What Is Synchrony B and How Does It Work?

Synchrony XP is a selective herbicide used in agriculture to manage specific types of weeds in soybean crops. Its function is to eliminate unwanted broadleaf plants that compete with crops for resources. The product combines two active ingredients to provide both foliar and soil activity. This allows it to control weeds that have already emerged and those that may germinate after application, offering a flexible tool for farmers.

The Mechanism of Action

The effectiveness of Synchrony XP lies in its specific biochemical interaction within susceptible plants. Its active ingredients, chlorimuron-ethyl and thifensulfuron-methyl, are Group 2 herbicides that work by inhibiting the acetolactate synthase (ALS) enzyme. This enzyme is a catalyst in the production of branched-chain amino acids necessary for protein synthesis and plant growth.

When a susceptible weed absorbs Synchrony XP through its roots or foliage, the herbicide travels to its growing points. There, it blocks the ALS enzyme, halting the production of these amino acids. Without these building blocks, the plant cannot create new proteins, which stops cell division and growth. Susceptible weeds typically show symptoms within days, turning yellow before growth ceases entirely.

Applications in Agriculture

In the field, Synchrony XP is used primarily in soybean cultivation to control a wide spectrum of broadleaf weeds. Farmers utilize it as a “burndown” application before planting to clear fields of existing weeds. It can also be applied after planting but before the crop emerges (preemergence) or after the soybeans have started to grow (postemergence).

A common practice is to tank-mix Synchrony XP with other herbicides, such as glyphosate, to broaden the range of weeds controlled. The herbicide is particularly effective against several challenging weeds. These include:

• Marestail
• Lambsquarters
• Ragweed
• Velvetleaf
• Cocklebur

Application rates are carefully calibrated based on soil type, pH, and the specific weeds present in the field.

Safety and Environmental Profile

The active ingredients in Synchrony XP have the potential to leach through permeable soils, particularly where the water table is shallow. The U.S. Environmental Protection Agency (EPA) notes that chlorimuron-ethyl can also enter surface water through runoff from poorly draining soils and advises against application when heavy rainfall is imminent. To mitigate impact on non-target areas, product labels mandate specific spray buffer zones and droplet size requirements to minimize spray drift.

While the active ingredients show low toxicity to mammals, they are inherently toxic to sensitive, non-target plants. This includes adjacent crops, natural vegetation, and the forage that pollinators and other wildlife depend on. The breakdown of these chemicals is influenced by soil pH and microbial activity. Because residues can persist in the soil, there are specific guidelines regarding crop rotation to prevent injury to subsequent, sensitive crops.

Managing Weed Resistance

The development of herbicide-resistant weeds is a challenge in modern agriculture, and Group 2 herbicides like those in Synchrony XP are prone to selecting for resistant populations. Resistance occurs when weeds with a natural genetic tolerance survive an application, reproduce, and eventually dominate the population.

To preserve the long-term effectiveness of Synchrony XP, the primary strategy is rotating herbicide modes of action. This means growers avoid using only Group 2 herbicides year after year, instead using herbicides that kill weeds through different biochemical pathways. Using tank-mixes that combine Synchrony XP with a herbicide from another group is another effective tactic to make it harder for resistance to develop.