Every aspect of soybean production has centered on yield and the need to strive for constant yield improvement. This makes perfect sense as the yield of a marketable crop has always and will continue to pay the bills.

However, in 2009 after eight weeks of continuous rain, the onslaught of Phomopsis seed decay and seed rot wiped out practically 40 percent of the farm gate value of the Mississippi soybean crop. After that happened, we came to understand the importance of seed quality at harvest time. A 70 bu/A soybean crop that was 90 percent damaged and not marketable at average market selling price was virtually worthless.

Maintain soybean yield and quality
Research funded by the Mississippi Soybean Promotion Board (MSPB) over the past 10 years has found that a R3/R4 application of a strobilurin fungicide often provides a yield increase of approximately 2.9 to 3.5 bu/A, with yield increases typically ranging from 0.5 to 15 bu/A, depending on numerous factors such as environmental conditions, variety selection, crop rotation and planting date. This research has found that yield increases are often consistently higher for soybean grown in a continuous monoculture in the absence of crop rotation.

Current research funded by the MSPB on potential benefits and utility of foliar fungicides in soybean continues to focus on improving soybean yield but also on the potential benefits from foliar fungicides for maintaining seed quality at time of harvest. The focus of this research is to identify potential benefits from foliar fungicide applications coupled with warranted insecticide applications at growth stages, ranging from R5 to R6 with the objective of maintaining soybean yield and quality, resulting in a soybean crop that is marketable at current market prices.

If we can consistently improve yields with R3/R4 fungicide applications and identify methods to maintain the quality of a good yielding crop with the end goal being able to show these additional inputs provide an economic return, then we are doing a good job of judiciously utilizing grower checkoff funds. Our overall goal is to improve soybean yields and profitability.

Observations from 2009 research
Research in 2009 demonstrated three points around which we are building our 2010 research. First, where we were able to harvest research plots before the rains ever started and where we never encountered any measurable level of insect pressure, the seed quality was excellent, regardless of whether we used or didn’t use a R5/R6 foliar fungicide. Second, in situations where we weren’t able to harvest until after six weeks of continuous wet weather that occurred after soybean maturity, any and all potential benefits from R5/R6 fungicide applications were negated by the extreme adverse conditions. Basically everything, regardless of treatment, was 70 to 85 percent damaged.

Third, where we encountered measurable stink bug pressure through much of the soybean reproductive cycle (R1 to R7) coupled with wet weather for two weeks after maturity but before harvest, we saw tremendous benefits from a R5.5 application of a strobilurin fungicide application. An application of Quadris plus a pyrethroid insecticide at R5.5 resulted in minimal seed quality losses (2.4 to 5 percent damage) compared to 85 percent damage for the untreated check.

Net returns were $110/acre higher from an R5.5 application of Quadris plus pyrethroid insecticide application compared to net returns for the untreated check. This research, conducted over multiple locations in 2009, demonstrated potential benefits and utility from foliar fungicides applied at reproductive growth stages, ranging from R5 to R6. However, the overwhelming factor that influenced these potential benefits was influenced more by presence or absence of pest pressure and even more by timing of wet weather in relation to the ability to harvest the crop in close proximity to maturity before receiving significant moisture.

These late fungicide applications (R5/R6) are much more complex than the R3/R4 application, which we have always considered to be our yield enhancement application. The R5/R6 application is more dependent upon presence or absence of pest pressure and environmental conditions after the application.

Contact Trey Koger, Mississippi Extension soybean specialist at tkoger@drec.msstate.edu.