Volume 5, No.7 May 21, 1997
Prepared by the University of Massachusetts Apple IPM Project
Team in cooperation with New England Fruit Consultants and Polaris
Orchard Management
In the earlier-developing areas of the state, McIntosh development
ranges from late bloom to early petal fall. In the later-developing
areas, trees are for the most part at mid- to late pink.
In some areas, leafminer captures are continuing to build even
at this late date, which is reflective of a large overall population
statewide. Egg densities of 1-2 eggs per cluster have been seen
in some monitored orchards, particularly those with high trap
captures. As mentioned in previous issues of Healthy Fruit, the
time to treat using either Provado or Agrimek is at petal fall
or closely thereafter. This year, cool weather has prevailed
and the development of LM eggs and larvae can be expected to be
slower. Because of this, orchards which have exceeded treatment
thresholds on LM traps can delay the post-bloom application against
LM to several days after petal fall with little risk.
The weather over the past week (during late pink and into bloom
in most orchards) has not been conducive to sawfly activity, nor
has it been conducive to EAS trap captures in potentially infested
orchards. Some blocks in some orchards have definitely exceeded
trap capture thresholds; in these areas consideration of a treatment
at petal fall or soon after is warranted. However, most orchards
have not approached thresholds for treatment, which either means
that the populations are low in these areas or that the weather
has yet to trigger a level of activity which is indicative of
the actual population density. In most areas this year, the weather
has simply been too cool to give an accurate indication of the
population present in the orchards.
In some monitored orchards, plum curculio adults were caught
in black pyramid traps next to the tree trunks. The moderate
temperatures on Monday, coupled with the damp conditions, allowed
PC adults to crawl into traps next to the tree trunks, the first
captures of this season. So far, no PC feeding or egglaying has
been observed even on wild plums, which generally harbor large
populations of PC and are currently at the stage of development
when PC injury is most likely to begin. No PC have yet been observed
from tapping over groundcloths either, which tells us that while
the weather has allowed the PC to arrive at or near the bases
of orchard trees, it has not yet allowed movement into the canopies.
As mentioned earlier, the cool weather has delayed the development
and activity of both sawfly and leafminer larvae. Because of
this, growers may be wise to withhold the petal fall PC treatment
until the weather is warmer and there are signs of PC present
in the tree canopies. This calls for a vigilant monitoring of
traditional PC hotspots for indications of feeding and egglaying
activity and taking action when the first signs are seen. If
the orchard has little need for a petal fall treatment for leafminer,
sawfly or plant bug, then a border row spray may be sufficient
as the first PC treatment; waiting for warmer weather for a whole-orchard
treatment against the invading population.
In orchards where pre-bloom treatments were less than optimal,
a fair number of motile nymphs and some adults have been seen.
Refer to last week's Healthy Fruit or the 1997 March Message
for sampling and treatment recommendations.
In a few orchards, early instar gypsy moth have been seen on
trees bordering stands of oak. While we do not expect a big year
for gypsy moth, there could be a few local trouble spots. If
this is the case, growers should be concerned with young trees
which received no pre-bloom insecticide treatments and are adjacent
to stands of oak. Large numbers of young larvae, which blow into
the apple tree canopies from adjacent oak trees, can cause significant
damage to young trees, stunting their development.
Petal fall is the time to begin thinking seriously about options
for insecticide applications against pear psylla. According to
research done in New York state, Agrimek in conjunction with horticultural
spray oil applied 1-2 weeks after petal fall provides 4-6 weeks
of protection under normal conditions. If the material of choice
is Mitac, back-to-back sprays are recommended, with the first
occurring 2 weeks after petal fall and the second 7-10 days later.
To reiterate, if Agrimek is used, it should be applied with 1
gallon of horticultural (not dormant) oil per acre. Agrimek is
not effective unless it is used in conjunction with a material
which facilitates penetration into the leaf tissue. Up until
now, horticultural oil has been the recommended material to aid
in penetration, but the manufacturer of Agrimek has indicated
that it may work as well in conjunction with a penetration facilitator
other than horticultural oil. This would alleviate the compatibility
problems encountered in an orhard management program which includes
Captan or sulfur. At present, the manufacturer is not recommending
any specific alternatives to horticultural oil, but materials
such as Sil-Wet may become an alternative.
Of course, weather can never be windy and dry, or wet with calm
intervals. In New England, it has to be windy and wet, making
it nearly impossible to spray, but keeping the primary scab season
filled with infection periods. Fortunately, among us we have
observed only one commercial orchard with any signs of apple scab.
We have not quite accumulated enough degree days to call primary
season done and over, but may, with any warm weather, be there
by the middle of next week. At that time, we will provide an
update on treatment.
With most of Massachusetts McIntosh in some phase of bloom, a
check of the MaryBlyt model shows that the risk of infection is
very low. It's been too cold, as if you didn't know. However,
a prolonged bloom and some warm weather may tip the balance to
cause problems on late-blooming varieties in some areas by the
end of the bloom period.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, and Wes Autio, except where other contributors are noted. Final copy is edited by Dan Cooley. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. Please cite source if reprinting information.