Generally dry conditions prevailed the past two weeks in NW Michigan. Precipitation during the past two weeks at the NWMHRS totaled 0.18 inches. July rainfall has totaled 1.25 inches. Degree day accumulations for the season are well behind normal. As of 7/26, the base 42 accumulation is the third lowest of the past 15 seasons (1992 and '96 were lower), while base 50 is the second lowest during the same period (only 1992 was lower.)
GROWING DEGREE DAY ACCUMULATIONS
as of July 26, 2004 at the NWMHRS
GROWTH STAGES at NWMHRS (7/26/04)
Apple: Red Delicious
-- 45 mm
Cherries: Mostly dry conditions over the past two weeks have greatly benefited the sweet cherry crop. Early season brown rot (BR) infections were present in many blocks. In many blocks it was the combination of fungicides and dry weather that kept the BR from exploding into a disaster. Cherry leaf spot (CLS) has also been a very serious problem this year. Defoliation is nearly complete at this time on the untreated tart cherries in the fungicide trials at the NWMHRS, leaving only immature fruit hanging on the trees. While CLS is currently present in many orchards, growers in NW MI overall have done a good job containing the disease from excessive defoliation. Unfortunately, though, the price tag for fungicides in 2004 is already at record levels, and we still have post-harvest treatments to apply. (see accompanying article on post-harvest CLS management). Powdery mildew is common, but at lower levels than during recent years. Cherry fruit fly (CFF) adult numbers are increasing but continue to be at lower levels than experienced prior to 2002. The one good result of the 2002 crop wipe out was a huge reduction in the overall CFF population. Still, populations are increasing from 2003. Greater peach tree borer (GPTB) are causing serious damage in a few sites. This is a good time to check the bases of trees for the presence of the pupal cases that are left behind when the adult emerges. GPTB will infest all types of stone fruits.
Apples: Codling moth has not yet reached second generation. Apple maggot (AM) emergence is underway, but is still at generally low levels. Expect AM activity to increase during the next four weeks or so. 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.
Grapes: As leaf canopies get denser, powdery mildew will become a much greater threat.
Irrigation systems should be operational at this time in apple and peach orchards.
Cherry Leaf Spot – Post
This has been an extremely difficult year to control cherry leaf spot (CLS). Most cherry orchards in Michigan (both tart and sweet) have some level of infection. This is a year when post-harvest treatment of both sweets and tarts for CLS is essential, particularly in blocks where any infection is present.
The material of choice is chlorothalonil (Bravo). This is a time of the season when we need a good protectant and Bravo has been the best since the industry lost Difolatan in the late 1980's. Bravo does not have the resistance concerns that we have with sterol inhibitors (Elite, Nova, Orbit, Indar, Rubigan), strobilurins (Pristine, Flint, Cabrio) or dodine (Syllit). Because Bravo can only be used through shuck split and then post-harvest, our best resistance management strategy is to use Bravo when the label allows. This reduces the resistance selection pressure on the alternatives that must be used after shuck split and before harvest. Use of SI's, strobilurins or dodine after harvest hastens the development of CLS resistance to whichever chemical is used.
Captan, like Bravo, does not have resistance concerns, but the maximum labeled rate on cherries of 4 lbs. per acre of 50W is too low to depend on achieving adequate control by itself. Captan at the labeled rate is a good tank mix partner with resistance susceptible fungicides such as SI's to help delay the onset of resistance to the materials tank mixed with the captan. (Captan is a good pre-harvest tank mix partner to help delay brown rot resistance as well as CLS). Adding sulfur to a tank mix does not help delay CLS resistance because sulfur is not effective against CLS. It may help delay resistance development in powdery mildew and brown rot.
So, for post-harvest leaf spot control, Bravo is currently the only good choice. In blocks where CLS pressure is high, I suggest using higher rates. If August is a wet month, a second post-harvest spray may be required this season.
CIAB Weekly Raw Product
Report for July 27, 2004:
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