An early spring seedbed is no bed of roses. It's apt to be cold and wet, swarming with pests and pathogens, lashed by frigid rains, pocked with standing water or pounded to a crust.
“We put our expensive seeds into an environment that's stressful,” says Bill Wiebold, University of Missouri Extension plant scientist. “Unfortunately, a number of bad things — including things other than diseases and insect pests — can happen to high-quality seeds.”
As every farmer knows, good seeds get exposed to lots of bad things that can delay or prevent emergence. “Seed costs are really increasing,” says University of Illinois Soybean Agronomist Vince Davis, “so it is more important than ever to evaluate emergence patterns.”
Too much rain after planting caused emergence woes last spring for many farmers in Missouri and Illinois, including Mark Wilson, who raises corn, soybeans and cattle in Shelbyville, MO.
Between April 20 and May 16, 7 in. of rain fell on Wilson's farm. It kept on raining in June and by the end of August his rain gauge had recorded 23.15 in. of precipitation. “I thought we were in Seattle,” he says. He had to replant 35 acres of corn and suffered stand reductions on another 70 acres. “Seeds germinated,” he says, “but it was so wet they rotted in the ground.”
Flooded or waterlogged soil can be devastating to corn and soybean emergence, Wiebold says. Germinating seeds need oxygen to stay alive. Saturated soils hold less oxygen, so seedlings quickly deplete the supply and may die within a few days. The symptoms of oxygen starvation are thin, weak-looking roots.
SEEDLINGS THAT GROW slowly because of overly wet or cool soil are much more vulnerable to soilborne diseases, too, says Max Glover, a Missouri Extension specialist. Glover worked with many northeastern Missouri growers who had emergence issues in 2009. Pythium, for example, thrives in cool, soggy soil. Other pathogens, such as Fusarium and Phytophthora, are a threat when soil temperatures climb above 60° F. “A lot of times, excess rain leads to disease problems,” Glover says. Infected seedlings quickly turn brown and mushy as tissue dies.
Seeds that sit for a long time in cold, wet soil are also susceptible to damage from certain soil-applied residual herbicides, says Peter Thomison, Ohio State University agronomist. Symptoms include improper leaf unfurling and leafing out underground.
Chilling injuries hindered corn emergence in Minnesota in 2009, says Dave Pfarr, a Pioneer regional agronomist in southern Minnesota.
Emergence is reduced when seeds are planted into soil that's colder than about 50° F, Pfarr notes. But farmers, fearing weather delays if they wait, “are always pushing the envelope on planting dates. If the soil is fit, they are going to plant, even if it's cold.”
When early planted seeds absorb cold water from a chilly rain — or a spring snowfall — the seed's cell membranes may rupture, allowing pathogens and insects to invade. In Minnesota, it's common to see stand losses of 10% or more from cold stress, Pfarr says.
Soil crusting impeded emergence in many Ohio fields last season, Thomison reports. The growing corn shoot thickens and twists when it encounters resistance from surface compaction formed by a hard rain followed by fast drying. The corn plant's spike may “corkscrew” or split pre-maturely and leaf out underground.
“Soil crusting can be even worse for soybean emergence than for corn emergence,” says Davis, the Illinois soybean agronomist, “because soybeans must ‘lift’ larger cotyledons through the soil surface.” When soybean cotyledons can't break through a crusted surface, the hypocotyls swell as growth continues and may break under pressure.
Tillage or planting when it's too wet can cause uneven or delayed emergence, too, Wiebold says. Of course, you can't always avoid planting into marginal conditions, he adds, but seed slot compaction “makes it really difficult for a good root system to develop. You'll pay for that all season.”
Damage can also occur if starter fertilizer is placed too close to the corn seed, or when “pop-up” fertilizer is applied with the seed, says Emerson Nafziger, University of Illinois Extension agronomist. For growers who feel they need seed-applied fertilizer, he suggests keeping the rates low. “Emergence is often constrained by temperature and moisture, and we do not want to add to that stress.”
It's not always easy to diagnose the reasons for poor emergence, Wiebold says. Cold water damage, for example, “stimulates other problems that are more often considered the cause of emergence problems.”
But examining damaged seedlings can give you some clues about what went wrong below ground, he says. And knowing what happened might help you avoid some of those problems next year. If you had Phytophthora damage in a field, for instance, “that may influence seed treatments or variety selection next year.”
Although spring is a busy time, “farmers should be in their fields often during the emergence period, observing if there are issues,” agrees Pfarr, the Minnesota agronomist. If you see stand problems, “try to understand why, and if they are avoidable next year.”
Seedbed preparation and planting practices have a big influence on stand establishment. Here are some tips for improving emergence.
Monitor soil temperature. Waiting to plant until the soil temperature is 50° F is the best way to lower your risk of poor emergence, says Bill Wiebold, University of Missouri. Some growers watch the near-term weather forecast and try to avoid planting ahead of a cold front, adds Emerson Nafziger, University of Illinois.
Avoid compacting the soil. Delay tillage and planting until the soil is dry enough to minimize compaction, Wiebold says.
Protect seeds. Early planting and cool, wet conditions favor soilborne diseases, especially in high-residue fields. “Effective seed treatments can help, but they won't eliminate all problems leading to poor stands,” Wiebold says.
Tinker with your planter. “Your planter should be well tuned so it does all its jobs properly,” Wiebold says. It should open the seed furrow without sidewall compaction, place seeds at a uniform depth and close the seed slot without compaction. Tools such as row cleaners and seed firmers can be very helpful, he says. “Growers should experiment to see what works for them.”
Check behind the planter frequently to make sure you are getting uniform seed depth and good seed-to-soil contact, adds Dave Pfarr, Pioneer area agronomist. “Stop the planter often and look, look, look!”