Spotting SCN females in soybeans early

By Andi Anderson

As soybean planting concludes, it's crucial for growers to begin scouting for soybean cyst nematode (SCN) females on young plant roots. This routine check is key to early detection and management of one of the most yield-reducing pests in soybean fields.

To find SCN females, carefully dig up soybean roots from the top 12 inches of soil using a spade or shovel—avoid pulling the plants directly to prevent root damage. Once extracted, gently shake or crumble the soil away from the roots.

Look for SCN females, which appear as small, white, or light-yellow round objects about the size of a printed period, visible without magnification. Unlike the larger and darker nitrogen-fixing nodules, these pests are subtler but distinctly different.

SCN females typically emerge around four weeks post-planting but can appear as early as 26 days depending on conditions, as noted in an ICM News article. Unlike other pests, SCN females do not appear all at once; they gradually become visible over several days and can continue to be observed late into the summer due to their life cycle of approximately 28 days per generation.

SCN presence was noted in 70% to 75% of Iowa soybean fields across three separate decades-long surveys by Iowa State. Often, these infestations are not immediately apparent as the affected plants may not exhibit stunted growth or yellowing early in the season.

Key areas to check include field entryways, along fence lines, and parts of fields that have previously shown lower yields without an obvious cause.

Once SCN females are observed, no immediate remedy can be applied during the current growing season. This mid-season discovery is an opportune time to research SCN-resistant soybean varieties and nematode-protectant seed treatments for future planting. Resources from Iowa State University and the SCN Coalition offer extensive guidance on managing SCN.

Independent of current season discoveries, it is advisable to plan for soil sampling post-harvest if such tests haven't been conducted in the past five years.

This not only helps assess the SCN presence but also aids in planning for the next season, particularly if soybeans are to be planted. Sampling is also beneficial for corn fields slated for future soybean cultivation.

Photo Credit -istock-sandramatic