According to the Climate Prediction Center of the National Weather Service (NWS), most of the Coastal Bend of Texas is now classified as in an exceptional drought, the greatest intensity level that is measured. On the other hand NWS, has also released their Drought Outlook through July 2009, and it suggests that drought conditions are likely to improve during this time period. However, when you are currently at the driest level measured, it does not take much to improve in the moisture department, and this past weekend was sure a disappointment in the rainfall department. Oh well, at least our friends to the north of us got some good rains.
Well, if you are in South Texas and look at your pastures now and find something green out there, there is a good chance it might just happen to be a mesquite tree. And when that is the only plant out there on the range that is green, it sure gets one to thinking that controlling this pesky brush plant should be considered, as it is using very valuable soil moisture that otherwise more desirable plants could have used in this drought.
Let's consider some factors about the mesquite plant. Yes, the mesquite causes damage to the range land by crowding out native bunchgrasses which provide forage for livestock, habitat for quail and ground-nesting birds, and erosion control and by transpiring vast amounts of water.
Mesquite have both a deep taproot to reach underground moisture and an advantageous root system just below the soil surface to capture moisture from even the smallest rainfalls. Once a mesquite seed germinates, it quickly roots down to capture underground moisture, so yes, it can survive a drought.
Since water is the main issue here, just how much water does a mesquite plant use, you may ask? According to some research by R. James Ansley, professor, Texas Agricultural Experiment Station, Vernon, a typical mesquite leaf transpiration rate on a sunny midsummer day is about .06 gallons of water per square foot of leaf area per day. A typical 12-foot, multi-stemmed mesquite tree in a dense stand has about 130 square feet of leaf area. Multiplying these two values gives us a transpiration rate of about eight gallons per tree per day. So, if we had 200 average sized mesquite plants per acre, they could be using 1,600 gallons of water per acre per day or 48,000 gallons of water, per acre per month. Folks, that is a lot of water that could have kept those grasses growing longer in an extended drought.
With that knowledge of mesquite's water-loving characteristics, you now might be more inclined to consider controlling, or should I say managing, your mesquite plants in your pastures. If we want to control mesquite with herbicides using foliar applications, there are some factors that we must consider. Timing, picking the right year, and the right day to spray, are some of the most important factors to achieving acceptable control, especially when we foliar spray mesquite.
If you marked your calendar when mesquite broke bud this year, then count forward 45 days, this will be the approximate beginning of your spray window. Not only do we need to be 45 days past mesquite bud break before we spray, but also required are soil temperatures 75 degrees or warmer at one-foot depth. The warmer the better. If you break bud in mid-March, your spray season will begin around the first week of May. Do not spray if you have more than 25 percent damages to the mesquite foliage from insect, hail or disease (rust. This is one of the reasons it is best to spray as early as possible, before these conditions occur.
So you say, well, what about the current drought? As long as the mesquite plant has good foliage, not stressed from the drought, then spray. Should rains begin in May, then conditions could change. Do not spray if soil temperatures fall below 75 degrees, at one-foot depth. This can occur, especially in the beginning of the spray season, if you receive cooling rainfall.
A significant rainfall event can also stimulate new growth and this new growth is easily spotted on the mesquite twig tips by its light green color. Do not spray under these conditions.
If you have questions about brush control in South Texas, mark your calendar for Thursday, May 7, 2009. A Brush Buster Seminar will be held at the Texas AgriLife Research & Extension Center on Hwy. 44 just west of the Corpus Christi Airport beginning at 6:45 a.m. and conclude by 9 p.m. This will be an in-depth seminar on brush control.
Jeffrey Stapper is the Agricultural and Natural Resources Agent for Nueces County. Readers may contact him at 767-5217.