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Harlene M. Hatterman-Valenti, Collin P. Auwarter, and Paul G. Mayland

Field trials were initiated during 2004 at a dryland site near Prosper, N.D., to evaluate the effects of simulated drift from glyphosate to `Russet Burbank' and `Red Lasoda' seed potato during the early senescence stage. Glyphosate was applied at rates 1/3, 1/6, 1/12, 1/24, and 1/48 the use rate for spring wheat desiccation on 10 Sept. 2004 with a CO2 pressurized sprayer operated at 280 L/ha and 276 kPa. The amount of a.m.S added to the spray solution was also reduced accordingly. Following harvest, samples from each plot were placed into cold storage until the following March. A subsample from each plot was slowly warmed to initiate sprout formation. Remaining samples were cut into 57-g pieces, dusted with a seed piece treatment, and stored at 18 °C with about 90% RH until planted. Plots consisted of two 3-m rows at 91 cm-row spacing with a border row on each side and three spacer plants between plots. The trial was arranged as a randomized complete block with four replications. Plots were desiccated on 12 and 19 Sept. and harvested 11 Oct. Tubers were hand-graded shortly after harvest. Results indicated that glyphosate at 70 g ae/ha or more inhibited tuber budbreak by 75% or more compared to untreated. In the field, injury was observed as delayed emergence and, in several instances, no plants emerged. Total yield for `Red Lasoda' was 34.8 Mg/ha for the untreated, which was significantly greater than glyphosate treatments of 280, 140, and 70 g ae/ha. `Russet Burbank' total yield was considerably less at 23.5 Mg/ha for the untreated. Both the untreated and glyphosate at 18 g ae/ha had significantly greater total yields compared with glyphosate treatments of 280, 140, and 70 g ae/ha.

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Harlene M. Hatterman-Valenti, Carrie E. Schumacher, Collin P. Auwarter, and Paul E. Hendrickson

Field studies were conducted at Absaraka, Carrington, and Oakes, N.D., in 2005 to evaluate early season broadleaf weed control and onion (Allium cepa L.) injury with herbicides applied preemergence to the crop. DCPA is a common preemergence herbicide used in onion. However, DCPA can be uneconomical in most high-weed situations, or the usage may be restricted due to possible groundwater contamination. Potential substitutes evaluated were bromoxynil, dimethenamid-P, and pendimethalin. Main broadleaf weeds were redroot pigweed (Amaranthus retroflexus L.) and common lambsquarters (Chenopodium album L.). In general, all herbicides, except bromoxynil, provided acceptable broadleaf weed control 4 weeks after treatment. The highest herbicide rate provided greater weed control compared with the lowest rate for each herbicide. However, onion height was also reduced with the highest herbicide rate. In addition, the two highest rates of dimethenamid-P reduced the onion stand compared with the untreated. A postemergence application of bromoxynil + oxyfluorfen + pendimethalin to onion at the four- to five-leaf stage controlled the few broadleaf weeds that escaped the preemergence treatments and provided residual control of mid- and late-season germinating broadleaf weeds at two of the three locations. Intense germination of redroot pigweed during July at the Oakes location reduced onion yield with all treatments compared with the hand-weeded check. In contrast, total onion yields with all herbicide treatments except the high rate of dimethenamid-P were similar to the hand-weeded check at Absaraka and Carrington.