Needlecast Diseases
Gary W. Moorman, Professor of Plant Pathology
Needlecast diseases of evergreens are caused by several fungi. We have much to learn about when these fungi attack a tree, how long the fungus must be in the tree before needles are shed, when is the best time to apply a fungicide, and which chemicals provide the best protection. However, progress is being made in these areas. Needles infected with fungi generally fall several months after the actual period of infection. The period of greatest infection for most needlecast fungi is during the late spring and early summer months. Symptoms, the visible indications that the needle is diseased, do not appear until the late winter, spring, and early summer of the next year.
All the needlecast fungi form small structures on the infected needle in which thousands of spores form. These "fruiting structures" may be black, orange-red, or tan, depending upon the fungus. Other fungi that grow on dead or dying needles but do not cause needlecast may form similar structures. Finding a fungal fruiting structure on a dead needle is not proof that the tree has a needlecast disease. Send a sample to the Plant Disease Clinic for verification.
Managing Needlecast Diseases
Needlecast fungi require abundant moisture for their growth and development. Therefore, plant so that the air circulation around trees will be good. Maintain good weed control so that tall weeds do not impede air circulation around the lower branches. Avoid planting susceptible trees in low or shady areas where humidity and needle wetness tends to be high for prolonged periods. The fungicides listed below can be applied to protect healthy foliage. If needles are already infected, a fungicide will not prevent their falling off the branch.
Rhabdocline needlecast symptoms on Douglas-fir
Swiss needlecast on Douglas-fir needle.
Rhizosphaeria needlecast on spruce.
Cyclaneusma fruiting one pine. Aphid feeding injury (left) Cyclaneusma banding (right) on pine.
Cyclaneusma needlecast on pine. Lophodermium fruiting on pine needle.
Dothistroma on pine (Photo courtesy of M. Concklin.)
Active Ingredients and Trade Names of the Chemicals
REI
Restricted
FRAC Risk Entry
Group No. Level Class Active ingredient Interval Trade names (EPA Reg. no.)
3 2 Triazole triadimefon 12 Strike (3125-436), Bayleton (432-1360)
11 3 Strobilurin azoxystrobin 4 Heritage (10182-408)
M 1 Chloronitrile chlorothalonil 48 Daconil (50534-9), Bravo (50534-204-100)
Copper, complex copper sulfate 12 Camelot (1812-381)
Dithiocarbamate mancozeb 24 Dithane (707-180), FORE (707-87), Pentathlon (1818-251)
manganese + zinc 24 Protect T/O (1001-65)
Fungicides and Fungicide Resistance Management - Certain fungicides, usually systemic fungicides, are said to be 'at risk' to the development of resistance if they are used repeatedly. See the Risk Level in the above table (1 = low risk; 3 = high risk). The Fungicide Resistance Action Committee has developed a numbering system in which chemicals with the same FRAC Group number have the same mode of action (See http://www.frac.info/frac/index.htm ). It is recommended that chemicals at high risk be used sparingly and in rotation or mixed with chemicals with different modes of actions (different FRAC number).
DISCLAIMER
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
Issued in furtherance of Cooperative Extension work, Acts of Congress, May 8 and June 30, 1914, in cooperation with the U. S. Department of Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
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