Top Crop Manager

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Getting planted earlier?

Stress emergence issues remain.


November 13, 2007
By Top Crop Manager

Topics

38aMuch has been made in the last decade about planting dates in corn. Where planting
sometime after the first of May was a traditional norm, the trend now is to
plant in April if conditions present themselves. For some, it seems, the earlier
the better.

However, there is a growing body of evidence to suggest that early planting
subjects the crop to potentially damaging stress, and those growers who have
managed to push the limit on early planting have done so at, perhaps, greater
risk.

Dr. Imad Saab, research scientist with Pioneer Hi-Bred in Des Moines, Iowa,
acknowledges the benefits of early planting. Anecdotally, growers can take advantage
of suitable conditions early in the spring, and help the crop reach maturity
earlier in the fall. Some can grow fuller-season hybrids with greater yield
potential. For the most part though, corn's physiology is such that it does
not respond well to conditions that are consistently adverse. In one or two
years, the weather may favour early planting, but to push the bounds year after
year may wind-up costing growers.

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To start, modern corn hybrids have descended from what was a tropical plant,
with ideal soil temperatures of 26 to 30 degrees C at emergence. Add to that,
notes Saab, the fact there has not been as much progress in improving cold stress
tolerance as there has been in other stresses such as high density and drought.

"There's not a great deal of genetic variation for cold tolerance in corn,"
says Saab. "So the progress in making hybrids more tolerant to early season
cold has been limited."

Stress emergence scores help rate hybrids
To help growers with early planting, Pioneer Hi-Bred has developed a stress
emergence rating for their hybrids. Developed in 2003 and now included in a
catalog, the ratings measure the relative ability of a hybrid to establish stand
under early season cold, wet conditions. Testing is done in the US, and in Canada
in Quebec, Ontario, Manitoba, Saskatchewan and Alberta. Sites are chosen to
reflect the various seedbed and environmental conditions likely to be experienced
by growers. In the east, for example, sites represent extended cold, wet conditions
that can persist into late spring and early summer. Northern and midwestern
sites are likely to provide more extreme variations in day and nighttime temperatures.

With such diversity of conditions, researchers gain a better understanding
of hybrid responses to early-season stress. Typically, testing sites are characterized
by cold soil (below 10 degrees C) at planting, followed by cold rain or snow,
with emergence taking as much as three to four weeks.

Testing also is carried out in Pioneer laboratories, using assays that simulate
stressful field conditions. Laboratory tests, which are validated by multi-year
field trials, provide consistent tests that can be reproduced, coupled with
the flexibility of year-round studies. The assays are used to support decisions
on advancing hybrids, as well as screen early-generation material to help breeding
and selection processes in efforts to improve early-season performance.

All comes back to the farm
"We recommend that growers look at those scores in making hybrid decisions
for their specific conditions," says Saab. He adds that growers should
consider other management practices to reduce risk, including insecticide seed
treatments (IST) like Poncho 250 or Poncho 1250. These ISTs control most seed-damaging
soil insects common in high residue and other stressful emergence environments.
"The longer seedlings have to sit in cold, wet conditions, the more likely
they are to be chewed by insects and develop poor vigour and subsequent disease."

The stress emergence ratings are based on a scale of one to nine, where six
and higher are best, indicating above average or better potential for normal
stands under stressful conditions compared to other Pioneer hybrids. Stressful
conditions include cold and wet soils, or short lengths of time with severely
low temperatures. A rating of five indicates average potential, and one to four
have below average potential for normal stands under stress. Saab emphasizes
the stress emergence rating does not indicate the susceptibility for seedling
disease.

The other point he makes is that regardless of a high stress emergence, early
planting into unfavourable conditions can lead to some level of injury or yield
loss. "Farmers need to monitor seedbed conditions on their farms to decide
on a planting date," says Saab. Monitoring soil temperatures is a good
idea, he adds.

One other consideration in seed health is its reaction to cold water imbibition.
If there is a prolonged cold spell at planting, or if a late snow thaws, water
at less than 10 degrees C can harm the seed. Further damage can come with a
prolonged cool stretch, where emergence is delayed by several weeks.

Use weather data wisely
Watching the weather is particularly valuable and perhaps under-rated, according
to Greg Stewart, corn program lead for the Ontario Ministry of Agriculture,
Food and Rural Affairs in Guelph, Ontario. When discussing early season stresses,
Stewart believes growers are discounting two key elements: the value of 10 day
temperature forecasts and planting depth relative to available moisture.

"We've underestimated that 10 day temperature trend as a tool to decide
whether to plant 30 percent of your corn or 60 percent in a good week that presents
itself, for instance, April 15th to the 25th," says Stewart. He notes that
10 day precipitation forecasts are much less reliable than those for temperature.
That sentiment has been expressed repeatedly by climatologists like David Phillips
of Environment Canada. "In terms of temperature, it's a reasonable tool
for growers to look at when they consider planting corn on the 22nd of April,"
adds Stewart.

On the issue of planting depth, Stewart adds that 2005 taught him not to plant
into moisture if moisture requires planting to a depth of two inches. He says
there is a risk limit in terms of pushing corn planting depth. The two guidelines
can help minimize risks for early planting, but Stewart insists the practice
be considered as a means of getting the crop planted early, as opposed to late
or not at all. It should not be considered solely as a means of increasing yield,
since prolonged research does not indicate it has any consistency.

Simply more options
The stress emergence issue and the stress emergence rating system serve to offer
growers more options and more information. And that is an important plus for
Tim Welbanks. As technical information manager at Pioneer Hi-Bred's Chatham,
Ontario, office, the added information component is a definite asset for growers.

"For the larger growers who start to plant early, and who has four or
five hybrids, the rating system gives them a little more guidance on which hybrid
to choose to plant in that mid-April to 20th of April range," says Welbanks.
"If planting early is here to stay, it's a good idea to have 10 or 20 percent
of your hybrid mix with a stress emergence score of five to seven, so if you
get that window of opportunity, you can plant early with confidence." -30-