Remember the sweaty palms and churning stomach that you endured during high school or college final exam week?

Well, you have a similar final exam coming up as you learn lessons about your 2024 crop during harvest.

“I don’t think the combine gets enough credit for being the good scouting tool that it is,” says Jesse Grote, a Syngenta agronomic services representative. “You’ll be able to use it to learn a lot about cornstalk quality in the next few weeks. You’ll be able to see if your residual herbicides held. You’ll find out if your corn rootworm strategy worked.”

The lessons you learned this year can help you form your 2025 cropping plan. Here are some exam questions you’ll face in the coming weeks.

1. Did you correctly manage corn rootworm? Well, toppled-over stalks at harvest may be a sign that you didn’t.

“If you have rootworm feeding, you’re also introducing diseases like fusarium crown, root and stalk rot,” adds Nicole Stecklein, a Dekalb Asgrow technical agronomist. These contribute to the risk of stalk deterioration, she adds.

Rootworm feeding that translates into fewer roots also affects the amount of nutrients that corn plants may access.

“Those missing nutrients can lead to cannibalization of the stalk, which affects standability,” she says. “You will want to harvest these fields sooner than other ones.

“In corn-on-corn areas in northeastern Iowa, our management strategy for years has been using traits,” she continues. This can be supplemented by applying soil-applied insecticides at planting, Stecklein adds.

If these methods do not work, rotating from corn to another crop, such as soybeans, remains an option.

Well, most of the time, that is. Variant rootworm populations complicate this strategy in parts of the Corn Belt, including Iowa.

“Through extended diapause, northern corn rootworm has been able to overcome this management strategy,” Stecklein says. That’s because eggs persist in the soil for two or more years.

The western corn rootworm variant maintains the original one-year life cycle. However, female beetles lay eggs adjacent to a current cornfield, often in soybean fields. Root-chomping larvae that hatch the following year can emerge if those fields are planted to corn the next year.

2. Do you know why your corn is lodging?  “When we see root lodging or tipping, we often assume it's rootworm damage,” says Adam Rahe, a sales agronomist for Three Rivers FS who also farms with family near Dyersville, Iowa. “Sometimes it is, sometimes it isn't.”

Lodging this year could also be caused by saturated soils due to rampant rain that fell before corn plants formed brace roots.

SEED FOCUS: Preventing waterhemp from emerging in the first place is why weed management programs are increasingly focused on nixing waterhemp seed.

“In these cases, plants just tipped out of the soil,” Rahe says. “The root system was poor from the start, due to saturated soils. The [resulting] lodging had nothing to do with rootworm.”

If you haven’t done so already, root digs in your fields can help detect the degree of rootworm infestations and help form next year’s management plan.

“Your best management strategy is knowledge,” Stecklein says. “There are many things that affect how you manage rootworm. If you have no idea as to what populations are in fields, you have to manage for worst-case scenarios. If you get out in your fields and dig up roots, you will know what levels of damage and populations that you face.”

3. Did you notice corn rootworm’s early warning sign? Although it’s not a substitute for root digs, detecting small tangled and lodged areas of a field from your combine cab can indicate corn rootworm infestations, Stecklein says.

“If you have hot spots, that is a warning you have to do something before they spread across the entire field,” she says. “If you see one of these areas, take the time to check roots to see if the damage is caused by rootworm feeding.”

4. Did you hope weather would help control corn rootworm?  This is a big mistake.

“Those eggs are very, very tough,” Stecklein says. “It takes very cold temperatures for an extended period of time to hurt egg survival.”

CONCENTRATE ON CORN. Although weed management often focuses on soybeans, it’s also important to evaluate weed control in corn.

In the spring, rainfall that saturates soil can drown eggs and larvae. Still, relying on weather as a corn rootworm management strategy is not recommended, she adds.

5. Did you manage weeds by targeting seeds rather than weeds? “We need to kill seeds, not weeds,” Grote says. “Let’s be honest. The postemergence toolbox we’re using is getting pretty bare against emerged waterhemp — especially with plants taller than 4 inches — no matter which [herbicide] portfolio you’re using. We stress controlling weeds before they emerge. And if they emerge, control the weeds while they’re small.”

Residual preemergence herbicides followed by overlapping postemergence residuals are a way to do this.

But — and there’s always a but — weather can complicate this strategy. This year, some areas of the Midwest, including Iowa, were so wet that farmers could not apply preemergence herbicides. At that point, postemergence herbicide applications were the only remaining options, he says.

When farmers could apply preemergence herbicides that landed in the weed seed zone, clean fields resulted, Grote says.

“If weeds emerge, they’re a lot harder to kill,” Grote says. If they do emerge, overlapping residual postemergence herbicides can prevent weeds from piercing the crop canopy later in the season, he adds.

6. Did you cut herbicide rates to reduce costs? Bad idea, for it likely led to poor weed control and even worse. “If we’re not using full rates, we speed up resistance,” Grote says.

IT’S CRAZY. Crazy top — exhibited here by distorted tassels with prolific leaflike growth — is one of several bacterial diseases that surfaced in 2024.

Somewhere, in some place in a field, a weed biotype that’s one in 100 million resists even the most effective herbicide mix. “Applying a [preemergence] below label rate only speeds up selection pressure and resistance — and puts even more selection pressure on a postemergence application,” Grote says.

7. Did you pay attention to herbicide-resistant weeds in corn? Heavy reliance on Group 27 corn herbicides (Balance Flexx, Callisto, Laudis) has spurred waterhemp that resists these HPPD inhibitor compounds, says Kurt Maertens, BASF technical services manager.

“I’d say resistance is more of a concern on the corn side than the soybean side,” he says. “A lot of farmers have used Liberty along with Enlist on soybeans, and these programs have helped with waterhemp control and resistance management. With corn, we have relied heavily upon HPPDs, and we have more HPPD resistance out there than you’d think. “

This underlies the importance of using a multiple herbicide site of action mix of preemergence residual and overlapping residual postemergence herbicide programs. 

“Waterhemp is not going away,” Maertens says.

8. Did you think fungicides would control all corn diseases? They do a good job on ones caused by fungi. However, this year’s prolific precipitation spurred bacterial diseases to bloom.