Summary Content
Soybean cyst nematode (SCN) is the most yield-limiting pathogen of soybean. Other than an errant frost, drought or flooding, we argue that iron deficiency chlorosis (IDC) is the abiotic disease most limiting to soybean yield potential in western MN.
On June 9, 2024, 160,000-165,000 seeds/ A were planted at 1 inch with seed with/without 0.8 fl oz/140,000 seeds Saltro (a.i. pydiflymetofen) labeled for SCN. Ferrilene, an EDDHA-chelated form of iron (6%) was applied at 3 lbs/A in-furrow at planting. Treatments included, 1) untreated control (UTC), 2) Saltro + Ferrilene, 3) Saltro alone and 4) Ferrilene alone. Each 700-foot long plot was planted to a variety with PI88788 SCN resistance in an RCB design with four replicates. Foliar IDC symptoms were collected from two locations throughout each plot using a ratings scale used by NDSU soybean breeders as were stand counts. Plot yields were determined with a combine and weigh-wagon. Fifteen, eight-inch soil cores were collected within the soybean rooting zone in spring and fall.
Findings
Soybean stands were statistically similar and ranged from 104,940 to 114,840 plants/A. Later planting into warmer soils into a tiled field may not have provided the most conducive IDC environment, with IDC symptoms similar among treatments. Yields were also similar, although the UTC had the numerically lowest yield (49.6 bu/A) and the Saltro + Ferrilene treatment the highest (54.0 bu/A).
Spring, SCN egg counts ranged from 350 to 850/100 cc and fall counts from 2,483 to 3,917/100 cc. The lowest fall counts were in plots planted to treated seed, suggesting a potential trend in limiting SCN population growth; 1,200-1,400 more eggs/100 cc were observed in treated plots than non-treated.
Economic benefit to a typical 500 acre-soybean enterprise: Inherent soil variability and limited replications mean that we have little certainty that the results observed would be similar in different fields or years.
SCN population growth in 2024 in plots planted to treated seed was ~half that of plots without SCN seed treatment. While the soybean variety planted had PI88788 SCN resistance, reproduction in 2024 added up to 10 times the population density present in the spring. As PI88788 SCN resistance continues to lose its potency, farmers may consider using seed treatments labeled for SCN management, rendering this work necessary.
