Question
Hi,

I'm really having a rough time with clovers and crabgrass at the moment.  Me and my father in law just planted new grass (combination of different types of grass, mostly bluegrass) and it hasn't even been a year and now there's so many clovers and crabgrass that's growing on it.  So now I have combination of grass and weed all over.  It's pretty hot here, I live in PA and the temp. right now is around 90's during the day.  I bought a weed killer spray that fits onto a hose and I'm planning on using towards the evening time (after it rains, since that's what the directions says).  Do you recommend using this since I'm really desperate to kill those nasty weeds b/f it takes over my new grass.  If not what do you recommend I do?  And finally what should I do in the future to prevent this happening?

Thank you so much
day  

Answer
Good morning Day:
Clover and crabgrass must be treated differently in order to eradicate them.
Clover is a broad leaf perennial (meaning it comes up year after year) and crabgrass is an annual (meaning it will grow set seed and die within a twelve month period).

Managing Clover: There are a number of broadleaf weed herbicides (weed killers) available for use on lawns to control clover. Only apply to actively growing clover. Choices found in garden centers typically include 2,4-D (2,4-dichlorophenoxyacetic acid); mecoprop or MCPP (2-(2-methyl-4-chlorophenoxy) propionic acid); or dicamba (3,6-dichloro-o-anisic acid); with two and three-way combinations available.
Thoroughly read, understand, and follow all information on herbicide labels. There are general guidelines for using broadleaf herbicides on lawns. Avoid windy days, as these materials can damage many landscape and garden plants if they drift. Also avoid hot days (over 85 degrees F). It's best to have adequate soil moisture, but no rain for 24 hours after application. Don't mow for few days before and after application. Consider spot treating rather than broadcasting broadleaf herbicide over the entire area. Use caution on newly seeded areas; wait 4 mowings before treating a newly seeded lawn and wait 30 days before seeding an area treated with broadleaf herbicides. Refer to the label regarding any potential hazards when used on lawns over the root zone of trees (such as with dicamba).
Early to mid fall can be a good time to control clover. Spring and early summer applications may not provide as good of control as fall. In addition, warmer temperatures increase the chance of lawn injury. Regardless the time of the year, clover needs to be actively growing for herbicides to work.
My suggestion would be to begin in early September using broadleaf herbicides to eliminate the clover. If you can spot treat that would be better and more economical. Wait thirty days and begin to overseed the lawn in the bare areas.

Crabgrass and its Control: Crabgrass is usually lighter green in color, has wider leaf blades and a more spreading growth habit than  cool season cultured lawn grasses. Both preventive and control programs must be implemented to ensure crabgrass does not establish itself in the lawn. Crabgrass can be prevented to a large degree by maintaining a dense, healthy stand of grass. A high quality lawn will  shade the soil surface and discourage crabgrass germination along with the seedlings of other annual grass weeds. Therefore, it is important to select the proper species and cultivars of turfgrass for the site to be established. Proper mowing (height of two and a half to three inches (6.35 to 7.62 cm) removing no more than one third of the grass blade at each mowing), fertilizer and water usage are the most important factors in maintaining turfgrass density.
Crabgrass seeds in the soil begin to germinate in the spring once the soil temperatures warm to nighttime minimum temperatures of 52 to 54 degrees F (11.1 to 12.2 C) for at least 5 consecutive nights under conditions of moist soils (Although not 100% reliable, it is about the time the Forsythia begin to bloom).
The best way to stop crabgrass and other annual grass weeds from establishing themselves in the lawn is through the use of preemergent herbicides. These are products that stop the development of unwanted weed plants before they emerge from the soil. These herbicides control annual grass weeds by inhibiting cell division in the young root system. Lawns with thin stands of grass may require yearly applications of a preemergent herbicide. Scotts Halts is a pre-emergent herbicide. Apply Scotts Halts or Scotts Turf Builder with Halts Crabgrass Preventer before your daytime temperatures are consistently above 65?F.  A pre-emergent like Scotts Halts will create a barrier that will prevent crabgrass seeds from germinating.
Preemergent herbicides are generally only effective if applied before the annual crabgrass weeds germinate. Therefore, early spring applications are essential if satisfactory crabgrass control is to be achieved.
As with any herbicide, always read and follow the package directions.

1. This fall control the clover with a broad leaf herbicide.
2. Early next spring control the crabgrass with a preemergent herbicide.
3. Keep your lawn as dense and thick as possible to prevent the clover and crabgrass from returning in future years.
4. Do not use the weed killer you have unless it fits into one of  the categories above and only use it at the time it should be used. If the weed killer you have is a non-selective killer ( meaning it kills all vegetation such as Round-up does ) use it only in the areas that you want all of the vegetation to be killed off.

Have a good lawn:
Floyd McMahon