1991 Annual Report for LW91-022
Brassica Utilization in Sugar Beet Rotations for Biological Control of Cyst Nematode
Summary
Objectives
1.Determine the effects of various cultural practices on biological control of sugar beet cyst nematodes and demonstrate the use of nematode-resistant brassicas in sugar beet rotations.
2.Determine costs, returns and benefits of practices utilizing nematode-resistant brassicas for potential use in sugar beet rotations.
3.Develop and deliver educational information and materials for sugar beet producers and conduct in-service training for Cooperative Extension personnel.
Abstract of Results
Trap-crops radish and mustard, introduced into sugar beet rotations, as alternatives to nematicides, were evaluated during 1992-94.
Trap-crop radishes were most effective in reducing the Sugar Beet (Cyst) Nematode population and increasing sugar beet yields the following year when following malt barley in the rotation. Soil populations of the Sugar Beet Nematode were reduced 54 to 75 percent over a two-and-a-half month period, resulting in a 3.91 ton/acre increase in sugar beet yield. When radishes followed removal of silage corn the increase in sugar beet yield was 2.60 tons/acre. Radishes were less effective following dry beans, compared to barley and corn, because of the later planting date and the very high Sugar Beet Nematode population on the field studied. Soil populations of the pest were reduced on all five fields where radishes were planted.
Trap-crop radishes had a more positive effect on sugar beet yields than the full-label rate of chemical pesticide aldicarb in two of five cooperator tests. In two tests neither radishes nor aldicarb had a significant effect on yield. There appears to be no additive effect of radishes and aldicarb on Sugar Beet Nematode population reduction.
Estimated increase in sugar beet yield necessary to pay the cost of growing trap crops was 2.0 tons/acre; therefore, planting radishes following malt barley and silage corn in 1992 was a profitable operation. On two fields in 1994 (radishes in 1993), sugar beet yields were low due to environmental and other reasons, masking any effect of radish use.
Based on average lamb performance in the five grazing trials conducted and the five-year average lamb price in October, the value of lamb gain/acre more than offset the cost of producing and grazing trap-crops radish and mustard. Both species are readily grazed by lambs in the fall and provide a high-quality forage, allowing value to be added before marketing. Grazing did not negate the Sugar Beet Nematode reduction potential of radish because grazing was after soil temperatures had decreased below the minimum for nematode activity.
In summary, the nematode-trapping varieties of radish and mustard, which are currently used in Europe as a replacement for nematicides, are effective and profitable in the sugar beet rotation of Wyoming in which malt barley is grown. Trap-crop radish can be grown in lieu of aldicarb, provided that the initial population of Sugar Beet Nematode does not exceed ten to twelve eggs and/or juveniles per cm3 of soil. The radish crop can be utilized as fall grazing to improve returns without sacrificing Sugar Beet Nematode control. Crop rotation is still an essential part of an integrated Sugar Beet Nematode control program. In sugar beet-growing areas not utilizing malt barley in rotation, further work is needed to adapt the biological method of trap cropping.
Potential Contributions
Use of trap crops could have potential benefit to sugar beet growers in several ways. (1) They could reduce the need for the nematicide, aldicarb. (2) They might help maintain short sugar beet rotations and increase grower profits, since sugar beets are the state's most profitable crop. (3) By reducing aldicarb use, the potential hazard to ground water contamination would be reduced. (4) Effective reduction in Sugar Beet Nematode by trap crops would reduce the potential impact if aldicarb is removed from the market. (5) Trap crops may be an effective means of recycling nutrients. The capture of residual nitrates would be particularly important in reducing ground water contamination. (6) Reducing the use of aldicarb would reduce hazard to growers and farm workers. (7) They would provide fall and winter cover for soils which are subject to severe wind erosion. (8) They provide high-quality organic matter to soils which have been somewhat depleted of organic matter as a result of intensive production for as long as 50 years. (9) And, they provide an additional source of income from grazing animals, thereby diversifying farm operations.
Farmer Adoption
Seed for trap crops has only recently become available, although it still is not available at local co-op's or retail seed stores. Sugar companies, which play a key role in change of practices, have been slow in promoting the practice of using trap crops. In 1995, however, one of the sugar companies sponsored an aggressive trap crop demonstration program. Since all sugar beet acreage is contracted, farmers are hesitant to utilize a practice if it is not promoted by the sugar beet company. Farmer cooperative's are a key element in the infrastructure in that they provide services which will be important to the selection of fields and timely planting of trap crops. Their service role is in procuring seed, assisting in taking soil samples, and in applying fertilizer and seed. To be successful, trap crops need to be planted before completion of the main crop (in this case, malt barley). Therefore, the role of the cooperative is in assisting the farmer in planting trap crops without the need to stop harvesting the main crop.
Operational Recommendations.
1. Farmers should plant trap crop radishes or mustard following malt barley harvest. 'Pegletta' and 'Adagio' radish and 'Metex' and 'Maxi mustard are the varieties which have proven effective to date.
2. These crops should be planted as soon as possible. Waiting until after all barley is harvested will greatly reduce the growth of trap crops and diminish the ability to reduce Sugar Beet Nematode populations.
3. To facilitate early planting at a busy time, trap crops can be stubble planted if loose straw is removed or burned and a disk drill is used. Alternatively, seed can be mixed with fertilizer and broadcast, provided that the seed is then covered with a harrow and/or cultipacker.
4. To encourage maximum growth, trap crops will need good soil moisture and at least 50 lb/acre of nitrogen fertilizer.
5. Candidate fields for trap crop use should be targeted in the spring before barley is planted. Soil samples for Sugar Beet Nematode analysis should be taken. Planting these fields first with an early barley variety, if given a choice will facilitate the early planting of the trap crop.
6. On sandy soils trap crops should be left over winter as cover and plowed down in the spring.
7. Trap crops can be grazed to advantage with lambs (cattle grazing has not been evaluated). Since these crops are cold hardy, grazing can be delayed until late October without significant loss of forage quality.
New Hypotheses
1. Trap crops provide a positive benefit, other than reduction of Sugar Beet Nematode, to succeeding sugar beet crops in that they improve soil conditions through high quality organic matter addition.
2. Trap crops planted on light-textured soils conserve soil if not plowed down in the fall.
Reported in 1995