Stephen R. Kaffka

Introduction

Four sugarbeet seedling emergence trials were conducted on the University of California, Davis campus during the summer of 2000 at the request of Astec Seed Company of Sheridan, Wyoming. This report summarizes the performance of different seed lot-seed treatment combinations in these trials.

Methods

Seeds from differing seed lots, and with different pre-emergence seed treatments and coatings were received from ASTEC (Table 1). These were counted into one hundred seed lots and planted using a cone planter into 30 foot rows. There were 5 replications of each treatment and treatments were arranged in a Randomized Complete Block Design. Seeds were grouped into four different trials following suggestions from the company. All plots were furrow irrigated two to three times.

Each seedling was labeled with a small wooden stake at emergence. Using stakes allows for the identification of all emerging seedlings. The stake was removed if the seedling died and the cause of mortality was evaluated visually in the field at that time. The sum of the number appearing during the counting period is cumulative emergence. The last count, just prior to thinning was considered to be the final establishment. The difference between cumulative emergence and final establishment is cumulative mortality (post-emergence). If the amount of seed planted is known, pre-emergence losses can be calculated by difference using observed cumulative emergence, corrected for the percent viable seed from laboratory germination tests. Pre-emergence loss is defined from an agronomic perspective. If seedlings had not emerged after two or three irrigations and by the time the majority of seedlings had reached the five to six true leaf stage, they were included in the pre-emergence loss category. They may still been viable, but were of no agronomic use to growers. Late emerging seedlings may also act more like weeds than contribute to crop yields.

Stand counts were made from the first sign of emergence for five days in a row. Then one or two days were skipped, and stands were counted every other day. Usually, by 8 to 9 days from the start of emergence, the majority of seedlings had emerged. Afterwards, many fewer seedlings appeared. During the third week, two or three counts were made. The last count occurred during the fourth week from the start of emergence. Most seedlings surviving had reached the fourth to six true leaf stage.

No post-emergence control of insects occurred during the trials. It was not possible to use insecticides because of the daily field entry requirements, and systemic insecticides like imidicloprid were a treatment factor in some the trials, so could not be used generally. Imidicloprid can interfere with emergence under some conditions in any event. Summer is not an ideal time to carry out emergence trials because of variable to severe insect pressure, and such pressure was observed during the first set of trials (C and F), when an unusually intensive infestation of beet armyworm occurred. All data analysis was done using SAS (v7.0).

Results

Trail C (Commercial quickprime). July 12 to August 8, 2001.

This trial emphasized comparisons between bare, processed seed (N) and primed (QP) or "Quick Coated" (QC) treatments. QP and QC were regarded as separate treatments. Comparisons of seed treatments were made. Seed treatment main effects were significant (Table 2A), allowing for more detailed mean separation tests. The largest differences in the trial were due to seed lots. In this context, seed lot differences could also refer to variety differences, or reflect different storage and processing standards among seed companies. Overall, priming did not enhance cumulative emergence in this trial (Fig. 1; Table 2B). There were different reactions to QC and QP treatments, depending on seed lot (Table 2B), but the general response was negative.

Trial F. (Research and Development), July 12 to August 8, 2001.

This trial emphasized comparisons among seed lots and 4 pellet types or coatings which are under development at Astec. The pellet types were: N---bare, processed seed; U---Astec's standard; M and L--two new pellet types. Seed lot differences accounted for more variance than seed coatings (Table 3A). Means for the seed treatments and seed lots are reported in Table 3B. There were no significant differences among the pellet types with respect to cumulative emergence (Table 3B). Overall cumulative emergence was by far the lowest for all four trials in Davis. Even the untreated seed emerged poorly. Since this trial took place at the same time as Trial C and next to it, the poor performance is most likely seed related.

Trial E1. (Commercial and non-commercial Gaucho and Tachigaren) August 2 to August 27, 2001.

This trial emphasized the use of imidicloprid (Gaucho), an insecticide, and hymexazol (Tachigaren), a fungicide. These materials were applied at different rates and compared to untreated seed and a pelleted seed without the insecticide or the fungicide. Two biological control agents of an unknown type also were included in the trial. In comparison to the other trials, a single seed lot was used, allowing for un-confounded inferences about treatment differences.

This trial had the highest average cumulative emergence rate of any of the four, reflecting in my view particularly the use of imidicloprid. Gaucho was effective at increasing seedling emergence; Tachigaren was not (Table 4B). Higher rates of Tachigaren reduced seedling emergence. The biological control agents were similar to each other but not as effective as Gaucho at enhancing emergence, though differences were not significant.

All the treatments are compared in figure 2. From the figure, it is apparent that the control treatments did not differ from each other significantly, while all the Gaucho treated seeds emerged at the largest rate in the trial. The exception was the Gaucho treatment with the higher rate of Tachigaren, which harmed emergence.

Trial E2. (Commercial Tachigaren). August 2 to August 27.

Both seed lots and treatments differed, primarily the use and rate of Tachigaren. Results are reported in Tables 5A and 5B. There were no significant seed lot differences in this trial. Tachigaren was largely ineffective at increasing emergence. In this trial, there seemed to be no emergence penalty for using the higher rates of Tachigaren.

Discussion

In most of the trials, a large number of factors varied, reducing the number of comparisons that could be made and the overall effectiveness of the trials in measuring differences. Nevertheless, there were some larger trends and differences that could be observed. Seed lot differences in many cases were the most significant effects in many of the trials. These differences are hard to interpret without more information about the nature of these differences. Seed lot and varietal

differences have been observed in other trials we have conducted at Davis and elsewhere in California, and can be significant factors influencing stand establishment.

The superior performance of Gaucho-treated seeds has been observed consistently in trials in California over the last five years. We believe there is a chronic level of insect damage to seeds and emerging seedlings that has gone unrecognized in the past. This can vary from influencing only a small percentage of seedlings to quite significant amounts of damage (greater than 20 5 of the seed).

Tachigaren has been a difficult material to use in California. Occasionally, we have observed an increase in emergence, particularly in trials in eastern San Joaquin Valley, but more commonly in there has been no effect or damage has been observed. Its value is difficult to predict and it is not used much in California.

Pelleting seed always slowed and reduced emergence in our trials in California compared to bare seed. This was observed in this trial as well. Priming can overcome most of the disadvantages of the pelleting materials.

Post emergence losses.

A large amount of data was collected during these trials on post-emergence loss. It is not reported here. Trials C and F were carried out in early summer during one of the largest armyworm infestations in recent memory. Post emergence survival was largely uncorrelated with seed treatments or seed lots. In general, post-emergence losses to insects and pathogens is less well correlated with seed and seed treatment differences than pre-emergence losses. Pre-emergence losses are usually far more significant than post-emergence losses, so successful stand establishment commonly is a function of emergence rates. This is not the case in an exceptional year, however, like the one during which this trial occurred. Also, we do not control insect predation of seedlings during our trials, so the amount of damage observed is greater than might be found under field conditions where growers will treat insects during the establishment period.

Rates of emergence.

Emergence rates were calculated for different seed coatings. N was compared to MP and to MP plus Gaucho. We would expect N > MP > MP+G in terms of speed of emergence. In the trial, N seeds did emerge faster, but only marginally so. The t₅₀ or time to 50% emergence was 4.24 days for N seeds, 4.48 days for MP seeds, and 4.44 days for MP+G seeds (fig. 3 and 4). Gaucho did not substantially slow rates of emergence, so the MP pellet seemed to reduce the inhibitory effect of Gaucho as well.

Fig. 3. Cumulative emergence for different seed treatments

Fig. 4. Normalized emergence rates. (Cumulative emergence divided by maximum emergence). The horizontal line is t50.

Table 1. Seed treatments and seed lots

Table 2A

Trial C, Cumulative emergence ANOVA. Mean = 53.7 %.

Table 2B

Trial C, Single degree of freedom contrasts

Notes: (1) Compares C1, C9, C13, C19 with C2, C10, C14, C20. (2) Compares C21, C23 with C22, C24.

Table 3A

Trial F, Cumulative emergence ANOVA. Mean = 27.2 %.

Table 3B

Trial F, Single degree of freedom contrasts

Notes: differences between L and MP and UP are not significant

Table 4A

Trial E1, Cumulative emergence ANOVA. Mean = 73.3 %.

Table 4B

Trial E1, Single degree of freedom contrasts

Notes: Other contrasts were confounded by seed coat differences.

Table 5A

Trial E2, Cumulative emergence ANOVA. Mean = 73.3 %.

Table 5B

Trial E2, Single degree of freedom contrasts