Volume 5, No.11 June 18, 1997
Prepared by the University of Massachusetts Apple
IPM Project Team
in cooperation with New England Fruit Consultants and Polaris
Orchard Management
Most growers are wondering whether the lack of rain is beginning
to be a problem. In most soils, fruit trees are still getting
enough moisture. However, in sandy or shallow soils, lack of moisture
is getting to be a real problem.
The dry weather has all but stopped disease progress in commercial
orchards. With primary scab done, and very little brown rot pressure
on stone fruit, growers are looking at summer disease management
as the only disease issue of any concern. In fact, this is of
minor concern until humidity and/or rainfall increases. Low rates
of fungicide (no more than 3/4 lb. Captan 80 or equivalent) will
be enough to protect fruit for a 2 to 3 week period. In the table
below, Dave Rosenberger of Cornell has listed protection intervals
and rainfall needed to wash off a number of fungicides useful
against summer diseases.
| Fungicide | spray interval days | ||
| Benlate + | |||
| or Mancozeb | |||
| or Ziram/sulfur | |||
| Topsin M + | |||
| or Ziram 76W | |||
| or Captan 50W | |||
| Ziram 76W | |||
| Captan 80W | |||
With the very warm and humid weather of last week, we saw the
largest numbers of curculio captures of the year on sticky, clear
panels placed just outside the tree canopies. These traps are
designed to intercept PCs approaching the tree canopy by flight.
The number of PCs captured on these traps has since dropped significantly,
leading us to conclude that last week's immigration was likely
one of the largest PC influxes of the year, which was followed
by a large amount of egglaying activity late last week and into
this week. In a monitored block of unmanaged apple trees, PC damage
increased from 15% to 80% over the past week, and fresh PC egglaying
scars have been observed in many sampled commercial orchards as
well.
Thus, the question remains as to when the last PC spray should
be applied. In last week's Healthy Fruit, we discussed the temperature
driven model from New York state that aims to predict the timing
of the last PC treatment based on a degree-day (DD) model. Apparently
we misinterpreted the implications of the NYS model; a point which
waskindly brought to our attention by Glen Koehler of Maine earlier
this week. We had indicated that the last PC spray should occur
when 340 DD have been accumulated after petal fall. In truth,
the NYS model simply suggests that the final spray should be timed
such that the residual activity of the chemical is still effective
when 340 DD are accumulated.
To date in an orchard near Amherst, 295 DD have been accumulated
since petal fall. Given the dry weather pattern which we have
experienced thus far this season, coupled with the residual effectiveness
of Guthion and Imidan (approx. 10 days under dry weather conditions),
we conclude that a PC application made last weekend or early this
week should be enough to carry through to the end of the PC season
in early- and middle-developing areas. In Conway, as well as other
later-developing areas, the final PC spray will likely occur toward
this weekend. If there are any PC which have yet to immigrate
into the orchards, they should surely do so over the weekend,
and the residual effects of sprays this week should handle the
stragglers.
Provado, which was used this year in many monitored blocks as
a treatment against leafminer, seems to have arrested LM development
at the sap-feeding stage. Blocks which did receive such a treatment
are showing little or no evidence of mines progressing to tissue-feeders.
In blocks which received no LM treatment, tissue-feeding mines
are readily apparent, and the first pupae have been seen. Adult
parasites have been seen in blocks which were not treated for
LM this year; these parasites will contribute to suppression of
LM if they can endure the sprays directed at plum curculio.
Eggs of the first summer generation of European red mites are
just beginning to hatch. The very warm weather conditions of the
past week favor rapid ERM development, particularly in blocks
which received little or no early treatments against ERM. Growers
who did not apply Savey, Apollo or Agrimek should keep a careful
eye on the presence and developing population density of ERM nymphs.
Growers who used Provado this year for leafminer control should
have relatively little to worry about with leafhoppers. Also,
growers who have applied 2 sprays of Sevin XLR as a thinning agent
should experience reduced LH problems. If only a petal fall application
of Sevin XLR was used, or if neither Provado or Sevin was applied,
growers should keep a sharp eye out for immigrating rose leafhoppers
and developing nymphs of white apple leafhoppers. A good number
of RLH adults was seen earlier this week at the Horticultural
Research Center in Belchertown, indicating that RLH immigration
is now in progress. To achieve maximum effectiveness of sprays
against RLH, we suggest holding off on the treatment until RLH
nymphs hatch later this month.
With leafhoppers, it is the 3rd generation which causes the greatest
problems; substantial excrement on fruit and nuisance to pickers.
However, it will soon be the time to nip LH populations before
they can build numbers in their 2nd and 3rd generations. A half-rate
of Thiodan should go far toward control of the developing population.
In recent years, we have not seen much San Jose scale on fruit
at harvest in most orchards. However, some problem blocks do remain,
especially those comprised of full standard-sized trees. Oil at
1/2" green would have been a good first step toward control
of SJS, but this may need to be followed up by a pesticide treatment
in the next week or two. If such a treatment is necessary, a spray
of Lorsban against the crawlers in the next couple of weeks is
the next step in dealing with this pest.
The peach crop appears to be free of catfacing injury thus far
this year. In most orchards, regular treatments against PC have
occurred, and to date there have been no observations of summer
peach plant bugs active in the trees. For a detailed discussion
of control of peach plant bugs, refer to the 1997 March Message
or the June 4 issue of Healthy Fruit.
Healthy Fruit is available on the day of publication via
email by contacting Dan Cooley at
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.