Soybean Issues Tackled: 2007 Season, Varieties for Biofuel, Foliar Fungicides

By Jane Fyksen, Crops Editor
Thursday, January 24, 2008 12:26 PM CST

An overview of last season, selecting varieties in this new “biofuels era” and spraying fungicides in beans were topics covered recently by UW-Madison soybean specialist Shawn Conley at the Wausau Agronomy Update Meeting, one of many held around the state this month.

The No. 1 issue last year was drought, along with soybean aphids, which he characterized as “spotty” in terms of infestation statewide. Another ’07 issue was Sudden Death Syndrome or SDS, which is creeping into southcentral Wisconsin and which has become the No. 1 pathogen in neighbor states; this fungal problem is driven by early planting, according to Conley.

Stem canker reared its ugly head in ’07 in a U-shaped pattern from the northwestern part of the state, dipping down to the south and arcing back northwards toward Outagamie, Brown and Kewaunee counties.

Stem canker symptoms typically first appear during early reproductive stages as reddish-brown lesions at the base of branches or petioles and are often first noted after the petiole has fallen. As the lesion elongates, it becomes dark brown to black, forming a canker that’s sunken in appearance. The stem often becomes girdled. Foliar symptoms are due to the production of a toxin by the fungus and include interveinal chlorosis and necrosis. Above and below the site of the canker, tissue remains green, and while leaves may wither, they remain attached.

Stem canker symptoms around the soil line are often confused for Phytophthora root rot as the plant “melts” from the top down, notes Conley. However, stem canker doesn’t cause a root rot. Also, foliar symptoms due to stem canker may be confused with SDS, but the absence of a root rot is indicative of stem canker.

Cumulative rains during vegetative growth have been found to be a crucial driver in the development of stem canker. Infection is likely to occur after a rain that’s followed by at least 24 hours of dew and temperatures between 70 and 86 degrees. Plant death increases when dry weather follows infection.

The best option for managing stem canker is resistant cultivars, especially in fields where it’s previously been a problem. Research has shown seed infection can be as high as 20 percent. Seed treatment fungicides may help reduce its introduction in a field, but they won’t control infections in a field. Also, since the fungus overwinters in soybean debris, tillage can cut the risk of infection. Rotating to corn and small grains n which aren’t hosts n can also reduce the risk. Alfalfa, however, is a host and has the potential to build inoculum. Delaying planting may reduce risk as well, but this tactic must be balanced with the potential yield loss due to delayed planting.

Conley notes that stem canker had plagued soybean regions in the ‘70s and then “disappeared,” but is now “popping up throughout the Midwest.”

The other issue in 2007 was Soybean Cyst Nematode (SCN), which isn’t as prevalent here in Wisconsin as Iowa and Illinois, where they’ve grown more beans for a longer period of time. It’s especially problematic in droughty areas and is scattered across a field. It tends to show up in lower pockets and sandier soil. The soybean checkoff will pay for testing of four samples per grower free of charge. Several varieties carry SCN resistant now.

Conley also highlighted yields at UW variety plots around the state, giving low and high yields at each site, as well as the average: Spooner n 6 to 18, 13 bushels on average; Chippewa Falls n 10 to 25, 18 average; Marshfield n 28 to 50, 43 average; Seymour n 42 to 61, 52 average; Sturgeon Bay n 13 to 33, 26 average; Galesville n 54 to 73, 65 average; Hancock n 55 to 75, 68 average; Fond du Lac n 57 to 71, 63 average; Arlington n 53 to 79, 68 average; Lancaster n 55 to 83, 70 average; and Janesville n 55 to 79, 67 average.

Highlighting the importance of variety selection, Conley reported that in last season’s variety trials, the highest yielding variety made 76 bushels, while the lowest yielder turned in 59 bushels; the test average was 68. The yield loss between an average variety and the high one was 10.5 bushels. The yield difference between low versus high yielder was 22.3 bushels. Over the last five years, there was anywhere from an 8 to 12 percent yield loss associated with picking an average variety, and if you didn’t pick a good one, the yield loss was anywhere from 22 to 32 percent, based on the last five year’s data.

Conley noted that glyphosate resistant varieties outyielded conventional varieties in UW trial with 68 bushels versus 62, respectively, statewide. He mentions that in 1998, the UW tested 11 conventional varieties, but only 35 last year. By comparison, there were 109 RR varieties in UW trials.

Picking varieties for biofuels

The number of gallons of biodiesel a grower can produce per acre is based on two factors, according to Conley: Yield (with 1.5 gallons per bushel) and percent oil content (with 3.3 gallons per point). The relationship between pounds of oil produced per acre and pounds of biodiesel is 1:1, and one gallon of biodiesel, by the way, weighs 7.3 pounds. He says to first select varieties that are consistently high yielding over many environments and that possess an excellent disease package for your fields and then worry about high oil content.

Looking at the impact of grain composition and yield on B100 (100 percent biodiesel) output, Conley pointed out that 40 bushels beans at 18 percent oil will produce 59.2 gallons of B100 per acre, versus at 20 percent oil, 65.8 gallons of B100. In comparison, 60 bushel beans at 20 percent oil will output 98.6 gallons of B100 (assuming 100 percent extraction rate).

Varieties in last year’s UW trials averaged between 17.7 and 20.6 percent oil content.

Summing up variety selection, Conley warned growers to remember “GIGO” or “Garbage in Equals Garbage Out.”

Spraying fungicides in focus

Growers are very interested in spraying fungicides of late due to the risk of soybean rust and for general soybean health reasons. Does row spacing affect spray canopy penetration? Conley says UW studies show no difference in spray penetration or total coverage between beans in 7, 15 and 30-inch rows “across locations and years.”

He recommends farmers base row spacing decisions on other factors like yield potential, equipment availability or weed control.

How about the impact of wheel tracks when spraying on yield? Conley says sprayer wheel traffic from first flower (growth stage R1) through harvest can damage soybean plants and reduce yield if soybean stands are thin (under 100,000 plants per acre) or late planted.

Regardless of stand, plants can’t compensate for wheel tracks made at R3 (early pod development) or R5 (early seed). And yield loss per acre is based on boom width, he reminds.

Noting that planting date and timing of spraying is critical, Conley reported soybean losses for different boom widths of: 4.9 percent for 30; 2.5 percent for 60; 1.9 percent for 90; and 1.3 percent for 120.

What about a yield response from foliar fungicides in soybeans? Conley says in 2005 at nine locations, Headline at 6 ounces showed a significant pooled yield response of 1.4 more bushels per acre in UW on-farm research. In 2006 at five locations, Quadris at 6 ounces didn’t show a statistically significant pooled yield response. However, in individual fields, the yield advantage was two bushels. Also in 2006, at six locations, Headline at 6 ounces resulted in a pooled significant yield response of 2.8 bushels on-farm. In individual fields, in Green County, the results were greater n 5.6 bushels more. And at the Marshfield variety tests, there were advantages of 5 bushels at 0.8 milligrams and 6.4 bushels at 1.5 MG. And last year, at four locations, Quadris at 6 ounces in three fields showed no significant response. Headline turned in 6-plus bushels, he noted.

UW small plot trials in ’05 and ’06 were conducted at Madison, Arlington and Lancaster. Eight individual trials tested multiple products, multiple fungicide classes and various timings (from R2 to 21 days beyond R3). There were a total of 126 comparisons as some fungicides were used multiple times across locations and years. The results? One product had a significant yield difference and also economic gain from the application. Three resulted in a significant yield decrease. And 122 of the comparisons showed that the foliar applications made no significant difference.

Regional data from last year was also shared by Conley. Here it is: 74 trials with Headline, plus 2.4 bushels (15 of the 74 had significant results); 35 trials with Quadris, plus two bushels (10 of 35 trials had significant results); 28 trials with Folicur, plus one bushel (3 of 28 had significant results); 58 trials with Headline applied only at R3, plus 3.1 bushels (13 of 58 significant); 21 trials with Headline from small plots, plus 2.2 bushels (3 of 21 significant); 37 trials of Headline in large or medium strip trials, plus 3.6 bushels (10 of 37 significant).

Lastly, Conley shared this past season’s plant health soybean results. The treatments were: Quadris, plus 4.7 bushels (large areas) and 4.3 (small plots); Headline, plus 5.5 (large) and 4.4 (small); Folicur, plus 1.3 (large) and 1 bushel (small), compared to the checks which averaged 53 bushels to the acre (large) and 52.4 (small).

As for breakeven yield, Conley reminds growers that they need to count up the cost of the fungicide, adjuvant and making the application, which he figured comes to $21 on a 50 bushel yield. At $5 beans, you need four bushels to break even (figuring no wheel tracks). At $10 beans, you need two bushels to breakeven. However, wheel tracks cut into yields. At R3 bean and a 90-foot boom, you need three bushels to break even at $10 beans.

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