Pennsylvania Smart Weed

Asked November 20, 2014, 11:32 AM EST

2 questions... 1st - When is the best time to apply Pre-Emergent weed control for PSW? It seems to me that it germinates later than Crabgrass so that at least one separate treatment applied later should be done. If so when? I've found that even if I get good control of Crabgrass using granular pre-emergent applications of Dimension, it doesn't do a thing for PSW. 2nd Q - Have there been any studies that conclusively prove whether "Liquid" or "Granular" form of Pre-Emergent weed control is more effective? And is pre-emergent weed control effectiveness diminished by using a combination product containing both fertilizer and Dimension rather than doing separate applications of each? Please let me know, Thanks, Steve

Centre County Pennsylvania

1 Response

Dear Steve,

First, I recommend reviewing the Penn State Publication: It will help you understand that not all weeds in turf can be chemically managed the same way.

You seem to have the control of crabgrass down, using the pre-emergent herbicide Dimension. Crabgrass is a summer annual grass, whereas Pennsylvania smartweed ( PSW) is a summer annual, broad-leaf weed. A grass is a monocot, different biologically from a broadleaf plant, which is a dicot. Most turf herbicides are formulated to control one or the other, but not both.

Broad-leaf weeds are usually controlled with selective post-emergence herbicides.

Penn State Turf Science recommends the following herbicides for broadleaved weeds ( Quote below from the following publication: (

"The most common broadleaf herbicides used in turf include 2,4-D, 2,4-DP (dichlorprop), MCPP (mecoprop), dicamba, clopyralid, and triclopyr. There are many different commercial formulations and mixtures of these compounds (see Table 3).

Application of a post-emergent herbicide should be made when the weed is actively growing, in our area about mid June.( see recommendations in the following publication:

The various publications I have cited have extensive information about other ways to control and manage weeds in turf, such as cultural and physical control. I encourage you to read them.

As for question number 2, I am a volunteer Master Gardener and have limited knowledge of turf research. You have very good questions...I will continue to spend more time researching these questions, and I have sent an email to an Extension Turf expert, and hope to hear back. When I do, I will make sure I share the information with you.

If you need more information, please email us at the local Extension Office, address below.