Bob Mugaas, University of Minnesota Extension Educator
This spring began with the very early snowmelt in mid-March that left in its wake one of the highest incidences of snow mold on many residential and commercial lawns in recent memory. Much of that could be attributed to the very wet snow that fell around Christmas time on unfrozen or barely frozen lawn surfaces. The high moisture content of the snow combined with the mostly unfrozen lawn conditions provided nearly ideal conditions for the snow mold fungi to grow and thrive. In addition, that snow cover was maintained throughout the winter months providing a very long period of total snow cover and good conditions for snow mold growth. However, as is often the case, even with as much snowmold as was evident this spring, most lawns will have recovered on their own and returned to healthy growth and good green color by early May. The severity of snowmold on some lawns did result in the need for some reseeding to fill in thin areas resulting from that injury. Photos 1 and 2 show a commercial site affected with snowmold earlier this spring that has now grown out of those symptoms without the need for reseeding or other repair. A light application of fertilizer and some watering as needed this spring will help further restore and invigorate those areas.
Photos 1 and 2: Snowmold infestation and turf recovery. Bob Mugaas
Meadow vole damage and recovery
That continuous snow cover over winter also created a good habitat for meadow voles to invade our lawns resulting in slight to extensive surface tunneling in lawns, especially those close to unmaintained grassy areas such as next to vacant lots, prairie edges or other nearby grassy areas where voles retreat to after the snow melts. See Photo 3 for typical injury associated with meadow voles in lawns. For the most part, these critters tunnel along the surface eating a variety of vegetative material including the grass. One may observe tunnels traveling over and through the lawn surface. It is often common to see loose grass 'clippings' mounded up over the tunnels creating a slightly raised appearance to the seemingly random tunnel patterns. While the grass foliage is eaten by the voles, the grass plant crowns (growing points) often escape being eaten and are responsible for the regeneration of new leaves and stems that ultimately fill in the tunneled areas. Since the plant is having to start from scratch in its spring regrowth, the tunneled areas frequently lag behind the rest of the lawn area in spring recovery but do ultimately catch up to the rest of lawn in terms of height and density. See Photo 4 of new grass shoots coming in a surface tunnel caused by voles. Again, a light application of fertilizer and water as needed will help restore the growth and vigor of these areas. In nearly all cases, recovery occurs without the need for reseeding or replacing the damaged areas.
Photos 3 and 4: Vole damage and indications of turf recovery. Bob Mugaas.
Early season mowing
Photo 5: Turfgrass color variances associated with differing heights of growth prior to first mowing. Bob Mugaas.
By the writing of this article most of us have had to mow our lawns at least once or even twice already this season. In some cases, there appears to be areas of yellow or lighter green grass following mowing, especially the very first mowing of the year. See Photo 5. With the typical unevenness of that very early spring growth prior to the first mowing, it's not uncommon to see lighter areas intermingled with normal darker green areas. The lighter areas are usually associated with grass that had grown vigorously early and was taller than much of the surrounding grass. Hence, when its mowed at regular mowing heights, the grass ends up being cut back into lower blade and sheath tissue which is often lighter green to almost yellow due to the lack of chlorophyll. Cutting into that area of the plant is very stressful for the grass plant as it eliminates much of the leaf surface responsible for making the plant's food and can slow or even stop root growth temporarily until the plant can regrow sufficient tissue to resume normal growth. Grass that has not grown so vigorously or just grown more slowly ends up not being cut back so severely and hence retains its normal medium to dark green color and relatively uninterrupted growth. In most instances these early growth differences even out by the third or fourth mowing. Mowing higher rather than shorter, especially for the first cutting or two may help avoid cutting those taller areas too short initially while still being fine for the rest of the lawn area. This will also avoid the generation of excessively long and large amounts of clippings as also seen in Photo 5. When this quantity of clippings is generated from mowing, they should be removed or at least more uniformly dispersed over the lawn surface so as not to remain in large clumps, which can interfere with the healthy growth of grass plants underneath the clumps.
Crabgrass arrives early too!
Photo 6: Crabgrass seedlings visible April 20, 2010 near a curbline in North St. Paul, MN. Bob Mugaas.
By the middle of April, crabgrass seedlings were already emerging in what are termed heat sink areas. These are areas that warm more quickly during the early part of the growing season and hence growth in these areas is usually well ahead of the majority of the main lawn areas. Examples include areas next to sidewalks, driveways, curbs, narrow boulevards, unprotected bare soil areas and the like. Usually the warming effect extends less than two feet from these paved areas back into the main lawn. Other exposed soil areas, especially those with south and west exposures generally warm more quickly than those covered with some form or vegetation or mulch. In addition, sandy soils tend to warm more quickly than heavier clay soils. Since drier soils are warmer soils compared to moist soils, the lack of early spring precipitation over much of the area caused soils to dry more quickly with the above average temperatures and sunlight. This also contributed to warmer than usual soils that in turn saw some of the earliest crabgrass germination in quite some time in the Twin Cities area. See Photo 6 of newly emerged crabgrass seedlings near a curb area.
Once crabgrass has emerged from the ground and is visible, it is too late to apply preemergence herbicides for crabgrass control. These products act on the newly germinating crabgrass seedlings prior to their emergence from the ground. In this case, one will need to use products containing the active ingredients quinclorac or fenoxaprop-p-ethyl. Both of these are available through commercial lawn care firms. Quinclorac can also be found in some homeowner lawn weed control formulations. Check the product label for its list of active ingredients. For very small infestations, it may be practical to manually remove them. In either case, treating the seedlings while they are still small and tender is much more effective than when plants are larger and more mature.
Just because you may have already observed some crabgrass germination in those heat sink areas, it doesn't necessarily mean you shouldn't apply a preemergent crabgrass control product to the rest of the lawn area if it's needed. However, it should be applied very soon, like within the first week or so of May, depending on your specific site conditions. Soil temperatures in the main lawn areas will lag behind those in heat sink areas, but they do catch up fairly quickly as temperatures continue to warm, especially overnight temperatures. Even though crabgrass germinates earlier in those warmer soils, it doesn't germinate all at once. Hence, an application of preemergence herbicide in those heat sink areas can help prevent later germinating seeds from getting started but won't kill those already sprouted.
Easy-does-it for spring fertilizing
Usually about the time the lawn is greening up and in need of its first mowing is a good time to consider applying a spring application of lawn fertilizer. For many of us, that time may have already passed. However, that doesn't mean it's too late to fertilize the lawn. In fact, sometime within the first three to four mowings of the year is still a good time to fertilize. Regardless of the situation, it's wise to not be aggressively fertilizing your lawn in the spring, especially with large amounts of nitrogen. That's best left for the late summer period.
In the spring, there is a natural, normal flush of growth by our grass plants. It begins with active root growth followed by rapid shoot growth. As shoot growth begins to accelerate, root growth tends to slow down. If too much nitrogen fertilizer is applied, shoot growth will be even more rapid resulting in a more frequent need for mowing but is also unhealthier for the grass plant. Excessive growth stimulated by too much nitrogen creates a more succulent plant that in turn requires greater amounts of moisture to sustain its growth. That increased succulence is more vulnerable to injury from summertime stresses and can be more prone to certain disease and insect infestation. The bottom line is, use moderate to low amounts of N in the spring to maintain balanced, but healthy, turfgrass growth. For more information on lawn fertilizing, see the publication Fertilizing Lawns (http://www.extension.umn.edu/distribution/horticulture/DG3338.html).
Water if needed to support early season growth
While we often don't think of watering our lawns much before sometime in May, this year, due to the drier than normal conditions and earlier than normal vigorous grass growth, watering may be needed to sustain healthy, early season turfgrass growth. Early spring is the time of year when grass plants are actively growing new and deeper roots. That allows the plant to mine water and nutrient reserves from a larger soil volume, which, in turn, sustains the continued healthy growth of new shoots and roots. At this time of year watering deeply but infrequently is a good practice. Thus, an inch of water per week (or longer interval depending on weather conditions) including any rainfall that occurs will help keep soils moist and promote healthy root growth. If you have heavier, more clay-like soils where it takes a long time for water to infiltrate into the soil, it's usually best to apply a couple of lighter applications allowing time in between for the water to soak into the soil. Likewise, on lighter sandy soils that drain more rapidly, infiltration is not so much a problem as is the likelihood of water moving too quickly down through the soil and beyond the grass plant's roots and therefore not benefiting the grass plant. Hence, a split application of water will also be more beneficial for the grass on sandy soils.
While spring has indeed arrived ahead of most years, the tasks of lawn care remain much the same except that they need to be carried out earlier than many of us are used to. Paying attention to prevailing weather conditions and observing what's happening in your lawn are very valuable aids when it comes to understanding what's going on and what to do next.