DEVELOPMENT OF HERBICIDE OPTIONS FOR WEED CONTROL IN POTATOES

DEVELOPMENT OF HERBICIDE OPTIONS FOR WEED CONTROL IN POTATOES Corey V. Ransom and Joey K. Ishida Malheur Experiment Station Oregon State University Ontario, Oregon, 1999 Introduction In 1999, four trials were conducted to evaluate new herbicides for weed control efficacy and potato tolerance. In all, 42 different herbicide treatments were investigated. These trials demonstrated that potatoes are tolerant to much higher rates of sulfentrazone than are necessary to achieve acceptable weed control. Potato tolerance to BAS 656 07 H and Dual Magnum was demonstrated, and yields were not reduced even when BAS 656 07 H and Dual Magnum were applied at two and four times the typical use rates. Postemergence combinations of Dual Magnum with or were shown to cause significant foliar injury, and the combination reduced marketable tuber yield. Under favorable environmental conditions, most of the herbicides evaluated provided exceptional weed control. Postemergence applications of Select provided good volunteer barley control without injury to the potatoes. Many of the herbicides investigated have promise for improving weed control in potatoes in the future. Procedures Four trials were conducted at the Malheur Experiment Station to evaluate new herbicides for weed control efficacy and crop tolerance in potatoes. A trial evaluating postemergence grass herbicides for volunteer barley control was furrow irrigated while the other trials were sprinkler irrigated. The sprinkler irrigated trials were planted April 13 in a silt loam soil with ph 7.8 and 1.5 percent organic matter. The volunteer barley control trial was planted April 15 in a loam soil with ph 8.0 and 1.1 percent organic matter. For all trials, 'Russet Burbank' seed pieces were planted every 9 inches in 36- inch-wide rows. Experimental plots were four rows wide and 30 ft long. Plots were sidedressed with fertilizer on April 22, and beds were reshaped with a lilliston on April 23. Preemergence herbicides were applied April 30 and immediately incorporated with overhead irrigation. Postemergence applications were made June 4. Treatments were applied with a CO 2-pressurized backpack sprayer delivering 20 gpa at 30 psi. Plots were irrigated with sprinklers according to crop requirements throughout the season. Potato injury and weed control were evaluated throughout the season, and tuber yields were taken by harvesting the center two rows of each plot. Potatoes were harvested on September 20, 21, and 22. 154

Potato Response and Weed Control with Sulfentrazone 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 including,, Eptam, Dual II Magnum, BAS 656 07 H, and Prowl. Treatments were replicated four times. Preemergence Herbicides for Weed Control in Russet Burbank Potatoes In this trial, treatments included combinations of different herbicides including BAS 656 07 H, Dual Magnum, Frontier, Eptam, Prowl,, and. Treatments were replicated three times. All treatments were applied preemergence, except for Dual Magnum combinations with either or, which were applied at the postemergence application time. Tolerance of Russet Burbank Potatoes to BAS 656 07 H This trial was conducted to evaluate BAS 656 07 H for crop injury at normal field use rates and at twice and four times the normal rate, and to compare it to other standard herbicides applied at twice their labeled rates. BAS 656 07 H is an active isomer of the herbicide Frontier (dimethenamid) and has been submitted to EPA for registration on potatoes. Treatments were replicated four times. The potato canopy covered the rows early this year, keeping us from hand weeding the plots. At the end of the season, weeds were apparent in some plots, but competitive effects were negligible. Volunteer Barley Control with Select Volunteer barley was broadcast over the entire trial on April 22. Prowl (0.75 lb ai/acre) was applied April 23 and incorporated with the lilliston. The lilliston also incorporated the barley seed. Prowl was used to control other weeds without having much impact on the barley. Grass herbicides were applied on June 4 when potatoes and barley both averaged 9 inches in height. Treatments were replicated four times. Potato injury and barley control were evaluated until the potato canopy outgrew the barley. potato yield was determined by harvesting the center two rows of each plot, but tubers were not graded. Results, Discussion, and Conclusions In 1999, the spring weather was cool and dry and then warmed up shortly after planting. Potatoes emerged and quickly formed a canopy while weed germination was low. The low weed germination and early potato canopy resulted in excellent weed control from almost all of the preemergence herbicide combinations evaluated. Potato Response and Weed Control with Sulfentrazone Combinations Sulfentrazone alone and in combination with other herbicides did not cause significant potato injury (Table 1). All of the treatments provided at least 87 percent control of redroot pigweed, common lambsquarters, and hairy nightshade. Barnyardgrass was not present at high enough populations to be evaluated. Sulfentrazone at the lowest rate evaluated provided at least 99 percent control of all three weed species. alone provided slightly less redroot pigweed control than the other treatments. On 155

September 1, alone and plus had slightly lower control of common lambsquarters and hairy nightshade than the other treatments, except for alone. tuber yields were not different among treatment (Table 2). All treatments increased U.S. Number One and total marketable tuber yields in comparison to the untreated check. Sulfentrazone plus Dual II Magnum had higher U.S. Number One and total marketable yields than sulfentrazone at the highest rate (0.375 lb ai/acre), sulfentrazone plus or or Eptam, plus, and alone. The results suggest that potatoes are tolerant to sulfentrazone at rates higher than needed for effective weed control. Preemergence Herbicides for Weed Control in Russet Burbank Potatoes Postemergence applications of Dual Magnum in combination with or caused significant foliar injury, with the injury being more severe with the Dual Magnum plus combination (Table 3). None of the preemergence treatments caused visible injury. Injury from the postemergence treatments became less apparent as the season progressed. On June 15, Dual Magnum applied preemergence and Dual Magnum plus applied postemergence provided the least control of redroot pigweed. The postemergence combination improved as the season progressed, but the preemergence application of Dual Magnum still had only 80 percent redroot pigweed control on September 1. All other treatments provided greater than 90 percent redroot pigweed control. Common lambsquarters and hairy nightshade control was also poor with the postemergence application of Dual Magnum plus at the early evaluation, but was among the best by the September evaluation. BAS 656 07 H plus, Prowl plus, and alone had greater than 95 percent control of redroot pigweed, common lambsquarters, and hairy nightshade throughout the entire season. All treatments increased total yields (Table 4) compared to the untreated check except for Dual Magnum plus. The reduced total yield may have been due to the severe injury early in the season. Prowl plus and Eptam plus had among the highest yields of U.S. Number One and total marketable tubers while Dual Magnum alone preemergence and Dual Magnum plus postemergence were not different from the untreated for total marketable yield. Prowl plus yielded higher than Prowl plus for total U.S. Number One and total marketable potato yields. Prowl plus (167 cwt/acre) produced more undersize tubers than plots treated with Prowl plus (139 cwt/acre). Slightly lower weed control with the Prowl and combination may have resulted in the lower yields. Tolerance of Russet Burbank Potatoes to BAS 656 07H No potato injury or differences in potato yield and quality were observed when BAS 656 07 H, Frontier, Dual II Magnum, and Prowl were applied at twice the labeled field rate (Table 5). Even at 4 times the typical use rate, BAS 656 07 H and Dual II Magnum did not cause significant injury or reduce potato yields. These results suggest that potato tolerance to the herbicides evaluated is very high. Although not significant, low weed pressure in the untreated check may have depressed yields for that treatment. 156

Volunteer Barley Control with Select Herbicide activity was slow because the barley was so large when the postemergence treatments were applied. On June 18, barley control (Table 6) was greatest with Select at the high rate (0.188 lb ai/acre). Poast alone and Select combined with provided the least control. The addition of to Select appeared to decrease early control. However, by June 23, barley control was similar for all Select treatments but lower with Poast. All herbicide treatments increased potato yield compared to the untreated check. Select would be useful for postemergence control of volunteer barley and other grass species in potatoes. 157

Table 1. Weed control and potato injury on June 15 and September 1 with sulfentrazone combinations, Malheur Experiment Station, Oregon State University, Ontario, Oregon, 1999. Weed control Potato Injury Redroot pigweed Common lambsquarters Hairy nightshade Treatment Rate 6-15 6-15 9-1 6-15 9-1 6-15 9-1 lb ai/acre % Sulfentrazone 0.125 6 99 99 100 100 99 100 Sulfentrazone 0.188 0 100 100 100 100 98 98 Sulfentrazone 0.25 8 100 99 99 100 99 99 Sulfentrazone 0.375 6 100 100 100 100 99 100 Sulfentrazone + 0.188 + 0.5 3 100 100 100 100 100 100 Sulfentrazone + 0.188 + 0.016 6 99 100 100 100 93 96 Sulfentrazone + Eptam 0.188 + 3.0 3 100 98 100 100 98 98 Sulfentrazone + Dual II Magnum 0.188 + 1.0 0 100 99 100 100 98 99 Sulfentrazone + BAS 656 07 H 0.188 + 0.64 0 100 100 100 100 96 100 Sulfentrazone + Prowl 0.188 + 1.0 1 99 100 100 100 99 100 + 0.5 + 0.016 0 100 100 94 90 99 87 Eptam + 3.0 + 0.5 0 100 96 100 100 100 96 0.5 0 100 96 93 97 99 92 0.016 0 94 88 94 91 91 88 Sulfentrazone 0.188 3 98 100 100 100 100 96 Untreated 0 0 0 0 0 0 0 LSD (0.05) NS 3 4 6 5 6 7 158

Table 2. Russet Burbank tuber yieldt and grade in response to sulfentrazone combinations, Malheur Experiment Station, Oregon State University, Ontario, Oregon, 1999. U.S. Number One Treatment Rate 4-6 oz 6-12 oz > 12 oz % no. 2 marketable yield lb ai/acre cwt/acre % cwt/acre Sulfentrazone 0.125 135 221 60 416 72 13 429 577 Sulfentrazone 0.188 143 215 48 405 72 8 413 561 Sulfentrazone 0.25 129 225 54 408 74 8 417 549 Sulfentrazone 0.375 134 196 53 383 69 12 395 550 Sulfentrazone + 0.188 + 0.5 144 195 58 396 73 7 404 541 Sulfentrazone + 0.188 + 0.016 125 194 59 378 71 14 391 531 Sulfentrazone + 0.188 + 3.0 134 200 57 391 71 8 399 552 Eptam Sulfentrazone + 0.188 + 1.0 141 234 65 440 76 14 454 578 Dual II Magnum Sulfentrazone + 0.188 + 0.64 151 226 49 427 75 5 432 569 BAS 656 07 H Sulfentrazone + 0.188 + 1.0 145 223 38 406 72 6 412 563 Prowl + 0.5 + 0.016 129 213 48 390 73 7 397 535 Eptam + 3.0 + 0.5 154 194 50 397 70 7 404 566 0.5 145 207 49 401 72 8 409 558 0.016 153 201 32 386 70 10 396 548 Sulfentrazone 0.188 140 215 51 405 73 7 412 554 Untreated 143 164 26 333 68 9 342 490 LSD (0.05) NS NS NS 44 4 NS 45 NS tpotatoes were harvested on September 21 and 22. 159

Table 3. Potato injury and weed control with preemergence and postemergence herbicide applications, Malheur Experiment Station, Oregon State University, Ontario, Oregon, 1999. Weed control Injury Redroot pigweed Common lambsquarters Hairy nightshade Treatment Rate Timing lb ai/acre 6-15 6-15 9-1 6-15 9-1 6-15 9-1 ok Frontier + 1.17 + 0.5 PRE 2 99 97 84 95 79 85 BAS 656 07 H + 0.64 + 0.5 PRE 2 100 100 100 100 100 100 BAS 656 07 H + 0.64 + 0.016 PRE 0 92 97 90 87 99 93 BAS 656 07 H + 0.64 + 1.0 PRE 0 99 90 92 92 85 83 Prowl Prowl + Eptam + 1.0 + 3.0 + 0.5 PRE 3 100 100 100 100 98 90 Prowl + 1.0 + 0.5 PRE 0 100 97 98 100 100 97 Prowl + 1.0 + 0.016 PRE 0 96 100 90 95 85 86 Eptam + 3.0 + 0.016 PRE 0 100 96 100 100 97 80 Eptam + 3.0 + 0.5 PRE 2 100 100 100 100 97 95 Dual Magnum + 1.6 + 0.016 POST 23 77 100 70 94 83 100 Dual Magnum + 1.6 + 0.5 POST 33 92 100 90 100 84 97 Dual Magnum 1.6 PRE 0 75 80 99 93 88 83 0.5 PRE 0 100 100 100 100 93 93 0.016 PRE 0 95 97 95 93 100 95 + 0.5 + 0.016 PRE 0 100 100 100 100 100 93 Untreated 0 0 0 0 0 0 0 LSD (0.05) 4 7 8 11 7 15 15 160

Table 4. Tuber yieldt and quality in response to preemergence and postemergence herbicide applications, Malheur Experiment Station, Oregon State University, Ontario, Oregon, 1999. Treatment Rate Timing U.S. Number One 4-6 oz 6-12 oz > 12 oz no. 2 marketable yield lb ai/acre cwt/acre % cwt/acre Frontier + 1.17 + 0.5 PRE 145 217 30 392 72 7 399 546 BAS 656 07 H + 0.64 + 0.5 PRE 147 249 34 430 74 12 443 581 BAS 656 07 H + 0.64 + 0.016 PRE 142 229 42 412 72 7 419 570 BAS 656 07 H + 0.64 + 1.0 PRE 149 223 46 417 72 8 425 577 Prowl Prowl + Eptam + 1.0 + 3.0 + PRE 144 239 52 435 75 11 447 581 0.5 Prowl + 1.0 + 0.5 PRE 156 253 42 451 74 16 467 610 Prowl + 1.0 + 0.016 PRE 143 215 32 391 69 9 400 568 Eptam + 3.0 + 0.016 PRE 148 208 37 393 70 7 400 565 Eptam + 3.0 + 0.5 PRE 151 253 46 450 77 7 457 587 Dual Magnum + Dual Magnum + - 1.6 + 0.016 POST 148 256 38 443 78 8 451 570 1.6 + 0.5 POST 145 223 24 392 76 2 394 518 Dual Magnum 1.6 PRE 142 215 26 383 70 7 390 550 0.5 PRE 144 244 42 429 75 10 439 571 0.016 PRE 148 244 45 436 74 8 443 589 + 0.5 + 0.016 PRE 139 253 40 432 75 10 442 575 Untreated 127 180 26 333 68 10 343 486 LSD (0.05) NS 38 NS 51 5 NS 53 49 t Potatoes were harvested on September 20. 161

Table 5. Potato injury and yield t in response to preemergence herbicide applications, Malheur Experiment Station, Oregon State University, Ontario, Oregon, 1999. Treatment Injury U.S. Number One Rate Field rate 5-29 6-29 4-6 oz 6-12 oz >12 oz Two's Marketable Yield lb al/acre cwt/acre % -----cwt/acre------ Frontier 6.0 2.34 2X 4 3 126 198 29 353 67 14 368 526 BAS 656 07 H 0.64 lx 6 3 129 165 22 316 63 13 329 499 BAS 656 07 H 1.29 2X 11 4 133 185 33 351 66 18 369 529 BAS 656 07 H 2.58 4X 9 5 132 190 22 344 66 21 365 524 Dual II Magnum 2.6 2X 4 0 140 179 23 343 64 21 364 533 Dual II Magnum 5.2 4X 4 1 130 190 22 342 65 23 365 524 Prowl 3 2X 1 1 144 180 31 355 66 26 381 537 Untreated 3 3 133 184 19 336 67 18 354 498 LSD (0.05) NS NS NS NS NS NS NS NS NS NS -p otatoes were harvested on September 21 and 22. Table 6. Volunteer barley control with postemergence grass herbicides, Malheur Experiment Station, Oregon State University, Ontario, Oregon, 1999. Injury Barley control Treatment Rate 6-18 6-23 7-7 6-18 6-23 7-7 Potato yieldt lb ai/acre cwt/acre Select + COC 0.094 + 1 qt 0 3 0 60 80 85 518 Select + COC 0.125 + 1 qt 0 3 0 60 77 82 552 Select + COC 0.188 + 1 qt 0 3 0 67 73 83 499 Select + + 0.125 + 0.38 + 3 8 0 48 72 83 520 COC 1 qt Poast + COC 0.188 + 1 qt 3 5 0 50 60 65 564 Untreated 0 0 0 0 0 0 366 LSD (0.05) NS NS NS 5 9 17.6 78 -Potatoes were harvested on September 22. 162