Larry Smith, Sugarbeet
Research
University of Minnesota--Northwest Experiment Station
Crookston, Minnesota
A split or lay-by application of Eptam at the first cultivation, or when the sugarbeets are in the 4-leaf stage, may be another tool in controlling weeds in sugarbeets. This lay-by application is applied about 3-4 weeks after the sugarbeets are planted, assuming normal conditions for germination and growth. At this time, preplant incorporated herbicides may be losing some activity and thus their ability to control unemerged or newly emerged weed seedlings. The lay-by application is made with a simple nozzle attachment on the discs of a sugarbeet cultivator and applied at the first or second cultivation.
The plots with the fall Eptam were planted on May 1, and the check and spring Eptam plots on May 13. The variety was American Crystal ACM-30. Lay-by Eptam applications were applied to the plot with the fall applied herbicide on May 25, and applied to the check and spring herbicide plots on June 6. Lay-by rates were 1.75 and 3.5 lb/A Eptam. Spray gallonage was 17.5 gpa at 20 psi and tractor speed of approximately 2.5 mph. The soil temperature was 71 F at a 6-inch depth when applied on May 25 and 76 F on June 6. The sugarbeets were in the 4-leaf stage of growth on May 25. Stage of growth ranged from the cotyledon to 4-leaf stage of growth when the June 6 lay-by treatment was applied, due to uneven germination. Twelve rows were treated at both rates and six rows were packed with a Swenson 3-pt. beet roller to determine if packing the soil enhanced herbicide action.
Three nozzle types, flat fan, hollow cone and solid stream, were compared to determine their effectiveness in the lay-by application. The hollow cone nozzles were fitted with short pieces of tubing to give a dripping affect.
The discs on the sugarbeet cultivator were set to make a surface cut of 3 inches. The depth of the cut varied from 2-3 inches depending on soil conditions. Two nozzles on each side of the disc were positioned to place the Eptam at the bottom of the disc cut. This was no problem with the solid stream nozzles, but some spray from the hollow cone and flat fan nozzles did hit the sides of the cut. The shields on the cultivator were set to allow soil to flow back into the disc cuts and cover the lay-by application.
Injury and stand reduction readings were made 10 and 21 days after application of lay-by treatments. Weed control ratings were made on July 27. Only the rows treated with the flat fan and solid stream nozzles were used in the above evaluations, as it was apparent at this time that these were the most satisfactory nozzle types.
Because of the differences in planting dates, plot sites, and weed populations, no comparisons between the plot with the fall applied Eptam versus the check and spring applied plots will be made.
The control plot with no lay-by application yielded only 3.5 ton of sugarbeets per acre. This was primarily due to an extremely high population of green foxtail. Where the lay-by treatments were applied, sugarbeet yields increased approximately 400 percent. Green and yellow foxtail control from the lay-by applications ranged from 51-94 percent control. Control was best where 3.5 lb/A of lay-by Eptam was used. While the control at 1.75 lb/A Eptam was less, the surviving plants were stunted and had a reduced root system. Redroot pigweed control ranged from 66-78 percent. While this percentage control is large, the amount of remaining pigweed was unsatisfactory and caused reduced yields, as the surviving plants grew vigorously due to reduced competition from other weeds, especially the foxtails. Wild buckwheat control ranged from 75-100 percent control.
The lay-by treatments increased weed control and yield when applied to the plot with spring applied Eptam (Table 2). The foxtail and lambsquarter control increased the most with the lay-by treatments. Additional pigweed control ranged from 0-33 percent. It should be noted, however, that the spring Eptam had controlled 93 percent of the pigweed in the plot (Table 4). Yield increase ranged from 3-4 ton per acre.
The plot with the fall applied Eptam did not have as great a weed population as the other two plots. Increases in weed control due to the lay-by treatments, were noted for all weed species measured (Table 3). Little yield increase was noted from the extra weed control due to the smaller weed population.
Table 4 and Table 5 show the effect on yield and weed control of fall and spring applied Eptam plus the lay-by applications versus a check plot with no herbicide.
Sugarbeet seedling injury was observed from all lay-by treatments. The injury rated involved curling and dying of the new growth in the sugarbeet seedling. The injury was the least when the lay-by treatments were applied to the check and fall Eptam plots (Table 1 and Table 3). The greatest injury occurred in the plot with the spring applied Eptam (Table 2). In this plot the lay-by treatments caused injury ranging from 18-25 percent when 3.5 lb/A lay-by Eptam was used. At the 1.75 lb/A rate, injury ranged from 10-12 percent.
In most cases the injury disappeared after a couple of weeks in the fall Eptam and check plots and no large stand reduction occurred. However, on the plot with spring Eptam, a stand reduction of 9-13 percent occurred at the higher lay-by rates. This amount of stand reduction would not be serious in a year with high sugarbeet seedling populations, but could well contribute to a yield reduction in years with poor stands. Another effect of the injury caused by the lay-by applications could be in the thinning operation, as the injured beets were smaller in size and may be removed or left by electronic thinners, causing changes in desired final populations.
No large advantage from packing the soil after the lay-by treatment was observed. Some increase in injury was noted, especially at the higher lay-by rates on the plot with spring applied Eptam. An advantage for packing could exist if adequate soil does not flow back into the disc cut following the lay-by application.
No large differences in weed control were observed between the solid stream or flat fan nozzles. However, more injury was observed with the flat fan nozzles. This injury was the greatest when the disc cut came within .5-.75 inches of the sugarbeet seedling. This put the seedling roots closer to the disc cut and with a greater herbicide coverage of the cut from the flat fan nozzles may increase root uptake by the seedling.
In the spring Eptam and control plots, the seedling size ranged from cotyledon to 4-leaf stage at the lay-by application. It was observed that the seedlings in the 4-leaf stage were injured more than those in the cotyledon or two leaf stage, suggesting an earlier application may reduce injury.
The data in this trial represents 1 year of study. Results may vary from year to year and conclusions drawn from 1 year of work may not hold true in another year. This trial will be expanded in 1979 to measure more parameters.
1978 Sugarbeet Research and Extension Reports. Volume 9, pages 89 - 94.
