Adam Thoms
Assistant Professor
Commercial Turfgrass
Iowa State University
Nick Christians
University Professor
Turfgrass Management
Iowa State University
The weather will soon be nice on a daily basis and it will be that time of year to begin working on your yard again. Spring is a busy time of the year for many people and tops on that list of activities is mowing. A cool-season turfgrass such as Kentucky bluegrass, perennial ryegrass, or tall fescue will have the greatest growth during the months of March to May. We always suggest never removing more than 1/3 of the leaf tissue in one mowing, so that means if you have a 2.5” tall yard you should mow every time the yard every time the grass grows to 3.25” tall. Also, try to keep your mower blade sharp so you get a better cut, and if you are mulching clippings then a sharp blade will do a better job than a dull blade. Additionally, to avoid compacting the same areas of your yard from the weight of the tires, always try to alternate mowing patterns.
Spring is also the time of year to prevent many annoying weeds from appearing. Preemergennce herbicides should be applied in the spring to prevent weeds annual weeds such as crabgrass, goosegrass, prostrate spurge, and black medic from germinating. Theses weeds are all summer annual weeds, which means their life cycle germinates in the spring and they will die with the frost in the fall. These weeds can easily be prevented from ever showing up in a yard with a well-timed preemergence herbicide application. Most preemergence applications are applied around the timing of the germination of crabgrass. Germination of crabgrass happens when the soil temperatures at four inches stay above 55 degrees Fahrenheit for three days straight. This typically happens in Iowa in early to mid-April. Another good indicator is when the forsythia bush flowers, which can tell you those conditions, are correct for crabgrass germination and the preemergence herbicide needs to go out soon.
Many different preemergence herbicides exist, but the following have demonstrated the highest control on crabgrass in various University trials: in cool-season grasses (Kentucky bluegrass, tall fescue, perennial ryegrass, and fine fescues): dimethenamid + pendimethalin (FreeHand), dithiopyr (Dimension), pendimethalin (Pendulum), prodiamine (Barricade), and prodiamine + quinclorac (Cavalcade PQ). For warm-season grasses (bermudagrass and zoysiagrass) benefin + oryzalin (Surflan XL) or simazine (Princep) work well but will kill cool-season grasses if your yard has those in them. All of these herbicides should be applied according to the label to ensure proper rates are applied to the yards. In addition, many of these preemergence herbicides need to be irrigated or watered in to help put the herbicide into a position to prevent germination.
Preemergence herbicides also come with fertilizers, and can be applied with a spring granular fertility application. These are available at just about any place that fertilizer is sold. The product should contain instructions on rates. If applying a fertility treatment alone, spring applications of ½ to ¾ of a pound of nitrogen per 1000 square feet are the suggested rate to use. Typically the turfgrass plant needs only nitrogen this time of year so avoid and fertility containing phosphorous, as it is unnecessary. This application should go out in April. Again consult the packaging on how to best apply the fertility and if it needs to be watered in or not. Corn gluten meal offers an alternative to traditional pesticides as a way to prevent crabgrass germination from a natural product, as well as some fertility with the application of corn gluten meal.
Early success in the growing season are timing of a preemergence application, and staying on top of the mowing. If these two steps are met, your yard will have a great start to this upcoming growing season. Good luck and enjoy your yard!
A general rule of thumb is to never to remove more than 1/3 of the leaf tissue with one mowing. (Photo courtesy of Home Depot)
Smooth crabgrass is a common weed that can be prevented with a well-timed preemergence application in mid-April.
Corn gluten meal (plots shown above without weeds) has the ability to naturally prevent weeds, as well as offer some nitrogen fertilizer for the turfgrass.