Current wheat situation in the Rolling Plains of Texas
By Todd Baughman
Texas Agrilife Extension Agronomist
Just like the rest of 2009 the wheat planting season has been anything but dull. While many producers have the best stands and most productive forage growth they have seen in many years other producers are still trying to get this crop planted. There have been several early issues with this year's wheat crop including armyworms and grubworms. Now producers are starting to see issues with fertilizer management, leaf rust, and weed control.
Several fields are exhibiting severe yellowing this year. Many of the fields that I have looked at are the result of nitrogen deficiency. The abundant rainfall in combination with cloudy weather has exasperated this problem in many fields. Nitrogen deficiency will show up in the older leaves first exhibiting a general yellowing of the bottom plants. The newest leaves will be green to pale green. Tillering along with plant growth can also be reduced in these situations.
While it is a little early for normal top dress applications, it is better to be too early rather than too late. I think that one of the common mistakes that are made is getting our top-dress nitrogen out too late to benefit us from a yield standpoint. Concern over leaching of nitrogen as we have already observed in many fields should always be considered to maximize nitrogen efficiency and economic benefit. However, grain yield will not be increased if nitrogen is applied after jointing. Depending on the year and variety, jointing has been observed as early as mid-February in the Northern Rolling Plains of Texas. Also we are entering the historically dry period of the growing season; therefore loss of nitrogen to leaching most likely will be minimized. I have often recommended that producers start applying nitrogen sometime in December to insure that they can get all of their acres covered before mid -February. This also increases the likelihood that the fertilizer will get a rain to help make it available to the wheat plant. Some producers may be concerned about loss of urea forms of nitrogen to volatilization. Loss of urea nitrogen through volatilization should be minimal at this time of year especially if applied to a dry soil surface. Producer planning to graze and harvest wheat should also consider the amount of nitrogen that the cattle will be removing from the field (0.45 lb-nitrogen/animal/day). This nitrogen will need to be replaced to adequately supply the subsequent grain crop. For example if your stocking rate is 1 animal per 2 acres and you will stock for 100 days, than you need to apply 23 pounds of actual nitrogen/acre (50 pounds of urea) to replace the loss due to grazing.
I have also received some wheat plant samples that are exhibiting leaf rust. While this is often a concern when this occurs, there is nothing that can be done economically to control rust at this time of the year. In fact colder temperatures should eliminate the spread of this disease further. We also lose many of these older leaves during the winter month due to freezing temperatures as well. There has been some push in recent years to apply fungicides to improve plant health. I am unaware of any university data in Texas to indicate that this is of economic value. Therefore, I would be hesitant to make these types of prophylactic treatments. In addition, if we have heavy leaf rust in the spring than a second fungicide treatment will be required to control this spring disease problem.
Now is also the time to apply many of your herbicides for grass control. We have consistently seen better control of grassy weeds (bromes, wild oat, ryegrass) and higher wheat yields where we have applied our herbicides in the fall rather than waiting for a spring application. Many fields now have these grassy weeds in the 2 to 3 leaf stage which is the ideal time to control these problem grasses. Also with the abundant moisture these weeds are actively growing and should be much easier controlled than in recent years. Tillered bromes and ryegrass can be especially difficult to control and often time's producers will be disappointed with later applications.
Finally, we are starting to see some greenbugs and bird-cherry-oat aphids in small numbers. None of the fields that I have looked at have numbers above threshold, but fields should continue to be scouted to make sure that these pests do not increase to levels that warrant spraying.