Use diligent scouting to identify yield killers and take action when ROI makes sense
It’s midseason—the critical summer growth window of July and August—and it’s time for you to do the proactive management and scouting that can help save your crops, and pocketbook, from major losses.
In corn, scout for anything that might stress the plant and detract from its development. Don’t discount what happens midseason; this is when the plant determines yield potential and, in turn, what you will harvest.
From V6 to V7 ear girth is determined, and from V6 to one week before pollination, kernel row length is
determined, says Brent Tharp, Wyffels Hybrids agronomy and product training manager. It’s critical to protect corn from damage during this time.
“Between the V6 or V7 stage and tasseling, hail and high wind can stress plants,” says Ken Ferrie, Farm Journal Field Agronomist. “If you had rootworm feeding early or an insecticide failed on a refuge, you might discover standability problems and goose-necking. These can change uniform fields into non-uniform fields.”
Hail and high wind are out of your control, but you can map out zones of damage and keep an eye on them for the remainder of the season. Areas with damage might be more prone to fungus and disease, so you’ll need to be mindful and ready to call an aerial applicator if infection occurs.
Perform root digs to determine the extent of insect damage, especially in fields with a history of rootworm damage. See “Tips to Scout for Rootworm,” for more details about corn rootworm.
Goose-necking, lodging and other standability problems can be related to insect damage, seed depth at planting, wind or a number of other issues. These standability problems could lead to a trickier harvest or even cause the corn plant to fall before pollination. Take note of where you see this issue in the field and be prepared to harvest early or spray fungicide to maintain plant health if needed.
Another threat during the V5 to V8 corn stage, when corn is rapidly growing, is losing an entire corn plant from green snap. Fields are often more susceptible to green snap in the following conditions: you use Banvel or 2,4-D herbicides post emergence; you experience severe temperature shifts; you see a significant increase in rainfall; you have severe thunderstorms; you use manure or fertilizers to increase growth; or you used conventional tillage, according to Wyffels research. Scout for breakage below the primordial ear. Stand loss of 25% cuts yield by 10%; 50% reduces it by 26% and 75% reduces it by 43%, according to the University of Minnesota.
Get your boots dirty by scouting for yield-robbing insects and disease this summer. Be sure to increase scouting to at least once per week at pollination.
While scouting, you might discover compaction from tillage, sprayer wheels or pinch rows. You can’t prevent compaction, seed depth, herbicide damage and other problems from impacting yield this year, but you can use the information to prepare for next year. Keep good notes throughout the season and make a plan to mitigate the risk of encountering the same obstacles the next time around.
“Compaction can change maturity and delay pollination, resulting in a non-uniform field,” Ferrie says. “At this stage, you can’t prevent yield loss from compaction. But you don’t want pollination problems on top of it.”
Pollination delays across an entire field, uneven pollination across a field and other non-uniform pollination events could make your field or section of a field a target for feeding pests. Manage stand uniformity to ready corn for pollination midseason.
Scout at pollination to reduce stress from insects and diseases.
“One of your main scouting goals should be to identify any issues that might have a direct effect on the pollinating crop,” says Jeremy Hogan, technical marketing agronomist at BASF. Scout for yield-robbing issues such as silk clippers and foliar diseases to keep the plant focused on fertilizing and retaining kernels.
Use notes from earlier in the season to target areas with uneven stands because silk-cutting pests flock to later-pollinating crops.
“Watch for silk cutters, such as adult corn rootworm beetles and Japanese beetles and aphids, which interfere with tasseling and pollen drop,” Ferrie says. “If you have 30,000 plants per acre pollinating at once, with good weather, and 30,000 rootworm beetles, that’s only one beetle per plant. They won’t be able to clip silks fast enough to create a pollination problem.
“But say you have 30,000 beetles per acre and 25,000 plants are pollinating this week. The insects probably still won’t create a problem, but if the remaining 5,000 plants pollinate just 10 dates later, and all 30,000 beetles migrate to them, those plants probably won’t pollinate,” Ferrie says.
If you notice silk-clipping pests, perform a pollination test by removing the husk and shaking the ear. Any silk that falls has been pollinated within the previous 24 to 48 hours.
If corn is less than 50% pollinated, silks are clipped within ½" of the plant and you’re seeing an average of five or more beetles (corn rootworm or Japanese) per plant, it’s likely you need your aerial applicator to spray.
Soybean defoliation can be deceptive. Compare what you see in your fields to these images to get an idea of true defoliation. See if you hit an economic threshold requiring insecticide spray.
Watch for corn leaf aphid if the summer is hot and dry. “Corn leaf aphids thrive in dryland,” Hogan says. They favor states with hot and dry conditions at pollination, but dry weather could mean any state is at risk.
While scouting for corn leaf aphids, be sure to check at least 20 plant whorls in at least five locations (for a total of 100 plants). If 50% have 100 aphids or more and the plant is under stress, consider treating the field.
Stress, from insects and other causes, leaves corn more vulnerable to fungus and disease. When infected, corn plants might lose leaf tissue, which decreases their ability to photosynthesize and shifts attention from pollination and grain fill to trying to regain health. When plants aren’t focused on pollination and grain fill, yields plummet.
“If I have corn-on-corn versus corn-on-soybeans versus corn-on-wheat, I’ll target scouting corn-on-corn and corn-on-wheat first,” Hogan says. Because many fungal diseases over-winter in residue, fields with similar previous crops are more likely to have inoculum since they won’t have a non-host break in rotation.
Keep an eye out for northern corn leaf blight, gray leaf spot, Goss’s wilt and anthracnose leaf blight and stalk rot in corn fields this summer. Identify these diseases early to save yield. Learn more about identification, causes and how to manage these diseases on page 18, “Corn and Soybean Diseases to Watch.”
As soybeans go from the vegetative to the reproductive stage midseason, be on watch for yield loss. Look for insect pests in soybeans that can defoliate leaves and clip pods. Bean leaf beetles, Japanese beetles, soybean aphids and stink bugs look to take a bite out of your yield.
Bean leaf beetles defoliate leaves and scar pods. Consider insecticide treatment when: you have greater than 40% defoliation prior to bloom; 15% defoliation from blooming to pod fill; greater than 25% defoliation and active feeding at full pod; or 10% pod damage and 10 or more beetles per row foot.
Japanese beetles also defoliate but tend to skeletonize leaves by eating all of the tissue and leaving veins. It could make sense to use insecticide if you have 40% defoliation pre-bloom, greater than 15% from blooming to pod fill or more than 25% with active feeding at full pod.
When corn doesn’t pollinate or undergoes late- season stress, kernels abort or fail to develop. One by one, kernel loss adds up to several bushels and dollars lost at harvest.
Tiny soybean aphids use needle-like sucking mouthparts to remove plant sap and can cause severely infested plant leaves to become sticky and gray to black from sooty mold growth on aphid exudates, according to Purdue University Extension. Consider spraying if you have approximately 250 aphids per plant from R1 to R4 or if aphids are increasing beyond 250 per plant and plants are experiencing moisture stress.
Stink bugs show up mid-July through harvest and damage pods by removing seed fluids, resulting in small, discolored and deformed seeds. If you grow soybeans for commercial production, consider treatment if you have 40 bugs per 100 sweeps (use a sweep net in different field locations) and pods are still green. Soybeans grown for seed production need to be treated sooner—if you see 20 bugs per 100 sweeps and pods are still green.
Manage factors outside your control, such as the weather. Wouldn’t it be nice if you could turn the rain on or off? Or dial down the temperature? While you can’t control the weather, you can manage it by planning ahead.
“Cold weather slows down corn, but hot and dry conditions can catch you where pollen doesn’t survive long enough—that can get you in trouble,” Ferrie says.
Hot and dry conditions hurt pollination in two ways—if insects clip silks, they won’t grow out as fast. This could mean you need to apply insecticide sooner and if it’s hot and dry, your corn plants might not pollinate at all. Without adequate moisture, silks will dehydrate and render themselves unable to successfully pollinate, which can leave you with a barren ear at the end of the season.
“You can’t change the weather, but that’s why you try to make sure all of your corn doesn’t pollinate at the same time,” Ferrie says.
When selecting seed, choose hybrids and varieties with differing maturities and plant the shortest growing season earliest and longest growing season last to stagger the pollination window. If every acre you plant is pollinating within the same two week window you could be looking at a disaster if hot, dry weather hits.
“We know in late summer we should see hotter, drier temperatures thanks to shifts from El Niño to La Niña,” says Ashley Mason, production evaluation lead at Rob-See-Co. She says it’s important to consider that shift when making fungicide decisions. If the disease triangle (host-inoculum-weather) is incomplete, some diseases likely won’t cause issues and you can save money by not spraying. Keep in mind, however, certain diseases will thrive in those conditions.
If you are seeing problems outside of your control, such as weather issues, it’s important to be in contact with those involved in your operation.
“Notify your insurance agent as soon as you see a problem, especially if the problem is localized rather than affecting an entire county,” Ferrie says.
Poor field health can make your crops a sorry sight from the road, but more importantly, can take a chunk out of your profit. Keep your boots dirty and money in your pocket with careful scouting and management.
Steps to Estimate Yield Potential
When scouting, it’s a good idea to track productivity in your fields. The Pro Farmer division of Farm Journal Media hosts an annual Midwest Crop Tour that sends out teams of scouts to visit corn and soybean fields throughout the Midwest to estimate yields. Use these steps to determine production potential by individual field.
Calculate Corn Bushels
1. Measure and record the row spacing (inches) used in the field.
2. Walk through the end rows into the bulk of the field, then walk 35 paces down the rows to the first sampling area.
3. Measure 30' down the row, then count all ears in the two adjacent rows. Divide that number by two and record it. For example: (42 ears in one row 45 ears in other row) ÷ 2 = 43.5 ears
4. Pull the fifth, eighth and 11th ears from plants in one row of the sampling area.
5. Measure length of the portion of each ear that successfully developed kernels. Calculate the average ear length of the three ears and record it. For the most accurate estimate, sample fields in late kernel dough stage or even kernel dent stage. For example: (6" 7" 5") ÷ 3 = 6"
6. Count the number of kernel rows on each ear. Calculate the average kernel row number and record it.
For example: (16 rows 14 rows 16 rows) ÷ 3 = 15.3 rows
7. Grain yield for the sampling area is calculated by multiplying the average ear count by the average ear length by the average kernel row number, then dividing by the row spacing. For example: (43.5 ears x 6" x 15.3 rows) ÷ 30" rows = 133 bu. per acre yield estimate
Discover if Your Soybeans Stack Up
1. Scout a representative area of the field and lay out a 3' plot. Count all plants in the plot, then pull three plants at random.
2. Count all pods on the three plants and average the number of pods per plant. Determine the total number of pods in 3' of row by multiplying the average number of pods per plant by the total number of plants in the 3' of row.
3. Take the total number of pods in the 3' of row and multiply it by 36. Divide your answer by your row spacing to calculate the number of pods in a 3'x3' square. Use this information to
compare field productivity.