This winter has been unseasonably warm and the projections are for the warm weather to continue through early-spring, as the wheat crop begins to green up. Because of the warm winter, some producers are concerned that their wheat may not have vernalized. This is understandable, since here in Ohio we grow winter wheat, and for this class of wheat to produce heads and grains, exposure to a period of cold temperatures is necessary. These temperatures provoke hormonal and chemical changes in the plant that are required for it to convert from vegetative to reproductive growth, in other words, cold temperatures are required for the plant to make the switch from producing leaves and stems to producing heads with grain. This process is called vernalizaton. Timing of exposure to cold temperatures relative to the growth stage of the plant is critical for vernalization. So, after planting in the fall, warm temperatures are required for rapid germination, growth, and tiller development, followed by cold temperatures in late-fall to winter for vernalization to occur.
Even though the winter has been mild, there were several days with temperatures in the mid-to-lower 40s, which is good enough for vernalization. The specific temperature/time requirement varies with variety, but for most of the materials grown here in Ohio, a few days or sets of days in the lower 40s is all we need. Here at the OARDC, in our greenhouse trials we usually expose germinated wheat to 35-40F for about 6 weeks and that is usually more than sufficient for vernalization. According to the weather data from the OARDC Weather System, average temperatures during the months of December, January, and February were below 40F on several days. For instance, data from the Northwest weather station shows that average daily temperatures were below 40F on 20 out of 31 days in December, 27 out of 31 days in January and 25 out of 29 days in February (Figure 1). Data from other weather stations across the state show very similar patterns. Average daily temperatures below 40F means that nighttime temperatures were fairly low, even though we had several warm days this winter. THE WHEAT HAS VERNALIZED!
Producers are also concerned about the state of this year’s crop. While there are some very good looking fields out there, there are also some very poor-looking fields. Coming out of the winter, it is not uncommon for the wheat to look bad, especially those fields that were planted
Unless fields are in extremely bad shape, with poor stands and huge bare patches, it is still a bit too early to say which fields will do well this year. The next few weeks will be critical. As the wheat continues to green-up and grow, some tillering will still occur (especially in field which did not have a chance to tiller due to late planting). Before making a decision to destroy wheat fields to plant corn or soybean, walk field and count the number plants or tillers per foot of row to get an estimate of the stand count. Yield potential is reduced if tiller numbers fall below 25 per square foot after green up. Pick about 10 to 15 spots in the field and count the number of plants per foot of row. A stand with an average of about 12 plants per foot of row may still result in a good population of head-bearing tillers per acre. For those fields with tillers, 15 tillers per square foot is considered minimum for an economic crop. The number of tillers per square foot is equal to the number of tillers in 19.2 inches of 7 inch wide rows or 14.5 inches of 10 inch wide rows. Our studies have shown that under adequate weather conditions, tillering may compensate for relatively poor initial stand establishment.