July 20, 2004
NW Michigan Horticultural Research
District Fruit IPM Agent
Farm Mgr, NWMHRS
Leelanau Extension Director
GROWING DEGREE DAY ACCUMULATIONS
as of July 19, 2004 at the NWMHRS
Temperatures this past week
finally warmed to more normal July levels. Scattered, light rainfall on
7/16 of 0 to 0.1 inches resulted in scab and leaf spot infections in some
localities in NW Michigan.
GROWTH STAGES at NWMHRS
Apple: Red Delicious
-- 40 mm
Sweet Cherry: Napoleon
– 18 mm
Tart Cherry: Montmorency
– 21 mm
Apricot: 34 mm
Plum: European type
– 25 mm
Tart and sweet cherry harvest
is getting underway. Tart and sweet maturity is overlapped more than normal.
This overlap is due at least in part to a generally heavy sweet crop and
generally light tart crop. Heavy crops of either sweets or tarts take longer
to mature than normal, while light crops mature slightly quicker than normal.
It is also possible that tarts have a slightly lower temperature developmental
threshold than sweets, but we have no data to confirm this. Brown rot
is a major concern at this time on sweet cherries. Alternaria rot
is present in some of the cracked sweet cherries. If it is necessary to
control Alternaria rot, suggest using the strobilurin plus boscalid fungicide,
Pristine. We have not collected data on this disease in Michigan, but Pristine
is registered for Alternaria on stone fruits. If Pristine is unavailable,
then suggest another strobilurin fungicide (Flint or Cabrio) as this class
of fungicides are generally quite effective on diseases caused by Alternaria
sp. on other crops. Unfortunately both Flint and Cabrio are weak on fruit
brown rot, which is generally much more of a threat to the crop than is
Alternaria. The SI fungicides have never provided Alternaria control.
Cherry leaf spot continues
to spread in some area orchards. This has been a challenging year for control
of this disease. All cherry orchards with any inoculum present will want
to be treated with Bravo after harvest. Powdery mildew is becoming
Cherry Fruit Fly (CFF)
numbers seem to be remaining fairly low this year. Likely, the one good
thing to have come out of the 2002 total crop disaster is the CFF populations
crashed in NW Michigan and are taking some time to recover. This is not
to say they aren't present, but their numbers are lower than we were seeing
by this time of the season in years prior to the 2002 disaster. In 2002,
not only were commercial cherry crops wiped out, but so were much of their
alternate hosts (particularly the forest black cherry). Mites remain
very low. Yesterday I observed a young block of cherry that was badly infested
with greater peach tree borer (GPTB). This pest does most of its
damage below ground on the tree collar, so it can easily go undetected.
GPTB will attack uninjured trees. High populations will cause tree death
by girdling. It is currently either in the pupal or adult stages. At this
time, look for their cast pupal case sticking out of the soil at the base
of the tree. Eggs are laid at the base of the trees and newly hatched larvae
find their way to the trunk generally below ground. Control should ideally
go on for this pest shortly before or after the beginning of adult emergence
(about 3 weeks ago). If the problem is found at this time, a pesticide
applied to the base of the tree as soon as possible should still provide
fairly good control.
Apple maggot has
been trapped in NW Michigan. Codling moth adult trap catches remain
low in most sites as second generation has not yet begun emergence. Oblique
banded leafroller adult trap catches are rising. White apple leafhopper
populations are generally low; potato leafhopper are more plentiful
than normal. Rosy apple aphids are pretty much done with apples
for the season. Green apple aphid populations have generally been
Apple scab in unsprayed
blocks is causing significant defoliation from this season's severe scab
infection. Fireblight shoot strikes are appearing in some susceptible
varieties, particularly in areas that retained moisture for longer periods.
Suggest making sure that potato leafhopper populations are kept low in
blocks with fireblight shoot strikes.
Berry set looks to be quite
variable thanks to some cool and damp weather during the peak of bloom.
Gewurztraminer appears the worst of the varieties I have checked. Overall,
cluster numbers look pretty good, and some vineyards will need to cluster
thin to achieve desired crop loads. Potato leafhopper adults and
nymphs are getting numerous in the unsprayed row at the Hort Station vineyard.
Larvae of sphinx moths and the eight-spotted forester moth
are appearing in low numbers at the station vineyard. I have not had reports
of them in commercial vineyards as of yet. Foliage condition still is generally
great, with little powdery mildew and almost no black rot
on the station’s unsprayed vines. Remember that warm and humid weather
encourages powdery mildew, as does dense leaf canopies—we are just getting
into these conditions.
2004 CA Clinic To Be Held.
The 2004 CA Clinic will
be held this year at the Clarksville Horticulture Experiment Station in
Clarksville, MI, Friday, August 13, 2004. Registration will start at 8:00
a.m. and the day's program will conclude at 4:45 p.m. The registration
fee for the clinic is $75, before August 6 and $85 AFTER August
6. For additional information or a registration form, call Sandy Allen
at 517/355-5191 ext.1339.
A key to a Kubota tractor
was found in Suttons Bay on July 19. The key has a tag attached that says
"Ginop Sales, Inc." If it belongs to you, it can be picked up at the NWMHRS.
CIAB Weekly Raw Product
Report, July 20, 2004:
AND PREDICTED DEGREE-DAY
SINCE MARCH 1, 2004
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Last Revised: 7-20-04