Volume 5, No.6 May14, 1997
Prepared by the University of Massachusetts Apple IPM Project Team in cooperation with New England Fruit Consultants and Polaris Orchard Management
While McIntosh in the early-developing areas of the state have
progressed into early bloom, the later-developing areas remain
at tight cluster. Last year at this time, McIntosh trees were
at late pink in the later-developing areas, with those earlier
orchards moving into petal fall. Overall, tree development continues
to progress extremely slowly throughout the state.
Symptoms of scab are now visible on leaves in some abandoned orchards,
as well as at least one commercial orchard. The most likely cause
of these lesions is the infection of April 28. Check the leaves
which emerged earliest if you are looking. They are not very easy
to see, so check carefully, starting in those places where scab
is most likely, like the corner near the abandoned trees or that
place which has had some scab the last two seasons.
The development of these infections makes scab management more
difficult. For the next few weeks, they will be producing inoculum,
in addition to the primary ascospore inoculum that is available.
Inside a well-managed commercial orchard, this isn't an issue,
but in abandoned trees on the border, or in orchards where the
early scab management wasn't entirely successful, scab pressure
will be intense. The problem is particularly nasty because this
comes when new fruit are most susceptible to scab. For 3 to 4
weeks after petal fall, fruit are highly susceptible to scab.
Remember that the SI fungicides (Rubigan, Nova and Procure) are
not as effective against fruit scab as they are against leaf scab.
If you are using these materials, make sure that you include at
least a half rate of a good protectant (captan, mancozeb, etc.).
What if scab lesions have appeared in an orchard? For several
reasons, I feel captan should be part of the eradicant fungicide
program used against existing scab. For a few years, New England
pathologists have pointed out that 2 lb./100 gal. of Captan 50W
will suppress spore development, that is, burn out existing scab.
This eradicant action is best at temperatures above 80
F. 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. The SI's will
also suppress spore development, and help burn out lesions. When
eradicating infections, the interval between sprays should be
kept short, at about 7 days. Spray intervals should be kept short,
at about 7 days, until lesions stop growing, usually after 2 to
4 applications.
As noted last week, even if you don't have to fight established
lesions in the orchard, we have reached the point in the season
where primary innoculum is abundant. This is a critical period
for scab managment.
Mite egg hatch is nearly complete in orchards that are in early bloom and is ongoing in the later-developing orchards
Tarnished plant bug captures on white sticky rectangle monitoring
traps remain low in most orchards across the state. Few orchards
have exceeded trap capture thresholds. Because of the low level
of TPB activity to date, many growers have decided to omit the
pre-bloom insecticide treatment for TPB. However, as mentioned
last week, a few warm days in a row can still initiate increases
in TPB activity, causing damage to the developing buds during
bloom and into petal fall. If this is the case, the only option
for treatment is a petal fall application of either Guthion or
Imidan. Whether such an application against TPB is warranted depends,
in part, on what else you might be spraying. First, the timing
of a petal fall spray against plum curculio may in fact cover
the need for a petal fall TPB spray. Second, if there is a damaging
population level of European apple sawfly present, then a petal
fall spray geared toward sawfly may also take care of the active
TPB population.
Large flights of leafminer were observed yesterday (5/13) in some
orchards and many sites are now exceeding 100 LM/trap. This is
in fact turning out to be a relatively large year on the LM front,
for reasons outlined in the April 30th issue of Healthy Fruit.
Irrespective of the reason for the high LM populations, many growers,
especially those exceeding threshold trap captures, would do well
to consider a petal fall application of either Provado or Agrimek
for LM control. If Agrimek (in conjunction with horticultural
spray oil) is the material of choice, a first-generation LM treatment
is also the optimal timing for mite control.
First, the good news. Pyrimite (also known as Oracle or Sanmite)
has received federal approval for use against mites in apple orchards
in 1997. Before the material can be used in Massachusetts, though,
the state Pesticide Bureau will also have to approve the material
for use. The Pesticide Bureau meets monthly, but the docket appears
full for the next two months. However, there may be a way around
the necessity of a full-committee approval; use of the material
in Massachusetts may be approved through a conference call between
sessions. If this can proceed, we anticipate state approval sometime
in June. We will keep you posted on the developments of the pending
approval.
Pyrimite can be viewed as a substitute for Omite in the sense
that it can knock down a building population of mites during the
summer. It is harsher on predator mites than Omite was, but is
less toxic to the predators than Carzol. It also carries the added
benefit that it is effective against rust mites.
The more sobering news is that mite egg hatch is nearly complete in orchards that are in early bloom and is ongoing in the later-developing orchards. Soon it will be time to assess mite abundance on fruit cluster leaves. As pointed out in the April 23rd issue of Healthy Fruit, mite populations exceeding 1 motile adult per leaf at pink or bloom merit strong consideration for treatment with a post-bloom miticide. Choices for post-bloom treatment include Agrimek with horticultural (refined) spray oil and Vendex in combination with horticultural oil. A single application of Agrimek will generally suffice, but for maximum effectiveness when using Vendex, 2-3 applications should be made about 10 days apart, beginning at petal fall. Hopefully, few orchards will have early mite populations exceeding 1 motile adult per leaf, but lower populations at bloom do not always mean that the mites cannot develop to a damaging level later in the year. It is very difficult to accurately determine the potential for damaging populations this early in the year, and the best remedy is consistent monitoring of the leaves.
In most monitored orchards which are between late pink and early
bloom, the numbers of European apple sawfly are relatively low.
We have not yet had the warm, sunny days (temperatures in the
high 70s to low 80s) on which EAS thrive. EAS exhibit little activity
when temperatures are any lower. There have been isolated incidents
of EAS captures of 20+ per trap, but these captures may be less
indicative of high populations than they are of limited opportunities
for activity. It is still too soon to make judgments regarding
the necessity of petal fall treatments against EAS.
There is no substitute for each grower going into PC 'hotspots' and daily examining fruit for signs of PC feeding and egglaying, particularly king fruit"
We have yet to detect any active plum curculios, but we are engaged
in a major effort across the state to monitor the buildup of PC
adult populations. This study involves the use of black pyramid
monitoring traps and regular assessment of damage to fruit by
PC feeding and egglaying. We will have a good handle on the development
of PC populations over the next month.
Last year, there were 3 successive days in late bloom with temperatures
in the high 80s and low 90s. This extended spell of hot weather
stimulated a concentrated emergence of PC. The weather pattern
of the past 2-3 months has not indicated that such an extended
heat wave will occur any time soon. If this pattern holds true,
the emergence of overwintering PC adults should be much more strung
out compared to last year. What does this mean as far as control
is concerned? First, there is no substitute for each grower going
into PC 'hotspots' and daily examining fruit for signs
of PC feeding and egglaying, particularly king fruit, as these
are most likely to receive the earliest injury. At the first sign
of PC activity in the orchard, growers should be prepared to move
into action, if the weather is favorable for continued PC activity.
Little injury is caused by PC when temperatures are below 60o,
but look out if temperatures remain at 70o or greater.
There are two basic approaches to the 1st application of pesticide
against PC; border row and whole-orchard spraying. There is no
sure-fire way to decide which will be the most efficient. In general,
if the weather is conducive to high levels of PC activity (2-3
days above 70o, or 2 days above 80o) then
a whole orchard spray is probably in order. If the weather after
the first detection of PC feeding or egglaying in the orchard
is cooler, then the invasion is slower, and a border row spray
is probably sufficient. In deciding which strategy to employ,
one also needs to consider the status of both tarnished plant
bug and European apple sawfly populations in the orchard.
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.