Tree Fruit & Grape News, April 1998
Newly Planted Trees
Don't plant problems in your orchard
When planting your new orchard blocks this spring, keep nursery
stock quality in mind. There are several diseases that can be
carried on nursery stock. Trees that are obviously diseased should
not be planted. Check with your suppli-er to determine their policy
on replacing or refunding diseased or damaged trees.
Viruses
Although viruses are not usually apparent on newly planted trees,
they can seriously affect the growth and performance of fruit trees
both in the nursery and the orchard. Make sure rootstocks and
scionwood come from a source certified as virus free.
Crown Gall
Crown gall is often a serious problem in nursery production, but
it can also be damaging in the orchard. Galls form most often in the
crown area, but also occur on the roots and trunk. The galls become
firm, woody tumors with irregular surfaces and great variation in
size. Crown gall in the orchard is associated with reduced life span
of the tree. In addition, crown gall bacteria can infest the soil.
Stone fruit are more susceptible than apples. On apple the union
between rootstock and scion is readily infected, while stone fruit
are usually infected through injuries. Grape vines are highly
susceptible; galls may form over the whole trunk, and affected
grapevines seldom survive. Winter injury and mechanical injury can
greatly increase crown gall infections.
Nursery stock with obvious galls should not be planted. The
product "Dygall" is an inoculant for use by the nursery
industry which can reduce crown gall infections. It has not proven
effective on apple, and is not registered for that use. It is also
unlikely to be effective on grape.
Fungal Cankers
Several canker diseases can be carried on nursery stock,
including anthracnose and European canker. Trees with cankers on the
main trunk should not be planted. Cankered branches may be pruned
off and removed from the orchard. Cankers that are allowed to
develop will produce spores that can cause new cankers and fruit rot
problems. Initially the spread will be localized, but if cankers are
permitted to overwinter they will start to produce air-borne
ascospores which can spread by wind throughout the orchard. The
climate in the Okanagan is not conducive to canker development every
year, but the potential for problems should be removed in any case.
Note that new cankers are not always obvious until after the trees
have been planted, and the cankers have more time to develop.
Fire Blight
Apple trees with fire blight infected rootstocks have been an
occasional but serious problem in new orchards in the past several
years. Unfortunately this problem is often not easy to detect until
after the trees have been planted out. Watch for oozing along the
trunk and crown area of trees that are not doing well. Have any
suspicious trees diagnosed. Fire blight is not a problem that should
be ignored.
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