Archive:Poplar/Bark Necrosis, Dieback, "Blackstem"

From Bugwoodwiki

From: Ostry, Michael E.; Wilson, Louis F.; McNabb, Harold S., Jr.; Moore, Lincoln M. 1988. A guide to insect, disease, and animal pests of poplars. Agric. Handb. 677. Washington, DC: U.S. Department of Agriculture. 118 p.

Importance

These fungi cause dieback, bark necrosis, and cankers on branches and main stems of native and introduced poplars. Unrooted hardwood cuttings can be damaged during storage or killed shortly after planting by Cytospora and Phomopsis.

Look For:

Slightly sunken cankers with definite margins or discolored patches of bark on branches or main stems. Infected tissues may be yellow, orange, brown, or black, in contrast to the green healthy bark.

Raised, pimple-like fruit bodies (pycnidia) in infected bark.

White, yellow, or orange tendrils (spore horns) of conidia exuding from pycnidia during moist weather. When dry, tendrils appear as fine white, yellow, or orange hairs.

Damaged cutting in field

Cytospora Sporulating

Symptoms produced by these fungi look alike, so examine spores or obtain a culture from diseased tissues to positively identify the casual organism.

Biology

These fungi are common on dead and dying poplars. However, they can also infect live trees of low vigor and injured tissues. Trees under stress from drought, insect attack, frost, sunscald, nutrient imbalance, or other diseases are particularly vulnerable to infection. Loss of internal bark moisture favors disease development. Rainsplashed spores (conidia) infect the tree through bud scales, leaf scars, and wounded or stressed bark. In addition to conidia of Cytospora and Dothichiza, windblown ascospores are also presumably involved. Infected twigs and small branches are quickly girdled. Elongated cankers and patches of dead bark develop on stems as the bark and sapwood are progressively invaded. Cultural practices that increase host vigor inhibit further bark infection.

Monitoring

Examine trees for factors that predispose them to infection by these fungi. Closely examine seedlings and hardwood cuttings for symptoms before planting.

Phomopsis Sporulating.

Dothichiza Sporulating.

Control:

Plant cuttings and seedlings during periods of favorable moisture and temperature to minimize stress.

Plant clones resistant to premature defoliation by Melampsora or Marssonina that can reduce tree vigor.

Plant only on sites suitable for good poplar growth.

Control weeds, irrigate, and fertilize trees to maintain good growth.

Plant trees far enough apart to minimize competition among them for available moisture, light, and nutrients.

Avoid wounded trees

Prevent sunscald by wrapping tree trunks with Kraft paper to reduce injury to bark tissues.

Protect cuttings or rooted stock from drying out or becoming heated during processing, storage, shipping, and planting. Maintain storage temperature at approximately 26 degrees F.

Collect cuttings only from disease-free, vigorously growing stock.

Cuttings affected by "blackstem" in storage.

Conidia of Phomosis.

For Additional Information:

Haywood, William F.; McNabb, Harold S., Jr. 1979. Moisture stress and incidence of stem cankers in intensively grown poplars. In: Proceedings, 1st North central tree improvement conference; 1979 August 21-23; Madison, WI: 123-132.

Ostry, Michael E.; McNabb, Harold S., 1980. How to identify and prevent injury to poplars caused by Cytospora, Phomopsis, and Dothichiza. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station 7 p.

Ostry, M.E.; McNabb, Harold S., Jr. 1982. Preventing blackstem damage to Populus hardwood cuttings. In: Zavitkovski, Jerry; Hansen, Edward A., eds. Proceedigs, North American poplar council meeting; 1982 July 20-22; Rhinelander, WI. Manhattan, KS: Kansas State University: 36-43.

Tao, Dali; Li, Paul H.; Carter, John V.; Ostry, Michael E. 1984. Relationship of environmental stress and Cytospora chrysosperma infection to spring dieback of poplar shoots. Forest Science. 30: 645-651.

Walla, J.A.; Stack, R.W. 1980. Dip treatment for control of blackstem on Populus cuttings. Plant Disease. 64: 1092-1095.

Conidia of Cytospora.

Conidia of Dothichiza.