ISSUE 1 May 3, 2001
WINTER DISCOLORATION OF CONIFERS
Every spring we can expect phone calls from people concerned about discolored conifers. The injury usually occurs several months before symptoms become evident and even though proper tree maintenance during the following spring and summer months may improve new growth of affected trees, only time will tell how well trees will recover.
Reddish-brown, dead foliage first seen on evergreen trees in the spring is often the result of injury sustained in the previous fall or winter. This injury may be the result of desiccation (drying of the foliage) or an early fall freeze. Desiccation occurs when the ground contains inadequate moisture due to drought or when a plant is unable to access moisture such as when the ground is frozen. Trees are then unable to take up enough moisture to replace water lost by the foliage. Early fall or late spring freezes (especially rapid drops in temperature to below freezing) can also kill evergreen foliage when it is not adequately hardened off. Discoloration can be greater when trees are improperly planted, stressed by insects/diseases/other environmental factors, fertilized at an improper time, or have poor winter hardiness.
Patterns of winter injury symptoms can vary based on many different factors. Since wind can accelerate water loss from foliage, desiccation is often directional toward prevailing winds. Winter desiccation may be greater near light colored surfaces (white siding, white rock mulch, etc.). Snow insulates needles, so damage may occur only above the snow line.
Winter desiccation and early fall freezes generally kill foliage but cause less damage to buds and branches. Foliage killed by both early fall freezes and winter desiccation often remains green as long as temperatures are cold. Damaged needles then turn brown when temperatures increase in late winter or early spring. New foliage usually emerges later in spring or early summer. Proper watering, fertility, and pest management during the following spring and summer months may improve new growth of affected trees, helping them to recover. Assessment of total injury should only be made after new growth has occurred. Winter discoloration is often only an aesthetic problem in conifers but it does stress plants and occasionally kills trees that are generally considered hardy.
Watering trees adequately during dry periods may reduce the incidence and severity of winter desiccation. Even though we understand that both tree genetics and environmental factors are important in development of winter injury, we cannot always fully explain patterns and why it appears more severe in certain trees than others and during certain years than other years.
"BUMPS" IN LAWNS
Clientele have complained about an abundance of "bumps" in their lawns this year. This is the result of wet summers producing a near ideal environment for nightcrawlers, or angle-worms. A few are good for the turfgrass environment, as they expertly recycle the nutrients through their digestive systems, and in doing so, aerate the lawn. But, too much of a good thing can lead to problems - like the "bumps."
Taken to excess, which is happening in many cases, the topography of the lawn becomes so choppy that it literally becomes difficult to walk across the lawn or mow it properly. At this point, appropriate action is necessary, and I like to start with the minimum effort first, to see if that is effective enough.
The minimum effort would be to use a ballast roller - one that can be filled with water - and go back and forth across the lawn while the soil is still soft from spring rains or snowmelt. This, along with the arrival of warmer and drier weather, limits the worm activity, and usually, there are no more bumps to contend with.
A step-up in effort would be to rent a power rake and run it over the lawn to a depth that would take off the surface bumps resulting in a smoother lawn surface. The problem with this method is that it involves quite a bit of work, as using the power rake also pulls up considerable thatch which then must be cleaned up, taking considerably more time than the power raking.
A final step is to apply a insecticide to control grubs - everybodyís lawn has them - donít worry. The product of choice is usually Sevin in the granular form and water it in. This step not only provides grub control, but also reduces the population of the worms by about 30%, which is usually tolerable enough to make the lawn surface acceptable. Subsequent insecticide applications would have similar reduction effects on the worms.
Ronald C. Smith
NDSU Extension Horticulturist and Turfgrass Specialist