What is recommended for pre-emergent use for grass burr control. I have heard of products called Halt and Dimension. Are these acceptable? I need to apply in the next few weeks in East Texas. this is in a small (3/4) acre family cemetery that I am gradually getting Centipede grass established. Half is currently covered with Centipede. I do have a watering system and am applying fertilizer once per year. The area of max grassburrs, is where the grass is not established yet, but is creeping into, and is in total sun.
Smith County Texas
Hi, both products have grassburs (or sandburs/sandspurs) on the label, and will give good pre-emergent control. You should be aware that they do have a downside - they are absorbed in the root and shoot, and inhibit mitosis. What that means is that they prevent the root tips, where cell division takes place, from growing, which is how they kill germinating seed. They also do the same as new growth from your centipede and other turfgrasses begin to spread and peg down new roots in the spring.
Like you said, the grassburs will be worse in thin areas where there is poor cover from the turfgrass. Applying these products (or others with the same mode of action - see below) can inhibit the spreading centipede from pegging roots into the soil. We often see clubbing on the new root tips where they have touched the chemical barrier that is laid down to prevent weed seed establishment. So, you just need to be aware of this double-edged sword. By all means, carefully follow application rate of whatever product you apply. Remember, to be effective, all products must be irrigated into the soil shortly after application. Lack of watering in is one of the main reasons for lack of control.
The active ingredient in Halts is pendimethalin; dithiopyr is the active ingredient in Dimension. Two other preemergent herbicides for grassburs are oryzalin and benefin. Like the first 2 they also will slow down the turfgrass growth in spring.
Application should be in mid-March to early April. Centipede will start growing in mid-late April, and you might see yellowing early on with the use of the above products. Grassburs can continue to germinate until late summer / early fall, and preemergent herbicides applied in spring will have broken down and not be effect at that time of year (unless another application is made in early to mid-summer).
There is another option for post-emergent control of grassburs in Centipede, and that is Vantage, the active ingredient is sethoxydim. This is applied to young sandbur seedlings after germination. (Probably not too effective on older, established grassburs that have started blooming and setting seed). It is only labeled for use on Centipede for this use.