Northwest Michigan fruit update – April 6, 2021

Emily Pochubay and Nikki Rothwell<rothwel3@msu.edu>, Michigan State University Extension - April 06, 2021

With the recent warm weather, development is three to four weeks ahead of normal, and growers are starting their apple management programs this week.

Graph of Enviroweather overnight temperatures.

Weather and pest report

The weather has certainly taken on a spring tone in the past week. There were cold overnight temperatures on April 1 into April 2, but since then conditions have warmed up considerably. The weather forecast is also predicting more warm temperatures throughout this week; mid- to high 60s for the remainder of this week and in the mid-50s to low 60s through the weekend. Many growers are saying they are four weeks ahead of where they were last year.

The forecast is also calling for rain which will interrupt recent dry conditions. There is a system on the radar this morning that has the potential to bring rain. According to MSU climatologist Jeff Andresen, the best chances for wet weather this week will be on Thursday and over the weekend. Temperatures for today (April 6) and tomorrow (April 7) will be in the 70s and potentially reaching 80 degrees Fahrenheit during the day with overnight temperatures in the 50s. Following a few days of warm weather, longer-range forecasts suggest that temperatures will cool somewhat, but still be higher than normal for this time of year. View Andresen’s weekly weather report.

As of today, Michigan State University Enviroweather stations in our five-county region are reporting 111-171 growing degree days (GDD) base 42 and 41-75 GDD base 50. The region is forecasted to reach 164-238 GDD base 42 and 58-106 GDD base 50 by Monday next week. Tree fruit buds are currently ahead of normal for this time of year, and we expect to see substantial development during this warm weather.

At the Northwest Michigan Horticulture Research Center, Gala and Honeycrisp are at green tip, sweet cherries are between side green and green tip, Montmorency are at side green and Balaton are at green tip. Based on the current forecast for the next 14 days, sweet cherries could be in full bloom by the third week of April this year. As growers and Michiganders are aware, this situation can change quickly as forecasts change.

Station	GDD Base 42 F Current (April 6)	GDD Base 42 F Forecast (April 12)	GDD Base 50 F Current (April 6)	GDD Base 50 F Forecast (April 12)
Benzonia	142	202	58	82
East Leland	138	207	58	88
Eastport	145	212	61	91
Elk Rapids	169	238	75	106
Kewadin	171	238	74	104
Northport	111	164	41	58
Old Mission	149	218	63	93
Onekama Twp/Bear Lake	138	198	59	83
Petoskey	131	178	54	66
Traverse City (NWMHRS)	149	218	63	93
Williamsburg 20m Tower	165	234	74	104

Growers have started or are getting ready to put on the first sprays of the season ahead of this week’s predicted wet weather. As previously noted, warm weather will accelerate bud development and we expect that there will be a good amount of apple scab susceptible green tissue exposed when the rains come.

Traps were set for oriental fruit moth and spotted tentiform leafminer in apple blocks at the Northwest Michigan Horticultural Research Center (NWMHRC) yesterday. It is also time to monitor for black stem borer emergence. Apple blocks at the station had very high European red mite populations last year, and bright red eggs are easy to find in bud scars on spurs and branches. We also have a healthy population of San Jose scale that has slowly increased over the past few years; trees with rough bark due to some form of injury seem to be especially attractive to the scale. In cherries, we put traps out for American plum borer, and we have been able to find San Jose scale overwintering on spurs in sweet cherry.

Cold temperature and crop update

With the recent warm temperatures, we have been receiving many calls from growers wondering what these conditions are doing to our fruit trees. At the station, we have been tracking the implications of weather conditions on fruit buds for the past two years. Over this past winter, we have been collecting buds to monitor bud hardiness through bloom this spring.

Temperate fruits can tolerate very cold winter temperatures. However, as we move into warmer weather in spring, fruit buds lose their winter hardiness. As trees break dormancy and buds swell, the ability to withstand cold temperature is dependent on the buds’ growth stage and the fruit cultivar. The range of potential damage coincides with the growth stages and fruit species and even the variety. Throughout bud development, there is a wide temperature range that cause little to extreme bud damage. As bloom nears each spring, temperatures in the upper 20s can cause considerable harm to an early blooming species because bud growth is more advanced.

In contrast, other fruit crops that bloom later in the spring could be relatively unaffected because bud development is not as far along when cold temperatures occur. The stage of bud development determines how susceptible the fruit crop is when freeze events occur.

To gauge the potential for cold temperature damage to fruit crops in Michigan, MSU researchers and MSU Extension educators partnered with the Michigan Tree Fruit Commission and the Michigan Department of Agriculture and Rural Development’s (MDARD) Michigan Specialty Block Grant program to purchase ultracold freezer units with the capacity to reach down to temperatures of below -68 degrees Celsius. We are using these freezers to monitor bud hardiness for different fruit crops across the state.

Each week, the statewide MSU team collects samples of apple, tart and sweet cherry, and peach to track changes in flower bud cold hardiness from late fall through bloom. At the NWMHRC, we are monitoring tart cherry, and apples—both Gala and Honeycrisp. Buds are exposed to incremental temperatures that range from -40 F early in the season (when buds are most hardy) through higher temperatures as we approach bloom about 10 F. Buds are removed from the freezers at different amounts of exposure time, and damage assessments are made to understand the extent of bud mortality observed at specific low temperatures.

These data will help MSU researchers, Extension educators and growers better understand how cold temperatures impact crop load and yield and guide decisions for ways to minimize the risks related to cold weather events.

Despite the recent warm weather, the buds we have been collecting in northwest Michigan still look very good. In Gala and Honeycrisp apple buds, we see bud mortality at a low of -4 F. In tart cherry, our data show that we are starting to see some damage at 3.2 F. Although we are not monitoring sweet cherries, our colleagues near Grand Rapids, Michigan, are showing no damage to sweet cherry varieties in the mid-teens to low 20s. These temperatures are quite low, and we are unlikely to dip down into those temperatures in the next month. However, we did have some single digits recorded at the Bear Lake Enviroweather station on April 1 through April 2. Temperatures dipped down to a low of 9.1 F. Several other stations were in the low to mid- teens and 20s.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).