Herbicide carryover concerns in soybeans

By Blake Jackson

Last spring and early summer saw an uptick in concerns about herbicide carryover to soybeans, a trend likely exacerbated by persistent drought conditions across many areas. Factors influencing this include the type of herbicide used and its persistence in the soil, environmental conditions post-application, and soil characteristics.

Certain herbicides, like those in the group 27 HPPD-inhibiting class such as mesotrione and topramezone, can pose a carryover risk, especially if applied later than usual or in multiple doses during the previous growing season. Clopyralid, found in various corn herbicide premixes, can also persist due to its reliance on soil microbes for degradation.

Environmental conditions play a crucial role; dry soils slow down herbicide degradation due to reduced microbial activity, potentially leading to longer persistence. Additionally, cooler temperatures can impede degradation, although warmer temperatures can expedite it.

Soil characteristics, particularly organic matter content, influence degradation rates. Higher organic matter promotes microbial degradation, while lower organic matter slows it down. Soil pH, however, may have less impact on the breakdown of certain herbicides like group 27 and clopyralid.

Fields at higher risk of carryover include those with minimal rainfall since the previous season, especially in drought-prone areas, sandy soils with lower organic matter content, and where herbicides were applied late or in multiple doses.

To mitigate risks, farmers can conduct soil bioassays to assess herbicide residues before planting. Resources guide on herbicide carryover testing offer practical steps for conducting these assays.

Understanding herbicide persistence, environmental conditions, and soil characteristics is crucial for managing carryover risks. Proactive measures like soil testing can help farmers make informed decisions to safeguard crop health and yield potential.

Photo Credit: istock-sandramatic