Weeds

Part 2, Section 2: Corn Pest Management

Corn Pest Management

WEEDS

Tables 2.2-1 through 2.2-18 list herbicide treatments labeled for use in corn at the time this guide was printed. Herbicide labels change continually. Always read the label of the specific product to determine current registered uses. For additional information online about weed management, please visit our Web site at extension.psu.edu/weeds.

Consider several factors when developing herbicide programs for use in corn: tillage, soil type, weeds present in field, management practices, and rotational plans.

No one herbicide program is best for all situations. In addition, continued reliance on a single program can lead to severe problems. The development of triazine-resistant weeds across the state is an example.

Tillage can be an important component of a weed management system. Primary tillage can help reduce the rate of spread of certain perennials such as hemp dogbane. Row cultivation also can be used to help control weeds and reduce herbicide dependency. Crop residue left on the surface in no-till and reduced tillage plantings may interfere with the activity of preemergence herbicides, resulting in the need for extra applications.

The herbicide effectiveness ratings listed here may be used as a guideline for comparing herbicides. Results obtained by individual farmers depend on environmental conditions, rates used, application techniques, and severity of weed pressure. The rates listed in the following tables encompass the entire range of rates found on the herbicide label. Refer to the product label to determine the appropriate rate for soils and weeds in a specific field. Do not exceed labeled rates, since crop injury may occur or illegal herbicide residues may be found in the crop.

Keys designed to assist you in identifying common grassy and broadleaf weed seedlings in Pennsylvania are located at the front of this guide.

• Table 2.2-1. Corn herbicides and their restrictions.
• Table 2.2-1a. Selected glyphosate products and premixes for agronomic use.
• Table 2.2-1b. Selected generic alternative herbicides for agronomic uses.
• Table 2.2-2. Future products for corn.
• Table 2.2-3. Corn herbicide prepackaged mixes or co-packs, and equivalents.
• Table 2.2-4. Characteristics of preemergence herbicides.
• Table 2.2-5. Characteristics of “burndown” and postemergence corn herbicides.
• Table 2.2-6. Relative effectiveness of “burndown” treatments for no-till corn.
• Table 2.2-7. Characteristics of “burndown” herbicides for no-till corn.
• Table 2.2-8. Relative effectiveness of corn herbicides on grasses, grasslike species, and broadleaf weeds.
• Table 2.2-9. Herbicide effectiveness on perennial broadleaf weeds.
• Table 2.2-10. Preplant or preemergence herbicides for conventional, min-, or no-till corn.
• Table 2.2-11. Corn herbicide preplant or preemergence rates per acre based on soil texture and organic matter.
• Table 2.2-12. Maximum corn and weed sizes for delayed preemergence/early postemergence herbicide applications.
• Table 2.2-13. Postemergence herbicides for corn.
• Table 2.2-14. Postemergence herbicide application restrictions for corn.
• Table 2.2-15. Weed sizes for postemergence corn herbicides.
• Table 2.2-16. Spray additives and rainfastness for “burndown” and postemergence corn herbicides.
• Table 2.2-17. Corn herbicide rotational restrictions.
• Table 2.2-18. Grazing and forage restrictions for corn herbicides.