Needle Evergreen Diseases

Phomopsis sp. & Kabatina sp. are two fungi that cause cankers on junipers (as well as other plants). Phomopsis attacks only new growth and stops growing when it gets too hot and/or dry. Kabatina attacks growth that is two or more years of age. Both are fatal long term. Grow resistant varieties.

Cytospora sp. causes canker on spruces (as well as other plants). The disease usually starts at the bottom and works upwards most of the time. Occasionally kills from the top down or from one side to the other. Sometimes Cytospora kills piece meal.

There are several pine needle diseases. Brown spot occurs in the spring as the new needles emerge. Death, browning and defoliation usually occur by fall. In addition, the new twig usually dies too. The disease often starts near the growth on the north side and works up and around the tree as the disease progresses.

Needle cast occurs on current year’s mature growth late in the growing season. Browning and defoliation of needles usually occur the following growing season. The result over several years is needles only on the current year’s growth. Needle blight starts on any needle. Current year growth matures before becoming susceptible. Needles often break off or fold at an angle at the lesion. Most often associated with Christmas tree farms but is becoming more and more a landscape disease.

Sphaeropsis sp. causes either tip blight or canker problems on pine. Austrian pine is the most susceptible pine. As a tip blight, the disease enters the candle as the new growth emerges from the bud. Girdling eventually occurs and the tip dies. A little later the dead tips dry out and turn brown. This disease over winters on needles, dead tips, and pine cones. It does not matter if the infected tissue is on the tree or on the ground.

Pine wilt is a disease caused by the pine wood nematode. These nematodes can reproduce at an extremely high rate. The nematodes eventually plug the plants vascular (xylem) system. The tree often times dies in about two to three months. Keep plants healthy, avoid injury or any long term stress to the pines. White pine is highly resistant to this disease.

Sooty mold is a fungus disease. It grows on the honeydew produced by "sucking" insects. Control the insects. Sooty mold kills by cutting off light to the chlorophyll.

Die back is often the result of root rot. Root rots occur due to poor drainage or over watering. There are several root rot fungi. The root rot that tends to kill more tree roots is one of the Phytophthora sp. Plant only in well-drained soils and do not over water.

Noninfectious Diseases

Natural needle drop (normal) is not a disease even though many gardeners think it is. All evergreen needles eventually die. The older needles are on the inside and usually die over an entire growing season and, therefore, are not noticed. Occasionally, they all die, turn yellow to brown together. This aging process is normal and is not an infectious disease.

Mutations can change plants from one growth habit to another such as a normal big plant to a dwarf. Sometimes these mutations are not stable and may revert back to their original growth pattern.

Animals can cause noninfectious diseases. On evergreens, deer and yellow- bellied sapsuckers are two of the more common animals to cause injury. Sapsuckers punch holes in a straight line in the trunks of many trees. Austrian and Scotch pines are the two evergreens most often attacked. This bird is migratory through this area every spring and fall. State, federal and international law protect it. DO NOT harm this animal.

Excessive heat can cause severe injury to many plants especially during drought stress or if the plant is not heat hardy. There are other environmental conditions that cause noninfectious diseases. They include drowning, cold injury, snow and ice.

Mites (MAY cause damage that looks like a disease problem) are not insects but are considered insect related. Insects have six legs. Mites have eight legs. The spruce mite is often the mite that attacks the needle evergreens. It is a cool weather mite. It feeds in the spring and fall when it is cool. During the heat of summer the mite is not found but the damage becomes very noticeable. A miticide is needed to control this pest. Insecticides may actually increase the damage by killing the predatory mites and not the plant mites.

April - May 2000: Gardening with Hebs - Part 1 | Discouraging Canada Geese | Needle Evergreen Diseases | May Insect Problems