Phomopsis blight is a fungal
disease that affects juniper shrubs, and to a lesser extent, cypress, false
cypress and arborvitae plants. This disease infects the foliage and then can
move into smaller stems and kill them by creating cankers and girdling the
stem. Larger stems can also develop cankers but usually don’t die back.
Plant tissue infected with
Phomopsis blight fades to a lighter green before dying and turning a reddish
brown color. Drought stressed plants can show similar dieback but the line
between live and dead tissue is not as clear as it is with Phomopsis. Other
needle blights in junipers usually begin with older needles and work their way
up the stem but Phomopsis starts at the tip and works down toward the center of
the shrub.
Another disease, Kabatina
blight is, to the naked eye, nearly indistinguishable from Phomopsis but is
active earlier in the year. Kabatina blight can become active as early as March
in Michigan. Kabatina is infective in the fall of the
previous year. Phomopsis is active in late March and April and again in August
and September, and the dieback can occur any time during the season. Even short
periods of high humidity and temperatures can initiate the development of
Phomopsis spores.
Control of Phomopsis blight involves
planting resistant varieties, spacing new plants so they can dry, avoiding
shaded areas, watering in the morning so the foliage can dry, and pruning on
dry summer days.
Because this shrub disease
is hard to diagnose in the field it may be necessary to submit a foliage sample
to a laboratory before starting a fungicide program. Phomopsis blight can be
reduced with a regimen of proper watering, adequate soil fertility, sanitation
pruning, and spraying with fungicides when necessary.
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