DEVELOPMENT OF NEW HERBICIDE OPTIONS FOR WEED CONTROL IN POTATO PRODUCTION

DEVELOPMENT OF NEW HERBICIDE OPTIONS FOR WEED CONTROL IN POTATO PRODUCTION Corey V. Ransom and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, OR, 2000 Introduction Four trials were conducted in 2000 to evaluate new herbicides for weed control efficacy and potato tolerance. These trials demonstrated that sulfentrazone (Spartan) at lower rates and flumioxazin (Valor) at all rates did not cause significant potato injury. Sulfentrazone and flumioxazin were highly effective in controlling redroot pigweed, common lambsquarters, hairy nightshade, and barnyardgrass when applied at the appropriate rates or in combination with certain herbicides. Sulfentrazone and flumioxazin represent a herbicide mode of action that is not currently used in potatoes and offer more effective hairy nightshade control than current herbicide programs. These products would benefit producers and this research will support efforts in obtaining registrations if the chemical manufacturers decide to pursue labels. Differences in hairy nightshade control with increased Matrix rates and various surfactants were not documented because of variable nightshade pressure. However, potato injury did not increase from either higher rates or the use of different surfactants with Matrix. Applications made when hairy nightshade plants are smaller may show advantages for some of the treatments investigated. Potato tolerance to high rates of dimethenamid-p and Dual II Magnum was documented, suggesting that rates typically used in production should pose little risk of injuring potatoes. A registration package for dimethenamid-p has been submitted to U.S. Environmental Protection Agency (EPA) and a label for use in potatoes should be approved in the next few years. The herbicide Select also was shown to effectively control volunteer barley in potatoes. Select would be a useful grass herbicide if it is registered for use in potatoes. Methods Four trials were conducted at the Malheur Experiment Station to evaluate new herbicides for weed control efficacy and crop tolerance in potatoes. All trials were sprinkler irrigated. Trials were planted April 19 in a silt loam soil with ph 7.0 and 1.6 percent organic matter (OM). 'Russet Burbank' seed pieces were planted every 9 inches in 36-inch-wide rows. Thimet 20G was applied at planting at a rate of 17.3 oz/1,000 ft of row. Experimental plots were four rows wide and 30 ft long. Plots were sidedressed with fertilizer (125 lb N, 10 lb Zn, 6 lb Mg, and 2 lb B/acre) on May 3 and beds were reshaped with a Lilliston on May 8. Preemergence herbicides were applied May 9 and immediately incorporated with overhead irrigation. Postemergence applications were made June 4. s were applied with a CO2-pressurized 145

backpack sprayer delivering 20 gal/acre at 30 psi. Plots were irrigated with sprinklers according to crop requirements throughout the season. Potatoes were sprayed with Bravo and Dithane to prevent late blight and with sulfur dust to control powdery mildew. Potato injury and weed control were evaluated throughout the growing season and tuber yields were taken by harvesting the center two rows of each plot. Potatoes were harvested September 15, 18, and 19. Potatoes were graded for yield and size on September 22, 25, 26, 27, 28, and 29. Potato Response and Weed Control with Sulfentrazone and Flumioxazin Combinations Sulfentrazone was applied alone at rates from 0.125 to 0.375 lb ai/acre and at 0.188 lb ai/acre in combinations with other herbicides. Flumioxazin was applied alone at rates from 0.047 to 0.125 lb ai/acre and at 0.063 lb ai/acre in combination with other herbicides. Sulfentrazone and flumioxazin were applied in combinations with Eptam, Dual Magnum, Outlook, and Prowl. Sulfentrazone and flumioxazin treatments were compared to Sencor plus Matrix, Eptam plus Sencor, and Dual Magnum plus Sencor. s were replicated four times. Hairy Nightshade Control with Postemergence Matrix This trial was conducted to evaluate various Matrix combinations for hairy nightshade control. To suppress other broadleaf weeds, all plots were treated with a preemergence application of Sencor (0.16 lb ai/acre). Matrix was applied at two rates (0.375 oz ai and 0.5 oz ai/acre) delayed preemergence (DPRE). Both rates were applied postemergence with either a non-ionic surfactant (NIS), crop oil concentrate (COC), or methylated seed oil (MSO). Delayed preemergence treatments were applied May 23 and postemergence treatments were applied on June 1. On June 1 hairy nightshade plants averaged 1.5 inches tall with an average density of 7 plants/ft2. s were replicated three times. Tolerance of Russet Burbank Potatoes to Dimethenamid-P This trial was conducted to evaluate preemergence dimethenamid-p for crop injury at normal field use rates and twice and four times the normal rate, and to compare it to other standard herbicides applied at twice their labeled rates. Dimethenamid-P is an active isomer of the herbicide Frontier (dimethenamid) and has been submitted to EPA for registration on potatoes. The proposed trade name for dimethenamid-p is "Outlook". s were replicated four times. The untreated plots were hand weeded prior to row closure, but weeds emerging later in the season were not removed to avoid mechanical injury to the potato canopy. Lower yields in the untreated plots are likely due to weed competition. Volunteer Barley Control with Select Barley seed was broadcast over the entire trial and incorporated with the Lilliston on May 8. Prowl (0.75 lb ai/acre) was applied May 9 to control other weeds impacting the potatoes. Select treatments were applied May 24 when potatoes were 5 inches tall and barley had five leaves. s were replicated three times. Potato injury and 146

barley control were evaluated throughout the season. Because the Prowl application did not control all the broadleaf weeds, redroot pigweed and hairy nightshade control was evaluated at the end of the season. Results and Discussion Spring weather was conducive for early potato growth and the rapid canopy closure helped make soil active herbicide treatments effective. July and August were extremely hot, resulting in less than ideal conditions for potato growth. Potato Response and Weed Control with Sulfentrazone and Flumioxazin Combinations Sulfentrazone applied alone at the lowest rate (0.094 lb is/acre) gave greater than 96 percent control of redroot pigweed, common lambsquarters, and hairy nightshade and 90 percent control of barnyardgrass (Table 1). The highest rate (0.25 lb ai/acre) gave complete control of all weeds, but also caused significant potato injury. Injury consisted of necrotic areas between veins on the leaves. Symptoms were not noticeable as the season progressed and injurious treatments did not reduce potato yield or quality (Table 2). Flumioxazin applied alone did not adequately control redroot pigweed or barnyardgrass. The lower rates were not as effective in controlling hairy nightshade. All the sulfentrazone treatments and flumioxazin alone at 0.094 lb ai/acre or higher or in combinations with Eptam, Dual Magnum, or Outlook provided greater hairy nightshade control than Sencor plus Matrix, Eptam plus Sencor, and Dual Magnum plus Sencor. The addition of Prowl to flumioxazin did not improve redroot pigweed or hairy nightshade control. Potato yields were strongly affected by weed competition, with treatments providing poor weed control resulting in lower potato yields. Flumioxazin will likely need to be applied in combination with other herbicides to provide acceptable control of a wide spectrum of weed species. Sulfentrazone rates likely can be reduced when applying it in combination with other herbicides. Hairy Nightshade Control with Postemergence Matrix All Matrix treatments provided hairy nightshade control, but differences between treatments were not observed (Table 3). This may be due to variable hairy nightshade populations in the trial. It was clear from this trial that potato yields are reduced when hairy nightshade is not controlled in potatoes (Table 4). Both marketable and total tuber yields were significantly lower in check treatment where hairy nightshade was not controlled compared to Matrix treatments. Tolerance of Russet Burbank Potatoes to Dimethenamid-P Higher rates of dimethenamid-p (1.29 and 2.58 lb ai/acre) and the highest rate of Dual II Magnum (5.2 lb ai/acre) caused significant stunting on May 19, but by June 13 no significant injury was apparent (Table 5). Even with the high levels of stunting observed initially, treatments did not reduce potato yields. Only the untreated plot had reduced marketable and total tuber yields compared to some of the other treatments. This was 147

probably due to competition from weeds that were not removed from the untreated plots after canopy closure. Volunteer Barley Control with Select The preemergence application of Prowl did not control all broadleaf weeds in the trial. Select was very effective at controlling volunteer barley regardless of the rate and control was nearly complete for the entire season (Table 6). Because barley is so competitive, marketable potato yields were increased by more than 282 percent and the percentage of No. 1 by 369 percent with Select treatments (Table 7). The addition of Sencor to Select significantly increased control of redroot pigweed and hairy nightshade, resulting in higher yields than Select alone. Select would be a useful herbicide for controlling grasses in potatoes. Table 1. Weed control and potato injury on June 1 with preemergence sulfentrazone and flumioxazin combinations. Malheur Experiment Station, Oregon State University, Ontario, OR, 2000. lb ai/acre Potato Injury Redroot pigweed Common lambsquarters Weed control Hairy nightshade Barnyard-grass Sulfentrazone 0.094 15 98 100 96 90 Sulfentrazone 0.125 16 100 100 99 93 Sulfentrazone 0.188 21 100 100 100 98 Sulfentrazone 0.25 34 100 100 100 100 Sulfentrazone + Eptam 0.188 + 3.0 16 100 100 100 98 Sulfentrazone + Dual Magnum 0.188 + 1.3 16 100 100 99 100 Sulfentrazone + Outlook 0.188 + 0.64 15 100 100 100 98 Sulfentrazone + Prowl 0.188 + 1.0 16 100 100 98 98 Sencor + Matrix 0.5 + 0.016 6 100 100 79 100 Eptam + Sencor 3.0 + 0.5 14 100 100 86 99 Dual Magnum + Sencor 1.3 + 0.5 9 100 100 75 100 Flumioxazin 0.047 3 56 100 75 65 Flumioxazin 0.063 3 66 88 94 68 Flumioxazin 0.094 9 73 98 98 79 Flumioxazin 0.125 5 85 91 100 86 Flumioxazin + Eptam 0.063 + 3.0 11 85 89 99 98 Flumioxazin + Dual Magnum 0.063 + 1.3 11 100 100 98 100 Flumioxazin + Prowl 0.063 + 1.0 5 66 100 79 84 Flumioxazin + Outlook 0.063 + 0.64 8 100 100 100 99 Untreated LSD (0.05) 11 9 9 9 8 148

Table 2. 'Russet Burbank' tuber yield and grade in response to preemergence sulfentrazone and flumioxazin combinations, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000. U.S. No. 1 4-6 oz 6-12 oz > 12 oz No. 2 marketable lb ai/acre cwt/acre cwt/acre---- Sulfentrazone 0.094 91 264 116 470 80 54 524 587 Sulfentrazone 0.125 87 271 115 472 80 44 516 594 Sulfentrazone 0.188 96 278 91 464 76 71 535 610 Sulfentrazone 0.25 85 261 108 453 77 72 525 590 Sulfentrazone + Eptam 0.188 + 3.0 84 260 93 437 73 88 525 598 Sulfentrazone + Dual Magnum 0.188 + 1.3 85 255 124 463 79 67 531 587 Sulfentrazone + Outlook 0.188 + 0.64 83 298 111 492 80 59 550 614 Sulfentrazone + Prowl 0.188 + 1.0 82 277 126 486 79 57 542 617 Sencor + Matrix 0.5 + 0.016 106 278 81 464 81 35 499 576 Eptam + Sencor 3.0 + 0.5 89 265 112 466 80 43 508 582 Dual Magnum + Sencor Flumioxazin Flumioxazin 1.3 + 0.5 93 255 89 437 77 55 492 564 0.047 100 234 50 384 80 15 399 480 0.063 99 236 54 389 77 25 414 506 Flumioxazin 0.094 105 227 50 381 76 41 422 499 Flumioxazin 0.125 104 266 84 454 80 35 489 564 Flumioxazin + Eptam 0.063 + 3.0 94 236 107 437 77 69 506 568 Flumioxazin + Dual Magnum 0.063 + 1.3 89 246 104 439 77 71 510 572 Flumioxazin + Prowl 0.063 + 1.0 96 251 62 408 78 32 440 521 Flumioxazin + Outlook 0.063 + 0.64 98 271 96 464 77 62 526 600 Untreated 120 119 9 248 71 1 249 347 LSD (0.05) NS 45 32 65 NS 37 49 50 yield 149

Table 3. Potato injury and hairy nightshade control with Matrix applications, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000. oz ai/acre Injury Hairy nightshade control Timing 6-13 6-13 9-11 Matrix 0.375 DPRE* 0 80 73 Matrix 0.5 DPRE 3 84 73 Matrix + NIS 0.375 + 0.25% v/v POST 2 91 83 Matrix + COC 0.375 + 1.0% v/v POST 3 86 68 Matrix + MSO 0.375 + 1.0 % v/v POST 2 96 94 Matrix + NIS 0.5 + 0.25% v/v POST 3 93 90 Matrix + COC 0.5 + 1.0% v/v POST 2 85 67 Matrix + MSO 0.5 + 1.0 % v/v POST 0 92 77 Matrix + Sencor + 0.375 + 0.5 + 0.25% v/v POST 7 90 79 Untreated - LSD (0.05) NS NS NS *DPRE = delayed preemergence. Table 4. Tuber yield and quality in response to postemergence Matrix applications, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000. Timing U.S. No. 1 4-6 oz 6-12 oz >12 oz % No. 2 marketable oz ai/acre cwt/acre % cwt/acre Matrix 0.375 DPRE* 83 262 105 449 76 76 526 594 Matrix 0.5 DPRE 92 267 74 433 75 57 489 577 0.375 + Matrix + NIS 0.25% v/v POST 89 268 98 455 75 68 522 602 0.375+ Matrix + COC 1.0% v/v POST 70 251 112 433 72 94 527 603 0.375 + 1.0 Matrix + MSO % v/v POST 90 235 99 433 70 90 514 609 0.5 + 0.25% Matrix + NIS v/v POST 75 253 108 437 73 82 518 596 0.5 + 1.0% Matrix + COC v/v POST 86 278 86 450 74 81 531 609 0.5 + 1.0 % Matrix + MSO v/v POST 80 287 84 451 77 56 506 584 Matrix + Sencor + 0.375 + 0.5 NIS + 0.25% v/v POST 84 249 94 427 75 63 489 567 yield Untreated 94 228 30 352 75 32 383 470 LSD (0.05) NS 32 NS NS NS NS 66 57 *DPRE = delayed preemergence. 150

Table 5. Potato injury and yield in response to preemergence herbicides, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000. lb ai/acre Field rate Injury U.S. No. 1 5-19 6-13 4-6 oz 6-12 oz >12 oz % cwt/acre U.S. No. 2s Marketable Yield cwt/acre Dimethenamid-P 0.64 1X 2 4 84 262 71 452 76 73 Dimethenamid-P 1.29 2X 25 4 88 254 105 436 73 90 Dimethenamid-P 2.58 4X 31 9 71 232 95 397 67 126 Dual II Magnum 2.6 2X 3 5 82 249 95 424 73 70 Dual II Magnum 5.2 4X 26 8 65 239 93 390 66 125 Prowl 3.0 2X 1 10 62 260 86 457 72 116 Untreated _ 9 0 89 240 135 399 74 63 LSD (0.05) 14 NS NS NS NS NS NS NS 525 599 526 599 523 591 494 580 516 590 573 636 461 537 42 45 Table 6. Volunteer barley control with postemergence herbicides, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000. Redroot Hairy Injury Barley control pigweed nightshade * 5-31 6-13 5-31 6-13 9-11 9-11 9-11 lb ai/acre Select + COC 0.125 + 1 qt 0 0 63 85 98 67 33 Select + COC + AMS 0.188 + 1 qt + 2.5 lb 3 0 67 96 99 63 37 Select + Sencor + COC 0.125 + 0.38 + 1 qt 5 0 67 91 100 99 70 Untreated LSD (0.05) NS NS NS NS NS 13 15 *COC = crop oil concentrate, AMS = ammonium sulfate. Table 7. Potato yield in response to postemergence herbicide applications, Malheur Experiment Station, Oregon State University, Ontario, OR, 2000. * U.S. No. 1 4-6 oz 6-12 oz >12 oz % No. 2 marketable lb ai/acre --cwt/acre % cwt/acre yield Select + COC 0.125 + 1 qt 93 213 64 370 79 33 403 469 Select + COC + AMS 0.188 + 1 qt + 2.5 lb 93 211 44 347 78 28 375 443 Select + Sencor + COC 0.125 + 0.38 + 1 qt 87 272 111 470 80 56 526 588 Untreated 53 39 2 94 44 38 133 203 LSD (0.05) 28 65 22 92 17 15 80 77 *COC = crop oil concentrate, AMS = ammonium sulfate. 151