Prioritize crop scouting throughout the growing season

Scouting for weeds, insects, and diseases is one of the best investments in money and time to protect crop yields and add bushels this fall.

“Scouting is so critical to be done timely and often,” says Eric Andersen, who farms outside Dike, Iowa, in the state’s northwest. “We make plans on inputs and applications all winter long, but the weather, environmental conditions, and soil conditions can vary so much from year to year and from field to field. It is really important to have boots on the ground and be out there assessing if those plans really are the right decision.”

With pest resistance on the rise, scouting remains the best way to prevent in-season issues. A proactive approach can allow for more informed management practices regarding pests and nutrient deficiencies before issues get out of hand. So lace up your boots, grab a shovel, and let’s dive in for a refresher!

Early season: emergence to mid-vegetative

A lot can change in two weeks during the growing season, so scout early and often. Early-season scouting should begin at crop emergence. If conditions have been wet, compaction may inhibit emergence. The cost of seed makes it essential to get the highest, most uniform emergence possible.

The easiest time to conduct stand assessments is at the first to third corn leaf stages (V1 to V3 growth stages), and the first to third trifoliate (V1 to V3 growth stages) for soybeans. However, conducting stand assessments at emergence can help sort out biotic issues from planter and operator performance.

To determine a plant stand for row crops, a report from Corteva recommends taking several sample counts to represent the area under consideration. For ease of calculation, the report recommends a sample size of one-thousandth acre. “Measure off the distance appropriate for your row width, count the number of live plants, and multiply by 1,000 to obtain a reasonable estimate of plants/acre,” the report says. “Stand counts should be taken randomly across the entire area of the field being considered for replant; this may include the entire field or a limited area where damage occurred. The accuracy of your stand estimate will improve with the number of locations sampled within the damaged area.”

As plants begin to emerge, be alert for potential damage from early-season insects and diseases. Crop scouting calendars can serve as guides for potential early-season problems. They’re all familiar pests, whose treatments are likely just as familiar. But chances are, you still need to do some good old-fashioned crop scouting to get a sense for whether you have your hands full taking care of them in the short and the long terms.

In soybeans, the risk of early-season disease pressure is greater with very early planted crops because of a higher likelihood of cool and wet soils. For this reason, it is recommended to use fungicide seed treatments effective against Fusarium, Pythium, Phytophthora, and Rhizoctonia. Variety selection also can reduce risks associated with sudden death syndrome and Phytophthora when planting early.

The critical time to scout fields for corn seedling diseases, such as Pythium, Rhizoctonia, Fusarium, and Penicillium, is 10 days to two weeks after planting, says Justin Schneider, an LG Seeds agronomist in Michigan. “If you don’t spot a problem until you are sidedressing with nitrogen or spraying an herbicide,” he says, “you’re too late.”

For more information about seedling diseases, visit this article.

Aaron Hager, a weed science professor at the University of Illinois in Champaign-Urbana, recommends planting into a clean field, with no existing weed vegetation. This is accomplished with a burn-down herbicide application, mechanical tillage, or a combination. After planting, apply a post-emergence herbicide before weeds grow taller than 3 to 4 inches.

The longer the weeds compete with the crop, Hager reasons, the greater the likelihood that competition could reduce the crop yield potential at the end of the growing season. “So, in other words,” he says, “it’s hard to be too early when you’re trying to remove weeds that are growing within an existing crop stand.”

Routinely scout and remove weeds that reinfest after the initial herbicide application. They can become competitive and should be controlled while small, reducing the possibility of producing seeds.

With the widespread evolution of herbicide resistance, Hager notes: “We need to really have an understanding of whether or not that one species, or the multiple species, in that field remain sensitive or susceptible to that herbicide. So, in other words, we really have to know what the weed species are and whether they’re still effectively controlled with the products we’re going to use in that field.”

Mid-season and late season: late vegetative through reproductive stages

When the canopy closes, weed worries begin subsiding, and it’s tempting to focus energy and attention elsewhere. But insects and diseases can impact yield tremendously if pests aren’t kept below economic thresholds. This is the time to ensure fields are as healthy as they appear from the road. These are the stages when yields are determined, so managing potential stresses, such as diseases and insects, is important to protecting yield potential.

The list of insects and diseases that can cause problems in your fields is long. The information provided in the scouting calendars is just a guide and doesn’t include every pest.

Foliar diseases can spur stalk rot development later in the season. This can cause problems with lodging prior to harvest. “Tar spot, northern corn leaf blight, and gray leaf spot are all foliar diseases to note,” says Nathan Kleczewski, a plant pathology and entomology technical specialist for Growmark, Inc. “These diseases are caused by fungi,” he notes, “meaning any conditions that promote humidity could lead to greater outbreaks.” Scouting fields just prior to tasseling can help determine field disease pressure.

“They’re the diseases that we have to keep in mind every season because they overwinter in the region,” Kleczewski says. He adds that scouting fields before harvest can help identify and mitigate potential harvest challenges.

“Just before physiological maturity, or R6, get into those fields and do some standability checks,” says Alison Robertson, an Iowa State University plant pathologist. A push test — where you push on a stalk to see if it stands — can tip off farmers if they need to harvest earlier than planned. For fields with significant disease pressure, an earlier harvest may be necessary to maximize yield potential.

Scouting before harvest can reveal whether weeds are a problem in soybeans. A late-season herbicide application may be needed to help alleviate combining issues.

Walking fields, looking at plant roots and leaves, and searching for insects and weeds all take effort. There is satisfaction from seeing those fields firsthand during the growing season and then seeing the impact at harvest. Orvin Bontrager is a 43-year certified crop adviser at ServiTech Crop Consulting, based in Aurora, Nebraska, who scouts 16,000 acres annually.

“Seeing those results now rolling in with harvest after I’ve looked at fields every week all summer is a real intangible that’s hard to measure — and to see it year after year on the same field,” he says.