Key Points
Scouting is a critical piece to any successful chemical weed control program. Here's a 101 on crop scouting to get you prepared.
- Weed Types
Resistance to herbicides varies based on weed type. - Weed Size and Density
Weed resilience is dependent on weed size. However, several small weeds that overlap may have the same resilience of that of a larger weed if their level of overlap prevents them from seeing the intended application rate. - Pest Damage
Pests pose a threat to all parts of the plant: leaves, stem, and roots. You must also consider economic thresholds when making decisions about your integrated pest management program. - Disease Damage
It's important to balance application time with disease pressure.
As a farmer, you have a long list of decisions to make regarding your chemical weed control program each season. You decide which chemicals to use, when to apply them, and determine the rate of each chemical during application. Knowing what’s in your fields, or what’s not, is a crucial step in driving these critical decisions.
By assessing a variety of factors like weed type, size, and density as well as pest and disease damage, you can better determine the chemicals you use, and the application rates needed to successfully manage your crops.
What to Consider While Scouting
Weed Types
Resistance to herbicides varies based on weed type. Tough weeds like Waterhemp and Palmer Amaranth may be harder to kill, ultimately requiring a higher rate. Weaker weeds like winter annuals may allow you to stay at the lower end of the rate range and, as a result, save on input costs.
Weed Size and Density
Small weeds that are earlier in their growth stages are much easier to kill than larger weeds.
Although weed size itself is a determining factor in application rate, you must also consider the density of those weeds. If there are small weeds that overlap, each of those individual plants may only see a 30% or 50% rate during application, depending on the level of overlap. However, standalone weeds with no overlap would receive the full rate.
To effectively manage the weed population, you must consider both weed size and weed density. Weed severity, a metric unique to Precision Planting that is utilized by the SymphonyVision camera-based spray system, combines weed size and density. With SymphonyVision | Rate, the weed severity metric helps determine the extent to which the rate of application is varied. With SymphonyVision | Spot, weed severity determines whether the nozzle is turned on or off and the rate of application.
Pest Damage
The presence of pests can come in all shapes and sizes. When scouting your fields, be sure to look for leaf damage as well as stem and root damage. Holes, stippling, discoloration, and boring at the stem are all common signs of pest activity.
Like weeds' tolerance to herbicides varies based on growth stage, pests' tolerance to pesticides is dependent on lifecycle stage. The most effective kill takes place when pests are targeted at earlier growth stages.
When it comes to your integrated pest management program, it's important to consider economic thresholds. Thresholds help determine the level of pest density where it becomes more cost-effective to apply pesticide and protect yields versus saving on costs by not applying and sacrificing yields as a result.
Disease Damage
Most systemic fungicides offer three to four weeks of protection, making it critical to balance application time with disease pressure.
Diseases like Northern Corn Leaf Blight and Grey Leaf Spot move in earlier in the season, whereas a disease like Tar Spot may not become an issue until later growth stages. When targeting Tar Spot, if there is little to no disease pressure present while scouting at tassel, you may wait until the R2 growth stage to apply your fungicide. However, if diseases like Northern Corn Leaf Blight and Grey Leaf Spot are present, it may be necessary to spray earlier.
Modes of Action
A mode of action is the way a chemical affects the plant at the tissue or cellular level. Having multiple modes of action within your chemical weed control program can increase your program’s effectiveness. However, you must also consider the added cost that comes with each additional mode of action.
Scouting allows you to assess last year's chemical weed control program and optimize it for a better return on this year's investment. Maybe last year’s weed control was less than ideal, and with a similar weed population this year, you know to increase the rates or explore an additional mode of action to see the results you want. Or perhaps last year’s control was more than enough, and this year you reduce rates to align towards the lower end of the application rate range or remove a mode of action entirely to save on input costs.
Methodical scouting efforts lead to better decision-making within your chemical weed control program. With the right data in the hands of the right people, you can fine-tune your chemical plan to ensure you find the right balance between effective control and cost efficiency.
Disclaimer: Always read and follow label instructions and consult your chemical representative if you have questions.
