When spring arrives, crabgrass will come

It is hard to focus on the arrival of spring when we are expecting another piece of the polar vortex to drop down next week. Looks like the groundhog got it wrong this year. But as sure as the sun will rise spring will come; and so will crabgrass. Crabgrass is ubiquitous across turf types from home lawns to golf courses.

Crabgrass is so prevalent that it has has become synonymous with the suburban experience. Scholarly books like “Crabgrass Frontier” have been written to describe the history of the American suburban experience. Although there few redeeming characteristics of crabgrass, it has practical uses as a summer forage and hay crop. Actually the first cut of crabgrass sometimes yields more than 15% crude protein and 60% total digestible nutrients (Univ. of Florida Extension). 

So much for the societal and food benefits of crabgrass. Crabgrass is an annual summer weed. Germination starts in January or February in the southern United States and as temperatures warm crabgrass appears throughout the northern areas in spring. Since the life span of crabgrass is pretty short, its life’s race begins at germination followed by growth and development to where it produces seed just prior to death at the first fall frost. 

Spring is the time when we focus on controlling crabgrass. Crabgrass germination occurs in a short period in the spring when soil temperatures rise above 55 °F.  In the Midwest, this falls around April 15.  We often don’t see early-germinating crabgrass because it is killed by late-season frosts or freezes. Although in the Midwest, we may see crabgrass germination in April, we do not see surviving crabgrass until mid-May.   

A pre-emergent herbicide application should be timed when Forsythia come into full bloom. Forsythia are common shrubs; and from year to year Forsythia flowering is an effective time to apply a pre-emergent herbicide. Further south, dogwoods and rhododendrons are effective indicators of when to apply a pre-emergent herbicide.

Pre-emergent herbicides work within a finite period of time. The interval can range from weeks to several months. Given the finite control period, you could risk crabcrass control failure later in the year if you apply the pre-emergent too early.  As a general guide, the warmer the temperature and the higher the rainfall, the faster the product will degrade. Increasing the rate is one option to account for a rapid herbicide barrier breakdown.

When using a pre-emergent herbicide product, is important that it has a long-lasting active ingredient like prodiamine (Barricade^® 4FL or Barricade 65WG ). Barricade and a few other long lasting pre-emergent herbicides applied within recommended rates provide 90% crabgrass control for up to 16 weeks. 

Effective control of crabgrass over a period of time will help reduce crabgrass seasonally. Because, as the life of the crabgrass is approaching its end, what was once a single small germinating plant just a few months ago, is now capable of producing 150 to 700 tillers and 150,000 seeds (Digitaria sanguinalis ).