VISITOR FROM THE EAST
(Art Agnello ama4@nysaes.cornell.edu,
Entomology, Geneva)
The oriental fruit moth (OFM), native to China, was introduced into
the United States from Japan about 1913 on infested nursery stock. The
OFM is now found in all regions of North America where peaches are grown.
Although it is most important as a pest of peach, the OFM has an extensive
host range that includes apple, quince, pear, plum, cherry, apricot, nectarine,
and some rosaceous ornamentals. In the northeastern United States, the
OFM has three generations (flights) per year. In areas with a longer growing
season, it may have up to five generations per year.
Oriental fruit moth adult
On peach, the OFM feeds in both vegetative growth and fruit. The
first generation, which is feeding when terminals are succulent and tender,
develops almost exclusively in the vegetative growth. The larvae often
enter the terminal at the base of a young leaf, and tunnel toward the
base of the shoot. Infested terminals wilt and die back to the margin
of feeding, and are commonly called "strikes" or "flagged shoots". Heavy
twig infestations of nursery stock can adversely affect the shape of the
tree. Axillary buds often begin to grow when the terminal shoot is killed,
causing the tree to have a bushy appearance.
Peach "strike" or "flagged shoot" from terminal feeding
by oriental fruit moth larva.
Fruit that are infested when very small often drop. Early infested
peaches that do not drop have obvious entrance holes with frass and gum
exuding from them. Larvae attacking nearly ripe peaches usually enter
the fruit near the stem, leaving only a very small, inconspicuous entrance
hole. The larvae tunnel in the fruit, and frequently excavate cavities
near the pit.
Peach infested by oriental fruit moth, showing frass and gum exuding from
entrance hole.
Oriental fruit moth internal injury to peach.
Terminal feeding on apple is similar to that on peach. Infested apples
have a collection of frass at the exit hole of the insect's feeding tunnel,
or at the calyx end.
Apple infested by oriental fruit moth, showing frass
exuding from entrance hole.
It is difficult to distinguish between OFM damage and codling moth damage.
OFM larvae feed randomly in the apple, and usually do not feed on the
seeds, while codling moth larvae usually tunnel directly to the core of
the apple and feed on the seeds. Later instar larvae of the two species
may be distinguished by the presence or absence of the anal comb at the
tip of the abdomen. The anal comb is present in the OFM and absent in
the codling moth.
More than 130 species of parasitoids have been reported attacking
OFM; however, parasitism probably plays a very minor role in OFM control
in today's commercial orchards because of the sensitivity of many parasitoids
to commonly used insecticides. Before the advent of the organochlorines,
attempts were made to supplement naturally occurring biological control
of the OFM. Inundative releases of the braconid wasp, Macrocentrus
ancilivorus, provided an average 50% reduction in number of infested
fruit. However, because of the large pest complex on apple, biological
control of one pest is difficult to achieve, since broad-spectrum insecticides
are still needed for other pests.
Research on mating disruption of OFM has shown that if a synthetic
sex pheromone is released in high concentrations during bloom, male Oriental
fruit moths cannot locate a female to mate. However, this approach is
economically justified in N.Y. only if 2-3 sprays are normally applied
to control this pest, and if no other insecticide sprays are routinely
needed after shuck split. For most commercial blocks, where 2nd brood
larvae threaten fruits as they ripen, an application of carbaryl (Sevin)
is recommended 2 weeks before harvest or, for those depending on scouting
results, when larval numbers reach 1 per 10 terminals.
Recent complaints of ineffective control in some peach blocks having
more severe pressure (particularly in far western NY) may indicate a failure
to take care of the early larvae sufficiently. The recommendations from
Ontario, where OFM is a more serious problem, are to spray about a week
after the peak of both the first and second flights (usually near the
end of shuck split and early to mid-July, respectively), possibly following
up with a second application in each case. The first flight peaked back
in mid-May, and the second flight should be getting under way in a week
or so. The second application against the resulting generation would correspond
with the 2-week pre-harvest spray noted above for many varieties. In recent
years, some tolerance or resistance tendencies have been noted in local
populations, so this is a case where rotation to alternative chemical
classes would be recommended; other choices would include Lorsban, Lannate,
or a pyrethroid. (Adapted from Oriental Fruit Moth Fact Sheet #17, by
A. J. Seaman and H. Riedl).
TAKE CARE OF YOUR CANOPY
(Art Agnello, ama4@nysaes.cornell.edu
Entomology, & Alan Lakso, and anl2@nysaes.cornell.edu
Horticultural Sciences, Geneva)
Regardless of how attentively you have watched the numbers of mites
in your specific orchards up to this point, a careful examination of at
least the traditional trouble spots is recommended at this time, for a
number of reasons. First, we are past the period of effectiveness of early
season applications of oil, and even the small percentage of survivors
from the most successful pre-bloom control programs could start to increase
to problematic levels by now. Also, this is normally the time when we
see a big jump in numbers of motile forms because the first crop of European
red mite summer eggs has completed their hatch. The hot weather we are
experiencing has been ideal for mite growth, so even though the ERM threshold
goes up to 5 per leaf in July, the mites tend to increase exponentially
now, so it's no contest for all that new growth the trees have been putting
on recently. Because of their early start this year, ERM could easily
squeeze in an entire extra generation before the summer's out. This may
not be evident just yet, but that extra flush of motile forms at the end
of August will seem like the coup de grace if they weren't properly attended
to when they pole-vaulted past threshold two months before.
This type of weather is also much favored by twospotted spider mites.
Recall that the TSSM overwinters as an inactive adult female beneath bark
scales or under debris on the orchard floor.
Occasionally, when winter temperatures are warm enough, the mites remain
active and maintain a low population on weed hosts or cover plants in
the orchard. As summer approaches and temperatures rise, mite populations
increase and they begin to move up the tree trunks to the foliage. Lower
portions and canopy centers are attacked first, then the mites spread
to the outside of the trees as their population increases. Feeding on
pear leaves causes a unique browning or blackening of the foliage. It
is not uncommon to have a colony of only 2-3 mites near the midrib of
a leaf, and as a result of their feeding there is a blackening of large
sections of leaf from the midrib to the margin. A low number of TSSM is
more damaging than a similar count of ERM, and foliar blackening may appear
after the mites have been controlled, brought about by a period of hot
weather shortly after an effective spray has been applied.
 It's
important to note that any foliar pests could become particularly troublesome
this season because of the combination of drought stress and relatively
high fruit loads evident in many areas. Even though we may do everything
well with our tree design and canopy management, the potential we've developed
may not be realized if the leaf health is destroyed by foliar pests like
mites, leafminers or leafhoppers. Research has shown that foliar pests
like mites, leafminers and leafhoppers reduce the leaf's ability to make
sugars by photosynthesis. We feel that reducing the carbohydrates available
to the fruit is probably the mechanism by which foliar pests affect apple
trees and the fruit. If true, then we should expect that other factors
that affect the carbohydrate supply or demand would interact with the
pest injury. The most obvious interacting factors is the crop load. Heavy
crops should make the trees more sensitive to pest stress.
In mature Delicious/M26 trees with different crop loads, ERM injury
reduced both leaf and whole tree photosynthesis, but yield differences
were not always related to ERM injury. The primary effect of the mites
was to decrease late season fruit growth and final fruit size. The effect
of high mite injury on fruit size was more severe in normally-cropped
trees.
Fig. 3. Mite effects on final fruit weight of 'Starkrimson
Delicious' depending on the crop load of the tree. Bar on left of each
pair is for healthy trees compared to high mite (>1500 mite-days) on
right. Note much greater effects on normally-cropped (a good commercial
crop) trees that already had smaller fruit size.
The fruit size distributions showed that for normally-cropped trees,
the mite injury dropped the percentage of fruit over 170 grams from about
50% to only 10%. This represented a double penalty in fruit size, since
the fruit was already smaller on heavy-cropping trees even before the
mites developed. Also, the next season's crop was reduced as well, giving
a triple whammy.
Effects on fruit quality were found to be primarily due to reduced
size and later maturity that occurred due to higher crop levels or higher
mites. All these mite effects on fruit quality and maturity are essentially
the same as those expected from heavier crop loads.
Check your foliage; if you miss the chance to control these pests
now, there may be no recovering before some significant damage is done
to this very susceptible stage of the trees and fruit.
End of this issue: Scaffolds 1999 Index
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