Northwest Michigan fruit update – April 25, 2017

Cooler temperatures are forecasted late this week and sweet cherry bloom is predicted for late next week.

Weather report

Temperatures over the weekend were pleasant, but the really warm weather came in on Monday, April 24, when the high hit just over 70 degrees Fahrenheit. Temperatures are expected to be warm at about 70-76 F for today, April 25, and Wednesday. On Thursday, temperatures will drop 20 degrees, when daytime highs are only predicted to be in the mid-50s.

The long-term forecast shows daytime temperatures remaining in the 50s with nighttime temperatures in the mid-30s and into the 40s. With these cool temperatures, our growing degree-day (GDD) accumulations will be moderate. If the forecast is close to accurate, we will likely be in full bloom in sweets around May 4. We are slightly ahead of our over 20 year average for GDD accumulations base 42 and spot on with our GDD accumulations for base 50.

We had 0.7 inch of rain April 20, and there were reports of spotty hail in the region. Despite this rainfall, soil conditions are beginning to dry out, but there is no shortage of predicted rainfall beginning April 26.

Crop report

Crop development is moving along, but the cool conditions that are predicted for the remainder of the week and through the weekend will keep movement to a minimum. We predict sweet cherries to be in bloom in the latter part of next week, and we are now seeing bud burst in sweet cherries here at the Northwest Michigan Horticulture Research Center. We are seeing green tissue in apples and growers are active to make sure this tissue is covered before the rain events.

We have been collecting tart cherry buds three times a week for MSU horticulturist Todd Einhorn. He has been testing these buds to develop a growth development curve; these data measure the cold hardiness of the different bud stages. His data are similar to the previously published charts (within about 1 F) that were developed in the 1970s. However, Einhorn is finding not only how similar (visually speaking) the buds are across certain dates, but how the buds continue to lose hardiness. In other words, we may not really differentiate buds in the photos for March 30 and April 3 or April 6–10, but there are big differences in kill temperatures. Einhorn thinks the relative water content will make for an excellent objective indicator of development.

Below are the results from this trial thus far—we will continue to collect buds through bloom:


March 30

April 3

April 6

April 10

April 12

April 17

Mortality tart cherry

First swell

First swell

Side green

Side green

Side green

Green tip


No data

23 F

24 F

24 F

24 F

26 F


8 F

21 F

21 F

20 F

23 F

24 F


-4 F

11 F

13 F

16 F

19 F

21 F

Tart cherry bud stages

Data collected by T. Einhorn, L. Hillmann, N. Rothwell, Michigan State University

Pest report

We found a low level of apple scab spores that discharged during the April 20–21 wetting period that resulted in a light infection period at the Northwest Michigan Horticulture Research Station (see chart below). While spore numbers are low, they are on the rise and growers with green tissue on scab-susceptible varieties should continue to protect tissue from infections during primary scab.

The next chance for rain is predicted for April 26, and growers have been covering orchards with susceptible tissue prior to this coming rain. Rain is predicted for many days in the coming week, so be sure to cover up prior to the first rain event on Wednesday, which has a 67 percent chance of rain.

Apple scab infection periods at the Northwest Michigan Horticulture Research Center. Data from MSU Enviroweather.

StationStart of wetting periodEnd of wetting periodDuration (Hrs.)Avg Temp (degrees F)Rainfall (in.)Apple Scab (leaf)Wet hrs @ avg temp for 1st infectionProgress towards infection
Traverse City (NWMHRS) 4/10 8-9AM 4/12 7-8AM Wet: 38; Span: 48 39.3 0.14 Light (Symptoms appear: 4/30) 33 121%
Traverse City (NWMHRS) 4/15 5-6AM 4/17 7-8AM Wet: 35; Span: 51 48.6 0.72 Heavy (Symptoms appear: 5/4) 15 231%
Traverse City (NWMHRS) 4/20 3-4AM 4/21 9-10AM Wet: 31; Span: 31 40 0.7 Light (Symptoms appear: 5/9) 29 104%

As we move into the coming week with the possibility of sweet cherry bloom late next week, MSU Extension suggests monitoring weather to assess the need for popcorn and bloom brown rot sprays. Warm and wet weather during pre-bloom and bloom time is conducive for American brown rot blossom blight infection.

We have not detected American plum borers, but green fruitworm have been active and we continue to find green fruitworm in American plum borer traps. Although our oriental fruit moth traps are up, oriental fruit moth have not been detected at the station.

We have received reports from local scouts that a few orchards have higher than usual scales, but most orchards have low or no scale incidence. Last season, there were reports of high mite populations, particularly in apples; hence, we encourage scouts to monitor for overwintering European red mite eggs.

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