Question
QUESTION: I live in Holiday, Fl. which is near Tampa.  I have 2.5-3 acres that is totally taken over by sandspurs.  I do have a horse, and have just divided my field so I can work with one area at a time.  I have been trying for 3 years to get rid of them - sprayed & killed the whole field, lymed, etc. I was told to have my soil tested for ph, but I do know that it is very low.  I used a granular lyme, but was also told to use the powder as it was more concentrated.

My question is,  what do I do first?  I am at my wits end!
I have spent so much time and effort & money just to have them come back worse.  I have even seeded with Arg. Bahia & Pen. Bahia  to no avail.

Please help.
         Cynthia

ANSWER:  The sandspur problem can be overcome but it will require a program of chemical spraying and mowing over a period of a year or more.
There are a few species of sandspur, one of which is a perennial but the others are annuals. They all reproduce by seed which are easily spread by people, pets and wind. Your plan to treat one area at a time means that there is the real possibility that reinfestation will occur.
But you can succeed. The first step is to prevent seeding.
Start by mowing the whole area. Use a catcher and dispose of the clippings either as bagged yard waste or in a tightly controlled composting pile. You do not want any seed escaping. If a turf or ground cover exists, give it every advantage to spread and grow (tall). You want to shade out any sandspur that wants to germinate. Mow the area every 7 to 10 days at a mowing height recommended for the turf/groundcover. Use a catcher because you are not going to give any growing sandspur even the slightest chance of seeding. Continue this regimented mowing program until you are sure that you have licked the problem.
Put down a good pre-emergent weedkiller as soon as possible after Valentine's Day next year and the year after. If permissible, use a liquid containing the active ingredient 'Pendimethalin'. Adjust the spraying equipment to ensure that the product gets through the groundcover. Use adequate water or apply after rain while the ground is still wet. You are trying to get the product over every square inch of ground.
Depending upon how your property is classified and the groundcover on it, you may be able to use a product containing the a.i. 'asulam' but the chemical is tightly controlled and might harm non target plants. Please check carefully or have a professional service do it.

---------- FOLLOW-UP ----------

QUESTION: Thank you for responding so fast.  I was afraid I would have to use a catcher.  My field has no turf or ground cover. Unfortunately, there is nothing but sandspurs.  Even the seed I put down did not take hold to help.  You mentioned nothing about sweetening the soil with lime.  I need to know How much lime to administer for about 3 acres when I am ready to put it down.  Also, is the pre-emergent "Pendimethalin" available to buy over the counter?
Can I spray the pre-emergent now, and then again later as you suggested?   Cynthia

Answer
I am not convinced that a lime application is going to help in the control of sandspur. Here's why.
The soils of the region have a high pH. It is possible that you are dealing with "fill" which can have a lower pH. To raise the pH value, one should have a soil test done in order to determine the lime requirement.
Some soils may be buffered i.e. they tend to resist attempts to alter their pH value.
In any case, the pH change takes some time to complete.
Limestone should be incorporated (tilled in) for best results.
I am not sure that soil pH is a limiting condition for sandspur growth.
Pendimethalin is the active ingredient in quite a few brands of pre-emergence weedkillers. Commercial outlets may sell the product in units- 2.5 gallons- which are too much for the average homeowner. The product stops root growth of the seedling so it is best applied when the conditions for germination prevail, usually in the spring.