Timing is Critical for Applying PPO-Inhibiting Pre-emergence Residual Herbicides in Soybean

Timing is Critical for Applying PPO-Inhibiting Pre-emergence Residual Herbicides in Soybean

Soybean planting is about to start in Nebraska and it’s time to select pre-emergence herbicides to be applied in soybean. Protoporphyrinogen oxidase (PPO)-inhibiting herbicides are one of the key components of weed management in soybean. Flumioxazin, saflufenacil, and sulfentrazone are very important chemistries in PPO-inhibiting herbicides applied pre-emergence in soybean.

The best way to effectively control glyphosate-resistant and other hard-to-control weeds is by applying residual, pre-emergence herbicides with multiple effective sites of action. Several pre-emergence herbicides labeled in soybean are PPO-inhibitors in this category and could be considered.

Flumioxazin-based herbicides are commonly used for weed control in soybean. They can be applied pre-plant or pre-emergence, but NOT after soybean emergence (Figure 1). This is applicable for herbicide products with flumioxazin (such as Rowel, Valor) as well as when flumioxazin is a part of the pre-mix (such as Afforia, Envive, Enlite, Fierce, Rowel FX, Valor XLT, Fierce XLT, Trivence) or when flumioxazin is tank-mixed with other herbicides.

Soybean emerging in a field
Figure 1. Soybean emerging in a field in south central Nebraska. Do NOT apply PPO-inhibiting herbicides after soybean have begun to crack or are emerged (Photos by Amit Jhala).

Sulfentrazone based herbicides are also important PPO-inhibiting herbicides applied in soybean. This is applicable for herbicide products with sulfentrazone (such as Spartan) as well as when sulfentrazone is a part of the pre-mix products (such as Authority brand herbicides, BroadAxe XC, Sonic). These herbicides can be applied prior to planting or up to 3 days after planting. When applications are delayed greater than 3 days after planting, injury may occur if seeds are germinating.

Saflufenacil based herbicides such as Sharpen and saflufenacil based pre-mixes (Optill PRO, Zidua PRO) are also PPO-inhibiting herbicides.

PPO-inhibiting herbicide premixes have shown excellent broad-spectrum weed control in soybean when applied pre-plant or pre-emergence. If growers are not able to apply them before soybean emergence, they must NOT apply post-emergence because severe crop injury may occur. Therefore, it is advisable to apply them within three to four days of planting soybean.

Application after soybeans have begun to crack, or are emerged, will result in severe crop injury. When PPO inhibiting herbicides are applied, it is also recommended NOT to irrigate when soybeans are cracking. It is also mentioned in certain PPO-inhibiting herbicides such as Zidua PRO that ‘If extreme conditions of high rainfall and extended periods of water saturated soil occur during soybean germination or early seedling development, it may result in temporary growth suspension.