The spores of fungal needle cast diseases of conifers infect needles when the humidity is high and the needles are wet. The most severe infections usually occur on the bottom half of the tree and on the shaded, northern side. The diseases are most severe at these sites because water tends to remain on the foliage for long periods, and this moisture favors spore germination. Dense foliage dries slowly and increases within tree spread of the disease from branch to branch. Tree-to-tree spread is increased by close spacing of trees that allows rain to splash spores from diseased to healthy trees.

Two major diseases of pine are Lophodermium needlecast of Scotch and red pines and Cyclaneusma or Naemacyclus needlecast of pines.


Lophodermium
causes needles on infected trees to turn brown in the spring. It may be confused with winter burn which will cause a uniform browning of the needles and is most common on the windward side of the tree. Lophodermium usually damages the lower branches of the tree while the upper foliage remains green.

The needles are dropped or "cast" in June and July. Infection occurs when the spores are released to the air starting in July and carrying on through the fall.

Needles infected with Lophodermium will form shiny, football-shaped, black fruiting bodies that may be found on fallen needles. In the spring, infected needles form brown spots with yellow borders appear and enlarge. The needle turns yellow and then brown by May or June.


Since this is a fungal disease, the key factor is moisture and how long it sits on the needles before evaporating. So, things like placing the plants in an area where there is good air circulation can help. Ironically, not pruning evergreens so that their foliage does not get thick and lush like a Christmas tree. Yes, those trees are pruned yearly but they are usually cut down when they are 5 or 6 years old. Also, Christmas tree growers often have to use fungicides to prevent their trees from getting needlecast diseases.


Control:
Most fungal diseases of conifers can be partially controlled by several cultural practices.

  • Avoid planting in low areas, depressions or shady sites where soil moisture, humidity and dew tend to remain high for prolonged periods.
     
  • Plant so that air can circulate freely around trees. Avoid dense plantings.
     
  • Control weeds and tall grasses so that weed growth does not favor the build-up of humidity and moisture around the lower branches.
     
  • Avoid drought sites that stress trees. Serious infections of tip blight and cankers are often associated with poor sites.
     
  • Maintain tree vigor by watering during the periodic droughts of summer. Early spring fertilization can help a diseased tree recuperate.
     
  • Buy only clean and healthy nursery stock to reduce the chance of bringing disease to your landscape. Remember that most needle casts are spread by rain splash, so distance of spread is limited.
     Lophodermium
    needle cast is spread by wind borne rather than rain-splashed spores.
     
  • Of course, always avoid planting young trees near older, diseased plantings, windbreaks or woodlots.

Chemical Control: For Lophodermium needle cast disease, apply a labeled fungicide starting in late July. Repeat the applications every 10 to 14 days through September.  

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

Copyright 2000-