Scout to Protect Yield and Profit

Scout to Protect Yield and Profit

Check for in-season damage to help avoid catastrophes

Mother Nature is giving farmers a run for their money this year, but, thankfully, there’s a growing crop to tend to in most areas. Or, as Farm Journal Field Agronomist Ken Ferrie describes, “There are dollars still left on the table.” 

Identifying and addressing issues during the growing season can result in up to 50 bu. per acre swings in corn and 10 bu. per acre in soybeans, he says. 

The best way to prevent in-season issues is to scout and ground truth thermal and Normalized Difference Vegetation Index (NDVI) images, photos and past yield maps. This proactive approach can alter management practices when it comes to diseases, insects, weeds and nutrient deficiencies before catastrophe strikes. 

“Higher yields require dirty boots,” Ferrie says. “You can’t walk away from a growing crop; you have to manage it.” 


Because of rain delays in the lower Midwest and Plains states, crop growth is erratic. Use this story to brush up on how corn and soybean plants evolve to maximize scouting efforts and cater to the needs of your crop. 

If you haven’t been tracking growing degree days (GDD)—which isn’t the same as actual days—it’s never too late to start (see instructions below). It takes 90 to 120 GDD from planting to emergence (VE) and another 84 GDD for every new leaf collar from VE to V10, explains Farm Journal Associate Field Agronomist Missy Bauer. From V11 to tassel, it takes 56 GDD per leaf. 

Ultimately, it’s bushels that matter, so it’s key to understand what influences production. 

“Yield is a function of three factors: number of plants per acre, number of kernels and size of kernels,” notes Joe Lauer, University of Wisconsin professor. “Emergence determines plants per acre.”

Emergence issues can stem from soil conditions that are too cold, too dry or too wet. They can also be linked to your planter, Bauer says. While you can’t fix non-uniform plant issues (misplaced, missing and extra plants) this year, you can learn from the situation and check each component of the planter and make adjustments next year, she adds.

“The more uniform the crop is during the first six growth stages, the easier it will be to scout all season long,” Ferrie adds.

At V6, the growing point is above ground, which makes the plant more vulnerable to yield loss. All necessary plant parts have developed.

“[At V6], the photosynthetic factory is determined,” Lauer says. This means leaves, tassels, ears and kernels are present, just not necessarily visible.

Click on picture to view larger image

Sidedressing nitrogen between V6 and V8 supplies the plant with the nutrients it needs while adding kernel rows, Lauer explains.

Since most of the plant’s energy is spent on growing, it’s more susceptible to green snap. Strong gusts of wind, for example, can snap the plant and cause detrimental stand loss.

Other potential stand killers include lodging and defoliation triggered by insects. Lodging this early can be caused by rootworm larvae feeding on the root. Perform root digs to determine if the field has damage. 

At this point, and all the way through the vegetative growth stages,  scout corn weekly and keep an eye out for European corn borer, eyespot and Goss’s Wilt as well, Ferrie suggests. 

At V12, the plant is adding kernels per row, which means poor management can have a big effect on yield. Environmental stress plays a huge role in how successfully the plant finishes setting kernels. 

“The second yield component, kernel number, is being determined,” Lauer explains.

Nutrient and water deficiencies have the greatest effect on yield between the V10 and V15 stages. While the plant is establishing kernel number and ear size, it uses large amounts of nitrogen, phosphorous and potassium.

“Knowing what nutrients bring to the table is important,” Ferrie says. “Phosphorus shows height and cell division, nitrogen brings a change in color and potassium plays a role in plant health and water management.”

Click on picture to view larger image

Environmental stress, such as drought, wind and hail, can take a toll on yield. Corn uses 0.25" water per day during V12. If severe heat or drought conditions occur (leaf rolls by midmorning), the plant can lose 3% yield per day. If the plant is completely stripped of leaves by wind or hail, it results in 81% yield loss, Lauer says. Be vigilant when checking fields at this time to set expectations for yields moving forward.

By V18, ear development is rapid, and the plant is about a week away from silking. Walk fields at least once a week and keep an eye out for overall plant health. 

Lack of water, for example, can cause a 4% yield loss per day in corn at V18 and 7% yield loss at R1. Depending on the severity, lodging can cause a 12% to 31% yield loss. Insects can cause poor pollination or prevent it all together by clipping silks. Defoliation due to disease decreases photosynthesis, which affects kernel fill.  

“Besides planting, pollination is one of the most crucial parts of corn production,” Ferrie says. “If you don’t get good pollination, everything else you do will be wasted.” 

By R1, the maximum kernel number has been determined, and the plant is entering the reproductive stage. 

Silks must be a minimum of 0.5" for successful pollination. When scouting, look for clipped silks from Japanese beetles or rootworm beetles. If there are five or more beetles near the tip of each plant, it’s time to consider an insecticide or other control method. 

Watch for leaf-rolling by midmorning, which signals drought or severe heat. If drought is severe enough it can cause the silks to dehydrate and miss pollination—resulting in a barren ear.

During the reproductive stages the final yield factor, size of kernels, is determined. Nutrients move from the plant into the kernels for grain fill. 

“There are about 40 days after pollination to fill kernels,” Lauer says.  “Kernel fill can account for about 5 bu. per day in yield effect.” 

Suitable photosynthesis, which requires water and light, is crucial to build yield in the homestretch.

At black layer, kernel fill is complete and true kernel weight is determined. At 30% moisture, the grain is not ready for storage, so it will need to stand in the field to dry. 

While scouting, perform push tests to check stalks for lodging or other damage and look for insects and diseases that could damage the ear or stalk. If stalks break or fall easily, consider harvesting early and using mechanical dryers for ease of harvest and better grain collection.

Like corn, soybeans shouldn’t be managed by the calendar. “Grow a crop by scouting,” advises Chad Lee, Extension professor and agronomist at the University of Kentucky.  

Soybean scouting starts before the crop is in the ground. Keep an eye out for soil compaction, ground temperature, early season weeds, fungus and insect pressures. 

“As a rule of thumb, if weeds emerge with the crop, don’t let it get to 6", Lee says. “If you do, you’ve probably lost yield potential.”

Once the soybean plant emerges, the unifoliate leaves unroll and the cotyledons supply nutrients to the plant for seven to 10 days. If both leaves are lost, yields can suffer 8% to 9%, according to Pioneer research. 

During vegetative soybean stages, one of the most important things to monitor is nitrogen fixation, Lee says. Cut nodules down the middle and look for pink insides. If you see gray it could indicate nodules are not correctly working.

While the canopy is open, regularly scout for weeds. If you don’t kill weeds before they reach 4", chances are you won’t be able to kill it.

While you’re looking for weeds, be aware of insect population and spray if necessary. Sometimes, aphids show up early, so don’t be surprised.

During late vegetative stages and early reproductive stages, be scouting for brown stem rot, frogeye leaf spot and sudden death syndrome. For brown stem rot and frogeye leaf spot, Lee suggests treating with a curative and preventative fungicide combination to clear up and prevent the diseases from spreading. If you find sudden death syndrome, there’s nothing you can do about it because it occurs at the seedling stage. Take note for next year, so you can plan seed treatment accordingly. 

During the reproductive stages (R1 to R6), you have the opportunity to increase or decrease yields based on management. Environmental factors and managing weeds, insects, fungi and diseases can influence the number of pods per plant.

Giving your soybeans the best growing conditions possible will help them add more pods. Some insect and fungus situations might be worth spraying.

“With a drop in commodity prices, you have to be more diligent about scouting. No longer does 2 bu. per acre pay the bill,” Ferrie says. “However, don’t risk giving up 10 bu. to 15 bu. if you don’t control an outbreak—specifically with spider mites or aphids.”

Thresholds for insects, diseases and fungi vary by state and environment. Reach out to your local Extension agent or company representative to find the threshold for your area. 

Tight margins leave less room for error. Give your crops the attention they need to maximize yields. If you skip scouting, you forfeit dollars.

To access a searchable database of more than 200 weeds, diseases and insects found in corn and soybeans, visit 

Top 10 Scouting Tips

1. Be proactive and timely. Know when to anticipate specific weeds, insects and diseases for your area and plan to scout accordingly.

2. Track local weather conditions. Environmental factors can influence when and whether weeds, diseases and insects develop in your fields.

3. To evaluate problem areas, start with aerial imagery and previous yield maps. If those tools aren’t available, walk through fields in a zigzag or “W” pattern.

4. Record the types, numbers and locations of weeds, diseases or insects in each field and the date. Hang on to these details for reference next year.

5. Designate a pest boss—someone who makes scouting their No. 1 priority all summer.

6. Use sound integrated pest management treatment practices if insect thresholds are met.

7. When scouting for diseases, check for plants that show signs of stunting, lesions, discoloration, yellowing or senescence. If you can’t identify the disease, send a sample to a plant clinic for diagnosis.

8. Check your fields preplant and post-emergence for weeds. Be vigilant during the first three weeks after emergence to evaluate weed pressure and to decide if you need supplemental control measures.

9. If you find weeds, diseases or insects you don’t recognize, consult your agronomist, Extension personnel or a pest identification guide.

10. Pack a pest kit that includes safety glasses, scouting guides, tape measure, hatchet, pocket knife, hand lens and vials or sandwich bags for samples.

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