South Dakotans Like 22" Rows' Impact on Weeds
When it comes to sunflower row spacing width, the pendulum has swung from one side to the other for father/son Ken and Vaughn Thorstenson - and it now has settled into a zone they believe is ideal for their north central South Dakota no-till operation.
The Thorstensons farm near Selby, S.D., with son-in-law and brother-in-law Brian Begeman. For a number of years, Ken planted sunflower with an IH Cyclo set up on 36-inch rows. While the Cyclo's seed placement was satisfactory, the Thorstensons didn't like the extra
"breathing room" afforded weeds by their unit's wide row spacing. That concern took on added weight when they began a transition into no-till crop production several years ago.
In 1997 Vaughn decided to plant a small portion of their sunflower acreage in 22-inch rows. His objective was two-fold: to (1) obtain inter-row weed suppression from the tighter sunflower canopy while (2) still allowing enough space for postemergence chemical applications with their high-profile sprayer. They didn't have another row-crop planter,
however, so Vaughn's interim answer was to simply plug alternate runs on the airseeder they used for their small grain crops.
The result? "I liked the 22-inch row spacing; but we weren't satisfied with the placement of the seed" within the rows, he reports. So for 1998 the Thorstensons purchased a used JD 7300 MaxEmerge set up on 22-inch rows. That acquisition allowed to achieve, in their view, the best of two worlds: improved in-row seed placement, and a tight crop canopy which significantly aided weed management on sunflower acreage. The more-equidistant spacing (about 10 inches between plants within the row) also contributed to better utilization of soil moisture and nutrients across the field, Vaughn states.
The Thorstensons' weed control program on no-till sunflower ground begins with an early preplant burndown, normally around the third week of April. They'll start seeding 'flowers as soon as they're finished with corn, which in 1998 was mid-May. Depending on emerged weed populations, they'll commonly apply a pre-emergence burndown as well, followed by a
post grass treatment.
While he's certainly not complaining, Vaughn says their narrower rows can complicate that postemergence treatment. "Often, there's only about a four- or five-day period between the time the last flush of grasses has emerged and when the 'flowers are closing the rows. If we don't get in there quickly, we may not be able to apply the grass herbicides without doing some crop damage," he indicates. "Those rows get so tight with leaves; plus, it becomes more difficult to get the spray down beneath the sunflower canopy.
"[Last year,] a week after I had sprayed the post herbicide, I went back in because there were a couple Canada thistle spots I wanted to hand spray," he illustrates. "Though I knew right where they were, I had a terrible time finding them because the canopy had closed so
The Thorstensons strive for at least a four-year rotation (and preferably five) between sunflower crops in order to minimize disease risk. Cheatgrass and bromes in the wheat are their biggest weed challenges; but they say that having sunflower slotted between their
winter and spring wheat crops has aided the manage-ment of these problem grasses. "You have those two shots of Roundup," Vaughn points out, noting that their sunflower grass herbicide also helps control cheatgrass when used at a higher-end rate.
They say their sunflower ground typically is quite clean for the succeeding spring wheat crop. "In our rotation, I'd guess that nine years out of 10 our best wheat is after sunflower," Vaughn adds.
Though their 7300 MaxEmerge is equipped with trash wheels, the Thorsten-sons lift the wheels when planting sunflower. While the row cleaners would probably help hasten emergence by leaving exposed soil strips, they believe they'd end up mixing additional weed seeds into the seed row. "So we tend to lift up our trash wheels and slot in the sunflower," Vaughn says. They have Keeton seed firmers behind the closing wheels and dribble in anywhere from three to seven gallons of 10-34-0 off the end of the firmers.
Even with their narrower rows, the Thorstensons have found a sunflower seed drop in the low 20s to be about as thick as they should go. They went to 25,000 on a couple fields last year, but found that was definitely too thick - particularly since rainfall was short on those
fields. Staying in the lower 20s provides them with a plant stand that's very satisfactory for both optimum yield and sufficient leaf canopy for weed suppression. - Don Lilleboe
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