Management of Diplodia/Sphaeropsis shoot blight of Austrian, Red and Scotch pine
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EmailEditor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
This
disease is different from the needle cast diseases in that it kills the
current year’s infected needles and stems. The fungal pathogen, Diplodia sapinea, (was known as Sphaeropsis)
will also kill seedling trees in nurseries, whereas the needle cast
diseases do not infect seedling trees because their needles dry so fast.
With Diplodia shoot blight and canker disease, mature trees usually
require a stress event to trigger a susceptible reaction, but seedlings
can be infected if a source of the pathogen is available. A typical
stress event last year was hail damage in localized areas.
This fungus infects growing and elongating shoots in the spring and
kills the main terminal of the seedlings. The black fruiting bodies are
relatively large and can be seen easily with a hand lens and even the
naked eye. These black dots will be on the needles, usually under the
sheath, as well as on the stems and cones.
Diplodia shoot blight is currently widespread, ravaging many landscape
pines. You should consider applying fungicides every two weeks, up to
four times to prevent the spores that are now being produced from
infecting the succulent new growth. During rain and windstorms, these
spores will disperse over long distances and conditions for infection
will remain favorable during rainy and humid days. If wounds are created
by hail, you should consider spraying to protect the trees from severe
disease. Also, if trees surrounding your nursery have severe blight this
year, you may want to reduce the number of susceptible species, such as
Austrian or red pine in the nursery for a couple of years, as this
infection period will probably be extended, even with management. If you
are planting mature Austrian and red pine, consider the fact that even
though they have been inspected, they may still have come from nurseries
or plantations with latent infections, and more than likely, spores
will have infected some of these trees. If the trees are stressed, shoot
blight will appear and you should be ready to manage this disease next
spring. If, later in the summer, more than 10 percent of the trees have
severe shoot blight, begin a spray program next spring. Do not shear
trees that have infections, or may have come from nurseries with
infections, as the shears will carry the spores to each new cut. Also,
in landscape situations, consider raking up cones, which can be a major
source of spores.
Manage this disease with a package of treatments
Consider turf removal under the tree and apply mulch and water. By eliminating the grass under the tree, it will remind you not to apply fertilizer to the tree. Use no nitrogen fertilizer. Water during dry periods to reduce stress. Prune out dead tips and clean pruners with a bleach mixture. Use Cleary’s 3336 thiophanate methyl or chlorothalonil for chemical control if needed.
