Early Crabgrass Germination ?

With the warm weather of the last few weeks, forsythia has bloomed in many areas through the Midwestern United States.  Does this mean crabbrass is germinating?  Although forsythia bloom is a phenological indicator, soil temperatures remain much too cold for crabgrass germination.  Most likely too, it pre-emergent herbicides go down too early the likelihood of season long control is low.  Below are some additional keys to predicting crabgrass control.

Effectiveness of many preemergent herbicides for crabgrass control is determined by timing. Although, many factors including soil moisture, turf density are involved temperature is a major key. The ideal situation is to apply a preemergent herbicide just prior to crabgrass germination. At this point in time your herbicide will prevent germination and last longer through the growing season. Plant phenological keys are often used to time crabgrass herbicide applications. The Eastern redbud tree is an example of a phenological timing event.    As the redbud tree approaches full bloom, crabgrass germinates. Obviously a draw back to this plant is that redbuds are not found in every landscape. The most common plant used is forsythia. When forsythia bloom apply crabgrass will start germinating. The problem with timing based on flowering is the wide variation in air temperature that can occur. For example, in some years forsythias may bloom multiple times based on the spring weather.


Soil temperatures are often utilized for determining crabgrass germination. When soil temperatures fall within the range of 52 to 58 F or 55 F at the 4-inch depth, crabgrass will begin germinating. Purchasing a soil temperature thermometer is a good investment if predicting crabgrass germination is important to you. In areas where the turf is thin, soil temperatures will warm quicker than soils under a dense turf.

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