By Tammy Jones
If I had a dream…
Future weed control consists of armies of drones being deployed to control specific weeds at specific growth stages optimizing herbicide efficacy, while heavily infested areas of weeds are controlled by patch management using inter-row tillage with advanced guidance systems and lasers or flame-thrower systems to precisely target and burn weeds to a crisp. In this scenario, prescriptions would need to be built, just as we do with variable rate applications of fertilizer. Precisely defined areas would ensure weeds are sufficiently controlled while avoiding excess use of the drones (battery life) and maximizing the economic advantage. To implement this effective and efficient weed control, the most important tool is a “back to the basics” of accurate field scouting. Regardless of technology, one of the easiest ways to enhance weed control now is that same tool.
Patches of weeds exist in the field, either due to the nature of the weed and its seed dispersal; for example, wild oat seeds shed prior to harvest and tend to form heavy patches and many perennials proliferate in patches because of spreading root systems. Or, because of the adaptation of the weed to certain areas of the field—green foxtail prefers good drainage and heat—as an example. Other weeds are not as patchy, typically volunteers from the year before and can be found scattered across the field. In a document about “Site-Specific Management” of weeds, Sharon Clay of South Dakota State University and Gregg Johnson at the University of Minnesota have noted that current scouting is casual, with very little detail on weed densities or distributions mainly due to time constraints. They ask two questions that impact on the implementation of precision tools for future of weed control: Do weeds vary enough in the field to require different management techniques for different areas? and, can we use technology to improve weed management and profitability?
Can you answer those questions now? And how accurate is our assessment? Scouting a 160-acre field in a “W” or “V” pattern with 10 or 20 assessments across the field in a pseudo-random pattern is a typical scouting strategy. It is cost-efficient and requires minimal time investment. But 20 assessments of an area of perhaps 100 square feet in 160 acres is an assessment of less than 0.002 per cent of the total area. Further to that, if there is one weed in 100 square feet, that’s about 435 weeds in an acre. If we use five gallons of water and 350 grams of active ingredient, that’s 43 mLs, or an ounce-and-a-half, of water and less than a gram of active ingredient per weed—if the spray is targeted specifically to the weed. With a spray pattern that is constant over an area, the water volume applied to one square foot of field is under one mL and the active ingredient is less than 0.01 gram. Making accurate assessments with little data, when relying on low treatment rates can lead to challenges. Clay and Johnson note that equipment is already developed that can match different chemical treatments and rates to different areas of the field, and the next step is to have accurate data collection to match the equipment with the field and get better weed control, lower herbicide costs and increased net returns.
What’s stopping us from doing that now? How do we improve our data collection strategy? Without changing equipment to variable rate and variable active ingredients, we can still improve scouting practices. Here’s how:
1. Minimize the time investment. Scouting while doing other operations—harvest is a great time to scout for post-harvest weed control. Drop a pin or mark the spot in the field with a flag where there is a patch of perennial weeds and address that issue easily after harvest.
2. Collect more details. By marking and writing down locations for weeds is good but noting densities and growth stages will also help to ensure the best decisions are made, as well as help to assess how well that weed control tactic worked. Knowing that there are 20 wild oats (or any weed) in a square foot and knowing the location, will give the opportunity to return to that spot after spraying, to assess the number of plants that have died, if the survivors are actively growing (larger growth stage than when they were sprayed) and help to decide if any further actions are required.
3. Increase scouting frequency. There are at least five times when scouting for weeds is important: Pre-seed (fast and easy to drive across the field and find any issues), before the first in-crop herbicide application (take great notes, and take the time to know the priority weeds), two weeks after the herbicide application (to make sure everything worked or assess opportunities to fix the issues), pre-harvest (so that harvest can be efficient without green weeds slowing things down) and post-harvest (the ultimate perennial control time). The time investment may be reduced significantly by knowing where there are trouble spots, but it’s also important to look for new issues.
4. Employ technology. Drones or satellite imagery can be used in-crop to detect unusual crop densities to make investigations more effective. Record keeping can easily kept on a smartphone or tablet, which then provides more timely sharing and analysis, as well as a backup option that you don’t get with a paper record that might get wiped out with a cup of coffee.
Timely and thorough scouting helps to avoid problems in the field. Putting boots in the field or using other surveillance options to improve the level of detail can provide earlier detection of new weed problems or the lack of control of a weed signaling the need for a new strategy. The level of detail provided with more scouting, will help avoid surprises in weed control now but it will also help to set up using these technologies in the future.
