Ontario Field Crop Report
Corn Seasonal Summary

We are likely to set a new record for Ontario corn yields in 2005 coming on the heels of a record breaking year in 2004. We appear to be closing in on 140 bu/ac average for 2005 compared to last years provincial average of 131. So the top question at the coffee shops for weeks now has been where did all this corn come from? This question is particularly poignant given that prior to July 15, most of us were anticipating significant and wide spread yield losses due to an extended period of dry weather.

Here are some points to consider:

Most of the 2005 corn crop was planted into good soil conditions prior to May 15. This situation promotes earlier canopy closure which captures more of the suns energy associated with the longest days of the year (June 21). April planted corn did have lower final plant stands then May planted corn. The combination of reduced moisture levels experienced over much of the growing season and a few less plants did not appear to negatively impact yields.

Some of the recent nitrogen and tillage research suggests that young corn plants which experience stress from soils that are frequently saturated in May and June can experience significant yield losses. While we had some corn that got damp and cold in late April and early May, the remainder of May and June were free from prolonged wet spells that saturate the ground and stress the corn plant. These cool wet conditions are particularly stressful to young corn plants if they occur at the ear initiation phase of development between the 9-12 leaf stage. The basis for high yields was set early in 2005 despite the dry conditions because of rapid canopy growth and good downward root proliferation.

Of course dry soils, good root growth, and good soil structure eventually take a back seat to the crops need for adequate water; particularly the water requirements around the time of pollination. Rainfall that fell on much of the province over the period of July 15-17 was a crop saver. A few days later and we could have been facing some real yield depression. As it was, timely rainfall generated average to above average kernel set in most parts of the province.

The early planting dates and good growing conditions resulted in most corn pollinating in mid-July. This timing allowed grain fill to occur under much warmer conditions and during a time of year when sunlight intensity and day length keeps the photosynthetic engine running harder. Dr. M. Tollenaar at the University of Guelph has measured actual photosynthetic rates during the grain-fill period on corn plants for years. He has found that there is very little change in the maximum photosynthetic rate from year to year. This year was the exception; with 2005 photosynthetic rates being nearly 20% above average. The explanation for this is not clear. Early silking dates may have resulted in plants experiencing warmer temperatures following pollination and some of it may be related to increased sunlight intensity. Sunlight intensity at Elora in 2005 was about 10% higher for June and July but about average in August compared to the last 6 years. The net result of excellent grain filling conditions was above average kernel density (test weight) and kernel size.

Research has suggested that photosynthetic activity and grain filling can be disrupted by cool nighttime temperatures. This is another reason why silking on July 18 is much better than silking on August 5^th as it moves the grain filling period forward and away from the cooler nights of September. How did 2005 compare on this front? We checked Kitchener weather data for the period August 10 to September 20^th for 2005 and for the previous few years to determine the number of nights where the minimum temperature dropped below 10 C. No cold snaps occurred in 2005 as you would expect but the number of nights when it dipped below 10 C was not much different in 2005 than in other recent years (back to 2001). CHUs do not make high yields by themselves but combined with some of the previously mentioned factors resulted in even the latest maturing hybrids having plenty of growing season to finish the season.

It has been interesting to read some of the debate over the genetic contribution to recent high yields. I don't doubt for a minute that improved stress tolerance in our modern hybrids is responsible for some of the above average yields that we have in 2005. The contribution, however, to record high yields from specific traits that confer resistance to European Corn Borer or specific herbicides is marginal. Growing conditions, not GMO events, are at the heart of sorting out why fields that traditionally average 135 Bu/ac reached 180 this year.

Common smut plagued many fields in 2005. Common smut in corn is promoted by high temperatures and is often associated with manure applications and/or excessive N application. Some hybrids showed up as being particularly prone to common smut infection. However, impact on yield appeared to be marginal. Leaf disease and stalk rots were of minor importance in 2005. For the most part, stalk quality and standability were good and did not factor into harvest losses.

2005 was a year for poor husk cover and more than average ear tip damage due to insects, birds and ear moulds. Some isolated areas did see Vomitoxin levels that were elevated in grain corn samples but the problem was minor on a provincial scale.