Volume 5, No.8 May 28, 1997
Prepared by the University of Massachusetts Apple IPM Project Team in cooperation with New England Fruit Consultants and Polaris Orchard Management
In the most advanced orchards, McIntosh trees are at petal fall to 1/4" fruit. In later-developing areas, McIntosh are at late pink to early bloom.
Development of peaches ranges from shuck split to early shuck
fall.
As petal fall happens or passes, depending on where you are, the
next big scab question is "When does this all stop?"
Good question. Used to be we would run to the lab with bags of
scabby leaves that had overwintered in different parts of the
state, and look at the spores in them, or see how many were released
when we got them wet. When we didn't see any mature spores, or
there weren't any released, then we would say the season was over.
As it turns out, we were doing a lot of extra work and not being
as accurate as we could. Extensive research at UNH and Cornell
shows that we can get a much better estimate of the end of scab
season using a degree day model, accumulating degree days from
green tip until we hit 860_(F). (The base temperature is 32_F.)
It turns out the old method of looking at spores under a microscope
consistently says that there is more scab inoculum than there
really is. When spores are sampled from the air in and around
orchards, the end of primary scab season is always a week or two
earlier than the lab exams indicate it is. The orchard air samples
are, of course, a more accurate picture of inoculum.
We can also use the degree day model to estimate where scab maturity
is for the season at any given point. Depending on location in
the state, right now areas are between 650 DD and 800 DD. By the
model, that means the latest areas have about 35% of the season's
spore load to go, and the earliest areas have only about 5% to
go. In most parts of the state, about 10 to 15% of the spores
are yet to be released.
By the end of the week, the primary season will be done in many
parts of the state, including southwestern, southeastern, Nashoba
Valley and North Shore areas. Growers should maintain fungicide
protection for about 10 days following the end of the primary
season. Then, as long as they don't see any, they can be assured
that scab has been controlled for the year.
Some of our readers may be skeptical. "What do you really
see if you do the squashes?" Fair enough. In Amherst, we
see 12% of the spores are either immature or mature and yet to
be released. We would estimate only 5% to be left. Since the squash
mounts consistently overestimate the number of spores yet to be
released at the end of the season, the degree day estimate looks
good. The temperature model says the inoculum in eastern Mass
should be down to around 5 to 10% left. New England Fruit Consultants
say "Spore squash from eastern Mass. 5/26 revealed approximately
10 - 20% immature or not yet discharged spores."
If you had a problem spraying this spring, what with the wind,
you should be seeing lesions from early primary infections and
even secondary infections. Incidentally, Polaris Consulting pointed
out that "The National Weather Service data for May through
the 21 showed only 4 days averaging less than 10 mph winds, and
12 days had peak winds of over 30 mph!" If you look at the
calm days, most of them had significant rain.
At present, we still have not had what we would consider good
weather for plum curculio immigration and egglaying. Over the
past couple of weeks, we have been sampling in many commercial
and unmanaged orchards; thus far we have seen no egglaying scars
in apples at any of the commercial sites. Nor have we seen any
egglaying scars in apples at the abandoned sites; only a handful
of egglaying scars have been observed in wild plums in an early-developing
PC hot spot. In one unmanaged site, captures on transparent, sticky
flight interception traps showed a small to moderate influx of
PC on Saturday and Tuesday (5/24 and 5/27). While there is some
incoming PC flight activity, it has been too cool to give rise
to any significant egglaying. Orchards will need to experience
a couple of days in a row with temperatures in the mid-70s or
higher to be susceptible to PC egglaying activity.
If there is little sign of significant feeding and egglaying by
PC within the orchard, then a border row spray is recommended
as the first treatment. This allows the grower to wait for warmer
weather, which will lead to a more substantial invasion of PC
and an increase of activity within the canopies. At that point,
a whole-orchard spray is recommended, if the PC population in
the orchard warrants any treatment. Of course, a whole orchard
spray is recommended at an earlier post-petal fall interval than
may be optimal for PC control if Provado or Agrimek are being
applied against leafminer or if an OP is being applied against
sawfly.
The development of leafminer eggs and larvae has certainly been
slowed by the cool weather, and only a small number of sap feeding
mines have been observed in the earliest-developing areas of the
state. In orchards which exceeded the trap capture thresholds,
the post-petal fall application of either Provado or Agrimek will
be in order this week.
In blocks that received a pre-bloom treatment of Apollo or Savey,
it is very difficult to find any red mites on blossom cluster
leaves, suggesting the good effectiveness of these materials.
In some blocks which received only a pre-bloom oil program, a
few mites are present on blossom cluster leaves. Regardless of
the pre-bloom management tactics, monitoring of leaves should
continue in accordance with the recommendations outlined in the
1997 March Message.
Shuck fall is the time to pay particular attention to signs of
attack by tarnished plant bug, oak plant bug and hickory plant
bug. Feeding by these insects peaks between shuck fall and when
the fruit reach 1/2"-3/4" in diameter. It is important
to protect fruit at this stage against 'catfacing' injury caused
by plant bugs. Research has shown that either Guthion or Imidan
alone are at best 50% effective in preventing plant bug injury.
Therefore, we suggest use of a full rate of Guthion or Imidan
in conjunction with a one-third labeled rate of a pyrethroid such
as Asana, Ambush or Pounce. We feel that because of the tendency
of pyrethroids toward high absorption into and slow release out
of the bark of the trees, the one-third rate of pyrethroid offers
a good compromise; extending the residual effects of the chemical
while limiting the well-known destructive effects against mite
predators. If mowing is planned in blocks of peaches, it is important
that an active protective insecticide cover be in place at the
time of the mowing. This will limit the effect of plant bugs,
which are numerous in the groundcover, when they are pushed into
the canopies by mowing.
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.