Northwest Michigan fruit regional report – June 3, 2014

With cherries coming out of the shuck and rain in the forecast, growers are protecting from diseases and insects.

Weather report

Weather conditions across the region continue to shake things up; we went through a long, slow start to the spring right into summer-like conditions. Last week, temperatures were slightly above average and most days were sunny, clear and in the low 70s. By Thursday, May 29, daytime temperatures increased and we have remained in the 80s through June 2. Cooler temperatures are predicted for the coming days, which will be welcomed by those working outside in the somewhat suddenly hot and humid conditions.

With the recent warm up, we have jumped in our growing degree day (GDD) accumulations; we have accumulated 576 GDD base 42 and 301 GDD base 50. When we compare our GDD in 2014 to our 24-year average, we are only about 50 GDD base 50 and about 100 GDD base 42 behind our average, which is considerably different than where we were two weeks ago.

Rain was predicted on Sunday, June 1, through Tuesday, June 3, and the region received varying amounts of rainfall. At the Northwest Michigan Horticulture Research Center (NWMHRC), we received only 0.06 inches of rain, but in Northport, Michigan, they received 0.31 inches of rain. The Michigan State University Bear Lake and Benzonia Enviro-weather stations received 0.14 inches and 0.31 inches, respectively. Growers have reported higher amounts of rainfall at their farms than what was reported at the weather stations. A hard rain fell in many parts of the region on Monday, June 2. After the afternoon rain, the NWMHRC received just under 1 inch of rain in less than an hour and a half.

Crop report

It is now very plain to see which wine grape varieties are going to show any significant shoot growth from buds that are above the snow line during our coldest temperatures. Riesling and Chardonnay are still looking better than most other vinifera varieties. We have many varieties at the research center that only have shoot growth at the very base of the vine, and we will be cutting out the trunks and the rest of the dead wood soon.

Where there is significant shoot growth, sucker shoots are in the 6- to 12-inch range, while higher shoots are in the 1- to 5-inch stage. Powdery mildew is the only disease threat at this time with many fungicide choices available at this point in the season.

Saskatoons bushes are in the green fruit stage and the crop looks good. The first rust infections on fruits and apple curculio adults appeared during the last week. This is a critical time for protecting the berries from diseases and insects.

With the soaring daytime temperatures, bloom came and went quickly. At one point during the past week, we had late sweet cherries at the end of bloom, tart cherries in full bloom, and early apple varieties had king blooms opening. Sweet cherries likely had a good pollination period as many orchards had open bloom during the warm and sunny days last week. Tart cherries also had a good window for pollination, but the time between first bloom and petal fall was much shorter.

Apple bloom in our warmer areas or early blooming varieties had good pollination weather. Later varieties or cooler areas of our region will have to contend with the heavy rainfall on Monday, June 2. Most growers protected against fire blight over the weekend when much of the apple bloom were susceptible to this disease with temperatures in the mid- to high 80s. Growers were also covering the fast growing foliage for other diseases over the weekend. Conditions for spraying were good as wind speeds were relatively low in the mornings and into the evening hours.

Even with sweet cherry bloom in full swing last week, green cherry fruit are already visible on the trees. Tart cherries are also coming out of the shuck, and at first glance fruit set appears to be off to a good start. We have had reports of lighter return bloom in tart cherries where blocks had a heavy crop in 2013, particularly in orchards where fruit hung for a while to ensure proper ripening. Growers are also moving from pollination and bloom to protecting fruit from pest insects. Insecticides will likely be going on in most cherry blocks this week.

Pest report

Fire blight bacteria overwinter on and around cankers formed during the previous season, and these bacteria rapidly develop during warm conditions, beginning when temperatures reach 65 degrees Fahrenheit. Rain, hail, dew, heavy wind and pollinators visiting flowers can transfer fire blight bacteria to flower pistils. Recent temperatures were very high with daytime highs reaching into the mid- to high 80s over the weekend, and these conditions were conducive for rapid growth of fire blight bacteria on open flowers. Heavy rain on Monday, June 2, may have washed the fire blight bacteria into open flowers, and infection can move systemically, particularly on susceptible apple varieties. Many growers sprayed for fire blight over the weekend in anticipation of rain predicted for Sunday and Monday.

In areas with streptomycin-resistant bacteria, oxytetracycline and Kasumin are the best option for control in counties where it is permitted by Section 18 exemption: Grand Traverse, Leelanau and Antrim. Growers need to be sure that they have used a registered alternative for fire blight control prior to the first application of Kasumin. In counties that do not have a Section 18 exemption for Kasumin use, streptomycin and oxytetracycline are the best options for fire blight control.

Minimizing shoot growth on apples reduces susceptibility to fire blight and the spread of fire blight bacteria to healthy tissue. Apogee is a locally systemic gibberellin biosynthesis inhibitor that slows shoot extension and reduces the potential for shoot blight. The optimal timing for application of Apogee is at king bloom petal fall. This tool is important in helping to minimize shoot blight infections and a great overall management strategy.

Yesterday’s rain resulted in the potential for apple scab infections across the region. At the NWMHRC, we were at green tip in McIntosh on May 9, and according to the apple scab model, 87 percent of apple scab spores are mature and 57 percent have been dispersed. The end of primary scab is not forecasted for the coming week and we are still catching spores in the field. Following evening rain on June 1 and morning rain on June 2, spore counts were at 55 spores per spore rod, and following the heavy afternoon rain on June 2, we found an average of 130 spores per spore rod at our site in Leelanau County.

Growers are currently covering for both fire blight and apple scab, and recent heavy rains have likely washed bactericides and fungicides from foliage. Michigan State University Extension advises growers to continue protecting from apple scab infection and for fire blight if varieties are still in bloom. We recommend that growers should prioritize managing fire blight in fire blight-susceptible varieties if possible and follow these applications with scab sprays. These warm conditions coupled with the potential coming rain will necessitate covering tissue for apple scab and powdery mildew. With forecasted warm and wet conditions, growers will need to be diligent about good coverage.

We have received reports of cherry leaf spot lesions on bract leaves in both Balaton and Montmorency tart cherries, and we hypothesize that these infections are likely a result of the infection period on May 20. If we are observing infection now, the cherry leaf spot conidia on the undersides of infected leaves will quickly spread to nearby leaves during wet periods for the duration of the season; growers will need to be diligent about adequately covering new tissue if cherry leaf spot signs are present on bract leaves. We have had substantial growth in the last week and newly expanded leaves are susceptible to potential cherry leaf spot infection and will need to be protected with more rain in the forecast.

During the recent rain, we had cherry leaf spot infection periods across the region, and heavy rains on Monday likely washed off fungicides that were applied prior to rain. Therefore, growers may need to reapply fungicides to protect from possible cherry leaf spot infection as there is rain forecasted for Tuesday evening into Wednesday this week, June 3-4. Growers need to be sure to check labels for re-application intervals for fungicide sprays.

Codling moth began flying during warm nights over the weekend. Although we have not captured codling moth at the NWMHRC, 20 codling moths were reported in a trap at a codling moth hotspot site in East Leland, Michigan. Plum curculio are also active, and we received reports that plum curculio are laying eggs in apricot fruits that are out of the shuck over the weekend. No plum curculio stings have been observed or reported in cherries, but sweet cherries are at shucksplit and tart cherries have just coming out of the shuck. Growers should be protecting fruit against plum curculio as this insect can target fruit as it is just emerging from the shuck.

American plum borer and lesser peach tree borer are active; this is our second consecutive week of American plum borer capture at 11.3 moths per trap and the first lesser peach tree borer were caught this week at 2.3 moths per trap. No green fruitworm moths were captured this week and spotted tentiform leafminers are still active at 127.5 moths per trap. This is the second consecutive catch of oriental fruit moth at 4.5 moths per trap).

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

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