Improper application timing in many cases is the leading cause of crabgrass breakthrough. Applied to late, crabgrass will germinate and begin growth before the herbicide is incorporated into the soil. Applications made to early will have a depleted residual before all weed’s seeds have germinated. This is also where slow release fertilizer could work against you as you may be feeding the weed’s seeds by accident. SumaGreen Turf, which can be applied with herbicides, can help reduce the outbreak of crabgrass by not giving it any room to grow by feeding grass right then and possible smothering out the crabgrass. SumaGreen with SumaGrow inside tends to keep grass all grasses (fescue, bermuda, kentucky bluegrass, St augustine, etc) thicker which makes things more difficult o the crabgrass. Crabgrass can be one of the most difficult weeds to control. There are many factors involved when attempting to control crabgrass by pre-emergent herbicides. These include herbicide selection, application rates, soils, cultural practices, environmental factors and most importantly timing.
When it comes to application timing there are a few theories that are used regarding application. These theories have some relevancy but with changing weather patterns a more precise determination may be necessary. Pre emergent timing is often based off of ornamental plant activity. These plants may include forsythia and lilac. It is often recommended to apply pre emergent herbicides when these plants begin to bloom. This theory is pretty accurate but does the germination of crabgrass really correlate with these plants?
A good example of this would be a short period of above normal temperatures, though misleading. These temperatures may cause ornamental plants to bloom but the soil temperatures may remain the same or increase only a little. Also, the ornamental plants may have certain stresses on them which may delay the blooming period. Another theory is based on the thickness of your lawn that can be used. This theory suggests a thin lawn should have herbicides applied a little early and later applications for thicker lawn in regards to forsythia blooming. As we have all seen crabgrass germinates and thrives in thick healthy turf as well as weak thin turf. For these reasons we must monitor soil temperatures when attempting to time herbicide applications.
By monitoring the soil temperature many turf maintenance companies can accurately plan for crabgrass germination. By most indications crabgrass will germinate when the soil temperatures reach 50o to 55o F for at least 3 days. This is also a good temperature (can apply SumaGreen Turf when temps are above 45o) to apply SumaGreen Turf. An example mentioned above, turf density can affect how the germination can continue to germinate into the summer. With inconsistency in weather patterns crabgrass is germinating earlier in certain areas. Unseasonably warm winter temperatures may cause earlier herbicide application resulting in subsequent applications thereafter. Several Universities base herbicide application timing by the temperatures of the soil.
To confidently make recommendations on application timing it is important to monitor the soil temperatures. The use of soil thermometers to record daily temperatures can provide accurate data for application timing. Soil temperatures should be monitored in the general area near client’s location and can be a valuable service for them as well as other clients in area. Accurate recommendations along with quality herbicides will provide us with the tools we need to insure good crabgrass control.
