Moles, Voles, Fido and Moss… Lawn Pests in Cold Weather.

In the winter months, there are pests of turfgrass that because of the dormancy of the lawns become far more noticeable to us.

Moles

Moles are small mammals, averaging between four and eight inches in length, that live almost their entire lives beneath the ground in vast networks of tunnels and chambers. They do not feed on plant material, rather their diet consists of earthworms, grubs and the like. Moles cause indirect damage to turfgrass by tunneling close to the surface in the late winter months looking for mates, and by building molehills, which are access points to their underground network.

Moles are present at all times of the year in just about all of Lawn Dawg’s service area. They prefer soils that are light in nature, like sand and loam, and are less populous in soils that are heavy, like clay, and are stony.

Molehills are not particularly common in home lawns, though not unheard of; rather it is their burrowing during the cold months of the season that we notice. During the dormant months of the season, the turfgrass is not growing and will not repair the damage as it occurs. During the growing months, the rate of recovery of the turfgrass exceeds the rate of damage – thus it is largely invisible.

Voles

I’m as guilty as the next guy for throwing moles and voles into the same category of pests, but they are quite different. First, voles, or meadow mice, are not related at all to moles and are about half the size. They are not insectivores like moles, rather they are herbivores, feeding upon and damaging plants such as lawns and ornamentals. They are similar in their habitat and their damage patterns, however the vole spends much more time above ground than does the mole.

Most of the damage that we attribute to moles is actually caused by voles – the tunneling through the thatch layer of lawns that becomes obvious upon the melting of snow cover.

Homeowners will often ask if there are any control measures that can be taken to control moles and voles. There are traps and chemicals that can be used, but to be honest, the sheer number of these animals that live just at the periphery of our landscapes and the relatively minor and recoverable nature of the damage they cause makes control futile and unnecessary. Mole hills never survive the next pass of the lawnmower and vole tunnels vanish quickly even without intervention as soon as decent growing conditions return.

Dogs

While we’re discussing mammals that cause winter damage to turfgrass, we can’t leave out the effects of Man’s Best Friend. Dog urine, specifically from females due to the anatomical differences, shall we say, from that of the male, will cause turf loss at any time of year, but the effects are most pronounced during the late winter and early spring. Urine contains the organic compound urea, which coincidently is the same organic compound that we use as a prime nitrogen source in agricultural fertilizers – except that the urea in fertilizer is synthetically produced from atmospheric nitrogen. When the dog urinates on a lawn, the urea in the urine (say that three times fast…) is metabolized in the soil in the identical manner as fertilizer, so it is interesting to describe what is going on in a dog spot.

The brown center of each patch in the photograph is the area where the urine, and thus the urea, was deposited. The turfgrass takes up far too much of the urea in the center of the spots resulting in burn – the plant is killed. As you move outward from the center, the concentration of urea diminishes to within the range that we apply fertilizers and it has the same effect – dramatic improvement in color and growth. Finally, the urea becomes so dilute that it has no effect upon turf growth.

Sometimes, we find ourselves in a situation like in the photograph above where the fertilizer that we apply does not provide the same rapid color and growth response as that provided by the dog. This is due to the coatings that are placed upon the fertilizer prills in order to allow them to release slowly over a longer period of time. Trying to emulate the response by the turfgrass to dog urine is not at all healthy for the lawn – heavy doses of quick release nitrogen will weaken cell walls, allowing for easy infection by fungi and leaving the plants vulnerable to extremes in temperature and soil moisture.

As to the damage caused by the urine of male dogs, I will leave that discussion to the fire chiefs.

Moss

Mosses are small, primitive plants that lack vascular systems, roots and do not produce seeds, as do higher plants. They inhabit areas that are sufficiently light enough to allow for photosynthesis, but are not in direct sunlight, are moist enough to allow for water to be drawn in through the leaves, are acidic enough to allow the moss to have a competitive advantage over other plants, like grass, and lack heavy traffic.

Mosses are cultivated in many gardens as a welcome plant for groundcover, but are visually unappealing in home lawns and (strangely) toxic in certain situations like putting greens.

In the colder months, moss is moderately active in lawns as opposed to the complete dormancy of the surrounding turfgrass – that is why questions and concerns are commonplace during late winter and early spring before turfgrass dormancy breaks. It is not that the moss was not there, it’s that it’s actively growing at a time when the turfgrass is not. Further, it is the natural progression of a landscape to become more shaded over time as trees that were once quite small achieve maturity. Turfgrasses that once enjoyed full sun in a particular area slowly but surely lose their competitive edge as the surrounding trees imperceptivity grow. Increased shade brings with it a microclimate that is moister, both of which are boons to the moss.

Soil pH also plays a role in moss development. Soils in New England will naturally become more acidic over time, more so with the addition of fertilizers necessary to properly manage stands of turfgrass. Without the application of limestone to mitigate and reverse the decline in soil pH, turfgrasses become less competitive against the mosses, which are more tolerant of low pH.

Thus, control of moss is achieved through cultural means rather than by chemical means. Only attempt to grow turfgrass in areas where there is sufficient sunlight to facilitate its growth. In deep shade, it may be better to replace thinned turf with groundcover such as ivy or pachysandra. Trees that have matured should be evaluated for structural pruning – it will not only allow more light to reach the soil surface, but it is highly beneficial to the tree as well. Manage applied water in shaded areas – it is not necessary to irrigate a shaded area at the same rate as an area in full sun.

One interesting phenomenon that has come to light recently is the symbiotic relationship between moss and blue-green algae growing on putting greens. Researchers were having a difficult time discerning why there was a correlation between the presence of moss, an algal crust and the loss of annual bluegrass. It seems as though there is a relationship between the moss and the algae, and that the algae is producing chemical compounds that are remarkably similar to compounds that are synthetically manufactured for use as herbicides in agriculture. In other words, the algae are "spraying" the grass for the benefit of the moss. I wonder if the algae have tiny white trucks and teenie weenie sprayers like we do/