THE EFFECT OF CULTIVATION ON TRANSGENIC SUGAR BEETS
Terry D. Miller
INTRODUCTION
Are cultivations necessary if herbicide resistant varieties are available to growers? If weeds can be controlled without cultivation, when does cultivation have beneficial effects other than weed control? Some growers believe the first cultivation of sugar beets allows the roots to be aerated and, therefore, promotes better growth. Sugar beets have not been grown without this first cultivation because genetically modified (transgenic) varieties that are resistant to herbicides, had not been developed. Today both Liberty Link and Roundup Ready sugar beets are available, but these varieties have yet to be approved for planting. It is now possible to evaluate the merits of cultivation when the weeds are controlled with herbicides.
MATERIALS AND METHODS
Two separate tests were established, one with Roundup Ready sugar beets, and another using a Liberty Link variety. Four treatments were devised to evaluate the effects of cultivation on sugar beet growth.
1) no cultivation
The least expensive option would be not to cultivate at all (treatment #1). The first cultivation occurs as soon as the beets can be seen well in the rows. This cultivation normally is the most difficult and slowest. A set of discs or knives are placed to cut as close to the beets as possible without injuring them. This leaves a narrow ribbon of soil with the young beet centered in the middle. All the soil between the rows is cultivated to kill any germinated weeds. A layaway cultivation is the final cultivation for the year and normally occurs just prior to row closure. This cultivation varies with the type of irrigation system used to water the crop. If the field is irrigated with a center pivot on medium or heavy soil, a reservoir tillage (dammer diker) cultivator is used. If the fields are irrigated by gravity, hand or wheel lines, the cultivation does not punch holes in the ground but pushes soil up around the beet trying to cover up any young weeds. Additional cultivations between cutaway and layaway are dictated by the germination of weeds throughout the early part of the season. Treatment #4 is a typical grower standard number of cultivations. Each plot received cultivations according to the listed treatments on the following dates:
First Cultivation - 24 May
Herbicides were applied as follows: All applications were broadcast with 11001VS Tee Jet nozzles @ 25 psi. Roundup was applied at 1 qt/A and Liberty at 28 oz/A. Both spray mixes included 3 lbs ammonium sulfate/A.
First Application - 24 May - 12.5 GPA
Yield data was collected on October 13. All beets were piled in a non-crop area and allowed to freeze over the winter.
RESULTS
The Roundup Ready plot was damaged by frost. The stand was reduced enough to reduce the yield and introduce additional variability into the study. An additional pass was harvested from the Roundup Ready study, hoping to reduce some of the yield variability. The stand, after the multiple frosts, would not normally be acceptable, but the decision was made to continue the test in spite of the stand reduction. The reduced stand produced skips that would allow sunlight to stimulate weed growth. Reduced competition from the sugar beet plants makes weed control more difficult. This situation provided additional control information in a reduced stand situation.
The weed control was exceptional in both studies. It was difficult to find weeds with any of the treatments, and there was not a single weed that grew above the beet canopy at harvest. The weeds were so few that we could not get any viable weed count results. Periodically, a small weed could be found in the soil that was disturbed with the dammer diker. The commercial plantings on either side of these tests looked weedy even after three Betamix applications and a hand hoeing.
There were no significant differences in yield in either study. All treatments produced equally well. The Liberty plot yielded about three tons/A (Figure 2) better than the Roundup study (Figure 1), but this was expected considering the stand reduction due to frost. It was more difficult to harvest the no cultivation plots because there was no furrow for the steering wheels of tractor pulling the harvester to follow. More attention had to be given to staying in the center of the row. This could cause some problems in harvesting a larger acreage because it takes attention away from watching the operation of the harvester.
It appears that if and when transgenic modified sugar beets are approved they will offer a significant benefit to the grower for weed control and that cultivation will not increase yield. Weed control will increase when transgenic varieties are available to growers. The deciding factor that will regulate these varieties acceptance will be the cost of the seed or the program presented by those who develop these varieties and the acceptance of the public.
No analysis of sugar content was performed because we did not want there to be any possibility of any transgenic materials getting into food channels.
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Presented at Snake River Sugar Beet Conference January 13-14, 2000
Miller, Terry D., President, Miller Research Inc. 1175 East 800 North, Rupert, Idaho 83350, Phone (208) 531-5124