The recent development of genetically modified varieties with resistance to Roundup and Liberty herbicides offers exciting opportunities for weed control cost savings. While processors currently are not accepting transgenic varieties, the future for this technology seems bright. Two varieites with Roundup resistance and one with Liberty resistance are under evaluation at KES in 1999.

Variety Trials

KES and the Intermountain Research and Extension Center at Tulelake, California conduct coded variety trials annually on behalf of the California Beet Growers Association (CBGA). Only varieties meeting minimum performance standards in these trials may be marketed in the region. Trials typically include about 30 entries from five seed companies. Approximately 20 varieties are approved for commercial use in the Klamath Basin.

Post-emergence Herbicides

Several post-emergence herbicides have been evaluated alone or in combinations for efficacy in controlling weeds and for crop tolerance. Untreated controls have also been evaluated to determine effects of weed competition on crop performance. When weeds were allowed to remain full season in a 1995 study, beet yield was reduced from about 20 tons/acre in treated culture to 8 tons/acre. In 1993, removing weeds by hand 12 weeks after planting resulted in a 50 percent yield loss and a reduction in sugar content of 1.5 percent compared to treatments that provided good early season weed control. Several products or combinations of products have been identified which provide good control of weed species common to the site with no crop injury.

Nitrogen Fertilizer

Sugarbeet response to nitrogen fertilizer applied at 50 to 200 lbs/acre was minimal in each of two years. Beet yields were not significantly affected in either year and were numerically greatest at 50 lbs N/acre in both years. Higher N rates resulted in elevated nitrate-nitrogen levels in petioles and a trend for reduced sugar content in beets. Studies were conducted on mineral soils with less than 2.0 percent organic matter in the top foot and less than 1.0 percent at greater depths. Residual nitrate-N and mineralizable N in the top three feet of the soil profile were estimated at less than 100 lb N/acre. In 1994, beet yields were over 35 tons/acre in all treatments. Estimates of 8 lb N required/ton of beets, reported from other production areas, appears to be too high for beets produced in the Klamath Basin.

Planting Date

Early planting is key to achieving high yields in the short growing season available. Research conducted over four years consistently demonstrated that each week delay in planting date after May 1 resulted in a 600 lb/acre reduction in total sugar production. The reduction was due to a loss in yield, not to reduced sugar content. Over a range of planting dates from early April through late May, sugar content has been quite consistent. The risk of stand failures due to frost injury does not appear to be much greater for early plantings, than for plantings in mid-May. Mid-May appears to be the latest planting date that can be expected to produce a profitable crop.

Plant Population

Populations from 8,000 to 32,000 plants/acre were evaluated over planting dates from mid-April through late May in 1994. High populations were more beneficial in early plantings. Yields were not significantly different at 15,000, 23,000, and 30,000 plants/acre averaged over planting dates. Further population reductions to 12,000 and 8,000 plants/acre significantly reduced beet and total sugar yields. Sugar content was slightly, but not significantly higher at the highest population. For late May planting, 23,000 plants/acre produced beets large enough for harvest efficiency. At 32,000 plants/acre a portion of beets were too small to recover with commercial equipment.