Happy April! The weather sure has been interesting! Since my last columns, UNL has come out with some altered recommendations for turf. So letting you know that according to Zac Reicher, Professor of Turfgrass Science, he is recommending an application at 50% of the high label rate rate of crabgrass control now in the form of dithiopyr and then plan on making a sequential application at 50% of the high label rate in early to mid-June with a dithiopyr product. Crabgrass is already emerging and this product helps with grass that’s already emerged as well as controlling crabgrass pre-emerge.
Also information from Zac: Preemergence herbicide applications for broadleaves can start anytime now and assuming typical weather, sequential applications should be planned for in June. Almost all of the current preemergence herbicides (dithiopyr, pendiamethalin, prodiamine) are available as fertilizer/herbicide combinations, but cool-season grasses need little nitrogen in the early spring regardless if it is in March this year or late April in most years. Therefore, it is important to use a herbicide/fertilizer combination with as little nitrogen as possible to avoid a large growth flush and maximize long-term health of the plant. The problem is finding a product with little or no N. If you find a selection of products, do some quick math and calculate which product delivers the lowest amount of N/1000 sq ft, preferably 0.50 to 0.75 lbs N/1000 sq ft. Additionally, slow release N will extend the window of N release and minimize the potential growth spike after application. Slow release sources include sulfur- or polymer-coated urea, urea formaldehyde, methylenediurea, dimethylenetriurea, or natural organic nitrogen. These are listed on the label as “slowly water soluble” or “water insoluble”. Pay special attention to N sources followed by an asterisk and be sure read and follow the entire label of any product you apply. With the unusual weather this year and the increased need for sequential applications, each application usually applies about 50 to 75% of that which would be applied when using a single application. Applying two applications at lower rates will also reduce the nitrogen applied in each application, which is beneficial at this time of year.
The following sources explain more about the math calculations:
• Update: Warm soils and forecast are revising recommendations for preemergence herbicides
• Lawn Care Pro Series: Crabgrass and Other Summer Annual Grasses
• Do it yourself: Choosing preemergence herbicides
• Crabgrass Control in Homelawns