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Bruce Burdick
1109 S. Birch St.
Albany, MO 64402
660-726-5610
Email: BurdickB@missouri.edu

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SOYBEAN SEED TREATMENTS

Summary: Three years of tests on a common, commercially used fungicide seed treatment, in relation to row width and plant population, were conducted between 1999-2001 at the Hundley-Whaley Farm at Albany, Missouri. Overall data suggested that there was an insignificant response to seedling establishment due to fungicide seed treatments. Fungicide treated seed provided significantly higher crop seed yields in one-half of the planting rates. There was no consistent interaction between row width and seed treatment for soybean seed yield.

Contrary to what was expected, thirty inch wide rows provided significantly higher yields than fifteen inch rows over the three year period.

While crop seed yields increased with increasing rate of planting, the cost of the additional seed resulted in economic losses in three out of four of the rate increases.

Objective: To determine the value of fungicide seed treatments for soybean producers, as influenced by planting rate and row width

Explanation: Two years of data from the study have been reported in previous years. This report provides details of the test in 2001 and gives a three year analysis of the work.

Situation: Soybean seeds planted into soils within 12-36 hours of a major rainfall event are most subject to seed and seedling diseases caused by fungi. Cool wet soils favor seedling diseases. The cool temperatures slow seed germination and seedling growth and favor the growth of many fungi that cause seedling diseases.

Seed treatment of soybeans with a fungicide before planting will usually help to improve germination and seedling vigor by reducing seed decay, damping off and seedling blights.

This study was designed to answer the question of whether the additional costs would yield profitable results.

Methods: The soybean variety used in this experiment varied by year. Merschman brand soybeans were used each year. The variety used was consistent across years, however, two different lots were used. One lot was fungicide treated and one lot was not. The treated seed was what Merschman calls Bonus Coated Seed^TM. The treated seed was treated with a formulation of four fungicides (Captan, PCNB, Thiabendazole and Metalaxy). The fungicides are supposed to provide seedling protection against Rhizoctonia and Pythium plus seed borne pathogens like White Mold, Pod & Stem Blight and Alternaria. The varieties used in the study were as follows:

• For 1999 Merschman Kennedy IV RR
• For 2000 Merschman Houston V RR
• For 2001 Merschman Kennedy V

We had hoped to plant this study at a time immediately preceding a rain event. Due to weather variables each year, this was not always possible. Rainfall following planting was as follows (Table 1).

The 2001 planting provided the rainfall following planting that should have favored the growth of fungi and the seed treated with fungicides.

The study was planted into a soil type characterized as a Grundy silt loam with 3.1% organic matter. The soil surface was dry at planting time, but there was adequate moisture in the soil profile to get rapid germination of the seed. The study was planted into a previously disked but stale seedbed. The previous crop was soybeans.

Seeding rates were 100, 150 & 200 thousand seeds per acre. The seed was counted to represent these seeding rates and then planted with a cone planter set to plant the seed 1" deep. The study was designed as a Split-plot with six replications. Gylling's Agriculture Research Manager 6.1 was used to design and analyze the yearly data. SAS statistical analysis program was used to evaluate the three year data.

Weed control was accomplished with multiple applications of Roundup Ultra or UltraMax applied as needed. All Roundup applications were made at the rate of 0.75 pound acid equivalent per acre.

Stand counts were taken each year when the soybeans were between Growth Stages V2 and V4. Counts were taken from two to three locations within each plot, depending upon the year. The location of the area counted was subjectively selected based on what was considered by the plant counters to be a representative stand within the plot. The area counted contained soybean seedlings within a 30" square. These counts were added together and averaged for the reported stand.

The soybeans were harvested each year with an MF 35 plot combine. The scales used to weigh the yield were spring-type (milk scales). Moisture content of the beans was taken from the first 15-20 plots harvested and the average moisture from these plots was used for calculating all plot yields. Harvest date each year was considered "timely".

Results: Tables 2 & 3 show the results of the 2001 stand counts. The three year mean data is in Table 4.

The seedling count data for 2001 indicates that fungicide seed treatments did aid in securing stands in some of the treatments, but not in all. The final stands ranged from a low of 29% to a high of 63.9% of the seed planted in 2001. Overall, the 30" wide rows resulted in better stands than the 15" wide rows in 2001.

The three year mean stand that was obtained in the study were 111,586 seedlings per acre for the plots treated with fungicides to 108,109 seedlings per acre for the untreated-seed treatments. The differences in stand were statistically insignificant.

Harvest was done on October 25 in 2001, and the yield data is shown in Table 5. Three year mean harvest data is shown in Table 6.

The 2001 data shows no significant difference in soybean yield between treated and untreated seed. The three year data shows that the fungicide treated seed provided significantly higher yields than the untreated seed in one-half of the planting rates.

Figure 1

Figure 2

Conclusions: The data for this study can be concluded as follows:

1. For 1999 and 2000 fungicidal seed treatments were of no value in securing soybean stands, regardless of row width or planting rate. The 2001 data showed a significant improvement in seedling establishment in 15" wide rows planted with 150,000 seeds per acre and to 30" wide rows planted with 200,000 seeds per acre. There were no other treatments showing a significant difference in stand due to seed treatment. A three year analysis of data showed that seed treatment provided significantly better seedling establishment in four out of six treatments, significantly poorer establishment in one out of six treatments and no significant difference in seedling establishment in one out of six treatments (Table 4).
2. There was no significant difference in soybean yield performance in 1999 or 2000 for soybeans planted at seeding rates of 100,000, 150,000 or 200,000. This occurred regardless of row widths of 15 or 30 inches wide. In 2001, differences did exist in soybean yield. The 30" wide rows yielded significantly higher yields than the 15" wide rows in two out of three planted populations and the 200,000 seeds per acre planting rate yielded significantly higher than the 100,000 seeds per acre planting rate three out of four times (Table 5). The analysis of the three year data showed a significant yield increase by increasing planting rates from 100,000 to 150,000 seeds per acre in 15" rows or by increasing planting rates from 150,000 to 200,000 seeds per acre in 30" wide rows. There was no other significant yield response to planting rate and the significance was not related to seed treatment (Table 6).
3. There was no significant difference in soybean yield performance in 1999 or 2000 for soybeans planted in either 15 or 30 inch wide rows. This resulted regardless of planting rates of 100, 150 or 200 thousand seeds per acre. In 2001, the 30" wide rows provided significantly higher yield than the 15" wide rows. The three-year yield data, when analyzed over the complete period of the study, indicated that 30" wide rows provided a highly significant increase in yields over the 15" wide rows (Figure 1).

Discussion: The year of 2001 was the only year to provide weather conditions immediately after planting to favor diseases of seedling soybeans. Indeed, much seedling mortality did take place and better stands were obtained with fungicide treated seed in five of six paired plantings. Statistically, the difference was only significant in ½ of the paired plantings (treated and untreated seed at the same plant population). Overall, fungicide seed treatments did not significantly impact the establishment of soybean seedlings when the three years of data from the study was analyzed.

Surprisingly, the data over the three years of the study indicates that 30" wide rows provided significantly higher yields than 15" rows. This yield difference could not be attributed to differences in obtained stand.

The three-year data shows that 200,000 seeds per acre in 30" wide rows provided significantly higher seed yields than the 100,000 or 150,000 planted rate. The planting rate of 150,000 seeds per acre in 15" wide rows provided seed yields significantly higher than the 100,000 planting rate, however, there was no significant difference in yields between the planting rate of 150,000 and 200,000 seeds per acre in 15" wide rows.

Significance of study: If the data from this experiment are representative of what actually happens in farm fields in northwest Missouri, several conclusions could be drawn. One would be that dollars spent on the fungicide seed treatments that are commercially common today are of questionable value.

Another conclusion would be that investing in a 15" wide row planter would yield negative returns. Not only would yields be less in 15" rows, but investment, maintenance and operating costs would be higher for 15" row planters.

If this data is relevant, the final conclusion would be that it is not profitable to plant in excess of 100,000 soybean seeds per acre. The calculations made in Table 10 show that the increased yields obtained from higher seeding rates were not high enough to justify the added expense if seed coss are high.

Outreach: The data for the 1999 experiment was shared with 165 soybean producers attending the NW Mo. District Soybean Meeting in Maryville in February, 2000. It was also included as a part of the 2000 and 2001 Hundley-Whaley Research Farm field day report that was distributed to over 1600 people who attended the field day and tour. This winter, the overall summary of the study data will be shared with producers at the District Soybean Producers Meeting, the Maryville Young Farmers and the NW Mo. Certified Crop Advisors training in St Joseph. I expect that a total of nearly 300 producers will be in attendance at those events.

Future Plans: 2002 concluded the three-year study.