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Project Leader(s): Terence Robinson, Dept. of
Hort. Sci., NYSAES, Cornell University, Geneva
Herb Aldwinckle, Dept.
of Plant Path., NYSAES, Cornell University, Geneva
Type of grant:
Cultural methods
Project location(s): Throughout the Northeast
Abstract: Control of fire blight control on
dwarf apple trees of highly-susceptible cultivars is an
increasing problem in NY. Fertilizer practices can have
a small but significant effect on tree growth and on
shoot blight severity. In general, we found that the
lower the nitrogen fertilization rate the lower the
severity of fire blight infection; however, the
unfertilized treatment had the poorest tree growth. High
K levels alone had a similar level of fire blight
infection as did the unfertilized control but much
better tree growth and production. Tree growth was poor
if nitrogen alone was added but if both nitrogen and
potassium were added then growth was much better. The
best combination of growth and the least severity of
fire blight was with the high K treatment. It appears
that the soils used in this experiment have adequate
levels of nitrogen to produce good tree growth if
supplemented with K.
The new
environmentally-friendly shoot growth retardant, Apogee,
has a suppressive effect on fire blight development in
shoots. Our results show that it does not control
blossom blight, but does significantly reduce the amount
and severity of shoot blight. Although shoot blight was
reduced on Apogee treated trees, rootstock fire blight
and tree death were not reduced.
From a practical point
of view apple growers should manage new orchards with a
relatively low level of N and a relatively high level of
K. This could be combined with late season applications
of Apogee to reduce the risk of fire blight infection.
Although Apogee will reduce shoot blight progress it
does not reduce rootstock death. Growers should utilize
the new fire blight resistant rootstocks from Geneva
(G.16 or G.30) to prevent tree death. An integrated
approach with fire blight resistant rootstocks, low
nitrogen fertilization, high K fertilization and late
season use of Apogee should give good tree growth and
minimize fire blight risk.
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