Herbicides are useful tools in most weed management programs. They should be used to supplement, not supplant, other methods or tools available. These other tools include good cultural practices, such as proper fertilization and liming, to give the crop a “head start,” and crop rotation and proper cultivation, which are essential for a total weed management program. The following are definitions of terms you will find in this and similar publications on herbicides:
The herbicide is applied to the soil before planting. Generally used in no-till to control existing vegetation and provide early residual control.
1. Early preplant (EPP)The herbicide is applied to the soil after plowing but before planting and mixed with the top few inches of soil with different incorporation implements.
2. Preplant incorporated (PPI)The herbicide is applied after the crop is planted but before it emerges from the ground. Soil moisture, light rainfall, or shallow cultivation may be necessary to obtain good weed control with many preemergence herbicides.
3. Preemergence (PRE)The herbicide is applied to the foliage of weeds after the crop has emerged.
4. Postemergence (POST)This is a surface-active agent that reduces the surface tension, thus permitting a more uniform application and spreading the herbicide solution evenly on the plant foliage or ground. Many terms designate particular surface activities, such as adjuvant, detergent, emulsifier, spreader, sticker, and wetting agent.
5. SurfactantMost of the herbicides recommended in this publication are selective. At the recommended rate of application, they will selectively control or injure weeds but will not seriously damage the crop in which these weeds are growing. In using most selective herbicides, you should carefully follow the recommended rate of application because higher rates may severely injure or kill the crop. You must accept the responsibility if you use a herbicide in a manner other than that directed on the label. Read the label on the container and follow the directions.
The precision required for herbicide application is greater than for many other farm tasks. Three factors govern the rate of application: pressure, nozzle size, and ground speed. Contact your county Extension office for related publications.
The recommended use rates of herbicides generally vary with soil texture and organic matter content. The herbicide rates given in this section will refer only to three soil texture groups: coarse, medium, and fine. The following is a list of soil textures included in these three soil texture groups.
Refer to this table to determine the soil texture group for the soil you want to treat. Low rates of herbicides generally are used on coarse soils low in organic matter, while high rates generally are used on fine soils high in organic matter. Consult the label for the proper herbicide rate for your soils.
Herbicide resistant weed populations may result through repeated use of herbicides with similar modes of action (see table on Guide to Single Active Ingredient Herbicides). Crop rotation, herbicide rotation or tank-mixing herbicides with different modes of action will help reduce buildup of herbicide resistant weeds.
| Soil Texture Group | Soil Texture |
|---|---|
| Coarse | Sand, loamy sand, sandy loam |
| Medium | Loam, silt loam, silt, sand clay loam |
| Fine | Silty clay loam, clay loam, sandy clay, silty clay, clay |
