Northern Michigan FruitNet 2004
Weekly Update
NW Michigan Horticultural Research Station

Jim Nugent                      Position Vacant                   Bill Klein
        District Horticulturist           District Fruit IPM Agent         Farm Mgr, NWMHRS

    Duke Elsner                                                       Jim Bardenhagen
            Agricultural Agent                                              Leelanau Extension Director

August 24, 2004

GROWTH STAGES at NWMHRS (8/23/04)

Apple: Red Delicious -- 57mm
Sweet Cherry: Napoleon – harvested
Tart Cherry: Montmorency – harvested
Apricot: harvested
Plum: European type – 33 mm
Grapes: Chardonnay – Green fruit

WEATHER

NW Michigan has received some rain in the past 2 weeks, but amounts varied considerably. Temperatures have generally remained below normal. Degree day accumulations at the NWMHRS are currently behind all but one year (1992) of the past 15 years at both base 42 and 50F.

CROP REPORT

Cherries: The last of the tart cherry harvest is wrapping up in NW Michigan. It appears that the actual national crop will be very close to the USDA's June estimate.

Peach harvest is under way.

Apples: Second generation codling moth adult emergence is just beginning this past week. Expect adult activity to significantly increase with this week's predicted warm weather. It is very important to continue to trap adults. If flight exceeds threshold, we can expect egg hatch, and hence spray time, to be approximately 250DD base 50 thereafter. This means that sprays may need to be applied well into September to control egg hatch. Beware of the potential for this late infestation. Apple maggot numbers generally remain low this season. A leaf drop disorder called necrotic leaf blotch is prevalent in some blocks of Golden Delicious. Dr. Dave Rosenberger wrote a very good article in this week's Scaffolds, published by Cornell University, which I have included in this report.

Grapes: Relatively cool weather has continued, keeping fruit development well behind normal. Cluster thinning and leaf pulling are under way in many vineyards. Powdery mildew has increased in severity and is now a significant problem in many vineyards. Downy mildew has become a problem in a few vineyards. Potato leafhopper activity will likely decline soon, whereas the larger sphinx moth caterpillars should be nearing the peak of their feeding injury at this time. The numbers of big caterpillars are low this year.

MISCELLANEOUS

NW Michigan Horticultural Research Station Celebrates 25^th

Reminder: Tomorrow, Thursday, August 26^th is the date for the NWMHRS's annual Open House and 25^th Anniversary Celebration beginning at 3:00 p.m. Dinner tickets are $10 per person and should be available at the door. Call in advance, 946-1510, to be sure of a place at the table!

SCHEDULE OF EVENTS

CIAB Weekly Raw Product Report for August 24, 2004: The latest raw product report may be found at: http://www.cherryboard.org/week8_2004.htm

As of Aug. 21, NW Michigan had harvested 87.9 m lb., with total U.S. at 2100m. This is extremely close to the 215m lb. USDA estimate. A very small amount of additional harvest is expected this week in NW Michigan.

NECROTIC LEAF BLOTCH OF GOLDEN DELICIOUS APPLES
Dr. Dave Rosenberger, Plant Pathology, Cornell University

Reprinted from Scaffolds, August 23, 2004

Within the last week, Golden Delicious apple trees in the Hudson Valley suddenly began developing necrotic spots on leaves, leaves turned yellow, and many of the yellowed leaves are dropping from the trees. Affected leaves frequently have irregular, brown, necrotic areas between veins and/or necrotic sections that extend to the leaf margins.  As leaves turned yellow during the week, small areas of the leaves remained bright green against the predominant deep yellow color.

This disorder is called necrotic leaf blotch (NLB).  Affected trees do not drop all of their leaves, and fruit do not drop or become blemished. In some seasons, however, more than 50% of terminal leaves can become affected and drop from the tree by early September. Unfortunately, no one has been able to determine the cause of NLB. Fungicides and/or foliar nutrients containing zinc can decrease severity of the disorder if sprays are applied every two weeks during later summer.  However, I doubt that control sprays are warranted when the disease appears as suddenly as it has this year. In my plots at the Hudson Valley Lab, Golden Delicious trees looked fine during a "windshield survey" on Tuesday afternoon (17 Aug), but a large proportion of the foliage was severely yellowed by Friday evening.

The last time that this disorder caused widespread leaf drop in the Hudson Valley was 1996.  With that kind of sporadic appearance, expenditures for annual control measures, especially when they are only moderately effective, are not warranted.

Necrotic leaf blotch was extensively studied in the early 1970's by Dr. Turner Sutton in North Carolina.  He found that the disorder is not caused by a fungus, bacterium, or air pollution and that it is not related to foliar nutrient levels.  Symptoms and subsequent leaf drop frequently occur in distinct "waves" in mid to late summer, but Sutton noted that there was considerable variability in severity between and within orchards.  The rootstock on which Golden Delicious were propagated did not appear to influence susceptibility or severity.  All strains of Golden Delicious were susceptible, but Sutton did not find the disorder on other apple cultivars unrelated to Golden Delicious.

In controlled environment tests, Sutton showed that the disorder failed to develop on leaves of trees held at 86/79 degreesF. day/night temperatures, whereas 33% of leaves on trees held at 79/72 or 72/64 degreesF. day/night temperatures developed leaf blotch.  He also showed that potted trees watered every day had roughly three times more leaves affected than did similar trees watered only every second or third day.  One might conclude that necrotic leaf blotch is favored by relatively cool, wet weather in late summer - conditions that accurately describe our weather pattern this year.

Although necrotic leaf blotch does not cause fruit drop or fruit blemishes, it may have adverse affects on fruit size and perhaps on the strength of flower buds for the following year.  No studies have reported on the effects of this disorder on fruit size because no one has figured out how to maintain affected and unaffected trees in the same field for side-by-side comparisons.

NLB is likely to remain as one of those sporadically-occurring "mystery" disorders that cannot be controlled.  Fortunately, it rarely causes significant crop loss.

Please send any comments or suggestions regarding this site to: 

Bill Klein, kleinw@msu.edu
Last Revised: 8-25-04