March Turf Tips

Jeffrey Derr and Adam Nichols

There are several considerations for turf management as we transition from winter into spring. These include weed control, fertilization and disease control.

Weed Control

March is the time to apply a preemergence herbicide for crabgrass control since this weed will start germinating when soil temperatures reach 50°F for several days in a row. It is hard to predict when that will occur, so it is best to treat in early March. There are only a few preemergence herbicides available for cool-season turf like tall fescue in home lawns, with the main ones being dithiopyr (Dimension, others), pendimethalin (Pendulum, Pre-M, others), and prodiamine (Barricade, Stonewall, others). These preemergence products prevent crabgrass germination for about three months or so, depending on weather conditions, application rate, and the product selected. Length of control is shorter under wet springs, which results in more rapid herbicide breakdown. Since crabgrass can germinate in Virginia from March through August, some applicators apply one half of the rate in March, with a second application in May or June to extend the length of crabgrass control.

These three active ingredients (dithiopyr, pendimethalin, prodiamine) are sold in sprayable as well as in granular form, sometimes on a fertilizer carrier. Keep in mind that spring is not the time to apply nitrogen as most, if not all of it, should be applied in fall to cool-season turf. So, we prefer products lacking nitrogen fertilizer when applying a granular product for crabgrass control. Also, it can be hard to apply the recommended rate of these herbicides without applying too much nitrogen if applied on a fertilizer granule. Keep in mind these three herbicides can only be applied to established turf (mowed 2 or 3 times) and cannot be applied at seeding. For commercial turf managers, preemergence chemicals used for crabgrass control in established turf also include benefin (Balan), benefin + trifluralin (Team), and bensulide (Bensumec).

There are two herbicides that can be applied at seeding or to young stands of cool-season turf – mesotrione (Tenacity) and quinclorac (Drive). These two herbicides will provide preemergence and postemergence control of crabgrass as well as control of certain broadleaf weeds. Mesotrione will also control yellow nutsedge, a perennial weed that will begin emerging in spring. Mesotrione is also available on a granular carrier for cool-season turf use.

Both mesotrione and quinclorac are relatively short-lived in soil compared to dithiopyr, pendimethalin, or prodiamine so they do not provide the length of control seen with these three herbicides. Quinclorac can be applied to bermudagrass and zoysiagrass turf but not to St Augustinegrass. Mesotrione is predominantly used in cool-season turfgrasses.

In established warm-season turf (bermudagrass, zoysia, St. Augustine), dithiopyr, pendimethalin, or prodiamine can be applied for crabgrass control, as well as indaziflam (Specticle). If one suspects winter damage that could result in bare patches, though, you may want to hold off on an application as these herbicides are root-inhibitors, thus inhibiting the pegging down of stolons, which is needed to fill in bare spots. For golf course and athletic field managers, oxadiazon

(Ronstar Flo) can be used on bermudagrass and zoysia while they are still dormant. An advantage of oxadiazon is that it is not a root inhibitor.

Control of emerged annual bluegrass is a challenge for commercial turf managers and is very difficult for homeowners with cool-season lawns. This weed is very apparent in lawns when the whitish seedheads appear in spring. One option is home lawns will be to live with annual bluegrass for now, as it will die off in lawns with the onset of hot dry weather. Commercial applicators have selective options for removing annual bluegrass from warm-season turf.

For control of emerged winter broadleaf weeds, one can apply a three-way or 4-way product (containing 2,4-D, dicamba, MCPP, and/or triclopyr) in tall fescue. Avoid applications of triclopyr to bermudagrass turf. Pick a warm, sunny day with air temperatures over 50 F with light winds. Best to treat winter broadleaf weeds like common chickweed, lawn burweed, and henbit when they are small and actively growing. These herbicides are both leaf and root absorbed by weeds. Granular formulations are available for some of the broadleaf herbicides but in our trials sprayed application work better. If applying a granular form, treat in the morning when there is dew on the weed leaves. The granules will stick, releasing the herbicide, providing some leaf uptake. Metsulfuron-methyl is a great option for warm-season turfgrasses for winter broadleaf control. Commercial applicators have 3-way products like Celsius and Celsius Xtra in a range of warm-season turf species, and Tribute Total in bermuda and zoysia for broadleaf control.

Fertilization

Fertilize cool-season turfgrasses lightly (0.5 pounds nitrogen per thousand square feet) in March or not at all. In warm-season turf, wait on fertilization until the turf has greened-up and is actively growing to prevent excessive early growth that can lead to problems later in the year.

Diseases

Scout for spring dead spot in warm-season grasses as they begin to green up. Look for circular patches not greening up like the rest of the lawn. Take pictures or make note of where these patches are, as they will need to be treated in the fall when the fungus is active. A little extra fertility (0.2lbs N/1000ft2) during your normal fertilizations will help to fill in those areas during the growing season. If the trend of regular precipitation with warm weather continues, conditions for large patch on warm-season turfgrasses are going to be present. Look for thinning patches with an orange, yellow, or purplish ring. Applications of the fungicide azoxystrobin (Heritage, Heritage G, others) when the rings are apparent will control the fungus causing these patches. Watering in the applications following treatment is necessary to move the fungicide to the fungus.