Magnum |
1.0 | 81 | 79 | 43 | 48 | 91 | 96 ab | 51 | 37 | 855 |
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Prowl |
1.0 | 20 | 47 | 15 | 26 | 10 | 94 ab | 24 | 26 | 822 |
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Eptam |
3.0 | 75 | 71 | 70 | 43 | 86 | 89 ab | 65 | 51 | 549 |
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Valor |
0.094 | 55 | 44 | 65 | 72 | 28 | 86 ab | 48 | 24 | 724 |
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Spartan |
0.141 | 100 | 100 | 100 | 96 | 91 | 87 ab | 100 | 99 | 5 |
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Valor + Outlook |
0.094 + 0.656 | 96 | 95 | 96 | 91 | 99 | 96 ab | 93 | 89 | 55 |
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Spartan + Outlook |
0.141 + 0.656 | 100 | 99 | 99 | 98 | 100 | 95 ab | 100 | 100 | 1 |
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Valor + Dual Magnum |
0.094 + 1.0 | 90 | 79 | 86 | 84 | 87 | 95 ab | 81 | 51 | 254 |
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Spartan + Dual Magnum |
0.141 + 1.0 | 100 | 100 | 100 | 100 | 95 | 95 ab | 100 | 100 | 3 |
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Valor + Prowl |
0.094 + 1.0 | 39 | 56 | 62 | 69 | 15 | 82 b | 40 | 36 | 764 |
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Spartan + Prowl |
0.141 + 1.0 | 100 | 99 | 99 | 98 | 86 | 87 ab | 100 | 99 | 20 |
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Valor + Eptam |
0.094 + 3.0 | 86 | 68 | 89 | 78 | 90 | 41 c | 77 | 62 | 291 |
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Spartan + Eptam |
0.141 + 3.0 | 100 | 98 | 100 | 100 | 92 | 84 ab | 100 | 100 | 2 |
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Sencor + Dual Magnum |
0.5 + 1.0 | 100 | 98 | 83 | 54 | 95 | 97 a | 100 | 98 | 101 |
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LSD (0.05) |
15 | 19 | 19 | 31 | 17 | -- | 19 | 31 | 359 | |
*Herbicide treatments were applied preemergence on
May 2, 2002.
†Pigweed species were predominantly Powell amaranth mixed
with some redroot pigweed.
‡The ANOVA was performed on arcsine square root percent
transformed data. Mean separations are applied to non-transformed data.
Table 4. Valor and Spartan combinations for weed control in potato, Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.
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Potato yield | ||||||||
| U.S. No. 1 | Total
No. 2 |
Total
marketable |
Total
yield |
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Treatment* |
Rate | 4-6 oz | 6-12 oz | >12 oz | Total | % | |||
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lb ai/acre | -------------------- cwt/acre -------------------- | % | ------------- cwt/acre ------------- | |||||
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Untreated check |
-- | 92 | 66 | 9 | 167 | 52 | 8 | 175 | 308 |
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Outlook |
0.656 | 119 | 154 | 47 | 320 | 68 | 53 | 373 | 474 |
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Dual Magnum |
1.0 | 105 | 81 | 25 | 211 | 58 | 18 | 228 | 353 |
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Prowl |
1.0 | 78 | 55 | 11 | 144 | 46 | 23 | 167 | 298 |
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Eptam |
3.0 | 130 | 109 | 28 | 266 | 63 | 19 | 286 | 410 |
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Valor |
0.094 | 78 | 53 | 11 | 143 | 48 | 23 | 165 | 283 |
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Spartan |
0.141 | 119 | 195 | 81 | 395 | 68 | 84 | 479 | 576 |
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Valor + Outlook |
0.094 + 0.656 | 128 | 189 | 59 | 377 | 67 | 82 | 458 | 565 |
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Spartan + Outlook |
0.141 + 0.656 | 112 | 165 | 47 | 324 | 64 | 77 | 401 | 508 |
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Valor + Dual Magnum |
0.094 + 1.0 | 114 | 140 | 25 | 278 | 64 | 38 | 316 | 423 |
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Spartan + Dual Magnum |
0.141 + 1.0 | 104 | 174 | 57 | 335 | 67 | 71 | 406 | 503 |
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Valor + Prowl |
0.094 + 1.0 | 87 | 71 | 7 | 165 | 53 | 19 | 185 | 303 |
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Spartan + Prowl |
0.141 + 1.0 | 117 | 187 | 66 | 370 | 70 | 56 | 426 | 525 |
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Valor + Eptam |
0.094 + 3.0 | 118 | 111 | 13 | 242 | 59 | 50 | 292 | 408 |
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Spartan + Eptam |
0.141 + 3.0 | 113 | 184 | 92 | 389 | 69 | 82 | 471 | 654 |
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Sencor + Dual Magnum |
0.5 + 1.0 | 105 | 163 | 66 | 333 | 69 | 61 | 394 | 486 |
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LSD (0.05) |
31 | 58 | 32 | 103 | 12 | 37 | 124 | 124 | |
*Herbicide treatments were applied preemergence on May 2, 2002.
Figure 2. Response of marketable potato yields to total weed biomass (dry-weight basis). Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.
Table 5. Outlook combinations for weed control in potato, Malheur Experiment Station, Oregon State University, Ontario, OR, 2002.
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Weed control | Total
weed biomass |
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Pigweed spp.† | Hairy
nightshade |
Barnyardgrass | Common
lambsquarters |
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Treatment* |
Rate | 6-05 | 8-26‡ | 6-05 | 8-26 | 6-05 | 8-26 | 6-05 | 8-26 | 8-26 |
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lb ai/acre | ----------------------------------------------- % ----------------------------------------------- | g/m2 | |||||||
|
Outlook + Prowl |
0.656 + 1.0 | 98 | 97 ab | 89 | 83 | 100 | 100 | 91 | 90 | 25 |
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Outlook + Prowl H2O |
0.656 + 1.0 | 95 | 93 b | 88 | 86 | 100 | 100 | 91 | 93 | 39 |
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Outlook + Sencor |
0.656 + 0.5 | 100 | 97 ab | 97 | 98 | 100 | 100 | 100 | 100 | 4 |
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Outlook + Matrix |
0.656 + 0.0156 | 99 | 99 ab | 94 | 88 | 100 | 100 | 94 | 90 | 15 |
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Prowl + Eptam + Sencor |
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