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The Pollination Period

March 9, 2013
By: Darrell Smith, Farm Journal Conservation and Machinery Editor
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Hybrid selection and scouting increase success

The management you lavish on a crop during its pollination window is time well spent. "Besides planting, pollination is one of the most crucial parts of corn production," says Farm Journal Field Agronomist Ken Ferrie says. "If you don’t get good pollination, everything else you do will be wasted."

Pollination Period p14

After planting, pollination is the most crucial element to high yield. Scout the crop early to identify areas where pollination problems are most likely to occur.


Pollination management begins long before plants shoot tassels. Hybrid selection is the first step, followed by disciplined scouting from planting through pollination.

Widen the window. The easiest way to reduce pollination problems is to lengthen the period during which your crop pollinates. By doing so, you reduce the chance that all your hybrids will be caught by a week of bad weather. "A prolonged wet spell can be just as harmful as a week of hot, dry weather," Ferrie notes. "During lengthy wet periods, corn tassels might fail to open and drop their pollen."

Diversifying the pollination window also makes scouting easier. "You need to check each field at least once a week when the corn is pollinating," Ferrie says. "If you have 3,000 acres of corn all pollinating at the same time, getting through every field on schedule will be pretty difficult."

You can lengthen your pollination window by planting hybrids with different physiological maturity and different flowering dates. You need to know both, Ferrie says, because two hybrids of the same physiological maturity might have different flowering dates. Your seed salesperson can provide flowering date information.

Although flowering and physiological maturity dates are important, always put yield first. "Choose high-yielding genetics first, and then select other characteristics," Ferrie says. "Pick hybrids that fit your soil type, fertility situation, disease pressure and insect problems. Finally, make sure you have a range of flowering dates."

You can also lengthen the pollination window by staggering your planting date. That’s easier to do in areas such as the High Plains of Texas, where spring rain, frost and heat are less likely than in areas such as the northern Corn Belt where rain and frost can stall planting, and in the Mississippi Delta where heat is an issue.

"Using both days to flowering and a staggered planting date is ideal," Ferrie says. "But if you have a short planting window, diversifying your flowering date might be your only option."

Resist the urge to plant all your corn as quickly as possible, unless you’re forced to by weather. "Many farmers are equipped to plant their entire corn crop in about seven days, and that’s good," Ferrie says. "But try to spread those seven days throughout the optimum planting period."

Have a strategy. Plan where and when you will plant each hybrid. "Plant early maturing hybrids first and later-maturing hybrids last," Ferrie recommends. "If you don’t, all your corn will pollinate in the same window.

"Even if planting season gets hectic, take time to document changes to your plan," Ferrie adds. "You will need to know which hybrids are in each field to effectively scout."

Based on long-term weather averages, estimate when each hybrid will start to pollinate. "Clear your schedule, or make sure an employee or crop consultant is available, to scout your fields during pollination," Ferrie says.

Scout from the start. Early season growth determines when pollination occurs. "Early season scouting tells you where to scout for problems after pollination begins, so you can react in time to prevent yield loss," Ferrie says.

"Early on, look for clues about how the crop is going to pollinate within individual fields," Ferrie says. "If you have growth and development problems in certain areas, map them as zones to scout later, during pollination.

"For example, in cold, wet seasons, plants in low-lying areas might emerge slowly and fall behind the plants in other parts of the field," he explains.

"At this point, you haven’t neces-sarily lost any yield, but it’s as if the low areas had been planted later. You might get frost in low-lying ground or high, well-drained areas might be too dry. During pollination, these areas will require scouting for a longer period because the flowering date will be later than the rest of the field," Ferrie says.

You can also use remote sensing, such as aerial photos and Normalized Differentiation Vegetation Index (NDVI) maps, to identify later-maturing areas. "There are various tools, such as smartphones and handheld GPS devices, that let you map zones, so you can find your way back to them later or share the map with another scout," Ferrie says.

In your early scouting, look for uniformity within the field. "The more uniform the crop is during its first six growth stages, the easier it will be to scout all season long," Ferrie says.

"If a field is uniform early in the season, you can make a wide circle through the field in later scouting trips and have a pretty good sense of the entire field."

If you find maturity zones within a field, scout each zone until pollination finishes. "You might find a week’s difference in maturity from one zone to another," Ferrie says.

The toughest early scouting situation is random and uneven plant growth within the row, which can be caused by poor planting conditions, poor planter operation, frost or insects.

"Areas in the field with uneven growth are at high-risk for pollination problems," Ferrie explains.
"When you find varying plant sizes that don’t break down into identifiable maturity zones, you need to scout almost every day of the pollination window to make sure that all the plants get pollinated."

Midseason scouting. Don’t sideline your scouting or aerial imagery efforts, even if fields look uniform early.

"Between the V6 or V7 stage and tasseling, hail and high wind can stress the plants," Ferrie says. "If you had rootworm feeding early, or an insecticide failed on a refuge, you might discover standability problems and goosenecking. These things can change a uniform field into a non-uniform field."

During midseason scouting, you might find compaction caused by tillage or by the wheels of a sprayer or pinch-row compaction from the wheels of a center-fill planter. "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 the compaction. But you don’t want pollination problems on top of it."

Make a list of your easiest- and hardest-pollinating fields, and prioritize them accordingly for scouting during pollination.

Scout during pollination. With uneven maturity, insects might be present throughout pollination and attack every plant. "They include silk cutters, such as adult corn rootworm beetles and Japanese beetles, as well as aphids, which interfere with tasseling and pollen drop," Ferrie says. Most silk-clipping insects are pheromone feeders. When they find a corn plant they like, they give off a pheromone that draws more insects to the feeding site.

"If you have 30,000 plants per acre, all pollinating at once, with good weather conditions, and you have 30,000 rootworm beetles, that’s only one beetle per plant," Ferrie says. "They won’t be able to clip silks fast enough to create a pollination problem; the silks will outgrow the damage.

"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 days later, and all 30,000 beetles migrate to them, those plants probably won’t pollinate," Ferrie says.
If you find 10 plants without any insects, and then find one plant covered up by insects, that plant probably pollinated later.

Treatment decisions. As you decide whether treatment is necessary, consider your environment. Some judgment might be required.

"Under ideal environmental conditions, a crop can deal with a lot of aphids or rootworm pressure and still pollinate successfully," Ferrie says. "If silk clipping is occurring, see if you have at least ½" of silk for the pollen to catch on to. Check whether silks have already pollinated. Cut the husk off an ear and shake the ear. Any silks that pollinated in the last 24 to 48 hours will fall off. If all the silks fall off, the ear is already pollinated, so there’s no need to spray."

Ideal pollination conditions give you more time to make decisions. "If you see insects the first day, come back on the second day or the end of the week and see how pollination is progressing," Ferrie says. "Silks grow ½" to 1" per day, so they might outgrow the pest.

"But if it’s hot and dry, silks won’t grow as fast; so if you see a problem, you need to react sooner."

Pollination Period p18

After planting, pollination is the most crucial element to high yield. Scout the crop early to identify areas where pollination problems are most likely to occur.


If pollination conditions are less than ideal, it’s wise to check with your aerial applicator
before pollination begins. "If it will take him two or three days to arrive that creates a dangerous situation," Ferrie says. "You need to know this before you go to the field, rather than finding it out after scouting."

Limited availability of applicators might force you to decide sooner about whether or not to treat, Ferrie says. If there are no aerial applicators available in your area, you might have to find an applicator with high-clearance ground equipment.

"With random uneven growth, you might find a situation in which the earlier plants in a field are starting to pollinate, but the later ones won’t pollinate for 10 days and silk-clipping insects are present," Ferrie says. 

"Under ideal pollination conditions, you might wait until about half the plants begin to pollinate, and then spray. But if the weather forecast is against you, or there are no applicators available and you see early signs of pollination problems, this might be a time to treat preventively."
Land-grant universities have different thresholds for treatment of silk clipping insects, so consult your local Extension adviser before treatment.
When you treat, follow all label restrictions, even though they can be a bit complicated. "For example, if you have two non-GMO hybrids in a field, and the field is not a refuge for other fields, you can treat only the hybrid that needs it," Ferrie says. "But if you have a GMO and a non-GMO in the field, and the non-GMO hybrid is a refuge, you must treat both hybrids."

Other Reasons to Scout Pollination

The possibility of another dry season makes it even more important to scout your corn crop early and often. "In 2012, we could tell by the second week of July that some fields were not going to pollinate at all," says Farm Journal Field agronomist Ken Ferrie. "I wouldn’t have thought that possible with today’s genetics, but that’s how bad the growing season was in some areas.

"By making that discovery early, growers who had over-sold corn had time to react and buy back their contracts," Ferrie continues. "Also, if you see a disaster looming, you can take photos to document that weather was the cause of poor pollination. The pictures will prove you did not fail to follow Best Management Practices by not applying an insecticide to prevent silk clipping.

"It’s a good idea to notify your insurance agent as soon as you see a problem developing. That becomes especially important if a problem is localized, rather than affecting an entire county."

Block out time for pollination scouting. Summer is a busy time, and the press of other activities sometimes causes farmers to neglect crop scouting just when it’s most important, during pollination. Scouting during pollination lets you monitor silk-clipping insects, whose impact might be determined by varying plant maturity within a field.

"Environmental conditions between planting and flowering, such as unusually cold or wet weather, can delay the onset of pollination," Ferrie explains. "So you have to watch the pace of crop development and be flexible. But if you know your kids will be showing cattle at the county fair during the first week of July, and a third of your hybrids are probably going to be pollinating at that time, you had better hire someone to help out and scout your fields."

Evaluate Pest Conditions Before You Treat

Unneeded pesticide applications waste money and might help insects develop resistance. So use the pest triangle to evaluate the threat, and consider threshold levels before you spray pollination-threatening insects.

"For any pest to become a problem, you need three things: a host plant, environmental conditions that favor the pest and the pest itself," says Farm Journal Field Agronomist Ken Ferrie. "Without the right environ-mental conditions, the pest may not show up. So rather than spraying preventively, in anticipation of a problem, continue scouting through the pollination window."

Earlier Hybrids Help Spread Flowering

Don’t be afraid to add some earlier-maturing hybrids to your mix in order to spread out the pollination period. "Years ago, shorter-season hybrids yielded less," says Farm Journal Field Agronomist Ken Ferrie. "But now we have high-yielding hybrids in all maturity ranges."

Midseason Aphid Check

If enough corn leaf aphids reach a corn tassel, it won’t open for pollination. The insects secrete a waxy substance, called honeydew, that prevents a tassel from shedding pollen. If enough plants have "waxed" tassels, there won’t be enough pollen shed to go around.

"Besides waxing the tassel, if aphid populations get high enough after pollination, that same honeydew secretion, deposited on the plants’ upper leaves, can shut down photosynthesis," says Farm Journal Field Agronomist Ken Ferrie. "That can cause kernels to abort."

Start scouting for the pests two or three weeks before tasseling, Ferrie advises. Pull the center whorl out of some plants and unwrap it.

"If you find aphids in the whorl, consider applying a pre-pollination treatment in the loose-whorl stage. You need to preserve one or two leaves wrapped around the tassel, so the aphids can’t get in."

"Aphids are tasting insects," Ferrie says. "An adult female tastes the corn plants; when she finds one she likes, she deposits her offspring.

"Aphids find some hybrids tastier than others; so if you plant two hybrids in a field, only one may have aphid problems. Ask your seed company rep which hybrids appeal to aphids. If you know one of your hybrids is susceptible, plan a pre-tassel scouting program for timely treatment."

Learn and Profit from Corn Navigator

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The Corn Navigator series will focus on various sources of crop stress and how to manage the situation in order to drive corn yields and profits higher. www.FarmJournal.com/corn_navigator


You can e-mail Darrell Smith at
dsmith@farmjournal.com.
 

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FEATURED IN: Farm Journal - March 2013

 
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