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It’s never too early to scout  for corn and soybean weeds
By Doug Schmitz
Iowa Correspondent

MARKLE, Ind. – With weeds already starting to emerge alongside crops, it’s never too early for farmers to get a jump on them by scouting their corn and soybean fields, which one agronomist said is critical for maximizing yields.
“By catching problems early, it’s easier to apply solutions,” Chad Threewits, Syngenta agronomy service representative for Indiana, said. “For example, with weeds like waterhemp, in many cases, once they get too big, they are very difficult to control. 
“In other cases, when low-yield areas show up at harvest, it’s very hard to diagnose from the combine seat,” he added. “Even by scouting early, there may not be solutions available to fix problems that were created this year, but we can learn from them and adapt practices in following years.” 
Threewits advised farmers to first look for weed escapes, as well as any holes in their weed management program. 
“This is a combination of the herbicides and trait system being utilized,” he said. “Managing weeds like waterhemp and marestail is becoming more challenging due to herbicide resistance. But due to prevent planted acres last year, I’m also seeing a resurgence of perennial weeds like thistles, dandelions and curly dock. 
“As we enter reproductive stages of crops, it’s important to start to watch for disease and insect issues,” he added. “Tar spot and Southern Rust on corn have been two key diseases recently to catch early and apply fungicides to limit yield loss.” 
Threewits said knowing the type, volume and location of weeds will be valuable information for protecting yield potential throughout the year. Scouting can also help farmers determine the most cost-effective options available to fight pest pressure and resistance.
Syngenta offered the following tips to help farmers scout early for weeds:
Follow an M-shaped walking pattern to get the best representation of weed pressure across the whole field. According to the University of Wisconsin Extension, your walking route is the foundation for effective scouting. For square and rectangular fields, an M-shaped pattern will be the most beneficial. For irregular shapes, ensure you cover a representative amount of the field.
Keep in mind that you can’t judge the weed population of an entire field by what you see on the edges.
For larger fields, you will likely need to split the area into smaller parts. This helps ensure you have the most accurate results, even if population data differs from one section of the field to another. Note the weed species you see, their locations in the field and the degree of control achieved with your current program and past herbicides.
Weed populations can be split into four categories, which can help determine your control options: 
Scattered – Occurs when there are not enough weeds to cause yield loss, but the population will produce seed and can increase the weed seed bank, if left uncontrolled.
Slight – In this case, yield loss is unlikely but possible in areas where pressure is heavier. The population is considered slight when there is one weed in every three feet of row.
Moderate – At this point, yield loss is likely unless an effective management program is used. Moderate pressure is an average of one weed per foot of row. You may also see spots with severe populations.
Severe – With this level of weed pressure, yield loss will undoubtedly occur unless effective control strategies are utilized. For broadleaf species, more than one weed per foot of row constitutes severe pressure. For grass weeds, it’s three plants per foot of row.
Use your findings to determine which weed control measures are right for your fields, both this season and next.
Scout early and often. Then use that information to plan your weed management program accordingly.
Threewits said new digital platforms, along with drone imagery, have also been very helpful in picking out macro issues in fields, like compaction, drainage, and nutrient deficiencies. 
“Now, we’re even able to do stand counts and identify weed problems,” he said. “They can help identify problem areas of fields but do not replace boots on the ground.”