1) SUMMARY

Pest Complexes and Variability:  (A) Environmental conditions: Sugarbeets are grown in a wide range of environments in California, from the low desert in Imperial County to 4,000 feet above sea level in Siskiyou and Modoc Counties.  Conditions in these diverse environments at the time of seedling establishment can be stressful.  Average sugarbeet stands in California commonly equal 50 to 60 percent of the seed sown.  For some growers, the percentage is lower.  The costs associated with stand establishment can vary from ten to 33 percent of total variable costs for the sugarbeet enterprise and equal a substantial fraction, if not all, of a grower's profit if replanting becomes necessary.  Replanting also can lower profits by reducing final yield or can discourage a grower from producing beets altogether.  Successful stand establishment and vigorous seedling growth are critical to profitable sugarbeet production.  Planting to a stand (or desired population) is not widely practiced in California, but if the crop is to remain profitable, it will have to become the common practice in most areas.  To achieve successful stand establishment without hand thinning, emergence will have to increase by 20 percent or more on average.  To improve sugarbeet seed emergence by 20 percent or more in California, a better understanding is needed of the factors most likely to cause a seed to fail to emerge under the diverse stand establishment conditions experienced by growers.  If the Food Quality Protection Act (FQPA) eliminates pesticides currently in use during the stand establishment phase, this improvement will be more difficult to accomplish.

Several factors influence successful stand establishment and can be divided into those associated with the seed and those associated with the seed's environment.  Environmental influences are the most important, but may be the most difficult for the grower to control.  For example, seed must germinate under soil temperatures ranging from extremely high in the desert regions (>100º F) to near freezing in the Intermountain areas.  Optimum soil moisture conditions can be difficult to achieve under field conditions.  In large fields, seeds may be planted a number of days before they are irrigated.  During that time, if sufficient moisture is available, seeds may germinate but then run out of moisture and dessicate before they emerge.  If furrow irrigation is used and soils are variable, seeds may experience variable moisture.  In places the soil will be too wet, in others too dry.  Fields may also vary in important chemical properties, particularly salinity (Rhoades, et al., 1997).  Salinity can adversely influence emergence by limiting available soil moisture.  For the most part, furrow irrigation is used for sugarbeet production in most regions of the state.  In the San Joaquin and Imperial Valleys, growers must also contend with soil salinity.

 (B)  Biotic factors:  The most common pathogens reducing sugarbeet stands are Pythium ultimum, P. aphanidermatum, Rhizoctonia solani, and Aphanomyces cochliodes.  Apart from a general understanding of the biology of these soil-borne pathogens, little is known specifically about the interactions among temperature, moisture, and soil chemical and biological factors under the diverse conditions found on California's farms.  For example, preplant incorporated thiocarbamate herbicides (Roneet® and Tillam®) have been shown to increase damping off in some environments (Kaffka, et al., in prep).  Reduced seedling vigor due to herbicide phytotoxicity might result in poor stand establishment under adverse conditions.  Similarly, below ground grazing of sugarbeet hypocotyls by springtails is hypothesized in Europe to lead to greater seedling loss by allowing damping-off organisms to infect emerging seedlings.  The effects of springtails under California conditions, if any, are unknown.

Regional Occurrence:  (A) Soil-borne pathogens:  Most pathogens are influenced by temperature as well as moisture.  There has been no systematic analysis of the occurrence of damping-off organisms in California, but a statewide stand establishment program is beginning to determine the scale of loss to pathogens at certain times and locations in the state, as well as identify the causative agent(s).  Losses to soil-borne pathogens seem to be most severe when sugarbeets are planted in late spring (after May 1).  Beets are planted during that period in areas in and around the Delta (San Joaquin, Sacramento, Solano, Yolo, and parts of Merced County).  In trials underway in 1997 and 1998 (Kaffka et al., in prep), pre-emergence losses to pathogens had the greatest effect on stand establishment, followed by postemergence losses to pathogens.  Of the postemergence losses, Pythium spp., were identified most commonly.  In the Imperial Valley in September and October, pre-emergence losses again accounted for the largest percentage of seed failure, but losses to insects postemergence were more important than, or equivalent to, losses to pathogens (Kaffka, et al., in prep).  The effects of pathogens and insects on seedlings during the early spring months in the northern Sacramento Valley and the eastern San Joaquin Valley have not yet been determined.

  (B)  Insect predation:  The effects of soil insects like springtails and mites on seedling emergence have not been well quantified.  In the Imperial Valley in early fall, armyworm and other lepidopteran insects preyed on seedlings and caused significant postemergence losses.  Losses to insects also occurred in the Delta region.  In Tulelake, flea beetles can be a severe stand establishment problem, but they are effectively controlled by imidicloprid (Gaucho®), a newer seed treatment.  Cutworms can occasionally damage sugarbeet stands.  Sevin® (carbaryl) is used when damage is observed.  Beet leafhopper (Circicular tenullis) does not harm seedlings directly but can transmit curly top virus to seedlings.  Even resistant sugarbeet cultivars can be harmed by curly top if they are infected as seedlings.  Imidicloprid is thought to control beet leafhopper, but its ability to reduce the transmittance of curly top virus is untested under field conditions.  If successful for sugarbeets, similar control strategies may also apply to melons, tomatoes, and other crops.  Viruliferous aphids, especially green peach and black been aphids, can transmit a number of yellowing viruses to seedling sugarbeets.  The yellowing viruses are most severe in and around the Delta.  Currently, soil-applied systemic insecticides are used to control aphids, and a beet free quarantine program is used to avoid transmission of viruses from old to seedling sugarbeets.

 2) CURRENT PEST MANAGEMENT PRACTICES

  Cultural Controls:  Currently, cultural methods emphasize rapid emergence based on shallow planting, preplant irrigation, and careful irrigation management during the seedling stage to avoid saturated, anoxic conditions.  Rhizoctonia may be favored by rotating with alfalfa or beans or cotton, so avoiding planting beets following these crops is urged (UC-IPM).
 Seed Treatments:  Effective pregermination seed treatments increase the rate of emergence and may improve uniformity of emergence and the number of seeds resulting in plants.  Pre-sowing seed treatments are used to leach out germination inhibitors, soften seed coats, and advance physiological processes.  Various methods such as soaking the seed in water, osmotic solutions, or media with known matric potentials have been investigated.  Seed coating treatments are used to make seed more uniform and easier to handle, apply plant protection materials, and apply nutrients or lime.  Two types of coatings are used commonly for sugarbeet seed: polyvinyl polymer film coat, and a clay-cellulose mixture used for pelleting.  These materials and the method of their application are proprietary and vary.  Coatings may slow the uptake of oxygen during the initial stages of the germination process or inhibit the diffusion of salts and inhibitory substances from the seed's natural coat.

The most commonly applied seed treatment chemicals are fungicides absorbed by the seed.  The ones used in California are Apron® (metalaxyl), Chloroneb®, and sometimes Thiram®.  Apron® is thought to be effective against Pythium species, Chloroneb® against Rhizoctonia solani, and Thiram® against seed-borne molds such as Phoma betae and a range of other opportunistic species that appear to occur only rarely.  Another fungicide (hymexazon, marketed as Tachigaren®) has activity against Aphanomyces cochliodes.  Many systemic chemicals applied to seed, including some of those commonly used on sugarbeets, may have negative as well as positive effects on emergence, depending on the treatment and its interactions with the environment in which the seed is placed.  Most seed treatment chemicals that are systemically absorbed have the potential to interfere with the metabolism of germinating seedlings.  In previous trials, Kaffka, et al. (in preparation) observed delayed emergence in a number of locations throughout California when Apron® was applied to bare processed seed at labelled rates.  Delayed emergence in these trials, however, did not reduce establishment.

Postemergence Pest Control:  Several lepidopteran pests of sugarbeets can affect stand establishment.  These include several species of armyworms, webworms, cutworms, and wireworms.  Currently, where pressure is thought to be intense, growers use prophylactic applications of pesticides like Lorsban® and Lannate® to reduce seedling loss.  The amount of loss has only recently begun to be documented, and there is no IPM-type threshold for application.  Materials are applied as soon as larvae are observed or, in some cases, as soon as seedlings begin to emerge.  Some current applications may be unnecessary; at other times, without an effective means of control, losses could be severe.

The control of viruliferous aphids can be important in preventing yield loss during the establishment and early seedling stage.  A number of pesticides under FQPA review are used for this purpose.  Similarly, infection with curly top virus at the seedling stage, even for resistant varieties, leads to crop failure.  A statewide program to control the curly top vector, a leafhopper (Curcicular tenullis), in its alternate host rage in the coastal and Sierra Nevada foothills, using malathion combined with the use of resistant cultivars is the current management practice.  Malathion is under FQPA review.

 Weed Control and Stand Establishment:  Sugarbeets are poor competitors with weeds.  They are slow to emerge and grow slowly during the early seedling stage because much of their photosynthate is partitioned to root development.  There is no single herbicide that controls all the weeds affecting sugarbeet stands, so growers commonly use a combination of materials and application times.  Preplant incorporated herbicides are used when weed pressure is likely to be severe.  Two (cycloate, or Roneet®, and pebulate, or Tillam®) are thiocarbamate materials.  While they control weeds, they also may reduce sugarbeet seedling emergence, perhaps by stimulating the development of soil pathogens.  The effects of thiocarbamate herbicides on emergence are being analyzed (Kaffka et al., in prep).

Unfortunately, because of the increasing costs of hand labor for thinning and weeding, there are no economic alternatives to the selective herbicides used for sugarbeets.  Herbicide tolerant sugarbeets will reduce, but likely not eliminate, the need for selective herbicides.

Botanical Seed Treatments:  The use of antagonistic bacteria and fungi to control seedling diseases has resulted in the development of several new ideas and a few commercial seed treatment products.  Antagonistic fungi have been reported to attack Rhizoctonia, Pythium, and Schlerotium rolfsii, (Lewis, et al., 1995; Lewis, Kiewnick and Jacobsen, 1997).  Antagonistic bacteria have been reported to affect Pythium spp. and perhaps other pathogens, as well (Roberts, 1993).  Seed treatments have been developed in some instances by commercial firms, but they have not yet been evaluated in California.  Botanical seed treatments may substitute for or increase the efficacy of existing and new pesticide-based seed treatments.

 3) REDUCED-RISK OPTIONS

Potential remedies for environmental and biotic factors include changes in irrigation practice, improved planter maintenance or substitution of improved planter types, changes in tillage and seedbed preparation, improved attention to soil organic matter, and the use of new (but costly) seed treatments like imidicloprid (an insecticide) and hymexazol (a fungicide).  Seed treatments use significantly less pesticide than soil or plant applied materials and virtually eliminate environmental loss.  Better quantification of the potential loss of seedlings, once they emerge, to insect predators is required to determine if insecticides must be used in a prophylactic way or if an economic threshold can be determined.  Pheromone confusion techniques proposed elsewhere for the control of armyworms during the growing season (discussed above under "armyworms") may also reduce the need for insecticides on a regional basis once the program has been demonstrated to be viable.  Botanical seed treatments have not been evaluated under California conditions but may prove useful.  Some of these remedies may simply be a matter of expense and must be justified based on results under field conditions; others involve more difficult changes in farming practices like modifications to tillage practices or attention to soil organic matter.  These changes, if justified for beets, also would favor establishment of a number of other crops.

 Yet another consideration in stand establishment is sugarbeet seed quality.  Sugarbeet is a biennial, and there is no selection for seed quality.  Rather, plant breeders focus their attention on yield and pest resistance characteristics.  Seed quality is variable and is lower in general than many other field crops.  By culling more seed or otherwise improving commercial seed quality, emergence may be improved.  Improving seed quality has not been evaluated in California.  Increased culling would raise the price of seed, so its utility should be evaluated under a range of conditions.

Previous Efforts:  During the late 1970's and early 1980's, the British sugar industry undertook a nationwide effort to improve stand establishment percentages in farmers' fields.  At the time the campaign began, stand establishment success was similar to that achieved currently in California on average, approximately 55 percent.  An attempt was made to study all aspects of stand establishment, from planting through final emergence.  The approach followed involved the analysis of emergence in 70 fields throughout Britain.  On 13 of those fields, careful seed excavation and diagnosis of pre-emergence seed loss factors were carried out.  A summary of their results is presented in Table 1.  In both research station and farm trials, they found that most seed did germinate (>90%) but that a significant portion of germinated seed did not emerge.

The remedies applied were varied and were based on the discoveries made combining results from the Broom's Barn Research Centre and farmers' fields.  They included improving planter maintenance, modifying seedbed preparation practices, using the new fungicides and insecticides as seed treatments, and improving seed vigor through quality control and seed priming.  Currently, stand establishment success in Britain is greater than 70 percent, and planting to stand is the rule.  No single modification or improvement was sufficient by itself.  Together, a number of small improvements added up to an overall gain of greater than 15 percent.  British efforts provide a precedent and model for California.
 

TABLE 1
 RESULTS FROM BRITISH TRIALS
 Percent Loss in Each Category

Cause of Loss	Mean	Range
Planter skips	4	1 - 9
Rodent predation		0 - 100
Non-viable seeds	8	3 - 16
Germinated but failed to emerge	18	6 - 29
Post-emergence losses	7	0 - 70
Total	37

Durrant, et al., 1998

  Previous Efforts in California:  In 1997, nine stand establishment trials were carried out on research station and farm sites throughout California.  Two more trials, one in Glenn County and one in Tulare County, were carried out in spring 1998 to complete that series, but results are not yet analyzed.  In brief:

   A. There were significant differences among seed treatments in most of the trials.  These differences mean that considerable room for improvement in stand establishment is possible, even under difficult conditions, based on the use of appropriate seed treatments.
  B. Postemergence mortality tended to be consistent among most seed treatments, while pre-emergence mortality varied.  Treatments with the highest plant numbers at the four- to six-leaf stage had the highest emergence percentage.
  C. The sources of mortality varied by location, but should be largely predictable, suggesting that stand establishment practices can be refined in each region where difficulties are experienced.
  D. Farm practices affecting irrigation and planting technology can be improved in some locations and should be the focus of additional research and extension efforts.

 4) CHALLENGES

Successful stand establishment and vigorous seedling growth are critical to profitable sugarbeet production.  Since sugarbeets are grown in a wide range of environments in California, conditions in these diverse environments at the time of seedling establishment can be stressful.  There is a high cost for stand establishment, and it is crucial to successful crop production.  A poor stand guarantees an unprofitable crop.  Since seedlings are the most vulnerable stage of crop growth, much of the management challenge and cost of production is associated with that stage.  Many of the pesticides applied to the crop are used during the stand establishment and seedling stage.  A focus on reducing risk and environmental exposure during that period could have substantial effects on pesticide use.

To remain viable as an industry, stand establishment and protection during the seedling stage must be improved while risk to the environment is reduced.  Ever-narrowing profit margins and the increasing costs and management difficulties associated with hiring thinning crews require better attention to seedbed preparation and irrigation and a better understanding of the relationship of environmental influences on sugarbeet germination and emergence.  A more precise diagnosis of the causes of stand failure would help farmers achieve better, more uniform stands and could lead to a higher likelihood of success in planting to stand.  Planting to stand would improve the profitability of the crop and the appeal of sugarbeet production to more growers, but will require improving stand establishment by 20 percent on average.  To improve sugarbeet seed emergence by 20 percent or more in California, a better, more predictable understanding is needed of the factors most likely to cause a seed to fail to emerge under the diverse stand establishment conditions experienced by growers.  The elimination of weed competition during the immediate postemergence period also is essential once seedlings have emerged; sugarbeets are a relatively poor competitor with weeds at this time.  Currently, herbicides are thought to be essential.

The improvement of stand establishment will require changes to a number of farming practices ranging from tillage to irrigation to pesticide use.  The FQPA, if it results in the loss of commonly used insecticides and herbicides, will be a significant challenge to the state's sugarbeet industry.

  5) INNOVATIVE FEATURES IN REDUCED-RISK PROGRAM

A systematic evaluation of the causes of stand failure is essential for the improvement of stand establishment.  Seed treatments can be substituted in part for soil and plant pesticide applications, reducing environmental risk.  New developments in sugarbeet breeding technology may reduce quantitatively the need for herbicides and change the mix of materials used.  Better assessment of the pests causing loss, the amount of loss inflicted, and the times and locations when they are most likely to be problematic will result in an improved approach to stand establishment.  The industry has undertaken a statewide effort to improve stand establishment and reduce risk.  Since the establishment and seedling period is critical for a number of significant sugarbeet pests such as nematodes and a range of insect pests damaging crops, stand establishment work integrates a number of pest management challenges.  This integration involves multiple pest challenges from weed control to reduced transmission of viruses by aphids and leafhoppers.  This integration makes it innovative.

 6) BARRIERS TO ADOPTION OF REDUCED-RISK METHODS

Changing established farming practices is not easy.  The management demands on growers farming large acreages and a number of crops are great.  Unpredictable events from weather to mechanical breakdowns and timeliness of the work of subcontractors all interact to frustrate good farming practices.  Limitations to management time represent the most significant barrier to adoption of changed stand establishment practices.  Nevertheless, improved stand establishment will require greater care in farming.  For greater care to be given, real economic advantage will have to be demonstrated in research and field trials.  To prove this advantage, trials must be carried out in diverse locations.  The results from stand establishment trials typically are variable, in part because the conditions experienced are variable.  A sufficient number of trials must be carried out in diverse locations to arrive at suitable recommendations given this diversity.

The phenomena influencing stand establishment are many, and they interact in ways that are often unpredictable.  Nonetheless, better attention to seedbed preparation, soil moisture, planting technology, and the substitution of seed treatments for soil and plant treatments appears rational.  The development of a better understanding of when losses are likely to occur also will rationalize the use of pesticides.
 

 REFERENCES

Durrant, M.J., Dunning, R.A., Jaggard, K.W., Bugg, R.B., and Scott, R.K. (1988).  A census of seedling establishment in sugar beet crops.  Ann. Appl. Biol.  113:327-345.

Kaffka, S. R., Brittan, K., Babb, T., Canevari, M., Ehler, L., and Peterson, G. (In preparation).  Sugarbeet Stand Establishment:   1997 Trials.  Sugarbeet Research Review. Univ. Calif., Davis.

Kiewnick, S., and Jacobsen, B.J. (1997).  Control of sugar beet crown and root rot caused by Rhizotonia solani Kuhn with biocontrol agents and fungicides.  Proceedings of the 29th Biennial Meeting of the American Society of Sugar Beet Technologists.  Denver, Colorado.

Lewis, J.A., Lumsden, R.D., and Locke, J.C. (1996).  Biocontrol of damping-off disease caused by Rhizoctonia solani and Pythium ultimum with alginate prills of Gliocladium virens, Trichoderma hamatum, and various food bases.  Biocontrol Science and Technology 6:163-173.

Rhoades, J.D., Lesch, S.M., Lemert, R.D., and Alves, W.J. (1997). Assessing irrigation/drainage/ salinity management using spatially referenced salinity measurements. Agric. Water Management 35:147-165.

Roberts, D.P. (1993).  Genetically modified bacteria for biocontrol of soilborne plant pathogens.  In:  Lumsden, R.D., and

Vaughn, J.L. (Eds.).  Pest Managment: Biologically Based Technologies.  American Chemical Society. P338-346.
UC IPM (1995).  Sugarbeet Pest Management Guidelines.  UCPMG Publication 24.  Division of Agriculture and Natural Resources.  Oakland, California.
 
 
 
 

Stand Establishment contributed by Stephen Kaffka, PhD., University of California, Davis.