|
Spreading the Benefits ...
Methods to Disperse T. pyri in your Orchard.
Typhlodromus pyri is an effective
predator of the European red mite. As you may know, we have been involved in a
project to release and monitor T.pyri in Vermont (see March 1999 issue of the Vermont
Apple Newsletter). However, based on sampling in orchards in which pesticides
harmful to T.pyri have not been used, it appears we have resident populations in
Vermont that will increase in numbers if given the chance.
If you have been successful in conserving and enhancing the predator mite population in
part of your orchard and would now like to 'spread the benefits' to other blocks, Dr. Jan
Nyrop from Cornell University outlines in the following article 4 different ways in which
this can be done. Note that the trunk wrap method can be done now and dispersing
prunings can be done this winter.
RELEASE THE HOUNDS
Jan Nyrop and Dave Kain, Entomology, Geneva
Scaffolds Fruit Journal, 1999, Vol. 8.
"The mite predator Typhlodromus pyri can give biological control of
European red mite when the predator is conserved in apple
orchards. Experiments have shown that, once established in an orchard, this mite can
completely eliminate the need for miticides. While T. pyri is endemic throughout
much of western New York, it can take as many as three years in specific orchard blocks
for predator numbers to increase to the point where biological control is realized.
Moving T. pyri from blocks where they are abundant to sites where more predators
are desired (seeding) can speed this process.
Instances will occur when it is necessary to use pesticides that are toxic to T. pyri
to control other orchard pests. To combat the resulting disruptions of
mite biological control caused by these pesticide applications, it has been
suggested that orchardists establish sites to be used as mite "nurseries".
These sites would not be treated with pesticides harmful to T. pyri and would
be used as sources of predators that could be moved to orchards where predators are
scarce; the practice of transferring them could therefore become an important ingredient
of any integrated mite control program.
The first method of moving T. pyri from one orchard block to another is to place
wood pruned from a source orchard in winter or early spring into a recipient orchard.
Because T. pyri overwinter as adult females, prunings harbor predators, although
numbers in each section of pruning are highly variable. We suggest placing all the
prunings from one tree into another tree. It is probably not effective to simply spread
the prunings beneath recipient trees. Pruned wood need not be placed in the recipient
trees immediately after pruning, but should be placed there before or just when trees
begin to produce green tissue the following spring.
The second method consists of transferring flower clusters from a source orchard to a
recipient site. T. pyri move into flower clusters at Tight Cluster and remain there
through bloom, probably to feed on apple pollen. As many as 2 to 3 predators can be found
in each flower cluster and surrounding leaves. To transfer predators in this manner, at
least 20 flower clusters (and associated wood and leaves) should be placed in each
recipient tree. The flower clusters are easily attached with paper clips, staples,
or twist ties. Flower clusters may be stored for several days in a cooler before being
affixed to receiver trees.
The third method of transferring T. pyri consists of collecting leaves during
the summer from trees where T. pyri are abundant, and
placing them into recipient trees. Leaves are easily affixed to
the target sites using staples. The number of leaves to use depends
on the density of T. pyri in the source orchard. As a guide, at least 50 predators should
be released in each target tree.
The fourth method of transferring T. pyri is perhaps the easiest and does not carry
the risks of also moving unwanted pests that the three prior methods have. Artificial
overwintering sites for T. pyri can be created by glueing burlap to the inside of
tree wrap. These composite bands, approximately 12 to 16 inches in length, are then placed
on source trees in early to mid-September by stapling them around the tree bole
and/or large scaffold branches. In early December, these bands should be collected,
tightly rolled with a rubber band used to hold them so, and placed in a sealed
plastic bag with a bit (i.e., a "puff") of wet cotton. The bag should be
placed in an insulated storage container, which in turn should be placed in a cold, though
protected, environment that will buffer large temperature fluctuations. Ideally,
temperatures should be maintained right at the freezing point. The following spring, the
burlap bands should be placed around recipient trees at around the Half-Inch Green bud
growth stage. While the number of predators that overwinter in bands is variable, as many
as 400 predators can be transferred in each band. We suggest placing a single band on each
recipient tree if the bands were collected from trees that harbored moderate to high
numbers of T. pyri (1-2 per leaf) the prior fall, and two bands in each tree
otherwise.
While T. pyri overwinter throughout the tree, there are apparently many predators
that overwinter on large branches or the trunk itself and that move into the canopy as
foliage appears. Use of nurseries in which T. pyri are cultivated, and transfer of
branches harboring T. pyri from these nurseries to target sites, should allow
biological mite control to be more persistent on a farm-wide scale. The second season
after seeding T. pyri and using nondisruptive pesticides in our IPM Demo blocks in
western N.Y., predator numbers were at levels of more than 1/leaf by the end of August,
and true biological control (that is, no oil or acaricides) of ERM was realized in all
blocks by the third year.
Unlike petroleum oils applied early in the growing season, oils applied during the summer
can have an adverse effect on phytoseiid numbers. However, this effect is apparently
only significant when high volumes of oil suspension are applied. Our opinion is that oil
applied using conventional airblast sprayers will have only a minimal negative effect
on phytoseiid numbers. As such, summer oil applications can be recommended as a way to
help manage European red mite numbers if predator numbers are insufficient for
biological control. For a more detailed discussion of the ins and outs of
establishing predator mites, refer to IPM Pub. #215, "Achieving biological control of
European red mite in northeast apples: An implementation guide for growers", by
D. Breth, J. Nyrop, and J. Kovach" (1998), from which much of this information was
adapted."
|
|
