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ISSUE 16  AUGUST 26, 1999


PROTECTING TREES FROM WINTER INJURY

    Winter is quickly approaching and every year many trees are injured or killed during this coldest season. Although we cannot protect trees from all types of injury, we can improve their chances by taking action before winter arrives.

    Watering. Trees need adequate water throughout the year and will be more susceptible to winter injury from drought conditions that occurred at any time during the year. In addition to reducing desiccation of needles and twigs during winter and early spring, deep watering before freeze-up will insulate the ground, protecting tree roots from rapid temperature fluctuations. The soil should be moist (not wet) when the ground freezes. Remember that roots extend beyond the tree’s drip line, so make
sure to water beyond the drip line.

    Mulching. During the growing season, mulches are great at suppressing weeds and keeping the soil moist. They also provide some distance between lawns and trees, reducing competition and preventing lawnmowers and weed whippers from ripping the bark off of young trees. Mulch provides insulation that will moderate soil temperatures, reducing rapid fluctuations which can damage roots and cause heaving of trees in new plantings. Reduce the potential for rodent feeding and disease
development of the bark by keeping mulch at least 3-4" away from the bark of young trees.

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    Wind Barriers. Trees that are planted in exposed sites and have a history of winter browning or dieback may benefit from a wind barrier. Wind barriers such as snow fencing or burlap tied to lath frames will slow down the cold, desiccating winds of winter.

    Trunk Wraps. Young, thin-barked trees such as birch, linden, maple, honey-locust, mountain-ash, and fruit trees are very susceptible to sun scald injury. Sun scald is an area of dead bark which is caused by rapid thawing and freezing. This injury usually occurs on the south or southwest side of a tree. In addition to being unsightly, the open wound produced by sun scald may serve as an entry site for insects and diseases. Plastic tree wraps are commonly used to prevent sun scald. These wraps are also effective in reducing physical damage to trees caused by lawnmowers, weed whippers, and rodents as well as
herbicides that could be absorbed through thin bark. Although they should be removed occasionally to encourage normal tree growth, there are year-long benefits to plastic tree wrap use on young, thin-barked trees.

    Tying Evergreens. Prevent breakage, by snow or ice, of multiple leader evergreens, such as upright junipers and arborvitae, by tying the leaders together with heavy twine. Entire trees may also be wrapped. Begin by fastening the twine at the base of the tree, then spiral around the tree to the top and back down the tree in a reverse spiral. Remove the twine in the spring, before buds begin to swell, to prevent girdling of the stems by the twine.

    Salt Damage. Much of the salt damage that we see to trees in North Dakota is from de-icing salts used on sidewalks. These salts often run off the sidewalks into the soil and damage the roots of trees. Although all trees can be damaged by de-icing salts, apple, linden, hackberry, and sugar maple trees have a low tolerance for salts in the soil. When applying salts to sidewalks this winter, keep the trees in mind. Other de-icing materials, such as calcium chloride or calcium magnesium acetate, may cause less damage to plants than the commonly used sodium chloride.

    Animal Damage. Rabbit, deer, and other animal feeding can cause substantial damage to trees when other foods are scarce during the winter months. Hardware cloth can be placed around the trunk of trees to prevent damage by rodents. The mesh should extend 2"-3" into the soil for protection from mice and be at least18"-24" above the anticipated snow line for protection against rabbits. Plastic tree shelters may be effective in controlling rodents on small trees, when extended into the soil. They may also be effective in reducing browse damage to trees; however, only tall shelters (5' tall shelters are available) are effective against deer. Repellents can be used to reduce damage from rodents and deer. Rotating a variety of repellents is often necessary, as animals may become familiar with a single repellent quickly. Commercial repellents are available, but suspending perfumed soap or small mesh bags containing human hair around the site where damage is anticipated may also be successful. Deer can be very damaging too young trees when terminal buds are nipped off. The use of a bud cap may prevent this type of damage. Bud caps are simply a piece of paper wrapped around the bud with the ends of the paper stapled together. Deer will often avoid covered buds, allowing the tree to maintain normal growth.

 

Marcus Jackson
Extension Forester
mjackson@ndsuext.nodak.edu

 

LAWN DISEASE COMPLEXES AND THEIR MANAGEMENT

    Lawn diseases have had an outstanding summer to proliferate in 1999! The unfortunate thing is that most are caused by the following mismanagement practices:

1. Over-irrigation. The every-other-day cycle that most people follow with their automatic irrigation systems are a beginning point. Lawn grasses will use anywhere from 0.10" to 0.30" of water per day, depending on the heat, humidity, and wind factors. Most properly managed lawns do not need more than two irrigation events per week under the worst conditions. The notable exception of course, would be where the soil is a sandy loam with an excellent perc rate and low water holding capacity.

2. Improper mowing. This involves two things; mowing too short and mowing with a dull blade. On the lawns that have the worst manifestation of the "patch disease" or "frog-eye" syndrome, the lawns are mowed to fairway height, and done so with an extremely dull mower blade. The mowing height should be 3" and the blade should be sharpened a minimum of once per season for home lawns.

3. Poor nutrient management. As a species, we humans are suckers for low prices. Why pay more for the same elements of N,P,&K, right? Wrong. The better fertilizers are "prilled" to have all the nutrients in each one, so separation cannot take place. Many also think an application of fertilizer every other year or so is adequate. After all, we don't want to mow too often, do we? Even minimal maintenance turf will need at least an annual application of a turfgrass type fertilizer, one that has an analysis such as 28-3-6, not a 10-10-10.The cool season grasses will thrive under good nutrient management where the N level
especially, can be maintained at about 0.75 to 1.0 pounds per 1000 square feet. This requires at least two applications per year -late spring and early fall, with three being preferred if the lawn is being irrigated. An annual application of an organic like Milorganite or Lawn Restore will also help to control the development of turf diseases.

4. Peat sod being used as turfgrass. Another constant I have found is the use of peat, muck, or organic sod on clay soil especially, developing this disease syndrome. The sod roots very poorly, if at all in the soil below, and stays soggy at the sod/soil interface after an irrigation event. This creates an ideal environment for disease organisms to proliferate. Core aerate to slowly overcome this problem.

5. Failure to think preventatively. The reaction always takes place after the symptoms show, when it is very difficult, if not impossible, to affect an immediate change (which almost everyone wants!). Fungicides generally do a poor job of "curing" the disease, and are used best as preventatives.

Keeping the Diseases Under Control:

Other than the tips mentioned in the above five points, consider the following:

1. Try to "think" like a fungus. What is it that is going to favor the development of diseases?

*Poor drainage- correct by core aeration spring and fall if necessary.

*Moist, humid weather in July and August usually sets the stage. Apply preventative fungicides like Banner, Rubigan, Fungo 85, Spot Kleen, Cllearys 3336, or Proturf Systemic, prior to the arrival of the symptoms

* Mow the grass when it is dry, ideally going into the evening hours when it will have lowered stress from heat. Forget what you see golf courses or athletic field managers do. They don't have the luxury of waiting for the weather to cooperate like you do!

* Don't be afraid to overseed on an annual basis with some of the newer, more disease resistant turf cultivars. Local distributors have them each season, and they are a small investment in order to assure the continued attractive appearance of your lawn. There are both low maintenance bluegrasses like 'Park' and 'Ram I' as well as a fleet of more elite cultivars that will soak up all the attention you wish to give them.

Ron Smith
NDSU Extension Horticulturist and Turfgrass Specialist
Department of Plant Sciences
ronsmith@ndsuext.nodak.edu


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