Weed management is critical for successful corn and soybean production, as it affects crop yield, quality, and overall profitability. Timely scouting for weeds and implementing appropriate control measures are essential for both crops.

Timing of scouting

Scouting for weeds should be done at least three times during the growing season for both corn and soybeans:

Weeds coming out of the ground in a field. Identification is essential for weed scouting.

  • Pre-planting: Scout the field before planting to identify any existing weed problems and determine the need for pre-emergent herbicides. It is important during this trip to look for winter annuals that are difficult to control, especially if you are in a no-till production system. Marestail is a key weed to check for in soybeans, for example.
  • Early post-emergence: Scout the field two to three weeks after planting. For corn, this corresponds to the V2-V4 growth stage; for soybeans, this is the V1-V2 stage. Scouting at this time will let you know if you need to make any adjustments to your post-emerge weed control plan.
  • Mid-season: Scout the field when corn is in the V6-V8 stage and soybeans are in the R1-R2 stage, as both crops have developed their canopy. This helps identify any problems that might have occurred with your post weed control pass and identify any late emerging weeds or other issues.

Identification of weeds

Proper weed identification is crucial for effective weed control. Learn to recognize common weeds in corn and soybean fields, including:

  • Broadleaf weeds: Examples include velvetleaf, water hemp, lambs quarters, and giant ragweed. Broadleaf weeds can be identified by their wide, flat leaves, and irregular leaf edges.
  • Grass weeds: Examples include foxtail, wooly cupgrass, and crabgrass. Grass weeds have narrow leaves with parallel veins and rounded stems.
  • Sedges: Yellow nutsedge is the most common sedge found in corn and soybean fields. Sedges have triangular stems and grass-like leaves. Only a few herbicides effectively control sedges, so identification of them is particularly important if your fields have a history of yellow nutsedge.

Scouting techniques

When scouting for weeds, walk through the field in a systematic pattern, such as a W or X pattern, to cover different areas of the field. Use the following techniques for effective scouting:

  • Observe the overall field condition: Look for patterns in weed distribution, such as areas with high weed density or specific weed species. This can indicate soil fertility issues, poor drainage, or herbicide resistance.
  • Examine individual plants: Inspect corn and soybean plants for signs of weed competition, such as reduced growth or discoloration.
  • Record your findings: Take notes on weed species, distribution, and density. There are many scouting apps available that allow you to record GPS reference points of particularly bad weed issues.

Monitoring herbicide resistance

Herbicide resistance is a growing concern in corn and soybean production. To detect and manage resistant weed populations:

  • Rotate herbicide modes of action: Use herbicides with different modes of action to reduce the selection pressure for resistance development.
  • Monitor weed populations after herbicide applications: Scout fields 10-14 days after herbicide application to assess control effectiveness. If weeds show little to no injury, they may be resistant to the applied herbicide.
  • Collect and submit weed samples for resistance testing: If you suspect herbicide resistance, collect weed samples, and submit them to a laboratory for testing.

Scouting for weeds in corn and soybean fields is a crucial component of integrated weed management. By following the best practices outlined above, growers can identify, and control weed problems early in the growing season, minimizing yield losses and maximizing profitability. Remember to scout regularly, identify weeds accurately, monitor herbicide resistance, and implement targeted control measures to achieve a successful harvest.

If you have questions regarding weed scouting, reach out to your ALCIVIA agronomist.