MSU Extension

Weather report

Northwest Michigan had a mixed bag for weather last week. We started off the week with warm daytime temperatures in the mid- to high 70s, but by Friday, June 13, we dropped off to a high of 60 degrees Fahrenheit. Warm weather returned into the weekend, which was coupled with windy conditions on Saturday, Sunday and into Monday, June 14-16.

We have accumulated 871 growing degree days (GDD) base 42 and 487 GDD base 50. We are still slightly behind our 24-year average of 984 GDD base 42 and 544 GDD base 50. The region is quite dry for this early in the season, although rain is predicted for many days this week. The last substantial rainfall was June 6 when we received just over an inch of rain. At the Northwest Michigan Horticultural Research Center (NWMHRC), we had 0.12 inches of rain June 13 and another 0.07 inches of rain on June 15. These wetting events triggered infection periods, but did little to add significant moisture to our dry soils.

Crop report

Crops seem to be sizing well despite the lack of rain. Growers that have a sizeable sweet cherry crop are somewhat concerned about rainfall and sizing a big load of fruit. In general, the sweet cherry crop is looking good. In early sweet cherry varieties here at the NWMHRC, cherries are taking on a red hue and birds have been noted feeding on these ripening fruits.

Tart cherries are sizing and the crop is quite variable. Some orchards that had a big crop last year have a smaller crop this season. There is considerable variability in the number of fruit from tree to tree within an orchard. We also expect the crop to vary in size by geographic area, and we will know more in the coming weeks.

Initial estimates of the tart cherry crop are out for the three regions of Michigan as well as the other tart cherry growing areas of the country. Michigan State University Extension expects these estimates to change somewhat with time, but as of last week, the following numbers were estimated for the tart cherry crop of 2014. Numbers are reported in millions of pounds.

Northwest Michigan: 110
West Central Michigan: 50
Southwest Michigan: 18-20
Michigan Total: 180

Other tart cherry growing states:
Pennsylvania: 2
New York: 8.5
Washington: 19
Oregon: 2
Wisconsin: 8-9
Utah: 27
U.S. Total: ~247.5

Apples are also looking good, and most growers did a nice job thinning the fruit this season. We had some warm temperatures for thinning.

Strawberry season will likely begin at the end of June rather than the first of July as we reported last week. Irrigation will be helpful for strawberry growers to size the fruit.

Pest report

Cherry leaf spot infection was possible on Sunday, June 15, following rain that much of the region received. Cherry leaf spot conidia have been developing on the undersides of bract leaves and first true leaves in both Balaton and Montmorency tart cherries and sweet cherries. Conidia on infected leaves likely moved to nearby leaves during the recent rain and could have caused infection on those leaves if they were not protected prior to Sunday’s rain. Most cherries are past shuck-split and growers planning to use the 24(c) Bravo WeatherStik past shuck-split label should check re-application intervals for fungicides and also check with processors for restrictions on fungicide use.

Powdery mildew is a concern at this time and MSU Extension recommends using one of the SDHI fungicides such as Luna Sensation at 5 fluid ounces per acre or Merivon at 5.5 fluid ounces per acre plus Captan at 2.5 pounds per acre at the first cover timing; these fungicides are excellent for both cherry leaf spot and powdery mildew.

Apple scab infection was also possible on Sunday in the region if tissue was not protected prior to rain. According to the MSU Enviro-weather apple scab model for the NWMHRC, apple scab spores are 100 percent mature and 90 percent discharged at this time. We are still in the primary infection of apple scab, and during rain on Sunday spores were discharged at our monitoring field site in Leelanau County. If we received a good amount of rainfall, which is predicted for this week, we may see the end of primary apple scab soon. However, good amounts of precipitation are needed for the remaining apple scab spores to discharge. In Southeast Michigan, primary scab is ongoing whereas Southwest and West Michigan have called the end to primary scab.

We have received more, but still just a few, isolated reports of American brown rot sporulation on green sweet cherry fruit as well as on last year’s mummies. Insect feeding, bacterial canker on green fruits, and other damage to developing sweet cherry fruit make those damaged fruit more susceptible to American brown rot infection. Spores developing now on green fruit and mummies have the potential to infect neighboring fruit. We have also seen blossom blight and canker symptoms in sweet cherries.

Currently, it is raining throughout the region and we are likely in the midst of disease infection periods even though the MSU Enviro-weather models are not yet reporting infection periods. There is a possible threat of rain for almost every day in the coming week; therefore, maintaining good coverage to protect tissue from infection will be critical and challenging.

Codling moths are active throughout the region and numbers are on the rise; several farms have set biofix dates. At the station, we caught codling moth for the second consecutive week and numbers are low at one moth per trap, which is not uncommon at the NWMHRC where few codling moths have been observed historically. Farms that set biofix dates last week may be at the optimal timing for targeting eggs (100 GDD post-biofix).

Plum curculio are still active and growers should continue to protect fruit from plum curculio damage. Most cherries are out of the shuck and vulnerable to feeding and oviposition. Growers should check their “hot spots” for oviposition scars as plum curculio stings are evident in most cherry blocks at this time.

Black cherry aphids were observed on new growth and terminal ends last week in sweet cherries at very low levels.

American plum borer at 7.6 moths per trap and lesser peach tree borer at 17 moths per trap are still flying, and although greater peach tree borer were active last week, we did not catch any this week. The control period for borers is still open and some growers are trunk spraying with Lorsban for borer control.

We have received reports that rose chafers are flying in Benzie County.

Spotted tentiform leafminer numbers are down this week at 12.5 moths per trap, and the optimal time for managing this pest has passed for most of the region. Oriental fruit moth adults continue to be active at 2.5 moths per trap.

Spotted wing Drosophila and cherry fruit fly traps are up across the region; we have not detected this pest yet this season.

Growers should check with processors for restrictions on insecticide and fungicide use to avoid possible issues with maximum residue limits.

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