Average sugarbeet stands in California commonly equal 50 to 60 % of the seed sown, but for some growers, the percentage is lower. For example, in the Imperial Valley where soil temperatures are high, salt is a problem and insect predation on seedlings can occur rapidly, Growers may only expect one in three or four seeds to result in a plant, and increase seed rates accordingly. Over-planting can be expensive and will become more so. Seed costs will rise, even without including the cost of new transgenic traits like herbicide tolerance or the use of seed treatments like imidicloprid (Gaucho®: an insecticide) or hymexazol (Tachigaren®: a fungicide) applied directly to the seed, or seed treatments like priming. But stand failure can be even more expensive, so currently growers tend to over plant seed to insure a stand. Planting to a final stand, common in Europe and other parts of the United States, is not widely practiced in California. But if the crop is to remain profitable over the long term, it will have to become more common in many areas. To achieve successful stand establishment without hand thinning, emergence will have to increase by 20 % or more on average. Simply increasing seeding rates to make up for mortality will not suffice because there will be areas in the field where all the seed comes up and these will still require thinning.

Seed quality. Several factors influence stand establishment and can be divided into those associated with the seed and those associated with the seed's environment. Seed quality can vary by seed lot, variety, and the year and location the seed is produced. It is difficult to produce sugarbeet seed, and plant breeders do not select sugarbeets for superior seed quality, but rather for root and sugar yield and disease resistance. Desirable root characteristics can be linked to reduced seed quality. When rhizomania first invaded California, there were no genetic defenses against it. Eventually a resistance gene was found by Holly and introduced into new sugarbeet varieties. The first of these (Rhizosen) also had the unfortunate characteristic of poor emergence. In trials we conducted in the Imperial Valley and elsewhere, it consistently resulted in about 5 % to 10 % fewer seedlings than the other varieties tested. Nonetheless, growers used it because it was the best variety available at the time where rhizomania was a problem.

The sugarbeet seed that growers receive for planting typically has been graded according to size, treated with fungicides to prevent loss to pathogens, and coated with a polyvinyl polymer film to reduce dust and make seed more uniform in shape. Despite apparent uniformity, a box of seed consists of a population with varying embryo sizes, water potentials, food reserves, and seed coat characteristics like operculum attachment, and the amount of germination inhibitors and salts present. The consequence of this variation is that sugarbeet seeds tend to be slow to emerge, emerge unevenly over a prolonged period of time, or may simply fail to emerge if an environmental hazard is encountered. Energy reserves are limited in sugarbeet seeds and emerging seedlings can starve to death before they appear above the soil surface.

Seed quality is difficult to define experimentally. Germination under standard laboratory conditions does not always correlate with performance in the field. In part because germination is not the same as emergence. Germination refers only to the appearance of the root tip or radical from the seed. What growers require is a six leaf plant. Sugarbeet seed quality has never been evaluated systematically in California to my knowledge. Typically, fifty percent or more of the sugarbeet seed harvested is thrown away or culled. For some seed lots the amount is larger and in Europe, where growers pay more for seed, the amount culled can be 80 %. Heavier culling tends to increase germination percent, eliminate double embryos, and may increase vigor, all desirable outcomes. The California industry may benefit from increased culling (and higher seed prices) if seed quality could be improved significantly, especially if growers attempt to plant to a stand.

Environmental influences. In California, soil temperatures at the time of planting may not be ideal. For example, seed must germinate under soil temperatures ranging from extremely high in the desert regions or in late spring/early summer in central California (> 100^o F) to near freezing in the Intermountain areas in April. Optimum soil moisture can be difficult to achieve under field conditions. If soils have a large percentage of clay, coarse, cloddy seed beds occur and seed can bounce and roll after it drops from the planter and end up covered to variable depth or have poor soil-seed contact. If soils are sandy, because of the low percentage of organic matter typically present, it may be difficult to maintain adequate soil moisture. In large fields, seeds may be planted a number of days before they are irrigated. During that time, if sufficient moisture is available from pre-irrigation, seeds may germinate but then run out of available water and desiccate before they emerge, especially primed seeds.

Furrow irrigation is used for sugarbeet production in most regions of the state. If furrow irrigation is used with long runs and soils are variable, uneven soil moisture conditions will occur. In places the soil will be too wet, in others too dry. Fields also vary in important chemical and physical properties, particularly those associated with salinity and sodicity. Salinity can adversely influence emergence by limiting available soil moisture. Sodicity can cause severe water infiltration and crusting problems. In the San Joaquin and Imperial Valleys, a number of growers must contend with these problems. Loam soils, because of low amounts of organic matter, tend to crust when sprinkled or if rain occurs. All of these factors must be managed by farmers wishing to improve stand establishment. Once they are, then attention must be paid to pathogens and insects.

Biotic factors. The most common pathogens reducing sugarbeet stands are Pythium ultimum, P. aphanidermatum, Rhizoctonia solani, and Aphanomyces cochlioides. Pathogens are influenced by temperature as well as moisture, and appear to be most severe during the late spring through early fall period when soils are warm. But apart from a general understanding of the biology of these soil-borne pathogens, little is known specifically about the interactions among temperature, moisture, and the soil’s chemical and biological factors under the diverse conditions found on California’s farms. Currently, cultural methods emphasize rapid emergence based on shallow planting, pre-plant 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 changing rotations may help.

Several different types of insects harm sugarbeet seedlings, including armyworms, webworms, cutworms, wireworms, cucumber beetle larvae and adults, flea beetles, grasshoppers, and leafhoppers. Spring tails, a small soil insect, can be damaging at times in Europe, but no one knows if they cause similar damage in California. The amount of loss to insects is variable and not all species occur at every location or time. Damage seems to be greatest in the warmer months.

Several lepidopteran pests of sugarbeets can affect stand establishment. These include several species of armyworms, web worms, cutworms and wireworms. The amount of loss has only recently begun to be documented, and there is no IPM type threshold for application. Currently, where pressure is thought to be intense, growers use prophylactic applications of pesticides like Lorsban® and Lannate® to reduce seedling loss. 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.

Can we improve stand establishment?

To evaluate the causes of seedling mortality in California and to assess some of the newer seed treatment technologies available, the California Sugarbeet Industry Research Committee has funded a series of research station and farm trials carried out around the state over the last two years (Table 1). A range of environmental conditions are encompassed by these trials. Almost all have compared a number of different seed treatments (Table 2), and some have evaluated irrigation methods, soil fumigation with metam sodium (Vapam), and the influence of a thiocarbamate preplant herbicide (cycloate or Roneet®). In three trials, salinity has been an experimental factor.

How we studied stand establishment and what the results mean

To study sugarbeet seedling emergence more carefully than it had been done before in California required an intensive approach. In most of the trials, seedling emergence was observed and recorded daily for 7 to 10 days from the first appearance of a seedling, and then at two to three day intervals afterwards until plants reached the five to six leaf stage, at which time they were considered established. In some of the trials, seedlings were labeled as they emerged with pot labels. If that seedling died, its death was recorded and the label removed. In a few of the trials (3, 7, 9, 14), the cause of seedling mortality (pathogens or insects) was evaluated and recorded. These determinations were carried out in the field and are not absolute because laboratory confirmation was not always available or successful. In each year, all the trials used seed from the same seed lot of SS781R, so the trials compare the performance of the same seed but under different conditions.

By knowing exactly how many seeds were planted, and the germination percentage, we could evaluate a number of important characteristics of the sugarbeet stand. Cumulative emergence is the sum of all the new seedlings appearing each day. By keeping track of dying seedlings, we could get daily mortality and by adding up all the seedling losses, we could estimate cumulative mortality. The number surviving on the last day of the trial was taken as the number established or the percent established. Because we knew the number of non-viable seeds, the number that emerged, and the number that died after they emerged, we could also estimate pre-emergence losses by assuming that all viable seed germinated. These measurements give us a better picture of the development of a sugarbeet stand than we have had before.

There is always a great deal of variability associated with emergence trials because soil and moisture conditions may differ over short distances, and pressure from pests and diseases is not uniform. Having a large number of trials is necessary to see if consistent patterns emerge, and how variation in time of year and location may influence establishment and the performance of seed treatments. Nevertheless, conflicting results can occur because of the interactions among management practices and environmental influences. So the conclusions that can be drawn from stand establishment trials are not as definitive or as easily generalized as those from other types of agricultural experimentation.

What we learned

A large amount of data has been gathered, but only a small amount of it can be presented here because of space limitations. What follows is my interpretation of the results from our trials to date. Some judgement is required because of the variability mentioned earlier. A more complete report will appear in the near future and can be found in part currently on the new web site called "Sweet Times" (http:\\agronomy.ucdavis.edu\sweettimes).

Irrigation comparisons

Irrigation method may influence uniformity, crusting, soil saturation, pathogens, salinity and other factors. Two trials (3, 7) involved comparisons between sprinkler and furrow irrigation. Trial 3 occurred in Davis, trial 7 in the Imperial Valley.

• At Davis, fewer plants were established using sprinkler irrigation than furrow irrigation. In the Imperial Valley there were no significant differences in the number of plants established.

Soil water measurements during both trials documented that moisture in the seed zone was maintained above the 50 % available moisture threshold during the emergence period. This is relatively easy to do in small plots, compared to farm fields. If soil salinity is not a problem and if adequate available water can be maintained in the seed zone in furrow irrigated fields, emergence should be similar between furrow and sprinkler irrigated fields. Where uniformity is a problem, or where soil salinity occurs, sprinkler irrigation may result in superior stands at a field scale. Analysis from trial 16 is not yet complete.

Soil treatments: fumigation with metam sodium and the use of cycloate

Direct comparisons were made in three station trials (3, 7, 14) and one farm trial (13) for one or both of these factors.

• There were no significant differences in emergence, mortality, or final establishment between fumigated and non-fumigated plots (Table 3).
• The use of cycloate as a pre-plant incorporated herbicide significantly reduced the number of sugarbeet plants in all three trials in which it was evaluated (Table 3).

Metam sodium had no adverse effects on the plots. It controlled most annual and perennial weeds found in the other plots as well. But it provided no significant advantage in controlling pathogens. The trials in which cycloate was used were all conducted at times when soil temperatures were in the optimum range for pathogen activity. Cycloate interferes with fatty acid metabolism and may weaken the cuticles of plants, making them more susceptible to pathogens. Older reports from the literature and farmer experience suggest that the adverse effects of cylcoate may not be pronounced when soil temperatures are low. If cycloate weakens seedling resistance to pathogens, then there would be a correlation between temperature and damage because pathogens are more active when soil temperatures are warmer. Growers who rely on this material because of difficult weed management problems must evaluate whether they can tolerate an increased amount of seedling loss.

Seed treatments

With one exception, all the trials included seed treatment comparisons. There was a wide range of values for cumulative emergence, pre-emergence mortality, and percent establishment among the different seed treatments. Untreated seed was the poorest treatment, resulting in the fewest seedlings (Table 4).

• In most of the trials conducted, imidicloprid treated seed, whether film-coated or primed and pelleted, resulted in greater cumulative emergence (See figure 1 for an example) and the largest number of seedlings at the five to six leaf stage (Table 4).
• The current standard industry treatment was among the poorer performing seed treatments in most of the trials.

By using untreated seed, we could compare sites based on the performance of the control treatment.

• As air and soil temperatures increased, the amount of post emergence loss tended to increase, and overall success in stand establishment declined.
• Increased seedling protection through the newer seed treatments appears to be most worthwhile when growers have to plant under high temperature conditions in late spring or early summer.

Diseases and insects

The determination of losses to pathogens was based largely on visual identification in the field.

• In general, post-emergence losses to diseases were approximately twice as great as losses to insects (see figure 2 for an example). This was true despite the fact that most seeds were treated with Apron and Chloroneb and post emergence applications of insecticides were not used in many of the trials.
• Post-emergence losses to diseases and insects tended to be similar for most seed treatments.
• The largest number of seedlings occurred when using seed treatments with the least pre-emergence losses. Most commonly, lower pre-emergence losses were associated with imidicloprid seed treatments, and sometimes with the use of Tachigaren where Aphanomyces was thought to be a problem.

Putting it all together

Grower experience over time suggests and observations from these trials confirm that late spring and summer periods are the most difficult times to establish sugarbeet crops. Improved seed treatments are most likely to be worthwhile to growers during this period, but we have less evidence so far from the winter-early spring period. In Europe and other parts of the United States, when temperatures are similar to those in California during the winter-early spring period, primed seed results in earlier and more uniform emergence. That may be the principal benefit in California when temperatures are moderate as well.

Commonly, we observed an increase of 10% to 20 % or more over the current standard seed treatment in most of our trials using imidicloprid either as a primed seed of simply applying it to film-coated seeds. Film coated and/or primed seed with imidicloprid should be evaluated more widely in the state. I suggest that growers take an experimental approach and try strips of treated seed in different locations in their fields.

An expensive seed treatment, however, will not make up for poor seed bed preparation or irrigation practices. Whatever growers can do to improve the uniformity of seed placement, particularly with respect to depth, or to improve soil-seed contact, and to maintain adequate supplies of moisture during the critical germination to emergence period will enhance the performance of sugarbeet seeds and seed treatments. When conditions are close to ideal, as they were in the Tulelake trial, large amounts of seed will emerge and establish even without expensive seed treatments (Table 4). But in the real world, soil, water and temperature conditions are rarely so ideal. Under less than ideal conditions the use of imidicloprid for the most part was beneficial in our trials. Its use should increase the number of seeds that become established plants when farming conditions are stressful, as they are in late spring. Additional data is required to evaluate seed treatments in winter and early spring.

Figure Captions

Figure 1 a. Cumulative emergence in trial 11, in Glenn County (1998), a farm trial.

Figure 1b. Cumulative mortality in Glenn County.

Figure 2. Proportions of seed resulting in losses or establishment in one of the San Joaquin County farm trials (trial 12). Non-viable: seed incapable of germinating. Pre-emerge: Losses of viable seed before they emerge above ground. Post-emerge: Losses of seedlings that emerged but failed to establish viable plants. Est.: Established plants (5 to 6 leaves).
 

Table 1. Locations, experimental, and environmetal factors
 

Location and cooperator(s)	Date	Variables evaluated	Special Characteristics
1. Tulelake- S. Orloff, UCCE; D. Kirby UC-DANR	May , 1997	Seed treatments	Low soil temperatures, high soil organic matter levels. Sprinkler irrigation. UC-IREC
2. San Joaquin Valley - M. Canevari, UCCE	May, 1997	Seed treatments	Adobe clay soils. Delayed irrigation. Pre-plant incorporated herbicides (cyclocel). Furrow irrigation. Farm site
3. Davis	May-June , 1997	eed treatments, irrigation treatments, soil treatments	Sprinkler vs furrow irrigation, vapam, pre-plant incorporated herbicides (UCD Agronomy Research Farm)
4. Woodland T Babb, Spreckels	May-June, 1997	Seed treatments	Sandy loam soil. Furrow irrigation. (Spreckels Research Farm)
5. Sutter County- K. Brittain, UCCE	June-July, 1997	Seed treatments	Clay soil, following rice. Furrow irrigation. (farm site)
6. Imperial Valley T. Babb, Spreckels	Sept., 1997	Seed treatments	Farm site (excessive irrigation and rainfall), soil salinity. Furrow irrigation. Farm site
7. Imperial Valley-UC DREC site) I. Miller, UCDANR	October, 1997	Seed treatments, irrigation, soil treatments	UCDREC site; sprinkler vs. furrow irrigation, vapam, soil salinity
8. Imperial Valley  T. Babb, Spreckels	October, 1997	Seed treatments	Farm site (typical conditions), soil salinity, furrow irrigation. Farm site
9. Fresno County (WSREC site), K. Hembree, UCCE	October-November, 1997	Seed treatments, soil and water salinity	Clay loam soil, low vs. high salinity water, low vs.high salinity soil. Furrow irrigation. UCWSREC site
10. Tulare Co.- C. Frate, UCCE	March-April, 1998	Seed treatments	Sandy loam soil. Not irrigated. Farm site
11. Glenn Co. (Farm site) D. Munier, UCCE.	April, 1998	Seed treatments	No till planting in overwinterd beds. No herbicides. Not irrigated. Farm site
12. San Joaquin Co., M. Canevari, UCCE	June-July, 1998	Seed treatments	Adobe clay soils. No herbicides. Delayed irrigation. Furrow irrigation. Farm site
13. Merced Co., W. Weir, UCCE; T. Babb, Spreckels		Seed treatments. Herbicides	Clay soils. Furrow irrigation. Comparison of cycloate use.
14. Davis	July-Aug., 1998	Seed treatments, soil fumigation, herbicides	Vapam, pre-plant incorporated herbicides, furrow irrigation (UCD Agronomy Research Farm)
15. Imperial Valley	Oct., 1998	Salinity	Clay soils. Moderate salinity. Furrow irrigation. Farm trial. No pre-plant herbicides. Lannate® applied in soil.
16. Davis	Sept.-Oct., 1998	Pre-irrigation vs. No pre-irrigation, primed vs. film coated seed.	Loam soil. Furrow irrigation. (UCD Agronomy Research Farm)
17. Kings Co.,	Nov. -Dec., 1998	Seed treatments. Soil amendments (gypsum, sulphuric acid), moderate to high salinity	Clay, sodic soils. Sprinkler irrigation. Farm trial. Pyramin used as a pre-plant herbicide.

Table 2. Seed treatments evaluated (SS781R)
 

Code	Seed treatment*	Trials in which treatment was evaluated (from Table 1)
1. C	Control (bare, processed seed)	All except 15, 16, 17
2. FC	Film coated¶	All
3. Pel	Pelleted§	Laboratory tests
4. FC+G	Film coated + imidicloprid £ (45g a.i. per unit)	All except 15
5. Pel+G	Pelleted + imidicloprid (45 g a.i. per unit)	---
6. Pel+T	Pelleted + hymexazol† (45 g a.i. per unit)	1, 2, 3, 12, 13
7. PAT	Primed (PAT treatment‡)	1,2,3,4,5, 6,7,8,9
8. PAT+ T+G	Primed + imidicloprid + hymexazol	1, 2, 3, 4, 5, 7,11,12,13
9. PAT+ G	Primed + imidicloprid	3, 4,5,6, 7, ,8 9,10,11, 12, 13, 14, 16, 17

*All seeds other than the control were also treated with chloroneb and apron fungicides. A unit of seed equals 100,000 seeds.¶ Polyvinyl polymer plus a dye. This is the most common treatment for sugarbeet seed sold in California.§ A clay cellulose mixture. Applied by Seed Systems, Inc., Gilroy, CA. Pelleting mixtures vary from company to company and the details are proprietary. £ Imidicloprid is sold under the trade name Gaucho®. † Hymexazol is sold under the trade name Tachigaren®. ‡ The treatment was applied by Seed Systems, Inc., of Gilroy, CA. The details are proprietary but it was based on work carried out at Broom’s Barn Research Center in England. Seed is steeped in a thiram mixture and then soaked in water until it reaches 124% of its initial weight, followed by drying in a forced air oven.
 

Table 3. Soil treatment results (Davis 1997 and 1998)
 

contrast	% difference	p=	significance
-------1997-------
cycloate vs. untreated	-11.0	0.0001	sig.
metam sodium vs. untreated	3.3	0.13	NS
cycloate vs. untreated+ metam sodium	-12.5	0.0001	sig.
-------1998-------
cycloate vs. untreated	-9.6	0.0003	sig.
metam sodium vs. untreated	2.3	0.325	NS
cycloate vs. untreated+ metam sodium	-10.7	0.0001	sig.

Single degree of freedom contrasts. % difference refers to the overall percentage of seeds emerging in that treatment. The probability of the diffrence being significant is given as p=.
 

Table 4. Final establishment in selected trials (% of seed resulting in plants at the 5 to 6 leaf stage)
 

C	87.8	28.0	21.8	44.9	37.6	64.1	38.0
FC	96.0	30.8	18.1	46.1	43.4	69.8	48.5
FC+G	95.8	53.2	40.9	63.4	42.9	---*	55.5
Pel+T	91.5	31.3	---	---	33.8	---	65.5
PAT	92.8	40.7	---	49.2	44.2	77.2	---
PAT+T+G	96.2	56.8	---	66.0	45.8	71.6	43.5
PAT+G	---	66.0	35.0	75.5	37.8	71.1	66.0
LSD (0.05)	NS	8.3	6.0	13.6	NS	8.0	12.8

The numbers next to the trial location refer to Table 1. Seed treatments are described in Table 2. FC+G was included in this trial, but had lost a significant amount of germination percentage after 10 months, so the results are not representative of freshly treated seed. The other seeds had maintained their viabilty. Applying imidicloprid directly to seeds can cause a loss of viability if seeds are stored too long before planting.