Northwest Michigan fruit regional report – May 27, 2014

Orchards in bloom have been buzzing with pollinator activity during this beautiful weather.

Weather report

The weather over the Memorial Day weekend, May 24-26, was beautiful with daytime temperatures in the mid- to high 70s. The sunny conditions were almost perfect for pollinating the open blooms on most of our sweet and tart cherries; bee activity was excellent. With the recent warm up, we have accumulated many growing degree day (GDD) units, and we are at 397 GDD base 42 and 178 GDD base 50. These accumulations are much closer to our over 20-year average than in past weeks; our average accumulations are 551 GDD base 42 and 271 GDD base 50.

Despite the wet start to the spring, soils have dried out in the past week. The last significant rainfall was on May 20 when we recorded 0.62 inches. Forecasts are not predicting much rainfall in the coming week. Fog was thick throughout Leelanau County this morning.

Crop report

In many wine grape sites, the condition of the Vinifera varieties looks very poor. Shoots low on vines – below the snow cover line – are 1-2 inches in growth. Chardonnay and Riesling are showing significant bud swell and bud break higher on the vines, but many other varieties have no bud swell above the snow line.

Hybrids, except for a few experimental varieties, look much better, with a good percentage of bud swell and bud break throughout the vine. Reports on bud survival and shoot growth from commercial vineyards would be appreciated so we can prepare a more complete report on Northwest Michigan vineyard conditions. Contact Duke Elsner at or 231-922-4822 to send in your reports.

Most saskatoon fruiting stems are in late bloom or petal fall. Some pest activity has been noted – all are leaf-feeding insects at this point, mostly beetles and aphids. No fruit-infesting insects have been detected thus far.

Over the weekend, sweet cherries were in full bloom, and here at the Northwest Michigan Horticulture Research Center (NWMHRC), many sweet cherry varieties are at petal fall. Tart cherries are in full bloom at the NWMHRC, and further north Montmorency are just coming into bloom. Balatons are also in bloom, and many growers experimenting with ReTain made applications in Balaton over the weekend; weather conditions were good for plant growth regulators (PGRs).

As mentioned above, the warm and sunny weather were excellent for bee activity in blooming cherry orchards. We expect these conditions were conducive for setting a good crop of both tarts and sweets in the region. Over the weekend, many growers were busy covering their crops for the potential rainfall that was expected on Memorial Day, May 26; weather conditions and the forecasts made the decision to spray difficult.

Pest report

Warm and sunny conditions in the last week have not been conducive for apple scab infection periods. Our heaviest potential primary apple scab infection period occurred May 12-13. The NWMHRC collected an average of 1,885 apple scab spores per spore rod from the NWMHRC apple scab monitoring field site in Leelanau County following the May 12 infection period. Since then, two rain events on May 15 and 20 have occurred and although these most recent rain events did not result in a potential apple scab infection at the NWMHRC, other areas in the region including Bear Lake, Benzonia and Old Mission did have the potential for infection on May 20.

Apple scab spores collected from the NWMHRC monitoring site following last week’s rain seem to be on the decline with an average of 110 spores on May 15 and no spores on May 20. However, research has shown that fewer apple scab spores are dispersed during nighttime rain and on May 15 and 20, rain began at approximately midnight and continued into the early morning the following day. Therefore, the lower average number of spores collected on these dates is likely due to a combination of cooler temperatures, duration of the wetting events, and because the wetting event occurred at night.

Apple scab spore count


Average number of apple scab spores per rod

















Many apple growers who had powdery mildew infection in their orchards last season sprayed an SDHI fungicide last week to manage both apple scab and powdery mildew in apples that have reached tight cluster and pink.

Fire blight blossom blight is a concern as apple and pear blossoms begin opening. Fire blight bacteria grow quickly on the tip of the flower pistil when temperatures reach 65 degrees Fahrenheit. Rain or heavy dew can wash the bacteria into the flower where infection can take place. The Section 18 for Kasumin in counties where resistance has been detected has been extended to June 15, 2014. A registered alternative must be used prior to a Kasumin application. Please refer to the Section 18 label for Kasumin for more information on the conditions of Kasumin use for fire blight blossom blight. For more information, see “Date extended for Section 18 Specific Exemption for Kasumin for fire blight control in 2014” from Michigan State University Extension.

Tart cherries progressed quickly from white bud to bloom over this long weekend. Although the weather has been warm and mostly dry, some growers have protected from European brown rot infection.

Warm, sunny days during bloom have been exceptional conditions for pollinators and they have been very active in the last week. Native pollinator activity seems to be high this season, and bumble bee numbers appear to be particularly abundant this year. Predators such as lady beetles and parasitoid wasps have also been active.

In our fourth consecutive week of monitoring green fruit worm, moth numbers have decreased from 17.6 moths per trap last week to 1.3 moths per trap this week. Spotted tentiform leafminer numbers jumped up to an average of 98.5 moths per trap and this is our third consecutive week of spotted tentiform leafminer moth capture. American plum borer and oriental fruit moth are active. Our first capture of American plum borer and oriental fruit moth was on May 26. We have also received reports of plum curculio activity in the region. Monitoring for codling moth will begin at the NWMHRC this week.

Dr. Rothwell’s work is funded in part by MSU’s AgBioResearch.

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