Volume 5, No.10 June 11, 1997
It has gotten dry, but in spite of the recent warm weather, overall
the season from March 1 remains about 4_F below normal. The rainfall
over the past month is about 2 in., about half of the normal amount,
and since the beginning of the month about a tenth of an inch
has fallen at Belchertown, compared to the 1 inch average.
In the earlier developing areas of the state, fruit have developed to 3/4". In the later areas, primarily in the western portion of the state, fruit size ranges from 1/4"-1/2".
Following the end of primary scab season, reports around the state
indicate that most conscietious spray programs, whether based
on Sis with a protectant, or on protectants alone, have stood
up well. Even with the wind, most growers have gotten good control.
Scab is generally absent in commercial orchards. A few notable
exceptions have occurred where early applications were not made.
If your orchard is one of these exceptions, take advantage of
the hot weather to apply an eradicant. As mentioned a month ago,
captan will suppress spore development, that is, burn out existing
scab. This eradicant action is best at temperatures above 80
F. The equivalent of 1 1/4 lb. per 100 gal. of Captan 80W
(it can be 80W, 50W or Captec, take your pick) will do the job.
Since we do not have obvious cases of Benlate, Topsin-M or Syllit
resistance in Massachusetts, either of these materials may be
combined with captan to improve burn out. Check out the May 14
Healthy Fruit for details.
In the 48 commercial orchard blocks which we are sampling on a
3-day interval, the cumulative curculio injury levels to date
range from zero injury to 4% injured fruit, with most blocks remaining
below .5% cumulative damage. With the very recent warm days, we
have seen a noticeable increase in PC egglaying in unmanaged apple
trees. In most commercial orchards, the sprays applied have thwarted
any significant increase in PC egglaying. Temperatures in the
mid-80s to low 90s over the past several days (6/8-6/11) is good
fortune for management of the immigrating PC population. The consistently
warm weather will bring out the bulk of the invading population,
effectively shortening the period of PC invasion and subsequent
egglaying.
At this point, the orchard management challenge is determining
when to apply the final treatment against PC. With no effective
monitoring trap as yet, we must rely on two other approaches.
First, there is no substitute for continuing to monitor orchard
trees for evidence of ongoing PC feeding and egglaying. This allows
for a reasonable estimate of the active PC populations present
in the orchard; any secondary PC invasions will be evidenced by
increases in fresh egglaying and feeding injury between sprays.
All told, regular monitoring of fruit for fresh PC injury during
the interval between applications offers a fairly reliable determination
of whether or not an additional application against PC is warranted.
The second approach aimed at determining when the last application
against PC should occur is use of the degree-day model developed
in Geneva, NY. According to this model, the last treatment against
PC should be applied when 340 degree days (DD) have been accumulated
since petal fall. To calculate DD, take the average of the day's
maximum and minimum temperatures (For example, 80o
max. and 60o min.=70o daily average.),
then subtract the base level of 50o to determine the
day's DD total (70o average minus base-level
50o=20 DD). In an orchard very near Amherst the
accumulation has reached 175 DD as of today. In some later areas
in the Berkshires, the accumulation to date is approximately 100
DD. Thus, if 20 DD are accumulated daily on average, the model
would indicate that 7-9 days remain before the last PC spray should
be applied. Refinements of this system are presently being made
by Glen Koehler in Maine to validate the model for New England
growing conditions, and we should know at the close of this PC
season what modifications need to be made.
In orchards where Provado was used at petal fall or shortly thereafter,
very few mines have progressed beyond the sap-feeding stage. In
orchards where populations have remained low this spring and have
not yet received a treatment against leafminer, a good proportion
of the mines have developed into the tissue-feeding stage. This
year, the majority of scouted orchards did receive a post-bloom
application against LM because trap captures and subsequent levels
of mines indicated a need for treatment.
Currently, we are approaching the end of the period during which
action can be taken against the first generation mines. As stated
in last week's issue of Healthy Fruit, our treatment thresholds
for first-generation sap-feeding mines are 7 mines per 100 leaves
for McIntosh and 14 mines per 100 leaves for non-McIntosh varieties.
If these thresholds are exceeded, we recommend a treatment with
Lannate within the next couple of days. Agrimek (with hort. spray
oil) can still be used, but its effectiveness will be reduced
due to increased hardening of the leaf tissue which does not allow
for maximum absorption of the chemical into the foliage.
This hot, dry weather is very conducive to rapid multiplication
of European red mites. Fortunately, orchards which received either
a pre-bloom or petal fall mite treatment remain quite free of
egglaying females. However, in blocks which received only 1 oil
application, or even 2 oil applications with less than optimal
weather conditions, egglaying females and eggs are definitely
in evidence.
We have now reached the point where mite control by use of either
Agrimek with oil or Vendex with oil is questionable. Neither of
these chemicals works to its maximum potential when applied this
late (two weeks after petal fall) because the hardening of leaf
tissue bars the proper absorption of the chemical into the foliage.
Based upon information from New York state, the action threshold
for treatment against ERM during the first 2 weeks of June is
1 or more motile mites present on 45% of middle-aged fruit cluster
leaves. If this threshold is exceeded, an application of Agrimek
or Vendex with oil is possible, but the effectiveness of such
an application will certainly be less than optimal. The best available
alternative is Kelthane. Carzol is also available for use, but
it is well known as being extremely harsh on predators.
Regarding Pyramite, the Pesticide Bureau will meet on June 25th
to consider registration of this chemical for use in Massachusetts,
and Ron has been asked to be in attendance. We are hopeful that
the outcome will be positive and the material will be available
for use by early July.
Thus far, treatments of either Provado or Agrimek against pear
psylla have worked extremely well, with few psylla remaining in
treated areas. In areas which did not receive a treatment of Provado
or Agrimek, moderate populations of psylla adults are present,
but no second generation egglaying has been observed as yet.
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.