Investigators: Stephen Kaffka, Kent Brittan, Tom Babb, Mik Canevari, Les Ehler, Gary Peterson1
Introduction.
To improve sugarbeet seed emergence by 10% to 20% or more on average in California, the factors most likely to cause a seed to fail to emerge must be understood. 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.
Environmental conditions. Apart from a general understanding of the biology of the common soil pathogens, little is known specifically about the interactions among temperature, moisture, and soil chemical and biological factors in the seed zone For example, pre-plant incorporated thiocarbamate herbicides may increase damping off in some environments. Reduced seedling vigor due to herbicide phytotoxicity would result in poor stand establishment under adverse conditions. Similarly, below ground grazing of sugarbeet hypocotyls by spring tails or other soil insects is hypothesized to lead to greater seedling loss by allowing damping off organisms to infect emerging seedlings. Potential remedies for environmental factors exist including changes in irrigation practice, improved planter maintenance or substitution of improved planter types, changes in tillage and seed bed preparation, improved attention to soil organic matter, and the use of new (but costly) seed treatments like imidicloprid (an insecticide) and hymexazol (a fungicide). 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.
Seed treatments. Effective pre-germination 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 films coat, and a clay-celluose mixtures used for pelleting. These materials and the method of their application are proprietary and vary. Coatings may slow the uptake or 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 agaisnt seed-borne molds such as Phoma betae and a range of other opportunistic species that appear to occur only rarely. Another fungicide (hymexazol, 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 in Davis and Imperial Valley, Kaffka et al. (In prep), 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 result in greater numbers of seedlings.
Table 1
Locations, experimental, and environmetal factors
| Location | Date | Factors evaluated | Special Characteristics |
| 1. Tulelake (IREC) | May | Seed treatments | Low soil temperatures, high soil organic matter levels. Sprinkler irrigation. Organic soil. |
| 2. San Joaquin Valley (farm site) | May | Seed treatments | Adobe clay soil. Delayed irrigation. Pre-plant incorporated herbicides (cyclocel). Furrow irrigation. |
| 3. Davis (Agronomy Research Farm) | May-June | Seed treatments, irrigation treatments, soil treatments | Sprinkler vs furrow irrigation, vapam, pre-plant incorporated herbicides |
| 4. Woodland (Spreckels Research Farm) | May-June | Seed treatments | Sandy loam soil. Furrow irrigation. |
| 5. Sutter County (farm site) | June-July | Seed treatments | Clay soil, following rice. Furrow irrigation. |
| 6. Imperial Valley
(UC DREC site) |
September
October
October
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Seed treatments
Seed treatments, irrigation, soil treatments
Seed treatments |
Farm site (excessive irrigation
and rainfall), soil salinity. Furrow irrigation.
DREC site; sprinkler vs. furrow irrigation, vapam, soil
salinity
Farm site (typical conditions), soil salinity, furrow irrigation. |
| 7. Fresno County | October-November | Seed treatments, soil and water salinity | Clay loam soil, low vs. high salinity water, low vs.high salinity soil. Furrow irrigation. |
Table 2
Seed treatments evaluated (SS781R)
| Code | Seed treatment | Locations evaluated (from Table 1) |
| 1. C | Control (bare, processed seed)* | All |
| 2. FC | Film coated | All |
| 3. Pel | Pelleted | Laboratory tests |
| 4. FC+G | Film coated + imidicloprid (45g a.i. per unit¶) | All |
| 5. Pel+G | Pelleted + imidicloprid (45 g a.i. per unit) | --- |
| 6. Pel+T | Pelleted + hymexazol (45 g a.i. per unit) | 1, 3, 5 |
| 7. PAT | Primed (PAT treatment) | All |
| 8. PAT+ T+G | Primed + imidicloprid + hymexazol | All |
| 9. PAT+ G | Primed + imidicloprid | 3, 5, 6, 7 |
* All seeds other than the control were treated with chloroneb and apron fungicides. ¶ a unit equals 100,000 seeds.
Methods
Nine different seed treatments were applied to a single seed lot of SS-781R sugarbeet seeds (Table 2). Film coated treamtents were carried out by Cel-Pro, Inc. Pelleted and PAT treatments were applied by Seed Systems, Inc. At all locations except Davis, seeds were planted in rows with 100 seeds per row using a cone planter. Row length varied between 25 and 30 feet. At all locations, rows were 30 inches apart. At farm locations, irrigation, weed control, and insect management practices varied. In all locations except the San Joaquin County location, two rows of each seed treatment were planted next ot each other. In the first row, daily counts of the number of seeds present were made. In the second row, more intensive monitoring of seedlings was carried out. Half the row length was measured, and all seeds emerging in that row were counted and labelled daily for the first seven days after emergence began, and then every other day. Only newly emerged seedlings were counted each day. Any seedling dying after emergence was recorded, and the cause of mortality noted if possible. Seedlings were classified as diseased, eaten or damaged by insects, or simply missing if no seedling was present next to a previously placed stake. Stakes next to dead seedlings were dated, removed and recorded. The proportion of emerged seedlings dying over the entire observation period was calculated and used to estimate total emergence for the entire 100 seed lot by dividing the number of seedlings established by the proprotion of the seedlings emerging that had died. The assumption was made that factors influencing emergence and establishment in adjacent rows were similar, and that the causes of mortality would be similar. Because the number of seedlings emerging in adjacent rows was not identical, and seed spacing in the trials using a cone planter was not uniform, the amounts of pre- and post-emergence mortality are estimates and values reported do not sum exactly to 100 %.
At Davis, a WIC vacuum planter was used to plant 120 seeds in 30 foot rows. Additonal soil and irrigation treatments were also applied at the Davis Agronomy Farm and the Desert Research and Extension Center sites. At Davis and DREC, half the plots were irrigated with sprinklers, and half with furrow methods. Metam sodium was applied to one fourth of the plots at Davis, and half of the plots at DREC. At Davis, additional plots were treated with cycloate (a pre-plant incorporated thiocarbamate herbicide), or with a combination of cycloate and metam sodium. At Davis and DREC, there were three replications of each seed-soil irrigation treatment. At other sites, there were five replications of each seed treatment.
Pitfall traps were placed throughout the field in Davis in an attempt to determine if soil arthropods, particularly springtails, were present in large numbers and if springtail numbers could be correlated with the numbers of seedlings established. Manure was added to some plots to increase the amount of organic matter avaialble to spring tails in an attempt to increase their population. Trap counts were made several times during the trial and numbers in fumigated plots (metam sodium) compared to those without fumigation, and to those with and without manure. Springtail numbers were correlated with the number of established seedlings.
At Davis, dying seedlings were collected on different days during the trial and placed in water and incubated to determine the pathogen responsible for an individual seedling’s death.
Percent emergence data were analyzed using analysis of variance and mean separation techniques (SAS, Inc.). Germination and emergence data tend to be right-skewed (the probability density function describing emergence is not a normal distribution), and often not all seed germinates during a trial, so the data are right censored. That is, trials are ended before the eventual germination of all the viable seed and the assumption cannot be made that seeds which did not germinate, would not eventually germinate (Scott et al., 1984). These problems were ignored in analyzing these emergence data. Caution about the analysis of right-pruned data is correct biologically, but of little relevance agronomically, since late emerging seedlings (20 to 30 days after the majority of the seeds have emerged) likely will fail to develop into a harvestable sugarbeet plant, acting instead as late germinating weeds. Assuming that very late germinating seed are irrelevant agronomically allows for the analysis of emergence data as a simple quantitative trait.
Germination data sometimes are transformed using the arcsin transformation because in some instances, means and corresponding variances are not proportional, and the assumptions underlying many descriptive statistics would be violated. In these analyses data were not transformed. For most of these trials, the range in final emergence values was less than 40 %. Little and Hills (1978) suggest that if differences between the means are less than 40 %, transformation is unnecessary.
Summary of results from 1997 trials
In 1997, several trials were conducted around the state focusing on improving stand establishment. Preliminary results are summarized here. Additional analyses of these data are ongoing.
A. Germination
In all the trials discussed, seeds from a single lot of 781R supplied by Spreckels Seed were used. This lot of seed had an inital germination percentage of 93.75 %. Additional germination tests were carried out to determine the number of seeds with more than one embryo and the number of multigerm seed balls. There were no seed balls but approximately 5% of the seed contained two embryos. Multiple embryo seeds germinated quicker than single embryo seeds. No correction of results for doubles has been carried out in the results reported because the proportion of double embryo seed used for each seed treatment was equal.
In October and November, to determine germination percentages of different seed treatments after eight months storage, additional germination tests were carried out. The rolled towel test was used with temperatures of 30o C for 12 hours and 20o C for 12 hours (AOSA). In the rolled towel test, six different seed treaments were evaluated (1, 2, 4, 7, 8, and 9--Table 3) using 400 seeds from each treatment. Results are reported in Table 4. Different seed treatments germinated at different rates with primed seed (tmt 7) germinating most rapidly, and film coated seed with imidicloprid germinating slowest. Adding systemic insecticides and fungicides to the seeds slowed germination in proportion to the number of materials used, while priming tended to overcome the inhibitory effects of seed treatment chemicals. Final germination percent remained high after eight months in storage except for film coated seed treated with imidicloprid, in which germination declined significantly after long periods of storage, and was 21 % lower than the average of the other treatments combined. There may be some phytotoxicity associated with applying imidicloprid directly to seed with a film coating and storing the seed for extended periods of time.
Table 3
Germination test (October, 1997)
| Treatment |
(21 days) |
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B. Trials conducted on field stations
1. Tulelake (Cooperators: Steve Orloff, Don Kirby).
Emergence began at seven days and by ten days, more than 50 % of the seed in all seed treatments had emerged. Primed seed emerged fastest with 50 % emergence occurring between days 7 and 8 from initial irrigation. Unprimed seed required an additional two days to reach 50% emergence. At 30 days after the first irrigation, all treatments had emerged in high numbers (Table 4). The average value for the experiment as a whole was 93.3 seedlings per 100 seeds. Flea beetles were not a significant source of post-emergence mortality during this trial, though they can be devasting at times in the region. Consequently, there was no advantage to the use of imidicloprid as a seed treatment. Nor was there any emergence penalty for using it, either when pelleted (and primed), or as part of a film coated treatment. When needed for flea beetle control, its use should present no problem for growers provided it has not been applied several months before use. There were no other significant causes of post-emergence mortality noted during the trial. Differences among the treatments reflect pre-emergence losses and were not significant, with the possible exception of the control treament, which resulted in the the establishment of 8 % fewer plants than the best treatment (tmt 8). Given the high germination percentage of control seeds, it is likely that most of the seed germinated. Since no fungicides were used on the control treament, and emergence levels were significantly lower than for other treatments with fungicides (Table 4), modest pre-emergence losses to rots (and possible losses to soil insects) may have occurred. No significant post emergence insect damage was observed.
Table 4
Emergence trial in Tulelake (May, 1997). Final counts and days to
50% emergence
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2. Davis (Cooperators: Les Ehler, Tom Babb, Kent Brittan, Mike Davis).
A trial was planted and irrigated at the Agronomy Research Farm on May 25. Two irrigation treatments (sprinkler and furrow), and four soil treatments (1. Metam sodium, 2. Cycloate, 3. Metam sodium plus cycloate, or 4. no treatment) were used together with eight seed treatments (1,2,3,4,6, 7,8,9-Table 3). There were three replications of each irrigation-soil-seed treatment combination.
Contrasts among different irrigation and soil treatments are presented in Table 5.
Irrigation treatments differed, with furrow irrigated treatments resulting in larger numbers of established plants at the the final count. This result was unexpected and was due to the loss of mature plants at the end of the trial. Crusts developed in sprinkler irrigated but not in furrow irrigated plots. High winds during the last week of the trial caused otherwise healthy plants to snap off near the ground, resulting in fewer established plants in sprinkler irrigated than in furrow irrigated plots. The use of cycloate, a pre-plant incorporated thiocarbamate herbicide, also reduced emergence. Metam sodium did not enhance emergence significantly compared to untreated plots.
Springtail numbers were reduced initially in Vapam treated plots, but quickly recovered to levels comparable to untreated plots. The addition of manure failed to increase springtail numbers compared to the no-manure treatment.
There was no significant difference in the number of seedlings established in the three different soil treatments compared for springtail and other soil arthropod damage, so no correlation with springtail numbers could be established. The identification of soil arthropods harming sugarbeet seedlings requires additonal effort.
The most commonly diagnosed pathogens occurring during the trial in Davis were Pythium sp.,. A few seedlings were diagnosed with Rhizoctonia solani and just two with Aphanomyces cochliodes.
Table 5
Contrasts among irrigation and soil treament main effects at 25 days
after inital irrigation (final counts). Davis, 1997
| Contrast | Estimate of difference (plants per 120 seed positions) | Percent difference
(%) |
T | p > T | s. e.
(plants per 120 seed positions) |
| furrow vs sprinkler | 10.49 | 9 | 5.67 | 0.0001 | 1.85 |
| control vs cycloate | 13.23 | 11 | 5.06 | 0.0001 | 2.62 |
| Metam sodium vs control | 4.02 | 3.3 | 1.54 | 0.1274 | 2.62 |
Table 6
Final counts and days to 50 % emergence. Irrigation and soil treatments
combined. Mean differences are LSD(0.05). Davis, 1997
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In Table 6, final stand counts and days to 50 % emergence are reported for individual seed treatments, combining all soil and irrigation treatments. Differences among seed treatments were greater than differences among environmental factors under the conditions of this experiment. The three seed treatments with imidicloprid resulted in the greatest number of established plants. Combining all soil and irrigation treatments, the largest average establishment occurred using the PAT+G treatment and was less than 70 % (Table 7). Two specific soil-irrigation treatment averages (furrow irrigation with metam sodium and with the control soil treatment), again using treatment 9, resulted in approximately 80 % establishment (data not reported), suggesting that even under the harsh conditons of late spring in the central valley, planting to stand may be possible. Otherwise, the number of plants established were low, reinforcing the common observation in grower practice that establishing sugarbeet stands in May and June in the Central Valley with current practices is a difficult task.
For treatments 9 and 8, post-emergence seedling losses were much greater than pre-emergence losses (failure to emerge). For all other treatments, pre-emergence losses were greater than post-emergence losses. In general, premergence losses occurred over a larger range and treatment differences were greater than for post emergence losses, suggesting that the pre-emergence seed environment is the most hazardous period for sugarbeet seeds and seedlings.
Table 7
Seed treatment rank and percent emergence and loss. Mean differences
are LSD (0.05). Davis, 1997
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(see Table 3 for seed treatments)
3. Imperial Valley (cooperator: Ivan Miller).
A trial was planted and irrigated at the DREC on September 19. Two irrigation treatments (sprinkler and furrow), and two soil treatments (plus or minus metam sodium) were used together with six seed treatments (1,2,4,7,8,9- Table 2). There were five replications of each irrigation-soil-seed treatment combination.
Initial emergence occurred on September 22, three days after irrigation, with somewhat more seedlings appearing in sprinkler irrigated plots than in furrow irrigated plots initially. Fifty percent emergence occurred at approximately 5.5 days from initial irrigation, and 7 days for unprimed treatments (Table 8). The greatest emergence occurred with primed seeds treated with imidicloprid. There were no significant differences between soil treatments nor significant soil treatment by irrigation treatment interactions. Sprinkler irrigation encouraged faster initial emergence than furrow irrigation, especially by primed seeds, but final emergence numbers were not significantly different. The use of hymexexazol together with imidicloprid had no positive effect on emergence compared to imidicloprid alone. No effort was made to protect seedlings once they had emerged from predation by insects. Despite this, treatment 9 resulted in establishment of greater than 70 seedlings per 100 seeds planted, compared to 50 % or less establishment in most other treatments. With post emergence protection, the number of seeds resulting in established plants would have been greater in most cases. Seed treatments alone resulted in a 30 % difference in establishment, while other management factors had little effect.
Table 8
Final establishment and days to 50% emergence, Imperial Valley-DREC
(1997)
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F: furrow irrigation, S: sprinkler irrigation
Table 9
Cumulative emergence and loss, Imperial Valley-DREC, 1997
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(82.0)* |
(63.4)* |
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(18) |
(27) |
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*adjusted for lower germination percentage (x 1.21).
4. Westside Research and Extension Center. (Cooperators: Kurt Hembree, Carol Frate).
See Kaffka, Hembree, and Peterson
C. Farm trials
1. San Joaquin County (Cooperator: Mik Canevari). A trial was established in early May in eastern San Joaquin County. Seeds were planted approximately 7 days before irrigation water was applied. Furrow irrigaton was used by the grower and two pre-plant incorporated thiocarbamate herbicides (Roneet and Tillam) were applied for weed control. Between 19 and 25 days after irrigation, a large loss of plants occurred in all treatments. This loss may have been due either all or in part to cultivation, which occurred between the two observation dates.
The two primed seed treatments, resulted in the greatest emegence, particulaly
treatment 7 which emerged fastest and in the greatest amount (Table 10).
The seed treatment with the greatest emergence (and therefore with the
lowest pre-emergence losses), resulted in the largest number of established
plants. There was a larger variance among seed treatmetns with respect
ot pre-emergence losses than there was for post-emergence seedling loss.
Many more seedlings emerged than became established plants.
Table 10
San Joaquin County Farm Trial Results (1997)
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* seed used by the farmer in the remainder of the field.
2. Yolo County Farm Trial Results (cooperator: Tom Babb).
A trial was established on the research farm at the Spreckels Sugar Factory in Woodland. It was planted on May 15 and irrigated on May 21. The soil is a sandy loam, with good internal structure and drainage. The trial was abandoned after 13 days following irrigation due to loss from herbicide drift, so post-emergence losses likely are lower than otherwise would have occurred over an additional 10 to 20 days and cannot be considered representative. This is reflected in the smaller percent loss of emerged seedlings observed at this site compared to other sites.
3. Sutter County (cooperator: Kent Brittan).
This trial was planted on a cooperator’s farm on June 9, 1997 in Sutter County. The previous crop had been rice, and soils had a very high clay content. The site was characteristic of locations in the region used for rice production. Planting in late spring on rice soils is known to be a difficult stand establishment challenge. At planting, the surface soil was dry and formed small clods. The first irrigation was applied on June 15, six days after planting. The first seedlings emerged 3 days later. Fifty percent emergence occurred between 3.5 and 5 days after irrigation, depending on seed treatment. Final establishment levels were low, ranging from approximately 35 to 45 %. Post emergence mortality averaged approximately 50 % of the seedlings emerging, and was relatvely uniform for all seed treatments, while 30 to 50 % pre-emergence mortality occurred as well. The greatest pre-emergence mortality occurred with imidicloprid treated-film coated seeds and hymexazol treated pelleted seeds, followed by untreated seeds. Since post-emergence mortaility was relatively uniform, the best establishment occurred among seed treatments with the lowest pre-emergence mortality.
4. Imperial County (Cooperators: Tom Babb, Dave Melin)
Two trials were planted in the Imperial Valley on cooperators’ farms. The first was planted on September 5, but watered only on September 11, and then water was allowed to remain int he furrows continuously for three days. Additionally, on the fourth day, one-half inch of rain fell, further saturating the soil. Seedlings were observed to emerge on Septmeber 15, 4 days after irrigation began. Data analysis is not yet complete for this trial, so only qulaitative conclusions can be made. Approximately 40 % of the ssed emerged in the best treatment under these conditions, but establishment never exceeded 30 % for any seed treatment. This trial illustrated what poor management can lead to with respect to stnad failure.
The second trial was planted on October 2 and irrigated on October 4. Seedlings were observed four days later on October 8. Data analysis is not yet complete on this trial. Average emergence by October 30 was greater than 50% for all treatments.
Table 11
Yolo County trial (Spreckels Research Farm, 1997)
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Table 12
Sutter County FarmTrial Results (1997)
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*seed used by farmer in remainder of the field
Table 13
Yolo County trial (Spreckels Research Farm, 1997)
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6. Glenn County. (Cooperator: Doug Munier). Trial not yet analyzed at the time of this report.
7. Tulare County. (Cooperator: Carol Frate). Trial not yet analyzed at the time of this report.
D. Combined analyses
Overall, there was a large range in performance among seed and soil-irrigaton treatment combinations, and among sites, suggesting that there is room for significant improvement under farm conditions, even during stressful times of year. Certain patterns have re-occurred in a number of trials. The PAT+G treatment resulted in the greatest number of established seedlings wherever it was used. In general, seed treatments using imidicloprid resulted in greater numbers of established seedlings than those that did not. There was a larger range in pre-emergence losses at each site than post emergence losses. The treatments with the largest number of seedlings emerging resulted in the largest number of established plants. If pre-emegence losses can be reduced by a ombination of seed treatments and agronomic practices, stand establishment will become easier withsugarbeets.
Table 13
Combined results from selected 1997 trials.
| Trial location |
(Seed treatment) |
(range) |
(range) |
(range) |
| Davis |
(PAT+G) (80)* |
(52) |
(18) |
(46) |
| Imperial Valley
(DREC) |
(PAT +G) |
(30) |
(7) |
(38) |
| San Joaquin County |
(PAT) |
(25) |
(10) |
(27) |
| Yolo County |
(PAT+T+G) |
(25) |
(7) |
(38) |
| Sutter County |
(PAT+G) |
(23) |
(11) |
(20) |
1Department of Agronomy and Range Science, UC Davis; UCCE, Sacramento County; Spreckels Sugar, Inc., Woodland; UCCE-San Joaquin County; Department of Entomology, UC Davis; Department of Agronomy and Range Science, UC Davis.
References:
Little, T.M. and Hills, FJ. (1979). Agricultural Experimentation. Design and Analysis. Wiley and Sons, New York. 350p.
SAS, Inc., Carey, North Carolina
Scott, S.J., Jones, R.A., and Williams, W. A. (1984).
Review of data analysis methods for seed germination. Crop Sci. 24:1192-1199.