Soil Active Herbicides: A Boon for Weed Management

Effective weed control has always been a challenge for farmers across the globe. Weeds compete with crops for nutrients, water and sunlight, thereby reducing crop yields significantly if left uncontrolled. Over the years, farmers have relied on multiple agronomic practices like manual weeding, crop rotation, and use of cultural practices for managing weeds. However, these traditional methods are time-consuming and require intensive labor. With the development of modern agriculture, herbicides have become an integral part of integrated weed management programs. Among the various types of herbicides available, soil active herbicides have emerged as one of the most effective pre-emergent options for managing weeds.

What are Soil Active Herbicides?
Soil active herbicides, also known as pre-emergent herbicides, work by forming a protective barrier in the soil which prevents the seed germination and emergence of weeds. They are applied to the soil surface prior to planting or right after seeding/transplanting crops. Once in the soil, these herbicides either disrupt the metabolic or physiological processes in the germinating weed seeds or inhibit the weed seedling growth. Common Soil Active Herbicides include trifluralin, pendimethalin, ethalfluralin, oxyfluorfen, oryzalin, and prodiamine.

Advantages of Soil Active Herbicides
Some of the key advantages of using soil active herbicides include:

- Broad Spectrum Control: Most soil herbicides provide control of both grassy and broadleaf weeds. This helps in managing the entire weed flora with a single application.

- Residual Action: They remain active in the soil for an extended period, ranging from 4-16 weeks, and preventflush of new weed seeds throughout the crop season. This provides a long lasting effect.

-Selective Action: Modern soil herbicides have been formulated to be selectively toxic to weeds and harmless to rotational crops when applied at recommended rates and timing.

-Cost Effective: A single pre-plant application of soil herbicide costs far less than multiple post-emergence spraying or hand weeding operations required otherwise.

-Time Saving: Laborious manual weeding operations are replaced by a single convenient application before crop planting/emergence.

-Prevents Crop Competition: Weeds that emerge with the crop are effectively controlled, avoiding early-season competition with the crop.

Key Aspects in Product Selection
While soil herbicides provide unmatched pre-emergent weed control, proper product selection based on the targeted weed flora, crop rotational practices, and soil conditions is crucial. Various key factors to consider include:

- Spectrum of Weed Control: Herbicides like pendimethalin, oxyfluorfen and oryzalin effectively control grasses as well as broadleaves. While trifluralin and ethalfluralin specialize in grass control.

-Crop Safety: Herbicides like pendimethalin, ethalfluralin show excellent crop safety with most crops. However, some products like trifluralin may injure sensitives like cucurbits and tomatoes.

-Soil Factors: Clay soils require lower rates than sandy soils for maximum residuals. Soil pH and organic matter also plays a role in herbicide selection.

-Cropping System: Product choice depends on whether it is a single or multiple crop rotation system. Short residual herbicides fit short rotations while medium to long residuals for long rotations.

-Application Timings: Preplant incorporated, pre-emergent or early post-emergent timings are recommended as per the herbicide label.

Combining Soil and Foliar Herbicides
While soil applied herbicides are very effective in suppressing the germinating flush of weeds prior to crop emergence, integrating them with selective post-emergence sprays provides better season-long control. This includes tank-mixing soil residual compounds like pendimethalin, ethalfluralin with contact herbicides like glyphosate, 2,4-D, atrazine. The residual herbicide handles the initial flush while foliar herbicides control any late germinating or emerged weeds that escape. This type of strategy with both soil and foliar herbicides provides the best possible weed control.

Key Concerns and Sustainability
However, the indiscriminate and repeated use of soil herbicides year after year without breaks can select for herbicide-resistant weed biotypes over time. It is advisable to follow an herbicide rotation approach using alternative modes of action and integrate cultural practices periodically to prevent resistance development. Excessive residue build up due to repeated use may also restrict crop rotation options on some farms. Adherence to label guidelines regarding rates, application windows and geographies is essential to avoid such issues. When used judiciously as part of an IPM program with other techniques, soil herbicides provide highly sustainable pre-emergent weed control.

Modern crop production heavily relies on high-yielding herbicide-tolerant hybrids and intensive weed management. Soil applied herbicides have emerged as an indispensable component of integrated weed control programs worldwide. Products that combine residual control of both grassy and broadleaf weeds, have high crop safety and are economical, are ideal choices. Proper product selection based on soil conditions, cropping systems and targeted weeds coupled with sound resistance management strategies ensure maximum benefits from these reliable pre-emergent herbicides. Their timely and judicious use helps boost agricultural productivity in a sustainable manner.

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