Fig 1. Cumulative emergence comparisons, for the two Gaucho rates applied and the Growers and Control treatments. Error bars are standard errors in all figures.
Interim Report to the California Department of Pesticide Regulation
(Agreement # 98-0330)
Sugar Beet Pest Alliance (1998-2001)
Objective 3: Improving Sugarbeet Stands and Reducing Pesticide Use in the Imperial Valley[1]
Stephen Kaffka
Summary
The effects of different methods of protecting emerging sugarbeet seedlings were compared in a field trial in the Imperial Valley. Treatments included the current preferred growers’ practice involving the use of an insecticide at planting combined with two or more post-emergence sprays for insect control, seed treatment with a systemic insecticide at two rates (imidicloprid or Gaucho®), and no control measures. Seedlings were counted four times until thinning. Pre-emergence pesticide applications resulted in significantly larger numbers of seedlings than when using untreated seeds. Gaucho® was as effective as the use of an organo-phosphate insecticide applied to soil at improving seedling emergence. Flea beetles were the principal cause of damage at emergence and are well controlled by Gaucho®, but it has no effect on armyworms. Armyworms caused little damage during the trial this year, but intensive pressure by flea beetles in the post-emergence period suggests that some post-emergence insect protection remains important in the Imperial Valley when fields are irrigated early in the fall.
The amount may be reduced significantly, however, by using a seed treatment insecticide like imidicloprid.
Introduction
Sugarbeets are an important crop in the Imperial Valley, and once established, they grow well during the winter and spring months in the low desert. Planting takes place, however, during September and early October, when air and soil temperatures are above optimum, and the populations of insects preying on sugarbeet seedlings such as flea beetles and armyworms are large. Growers believe that control of insects on sugarbeet seedlings should begin as soon as seedlings appear and continue until late autumn. Management based on this assumption has been successful for many years, but the most commonly used materials for control (Lannate® (methomyl), Lorsban® (chlorpyrifos), and Diazinon®) are carbamate or organophosphate type compounds which currently are under review by US EPA for possible future restriction under the provisions of the Food Quality Protection Act. Diazinon was recently withdrawn voluntarily from the home garden market because of concerns about public exposure.
Currently, there are no well-established alternatives to the use of these materials for sugarbeet seedling protection.
Methods
To demonstrate alternative seedling protection strategies and document loss to insects and other causes, a trial was conducted in the Imperial Valley near Brawley in a 22 acre sugarbeet field in the fall of 2001. Fifteen strips, each with 20 thirty inch rows a quarter mile long, were planted with Beta 4776R, a commonly planted variety in the area. All of the seed was from the same seed lot. Five different pre- and/or post emergence treatments were applied (Table 1). Each treatment was replicated three times. Emerging seedlings were counted in two twenty five foot long subplots in rows 7, 8, and 9 in each plot, at 10, 17, 22, and 28 days after irrigation. At the last date, seedling spacing was determined by measuring the distance between the first 100 seedlings in row 8 using the westernmost subplot. Also, the above-ground portions of 30 seedlings were collected from row 8 of each subplot, dried and weighed for comparison at thinning.
Each seedling was labeled with a small wooden stake at emergence. The stake was removed later if the seedling died and the cause of mortality was evaluated visually in the field. If a plant was chewed off or obviously damaged by insects, its loss was attributed to the insect damage category, if it was shriveled or desiccated, or a common seedling pathogen could be visually identified, it was classified in the shriveled or diseased category. If there was no seedling next to a stake, it was classified as missing. Using stakes allows for the identification of the majority of seedlings appearing. Those disappearing during the first three or four days from the start of emergence will not have been counted. The sum of the number appearing is cumulative emergence. The last count, just prior to thinning was considered to be the final establishment. Because the amount of seed planted is known, pre-emergence losses can be calculated by difference using observed cumulative emergence. The field was planted on September 12 and 13 using a Milton planter. The amount of seed remaining after planting the field was weighed to get an exact weight for the seed planted. In this trial, 70,000 seeds per acre were planted. This was divided by the known field area to get the seed population. We assume that planting occurred uniformly. The seeding rate used was a reduction from the previous year’s trial. Irrigation was initiated on September 15th, the day following planting. The field had been pre-irrigated the preceding August. At the final count in the fall the distances between one hundred beets in one row per plot were measured. Data were analyzed using SAS v7.0 software.
Results
The results reported here are from the fall stand establishment period only (September through October, 2001). Yields will be measured in spring, 2002 and reported at that time. Planter problems occurred because of insufficient seed amounts when planting plots 1 to 4, which were planted last. In some of the plots, very few seedlings emerged, compared to the other two replications. Uniformity of seeding rates is an essential assumption for this trial. ANOVA tests indicated that replications were a highly significant factor (not shown), in contrast to previous years, when replications were not significant. Data were analyzed including all three replications, and then excluding the damaged replication. The relative performance of the treatments was the same in both analyses, but treatment differences were more significant if the first replication was excluded. Because uniform seeding rates could not be assumed for the plots 1 to 4, the first replication was omitted from this analysis.
Cumulative emergence. On average, a larger percentage of seeds resulted in sugarbeet seedlings in 2001 than in 2000, but a smaller amount than in 1999. In 1999, emergence reached 80% of seeds planted while in 2000, the best treatment resulted in approximately 50% emergence, and in 2001, approximately 70 % emergence was observed in the best treatments. Seedling survival was greatest when pre-emergence insecticides were used (Table 2). There was no significant difference between the Grower’s treatment using pre-emergence Lorsban® applied to the soil and seed treated with Gaucho® (Tables 2 and 3). No delay in emergence was observed for Gaucho® treated seeds (fig. 1). Significantly fewer seedlings emerged in the control treatment, lacking pre-emergence seedling protection (Tables 2 and 3). The two different Gaucho® rates were not significantly different, even though somewhat more seedlings emerged in the lower rate plots (fig. 1, Tables 2 and 3)
Pre-emergence losses are determined by difference (Table 2). Average pre-emergence losses ranged from approximately 30 % to 50 % of the seed planted. These losses include a small percentage (5 %) of non-viable seed. Other causes of pre-emergence loss include uneven seed beds and planter performance.
Establishment at thinning. The percentage of seeds resulting in established seedlings immediately prior to thinning (six to eight true leaves) is reported in Table 2. The average number of seedlings counted at each date is also presented in figure 2. There were no significant differences between the Growers and Gaucho® treatments, but the Control treatment had significantly fewer plants (Tables 2 and 3).
Cumulative mortality. There was very little post-emergence seedling loss up to thinning in all of the treatments, including the control treatments (Table 2, fig. 3). Flea beetle pressure was observed to be quite intense in the first two weeks of counting. Nonetheless almost all the seedlings emerging survived. Cumulative mortality increased only slowly with time.
Seedling growth. The dry weight (DW) of seedlings at thinning is compared in Fig. 4. The Growers treatment resulted in significantly larger seedlings than any of the other treatments. Seedling DW was less but similar for the two identical Gaucho® treatments (45g a.i. per unit) and declined further for the 20 g rate and for control treatments. Spraying the Gaucho®-treated seed at 12 days after irrigation once with Lorsban/diazinon did not significantly increase seedling DW compared to the equivalent treatment that was unsprayed. The lower Gaucho® rate (20 g a.i. per unit of seed) resulted in significantly smaller seedlings than the higher rate Gaucho® treatments.
Discussion
Cumulative emergence and seedling establishment. Seedling numbers were not significantly different from each other if an insecticide was used but were significantly greater than the control treatment, in which only fungicides were used. Between approximately 50 % to 70 % of the seed planted resulted in stands in 2001. In the previous year 30 % to 50 % of the seed planted emerged, while in 1999, 50 % to 80% emerged. The most recent trial, like the one in 1999 was carried out in a pre-irrigated field. Results in these two years suggest that with average planter performance and the use of an insecticide at planting, between 65 % to 80 % of the seed planted can result in a useful sugarbeet plant in the Imperial Valley. This is a substantial improvement over the long term expectation of beet growers that only 50 % of the seed or less will result in a useful plant. The lower rate imidicloprid treatment (20 g a.i. per 100,000 seeds) performed as well as the higher rate treatment for the second year in a row. Since performance at a lower rate is satisfactory, the lower rate should be used by growers, except perhaps for the earliest planted fields.
Plant protection. In the Imperial Valley, and other locations where pre-emergence losses are high, an insecticide applied with or to the seed appears necessary. For the third year in a row, pre-emergence losses were significantly greater when no insecticide was used at planting compared to the use of an insecticide. On average in 2001, approximately 20 % fewer seedlings appeared when no insecticide was used. Over the three years of this trial, pre-emergence losses
varied from 20% to 40 % greater in the control treatment without an insecticide than in the other treatments. The significantly larger number of seedlings emerging in treatments including a pre-emergence insecticide in these three trials and in other trials conducted elsewhere in California leads to the inference that insect damage is occurring to seeds and emerging seedlings before they appear above ground.
Early seedling damage once again was due almost entirely to flea beetles. Armyworm larvae had not had time to develop and few were observed. Very few armyworm larvae were active in the plots during this trial and in the Imperial Valley generally this last autumn. From initial emergence onwards, flea beetles were present in the plots and damaged seedlings, even at the cotyledon stage. Based on visual estimation only, flea beetle pressure in plots seemed greater in 2001 than in any of the previous two years.
Gaucho® was very effective against flea beetles, and other cryptic insect pests affecting seedling emergence. At the lower rate (20 g a.i per unit), however, its effects against flea beetles diminished sooner. Post-emergence grazing by flea beetles resulted in smaller seedlings, but no increased mortality in this treatment. For the sake of seedling emergence, the lower rate of Gaucho® apparently is as effective as the higher rate, but its ability to protect seedlings lasts less long and may have to be combined with a post emergence treatment, depending on: 1) the amount of insect pressure observed, 2) how early in the season the field has been planted, and 3) the grower’s tolerance for seedling damage. Early planted fields may require more post-emergence control than later planted fields when insects are abundant.
Costs of establishment.
The costs of treating plots, derived from the grower’s records, are reported in Table 1. The most expensive treatment was the Grower’s treatment, and the least expensive was the control. Applying Gaucho at 20 g a.i. per unit resulted in a cost of only $14.00 per acre. This is a savings of $38.30 per acre compared to the grower’s treatment.
Increasing confidence in the potential success of stand establishment leads to lower establishment costs overall, even for conventional treatments. In each of the three years of this trial, costs for the stand establishment have declined. The growers have used fewer post emergence sprays, and reduced the amount of seed planted, saving themselves more than $50.00 an acre. By using imidicloprid at low rates, and then observing the field for post-emergence insect damage, a grower in the Imperial Valley should have the best chance to save money on stand establishment costs while insuring adequate plant stands.
Conclusions
1. Pre-emergence pesticide applications resulted in significantly larger numbers of seedlings than the control treatment without them.
2. Gaucho® applied to seeds was a satisfactory method of controlling per-emergence seedling losses and resulted in adequate numbers of sugarbeet seedlings for a successful commercial crop. Flea beetles were the principal cause of damage at emergence and were well controlled by Gaucho® at the 45 g a.i. per unit of seed rate. The lower rate of Gaucho® resulted in similar numbers of seedlings compared to the growers treatment and the other higher rate treatments, but apparently did not reduce post emergence flea beetle damage to seedlings as well as in the higher rate plots. If the lower rate of Gaucho® is used, there will need to be field scouting for flea beetle and army worm damage after emergence, and a decision made whether additional control measures are needed.
3. Establishing a large percentage of seeds as seedlings saves growers money on seed costs and reduces the amount of pesticides applied, with imputed environmental benefits.
4. Some post-emergence insect protection remains important in the Imperial Valley when fields are irrigated early in the fall, but the amount may be reduced by using a seed treatment insecticide like Gaucho®.
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.
List of tables
Table 1. Treatments and associated costs.
Table 2. Seedling emergence and establishment (percent)
Table 3. Treatment contrasts.
List of figures
Fig. 1. Imperial Valley, fall_2001. Cumulative emergence % (seedlings per 25 feet of row). Error bars are standard errors.
Fig. 2. Imperial Valley, fall_2000. Number of plants established (% or seedlings per 25 feet of row). Error bars are standard errors.
Fig. 3. Imperial Valley, fall_2000. Cumulative mortality from all causes (% or seedlings per 25 feet of row). Error bars are standard errors.
Fig. 4. Seedling dry weight at thinning (g per 30 seedlings).
Table 1
Treatments (2001)
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
19.30 52.70 (total) |
|
|
|
|
|
45
g per 100,00 seeds; 31.5 g |
|
31.50 (total) |
|
|
|
|
|
20
g per 100,00 seeds; 14 g |
|
14.00 (total) |
|
|
|
|
|
|
|
0 |
|
|
|
|
|
45 g per 100,00 seeds; 31.5 g
|
|
22.50 53.00 (total) |
* Seed planted at
the rate of 70,000 per acre.
Table 2
Seedling
emergence and establishment at
thinning
|
|
|
|
|
|
|
|
|
|
|
|
|
31.7 |
|
|
|
|
|
|
35.6 |
|
|
|
|
|
|
32.1 |
|
|
|
|
|
|
48.3 |
|
|
|
|
|
|
33.2 |
|
LSD(0.05) |
|
|
|
|
|
Imperial Valley,
(fall 2001). Data collected at 28 days
after initial irrigation.
Table 3
Treatment
contrasts (Days since initial irrigation = 28, final count)
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|
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|
|
|
|
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0.1456 |
|
|
|
|
|
0.1356 |
|
|
|
|
|
0.6726 |
|
|
|
|
|
0.0289 |
|
|
|
|
|
0.131 |
|
|
|
|
|
0.3010 |
|
|
|
|
|
<.0001 |
|
|
|
|
|
<0.0001 |
|
|
|
|
|
0.0073 |
Fig 1. Cumulative emergence comparisons, for the two Gaucho rates applied and the Growers and Control treatments. Error bars are standard errors in all figures.
Fig. 2. Established plants. Percent of seed sown. Imperial Valley, 2001.
Fig. 3. Cumulative mortality. Percent of seed sown. Imperial Valley, 2001.
Fig. 4. Seedling dry weights, g per 30 seedlings. Imperial Valley, 2001.
C:\Work\WORK\Projects\SB2002 stand\Interim DPR report_fall
2001.wpd
[1]Supported in part by a grant from the California Department of Pesticide Regulation, Betaseed, Inc, Spreckels Sugar, Inc., Gustafson, Inc., and the California Sugarbeet Industry Research Committee. Acknowledgments are extended to Tom and Kurt Rutherford, Larry Godfrey, Tom Terini, Gary Peterson, and Larry Gibbs for their cooperation and help with the field experiment.