MSU Extension

Weather report

The weather in northwest Michigan has gone from winter directly to summer without even stopping for spring. Last week’s daytime highs were in the low to mid-50s with cold north winds. Those conditions were replaced by warm and dry air over the weekend; we reached 80 degrees Fahrenheit at the Northwest Michigan Horticulture Research Center (NWMHRC) on Sunday, May 3. Despite the warm weekend, we are still lagging behind in our growing degree day (GDD) accumulations. So far we have accumulated 225 GDD base 42 and 91 GDD base 50. Our 20-plus-year averages are 254 GDD base 42 and 110 GDD base 50. If the weather forecasts are correct, we will be on target with our GDD average and tart cherry bloom around May 12 at the NWMHRC.

Prior to last evening, May 4, the region was dry as our last significant rainfall was April 20. We also had high winds May 3, but despite the dry conditions, there is still moisture present in the soil. We received only 0.1 inches of rain over Sunday night which was replaced by a dense fog on Monday morning. Current conditions are sunny and dry, which are predicted to continue throughout the week. The weekend forecast is rain on Friday, Saturday and Sunday (May 8-10) and potentially into Monday. Growers will be covering the fast growing tissue to protect from diseases prior to the weekend. No frosty overnight conditions are in the forecast.

Crop report

Very early signs of grape bud swell have been seen on canes close to the ground where they have received extra heat from the soil surface, but up in the canopy of the vine, buds still appear entirely dormant. Further examinations of cane cambium tissues has revealed lots of injury to all parts of canes that were above the snow cover line during the cold temperatures in February and March. I would not expect much from any buds on vinifera varieties that were not covered by snow. Some of the hybrid cultivars at the NWMHRC showed a lot of very poor cane wood during pruning, so we may see some challenges in these as well.

There is a lot of powdery mildew on canes in many sites. Dormant sprays for powdery mildew are suggested, and there is plenty of time left to get these on before bud break.

Saskatoon bushes are into the green tip to tight cluster stage in the Grand Traverse, Michigan area. We are setting up a demonstration of pruning practices for mature bushes at Jacob’s Farm on M-72 west of Traverse City, Michigan. Pruning methods are based on the “Saskatoon Berry Production Manual” from the Province of Alberta and methods typically used by Michigan highbush blueberry growers. At harvest time, the fruit yield and quality from the different pruning regimes and harvest systems will be compared.

After a week of developmental standstill, crops are again moving along – quite quickly with the recent warm weather. Cherries have seemed to move to bud burst almost overnight. If the weather predictions are correct, we will be in sweet cherry bloom May 7 and tart cherry bloom May 12; these dates are similar to our “old” bloom times we saw on a more annual basis in the mid-90s. There is and will continue to be lots of activity in the orchard to cover new growth prior to this weekend’s coming rains.

Most pruning is winding down at this time. Growers are busy planting and the soil moisture below the first few inches is a pleasant surprise for the newly planted trees. Honey bee rental time is approaching and beekeepers are trying to move bees back from other locations to prepare for the region’s upcoming cherry bloom. Honey bee hive strength is unknown at this time, but growers are hoping for good weather and strong hives as we head into the 2015 bloom.

Pest report

Sunday evening rain and the dense fog into Monday morning was brief and did not result in an apple scab infection event at any of the northwest Michigan Enviro-weather stations. Scab spore counting is underway and we are monitoring spore discharge in a minimally managed Jonamac block in Leelanau County. Although the scab model on Enviro-weather did not result in an apple scab infection event, we did find an average of three spores per spore rod that were discharged during the Sunday-Monday wetting period.

As mentioned above, tree growth was accelerated during the weekend warm conditions, and considerable green tissue is present on apples and will need to be covered prior to the possible predicted rains Thursday evening/Friday morning through Sunday to prevent infection during the primary scab season. Protectant materials are the best option for control at this time; these products also are less at risk of resistance development and should be used at this early-season timing.

With warm and wet conditions in the forecast, American brown rot blossom blight will be a concern in sweet cherries as they approach bloom likely over the weekend. Although the potential for infection is highest when flowers are open, the pathogen can infect flowers at white bud under favorable conditions, which has been documented as 68-86 F (75 F is optimal) with a minimum wetting period of 5-10 hours. Infection at the white bud stage has been severe if temperatures reach 75 F with 24 hours of wetting. Growers should be protecting against the blossom blight phase of this disease if we do have warm and wet conditions toward the end of the week as we move into sweet cherry bloom. Rovral is the product of choice for American brown rot control at this time.

European brown rot will also be developing and producing spores during this week’s warm temperatures. With an increased spore count and extended wetting period over the weekend, we have a chance of European brown rot infection. Based on the predicted weather forecast, Michigan State University Extension recommends growers treat for European brown rot following the traditional two applications timings: popcorn and one week later. If Montmorency orchards had past European brown rot infections, growers should make sure these orchards are treated this season.

At this time, Indar is the best control option for European brown rot. Balatons are more susceptible than Montmorency to European brown rot infection, and Balaton growers should be applying Indar at these two timings regardless of predicted weather conditions. However, we have also observed infection in Montmorency blocks, in particular in areas that commonly have spring fogs that settle over these orchards. Growers with this situation should also consider Indar applications. For more information, see “European brown rot control in tart cherries for 2015.”

As we approach the time to begin protecting for cherry leaf spot, growers should consider their options for early-season leaf spot management and check with processors on any fungicide and insecticide restrictions, in particular possible restrictions with the use of chlorothalonil. Additionally, growers should be aware of the 10-day retreatment interval for Bravo products. According the Michigan Department of Agriculture and Rural Development (MDARD) and the chlorothalonil pesticide labels, there must be a minimum of 10 days between applications of Bravo, whether the application is a full cover or alternate row middle spray.

We would also like to remind growers that cherry leaf spot infection can occur prior to bloom when this fungus can infect stomata on open bract leaves if conditions are favorable for cherry leaf spot infection. Infected bract leaves have been observed in previous seasons and could contribute to season-long challenges of keeping leaf spot in check or severe cherry leaf spot infection and early defoliation.

Green fruit worms and American plum borers are active at the station.