Weed Control with Pre-emergence Herbicides

With my hectic schedule these past couple weeks, I have done little more for my grass than traipse across the same few blades everyday to get to and from my car.  Feeling guilty about neglecting my lawn, I made it a priority to mow this weekend.  As I was walking across my lawn to hop on my tractor, I noticed my feet were covered in little green seeds.  I began to look for the weed that left these seeds on my feet, and noticed a patch of green where it had once been brown all summer from the previous year’s chinch bug invasion.  After a little research, I came to the conclusion that this is an old world diamond weed.  This type of weed is a warm season annual that reproduces by seed.  With this information, I began wondering why this weed is growing in my yard.  I pay a service company to control the weeds in my lawn and I have not had any problems with weeds this season.   It is obvious that a pre-emergent herbicide was applied to my lawn this spring so why am I getting warm season weeds now?  I began researching the longevity of pre-emergent herbicides.  Longevity differs with each product, but one factor remains the same for all and that is environment.  The excessive rain this season is giving us homeowners one more reason to pull out our hair in frustration.  Excessive rain breaks down the herbicide leaving your grass susceptible to weeds late in the season.

 Pre-emergent herbicides can be applied for warm season and cold season weeds.  It has to be applied before the weed germinates, and acts as a barrier that does not allow weeds to grow once germinated.  For some grasses, pre-emergent herbicides can only be applied when day time temperatures do not exceed 85 degrees.  This limits the dates a pre-emergent herbicide can be applied.  Since Florida’s warm season lasts for an extended period of time, it is quite possible that a pre-emergent herbicide will break down every year before the cold season arrives.  Keeping your lawn healthy by fertilizing at the proper rate, mowing your lawn at the proper height (not too short) and watering your grass when it is shows signs of wilting can reduce the emergence of weeds.   

I had planned to just wait for the grass fill back in over time where the chinch bugs had killed the grass last year. The area did fill back in, just not with grass.  I now need to spray the area with an herbicide to kill the weeds then resod.  I should have resodded the area this spring allowing the grass to become well established over the summer.  This would have minimized the chance for weeds to emerge.   Lesson learned.      

References:

Westmiller, R. (2011, February 7). Pre-Emergent Controls: Win the War on Weeds, Irrigation and Green Industry. Retrieved from: http://www.igin.com/article-1940-pre_emergent_control.html

Old world diamond weed from my yard.