Most damage or stress to plants in Montana is caused by non-infectious conditions. Insects, disease, animals, chemical and/or mechanical problems are expanded by environmental and soil conditions. Problems most often affecting Montana landscape plants are frost injury, winter injury, crown dieback, sun scorch, sun scald, inadequate pollination, thatch buildup in turf, yellowing and poor drainage.

Winter Injury/Winterkill

“Winter” injury can occur at several times of the year and when the plants are dormant, semi-dormant or actively growing. In spring or fall, repeated freezing and thawing of the soil can damage roots. Before plant tissue hardens, extreme cold can cause injury. Prolonged warm weather in mid-winter can break plant dormancy, making them vulnerable to injury if extremely cold weather follows. Heavy ice that remains on trees and shrubs can damage a plant.

Plants show winter injury in a variety of ways: blackened sapwood, injured cambium, death of leaves or fruit buds, twigs or branches, and injury to roots or crown. Full foliage may develop in the spring and then suddenly die if winter root injury is a factor.

Management: Grow trees and shrubs that are winter-hardy for Montana conditions. Plant the trees and shrubs where they are protected from snow or ice buildup or remove the buildup as it occurs.

Trees, shrubs and other ornamentals can be protected by mulching around the base during the winter. With both large deciduous and evergreen trees, the mulch should be placed to allow water to run off and away from the base. This is to prevent girdling by freezing and thawing of ice. On small shrubs, the mulch should be extended out to the edge of the dripline to protect the feeder roots. This method is used to conserve root moisture and slow rapid alternation of freezing and thawing of the soil. Remove and work remaining mulch into the soil in the spring. To prevent root kill, water trees/shrubs deeply in late fall and during warm periods in winter. Caution: Mulch may create added rodent activity.

Frost Injury

Flower buds are more delicate than leaves and can be damaged even when the temperature is above freezing. A spring freeze can kill tender young leaves. If damage occurs during flowering, it may prevent pollination and cause misshapen fruit. Sever injury can occur to buds, open flowers (especially the pistils), leaves and developing fruit. You can expect frost damage when the wind is calm and sky clear after a cloudy day. The clouds keep the soil surface cool, not allowing it to store heat that could warm night air.

If hit hard by a freeze, the plants could die or lose fruit and foliage production. When a spring freeze occurs on flower buds, damage to the plant may only effect that seasons’ fruit and foliage and fully recover the next season. Though a frost can also take place late in the growing season, the plant’s production usually is not reduced enough to be noticed because harvest has already taken place. Early fall frosts occurring before plants harden or become dormant for winter can increase winter kill. The entire mature plant may be effected or just growth produced that season.

Management: Plant gardens (flower and vegetable) outside after the last average frost-free day for the area. If plants are frozen, a person can irrigate during the early morning hours before and during freezing temperatures to prevent some of the cell damage. If the plants show visual decline after injury it may be advisable to start over and not waste water and effort.

When planting, keep soil temperature in mind. The soil must be warm enough for seeds to germinate or for plants to start growing without stress.

Garden plants and small bushes should be covered with cloth, hot caps, paper bags, plastic or other physical coverings when a freeze is predicted to eliminate damage from short freezes. If it frosts during the night and plants were uncovered, spray them with water to turn the frost to ice. The ice will melt slower than the simple frost and reduce cell damage. Do this before the sun hits and warms up the plant.

In late summer and early fall, nitrogen fertilizer should be avoided because it induces fall growth which can lead to freeze injury.

Also in early fall, about a month before average first frost date, watering should be decreased to induce maturation. Prior to soil freeze-up, a deep watering should be applied to woody ornamentals. If a warm dry winter should occur with temperatures in the 50’s or above for long periods of time, a person should consider watering their plants.

Crown Dieback

When the tops of trees die, foliage begins to thin out and leaves and needle growth is stunted. Drought, poor drainage, root rot, insects and disease can induce crown dieback.

Management: Water and fertilize trees and shrubs to maintain vigor. Spring fertilizing just prior to bud break, is best. Fertilization with nitrogen should not be practiced after June 1 to allow trees and shrubs to adjust to seasonal conditions and start to slow down their growth during summer stress periods. If fertilizers are used in late August or early September, it may stimulate tender vegetative growth (second growth) that may be damaged by early fall frosts.

Mulch and water in late fall. Plant adapted trees and shrubs in well drained, fertile soils and maintain a good insect and disease management program.

Sun Scald

There are two types of sun injury; winter and summer, though winter injury is a much more common cause of leaf drying and trunk cankers. Winter sun scald is caused by rapid temperature changes. On a sunny day, temperatures increase sufficiently on exposed bark surfaces to thaw normally dormant cells. When evening air temperatures drop or a cloud obscures the sun, rapid cooling causes cell injury. Injury is especially common on such thin, smooth barked trees as mountain ash, apple, maple, and shrubs like dogwood.

Following the injury, affected tissues appear dull or discolored, and there may be some shrinkage due to drying. The bark loosens from the wood and the brown, dead portions can be readily peeled from the underlying wood, which may also be discolored if not severely damaged. With severe injuries, the bark splits, cracks and produces an open wound. Moderate types of winter sun scald are confined to small, upper trunks or branches on the southwest facing side of the plant. Severely injured trees and shrubs may die later in the season, while those less injured will heal and survive.

Management: Follow practices that prevent excessive heating of the surfaces exposed to sun. Accomplish this by shading to protect the bark from direct action of the sun, or modify the plants’ surroundings to avoid reflection of sun rays. Control insects and prevent fungi and disease from entering the damaged tree tissue. Fertilize trees/shrubs in the spring to stimulate growth, maintain them in good condition during summer and fall.

Splits in trunk area and loose bark can be cut back to tight bark to help stimulate regrowth. Use a sharp knife and remove only the loosened bark up or down to where it is firmly attached. If possible, trim bark in an elliptical shape to enhance healing. In time, a new ridge of bark will come into the damaged area. Apply tree wound dressing to cracks and dry bark areas.

Reduce bark temperature fluctuations by wrapping with foil, tree wrap or other reflective material. Painting the trunks, especially on the southwest side, with white (non-lead) latex paint will also help even out the temperature changes.

Sun Scorch; Leaf Scorch

Tree foliage appears scorched as if by a fire. The needles or leaves dry and turn brown from the tips down or inward. Excess needle drop beyond the normal rate may occur in the interior of evergreens. Tips of the branches begin to die back. This type of injury shows up when hot, dry conditions follow periods of cloudy, rainy weather. Severe winter weather and mite injury cause similar symptoms. Trees, shrubs and ornamentals usually affected are those on exposed sites, close to buildings or poorly maintained.

Management: Keep plants watered when it is hot and dry. Grow in protected areas with rich soil. Plant winter hardy varieties and maintain a proper insect management program.

Pollination

Inadequate pollination occurs on all small fruit trees and vegetables. Without insects, berries tend to be small and are frequently malformed. Stamens of primary flowers may not form well during the cool weather of early spring, thereby creating a shortage of pollen. In such cases, large numbers of pollination insects are needed to insure a good fruit set. The careless application of insecticides during blooming could seriously reduce populations of pollinating insects. Maximum yields and fruit size are achieved when abundant pollinating insects are present. On cool, moist, windy days, pollinating insects do not fly, and on some days pollinating insects are only active in protected areas, such as shelterbelts.

Management: Plant in wind-protected and sheltered areas. Some varieties of apples and other fruits require two trees for cross pollination. Check with our expert staff for pollination information on your plants. Apply pesticides late in the day to avoid exposure to pollinating insects.

Thatch Build-up

Dead grass buildup on the soil surface can reduce lawn vigor. This organic layer is a medium for fungi growth. It also keeps the soil cool in the spring delaying grass emergence and prevents fertilizer and water penetration into the soil. Under summer heat stress, excessive thatch may aggravate turf desiccation problems by preventing water penetration to the soil. This may cause localized dry areas, especially on high spots where water runs off to surrounding turf.

When thatch builds up over one half inch, the lawn may die or at least become thinner. If mechanical aeration does not work, remove the thatch down to the soil before reseeding. Seeding over thatch does not allow the seed to reach the soil where the roots need to penetrate. Power rakes set to touch the soil surface will aid thatch removal.

Management: Remove the thatch and loosen the grass mat by mechanical aeration. Clippings from normally maintained lawns contribute little to thatch problems but do contribute a significant amount of nitrogen as they break down.

Snow Mold and Fusarium Patch

These diseases are especially severe on bent grasses, but may also occur on other lawn grasses. Snow mold, or winter scald, is caused by several different fungi. It is most severe when snow covers grass for long periods. It is particularly difficult to control if the grass is green and actively growing when covered by lasting snow.

Fusarium patch, also known as pink snow mold, can occur during the growing season when humidity is high and daily temperatures fall below 65 degrees Fahrenheit. Any condition that keeps the turf excessively wet, such as poor surface drainage, favors these diseases.

Symptoms: Snow mold symptoms appear first as a white cottony growth on the leaves. As the leaves die, they turn light brown and cling together. Diseased areas are usually 1 to 12 inches or more in diameter and discolored dirty white, gray, or slightly pink.

Fusarium patch is characterized by development of irregular pale yellow areas from several inches to several feet in diameter. Later, affected areas become whitish gray. Sometimes the edge of an affected area has a faint pinkish color.

Control: Condition of the turf as it goes into the winter determines whether the snow mold fungus can get established. Do not apply high nitrogen fertilizers late in the fall, because that may stimulate growth and result in a actively growing turf when it snows. Keep the lawn cut in the fall to prevent a mat of grass from developing.

In most situations, recovery occurs without special chemical treatments.

Poor Drainage

Most fruit and ornamental plants are affected by poorly drained soils. When roots sit in water, lack of oxygen keeps them from developing properly and the plants are weak. Root rot may result when roots are under these conditions for prolonged periods of time.

Management: Water until soil is saturated but not soggy. Allow soil to drain well between watering. You may need to modify the soil by adding organic matter or sand.

To avoid problems, you can use a moisture meter to indicate moisture levels. A simpler moisture test is to use a spade to dig down 6 to 8 inches to reveal the moisture conditions. If it is wet, wait several days (3 to 5) and check again. Once you do this several times, you can estimate the amount of time it takes your soil to use water and will be able to better manage your watering. You may need to repeat this process during hot or very windy weather, because the loss of moisture through evaporation will dry the soil more quickly than in cool calm periods.

To help loosen heavy clay soils, add gypsum or fish meal. Sulphur could also be used, but though it would lower the soil pH, it would do little to improve the soil. These products can be broadcast over an established lawn and watered in. Gardens, shrubs, trees and roses can be treated by top dressing or by tilling these products into the soil and by watering them in. Sand (80% by volume or greater) can be added as a permanent way to improve drainage. Use of french drains in localized poorly drained areas may also be helpful.

Yellowing Turf

Grass may turn yellow due to over watering, poor drainage or lack of nutrients. Nitrogen deficient turf appears yellowish throughout the plant, and if it lacks iron, the yellowing appears between leaf veins of new leaves only.

Over watering leaches out nutrients such as nitrogen and potash from the root zone of the grass and creates a deficiency.

Yellowing can occur because of porous soils (sandy, rocky, etc.). When the grass has a nutrient problem following drought, at first the symptoms will be a dark grey green color and wilting (foot printing when walked upon). These symptoms are usually followed by yellowing or browning.

Management: Manage water and add nitrogen and/or iron. In poor soils, fertilizing as often as once every two weeks may be needed if a lush lawn is desired. However, this depends upon analysis of the fertilizer. Organic fertilizers are available more slowly, can be applied at higher rates and used less frequently, perhaps twice a season. In sandy soils, nitrogen can leach out quickly. To alleviate this, apply half as much but twice as often.

Yellowing Plant Leaves

As with turf, yellowing may be the result of nitrogen deficiency, iron deficiency or poor soil and water drainage.

A frequent cause of chlorosis or yellowing plants is the unavailability of iron. Iron is required to form chlorophyll, the green pigment in plants. Without adequate iron, chlorophyll cannot by synthesized and the leaves yellow. Iron deficiency may lead to stunted or weakened plants and, often, decreased yields in fruits or reduced attractiveness in ornamentals.

Iron deficiency symptoms are seldom due to a lack of this element in the soil, but often are the result of soil conditions which make the element unavailable. In Montana, one of the major causes of iron deficiency in plants is alkaline soils. Under alkaline conditions, iron is complexed with phosphorus in a form not available to plants. For this reason, applications of the common iron compounds seldom correct iron deficiency chlorosis for long.

Certain plant species appear to have greater requirements for iron than others or else have less ability to acquire the element from the soil. Some of the plants most often observed to suffer from iron deficiency chlorosis in Montana are apple, gladiolus, maple, peony, plum raspberry, rose and strawberry. However, it is probable that vigor and appearance of others could be improved by adequate iron supply.

Affected plant leaves usually provide the quickest means of determining iron deficiency. Plants suffering from lack of iron typically show a yellow to white color in the interveinal areas of the younger leaves only, but the principal veins of the leaves are usually sharply marked in green. Iron deficiency symptoms may be expressed only by a few leaves, branches, or the entire foliage.

Management: Numerous practices have been used for correcting iron chlorosis, but some of these are effective only under limited conditions. Iron can be applied to plants by:

1. Foliage application: Plants can absorb materials through the surface of the leaves and overcome soil fixation of iron. Several spray treatments may be required during the season to prevent chlorosis in later developing leaves.

2. Soil application: This method involves direct treatment of the soil with iron compounds. The materials may be applied in holes or ditches around bases of plants or else broadcast on the soil surface and then worked in.

Chelated iron gives excellent results for soil treatment of iron deficiency chlorosis in many plants. It is important that the soil be well watered after the chelates are applied so that the compound penetrates to the roots. Excessive watering should be avoided to prevent leaching of the chelate.

3. Altering soil pH around affected plants root zone by incorporating elemental sulfur (95%), gypsum, aluminum sulfate, and other sulfur products to release soil pH bound iron, as well as improving the effectiveness of chelated iron products.

Acknowledgments: This information is taken from Circular 9001, by Laurence Hoffman, MSU Extension Agent, Lewis, and Clark County, supplemented and reviewed by: Amy Grandpre, Yellowstone County Horticulture Assistant; George Evans, MSU Extension Horticulturalist; and Kevin Laughlin, Toole County Extension