By Bruce Potter, Senyu Chen, Phil Glogoza and Ryan Miller
The soybean cyst nematode (SCN) is a serious pest of Minnesota soybean and has been managed with crop rotation and soybean varieties with resistance to SCN. SCN populations virulent on (able to infest, reproduce on and damage) SCN resistant soybeans are increasingly widespread. Virulence on the PI 88788 resistance source is the most common, but increasing numbers of field populations virulent on Peking or both PI88788 and Peking resistance sources have been observed (Chen, et al. 2011). Therefore, effective chemical or biological complements to resistant varieties would be helpful to soybean growers’ SCN management programs.
A new seed applied pesticide with potential for SCN management is the bacterium Pasteuria nishizawae, a biological nematicide and a component of Clariva™ Complete seed treatment, Syngenta Crop Protection®. The Minnesota Soybean Research and Promotion Council funded a 2014 project to provide geographically and environmentally robust data on Clariva for SCN management. One objective of this study was to evaluate the effects of the new biological nematicide on soybean yield, including potential interactions with SCN host plant resistance, environment and an insecticide plus fungicide combination.
Methods
The study was co-located at University of Minnesota Soybean Breeding Project sites throughout Minnesota. These sites varied by geography, soil type, long-term field histories, SCN populations and planting date. At 20 sites across Minnesota, four replications of each of six treatments were planted with a plot planter. One northern site was not harvested because of herbicide damage and one southern site was not harvested because of severe late season hail.
An SCN susceptible and a PI88788 SCN resistant variety were planted at each site. For each variety, seed was untreated, treated with Clariva Complete or treated with Cruiser Maxx + Vibrance, an insecticide/fungicide counterpart to Clariva Complete without the Pasteuria nematicide.
Results
Eight of 18 sites showed a significant yield difference by variety. In the south, these differences were the SCN resistant variety out yielding the susceptible in sites with SCN present. In the north, where differences occurred, the SCN resistant variety out-yielded the susceptible including a non-infested site in Polk County. There was an interaction between varietal yield differences and site where resistant varieties were most likely to yield more as compared with susceptible varieties in SCN infested sites
Significant yield responses to either seed treatment, above the untreated controls, were not common in 2014. Two of 18 sites showed a yield increase with treated seed with and without Clariva. It is possible that the yield responses to seed treatments were due to microbial pathogens or early season soybean aphids.
The SCN resistant variety significantly reduced nematode reproductive rates as compared to the susceptible at 11 of the 18 sites where SCN was detected. Seed treatments did not change SCN reproduction compared to untreated seed.