Wet soil is a major cause of fruit tree loss in Illinois. Most Illinois soils are heavy, with an excellent moisture-holding capacity. They have poor internal water drainage, though, and tend to stay soggy wet during rainy periods in the fall, winter, and spring. Illinois soils may have an impervious subsoil and often have a high water table.
Sour cherries, peaches, and nectarines are especially sensitive to damage from wet soils. Pears, apples, apricots, and plums are somewhat more tolerant. An excessively wet fall, winter, or spring may cause damage to fruit trees growing in soils that are not normally wet or soggy. The damage may not become apparent for six months or more after it occurs. Damage occurs to the roots and the below-ground portion of the trunk. The inner-bark of these parts will be brown instead of the normal light-yellow color.
Cold temperatures may have harmful effects on fruit trees throughout Illinois. Cold injuries may be mild or severe, depending on the time and severity of the low temperatures and on the type, variety and condition of the tree. For example, peaches are more susceptible to cold injury than apples, and Japanese-type plums are more susceptible than European type plums. ‘Red Delicious’ apple blossoms are more susceptible to spring frost injury than ‘Golden Delicious’ blossoms.
Cold injuries may be due to (1) very cold winter temperatures, (2) immaturity of tissues (cold occur- ring before the tree has developed cold hardiness), (3) fluctuating winter temperatures (cold immediately following a warm period), (4) widely fluctuating day and night temperatures, and (5) spring frosts.
Very cold winter temperatures may kill buds (especially of some stone fruit trees), stem tissues, and even the roots of fruit trees. Little can be done to protect trees from this type of injury. Select types and varieties of fruits that are known to be cold hardy in a given area.
Injuries due to immaturity of tissues usually result from conditions causing trees to continue vigorous growth into the fall, or by conditions that affect normal physiological processes in the plant. Too much water, abnormally warm fall temperatures, and excessive amounts of nitrogen, alone or in combination, may cause excessive fall growth and predispose the tissue to cold injury. To avoid immature tissues, keep trees moderately vigorous before winter arrives, avoiding practices such as late cultivation, excessive irrigation, and heavy or late applications of nitrogen fertilizers that tend to stimulate fall growth. Fall drought also may re- duce the development of cold hardiness by hindering normal physiological processes in the plant.
Injuries from fluctuating winter temperatures usually occur when unseasonably warm weather in late winter and early spring is followed by cold weather. The warm period causes trees to lose some of their cold hardiness, thus making them more susceptible to cold injury. Bark tissues and flower buds both may be damaged.
On sunny days in the winter the sun may warm the bark on the southwest side of the trunk and crotches to temperatures much above air temperatures. As the sun goes down, the bark quickly cools to air temperature. These fluctuating day night temperatures may cause injury to the bark (Figure N-11.).
Shading the trunks and vulnerable limbs with burlap or waterproofed paper can prevent such injury. Painting these areas with white latex house paint also may help by reflecting sunlight.
Spring frosts usually are most damaging to flower buds, flowers, and young fruits, but sometimes may injure the bark. Frequently only a few degrees of warmth for a short period on one or two nights are needed for protection. Small trees may be covered with plastic sealed to the ground. Or a 150 watt infrared heat lamp may be placed over the tree with the rays directed onto the tree.
Injuries to the trunk and limbs can be caused by all five types of cold injury. Usually this injury is to the inner bark and adjacent tissues, but sometimes to sap- wood as well. The inner bark may turn brown and both the inner and outer bark may split. The sapwood may darken. This injury is most frequent to the trunk at the groundline and in the branch crotches, but it can occur in all parts of the tree.
Drought alone usually will not kill healthy fruit trees, unless the drought is prolonged and severe. But short periods of hot, dry weather put severe stress on weak or injured trees and may cause them to die.
Fruit trees seldom die from nitrogen deficiency; however, trees showing a severe nitrogen deficiency are more susceptible to cold injury, borer attacks, and fungal diseases. The leaves of fruit trees suffering from nitrogen deficiency are small, sparse, and yellow to pale green. Peach leaves also show reddish-colored lesions.