Mid to late April has been one of the largest roller coasters ride in temperature that I can remember. On April 14 and 15 in Northwest Ohio the temperature record was broken with highs reaching the mid-80s Fahrenheit; then two days later, it was cold and snowing. Another three days later it was in the 80s again followed by rain and cold temperatures in the 40s.
This not only playing havoc with spring flowering trees and shrubs, but it is also playing havoc with turf grass. Most of the time, spring in Northwest Ohio is rather seasonable; however, this year, with temperatures that soared above normal, soil temperatures are warm enough to cause crabgrass to germinate.
According to the Ohio State University turf grass team, crabgrass germinates when the soil at approximately 2 inches deep reaches 54 degrees for seven consecutive days. A phenology indicator is when the Redbud tree starts to bloom, and the Forsythia’s yellow flowers begin to fade. Also, the weather station located at the Ohio Agricultural Research and Development Center in Hoytville recorded the average soil temperature from April 8-15 at above 54 degrees.
Another issue to consider is the best time to apply weed and feed products. This would be when the Dandelions enter the puff ball state, normally accruing two weeks after the Dandelions start to flower. This year it was April 15, placing the puff ball state around May 1.
What this all means is that it probably is too late to apply pre-emergent weed control products to the lawn for effective crabgrass weed control after April 15. If you applied the pre-emergent weed control in late March or the first couple weeks in April you should have effective crabgrass control.
The next issue to be considered is that our pre-emergent products are combined with some combination of turf grass fertilizer. Normally when pre-emergent products with fertilizer are applied there should be four to six weeks between the application of these products and weed and feed products for control of broadleaf weeds in the yard most notably dandelions. Remember weed and feed products also contain turfgrass fertilizer. This year, however, the time frame may only be two weeks between these two applications.
Applying weed and feed products to the yard at the two-week interval may cause burning of turf grass. Plant roots exert force to extract water from the soil, and excessive fertilization causes roots to shrivel, making it difficult for them to absorb water. The other issue is the compromised root system causes the roots to be more susceptible to disease primarily root rot. This will then cause the turf to become thin and more susceptible to insect activity.
Most post emergent turf grass weed control products, either as weed and feed or as a spray, have some type of combinations of active ingredients 2,4D, Mecoprop and Dicamba. These active ingredients are known as growth regulator chemistry products. The Environmental Protection Agency defines these products as Synthetic Auxin, Growth Regulators.
They are comprised of synthetic growth hormones that when applied to the foliage of dicots (broad leaf weeds) and then absorbed and transported through the vascular system will cause uncontrolled growth. This uncontrolled growth eventually controls the offending weed. That is why after applying these products you see twisting and curling of the dandelions.
To work around this dilemma, apply a postemergence spray as opposed to the weed and feed products. Post emergence sprays are normally mixed with water and applied with some type of sprayer. They are also available in ready to use products. Mid to late May you may apply a straight turf grass lawn fertilizer if the lawn warrants the additional fertilizer.
If you did not apply a pre-emergence product to your lawn, the application of the weed and feed products will not cause the over fertilization issue. Also, if the dandelions do not go into the puff ball state until mid or late May, then the applications of a weed and feed product should not cause an issue with your lawn after the pre-emergence product was applied.
Regardless of the product you choose as a pre-emergent or post emergent herbicide for the lawn, always remember to read the label for the correct rate, turfgrass tolerance, lawn reseeding and other specific instructions before applying any herbicide application to the lawn.
Have fun on the roller coaster of lawn care.