Northwest Michigan fruit update – May 15, 2018

Fruit trees have developed quickly in the last week and the coming week’s weather is looking promising for good pollinator activity during bloom.

Weather report

Temperatures are feeling much more seasonal with daytime temperatures that started out in the mid-60s during the weekend and hit a high of almost 77 degrees Fahrenheit yesterday, May 14. The forecast for the remainder of the week looks warm—60s for a day or two then hitting high 70s by the end of the week; conditions look seasonal over the coming weekend. There is a possible rain event on Saturday, but overall the conditions look sunny and warm. Pollinating conditions looks excellent for tart and sweet cherries that are blooming throughout the region.

Although we received 0.3 inch of rain at the Northwest Michigan Horticulture Research Center last Wednesday, May 9, conditions are quite dry across northwest Michigan. Despite our early rains, soils are drying out quickly and growers are trying to get irrigation systems up and running. With the dry conditions, growers are less concerned about disease pressure.

Growing degree-day (GDD) accumulations as of May 14, 2018, at the Northwest Michigan Horticulture Research Center

Year

2018

2017

2016

2015

2014

2013

28 Yr. Avg.

GDD42

267.7

342.7

344.1

360.3

240.3

307.6

371.7

GDD50

126.6

138.1

142.3

163.3

90.2

163.5

168.3

Growth stages at Northwest Michigan Horticulture Research Center as of May 14, 2018

  • Bartlett pear – Early white bud
  • Potomac pear – Green cluster
  • Mac – Tight cluster
  • Gala – Tight cluster
  • Red Delicious – Tight cluster
  • HoneyCrisp – Tight cluster
  • Montmorency – Bud burst
  • Balaton – Tight cluster
  • Hedelfingen – 80 percent bloom
  • Gold –  First bloom
  • Napoleon – 80 percent bloom
  • Riesling – Early bud swell

Crop report

With the coming dry weather, we anticipate a lot of sweet cherry pruning to be done this week. Growers have been dodging the past week’s wet weather, and this window will be a great opportunity to prune sweets. Growers are still pruning other crops, and brush is being removed from the orchards. Growers were able to burn brush piles during a small window with wet weather last week, but many burn piles have yet to be burned throughout the region. Growers are also planting trees at this time. We planted at the Northwest Michigan Horticulture Research Center yesterday, and soils were surprisingly dry even at depths of over 6 inches.

As mentioned above, conditions look excellent for pollinating cherries this week. Beekeepers have been delivering bees in sweet cherry orchards, and hive quality looks good. We have also seen a lot of activity from wild bee populations so far this season, particularly in cherry orchards.

If you are not planning to harvest brine cherries this season, we have written a Michigan State University Extension article on how to remove fruit, “How to manage brine cherries that will not be harvested in 2018.” However, these data are fairly preliminary, and most of our research has been conducted in tart cherry. We hypothesize that ethephon used at full bloom will also remove sweet cherries, but we have little data to support this hypothesis. Our data in tart cherry showed that 150 parts per million (ppm) at full bloom timing removed 70 percent of the fruit; 150 ppm is equal to 0.5 pint per 100. If you plan to remove fruit using ethephon, consider making these applications this week as sweet cherries are at various stages of bloom throughout the region.

Lastly, we recommend ReTain applications to be made as soon as possible in shy bearing sweet cherries. Our data has shown that the sooner these applications are made, popcorn to first bloom, the better the results. When later applications of ReTain are made, 50-70 percent bloom, we see fruit set drop considerably. One pouch per acre has been effective in our trials.

Pest report

Many apple growers were covered for apple scab prior to rain that came mid-week last week and those applications were well-timed; all northwest MSU Enviroweather stations reported apple scab infection periods last week. This rainfall came in the afternoon, and afternoon showers in contrast to nighttime rains are often associated with higher spore discharges. Historical data on the RIMpro model for May 9 reflects this phenomenon with an estimated peak spore discharge that occurred around 4 p.m.

Spores will continue to mature in this week’s predicted dry and warm weather. As we approach pink/bloom in apples, this phenological growth stage is associated with the highest spore discharge rates during primary apple scab. While the weather is currently predicted to be dry, coverage of new growth/susceptible tissue will be critical prior to the next rain event to minimize the potential for scab infections.

RIMpro-Venturia outputs

Degree-day predictions indicate some apple varieties could bloom early next week in warmer regions of northwest Michigan. Be ready for fire blight management if bloom occurs during weather conditions that favor this disease. Fire blight bacteria grow rapidly in temperatures in the 70s and 80s and wet weather washes the bacteria into floral nectaries where they can infect and cause blossom blight. Currently, the forecast is for dry days in the 70s for early next week. However, continue to monitor the weather and the MaryBlyt model on Enviroweather as we approach bloom.

We have observed some apple pest activity at the station in recent warm conditions, but pests have been relatively quiet and in low numbers in most commercial orchards. Green fruitworm adults have been flying over the last couple of weeks; small green fruitworm larvae became evident last week and we have observed this pest feeding on new leaves and flower buds. We have also received reports of leafroller caterpillars, tarnish plant bugs and aphid activity in low numbers. Spotted tentiform leafminer adults (12.5 per trap) were found in traps at the station this week.

We have had one report of black stem borer activity in the northwest region. We will check these traps again this week and will report back via FruitNet. However, forsythia is blooming throughout the region, and this phenological indicator is a good rule of thumb to begin black stem borer sprays. Black stem borers were detected in more southerly regions in previous weeks in traps. Growers planning to take action against this pest are encouraged to review: "Timing your black stem borer spray on tree fruit and “Managing Black Stem Borer in Michigan Tree Fruits.”

Scouts have been anticipating the spring flight of codling moth, and as pheromone delta traps are going into orchards, place the traps into the upper third of the canopy. Previous data have show that codling moth trap efficiency is improved when placed in the upper third of the canopy.

We deployed San Jose scale pheromone traps in apples and sweet cherries at the station this week; male flight typically occurs about 190 GDD base 50 F, which coincides with predicted degree-day accumulations for early next week. While taking action against male scales is not a suggested management strategy, peak male flight is used as a predictor for when to expect crawler activity; crawlers will be the next opportunity to implement management tools for San Jose scale.

Sweet cherries are blooming and tart cherries have just started to open blossoms at the station. Warm and dry weather in the forecast will be very good for pollinator activity as well as pose a lower risk of American brown rot infections. European brown rot is also not a concern in tart cherries with the current predicted warm and dry weather. Flower buds and green tissue are present on tart cherry, and cherry leaf spot will be a concern if wet weather moves into the region later this week.

We are currently in the midst of an ongoing wetting event following light early morning rain. As of 9:30 a.m. today, May 15, some Enviroweather stations are not reporting possible infections until after bloom; if you are concerned about the potential for cherry leaf spot infection, refer to the Eisensmith and Jones (1981) table to estimate whether an infection period may have occurred (Table 1).

Table 1. Approximate number of hours of wetting period required for conidial infection by the cherry leaf spot fungus at various air temperatures.

Temperature (F)

Wetting period (hours)

81 or warmer

28

80

21

79

18

78

16

77

14

76

12

75

11

74

9

73

8

72

7

71

7

70

6

69

6

63-68

5

62

6

61

6

60

7

59

7

58

8

57

9

56

10

55

11

54

12

53

14

52

15

51

17

50

19

49

20

48

23

47

25

46

28

Some growers may be considering removing light sweet cherry trees after pollination this season due to loss of markets. If San Jose scale has been a problem on these trees that will be removed, consider removing the trees from the orchard to avoid the spread of this pest to remaining trees. It is unknown how long the scale will survive on trees that have been pulled up, but be proactive with tree removal to minimize the potential for San Jose scale to infest adjacent varieties. While our previous observations have indicated there is a greater occurrence of San Jose scale in light sweet cherry varieties, this pest has also been observed in damaging numbers in dark varieties.

As a reminder, San Jose scale is a pest of many tree fruits and removed trees/infested brush piles should be kept away from orchards. Lastly, growers planning to remove light varieties should review cross-pollination partners to ensure that the remaining varieties in the orchard can successfully pollinize in future seasons.

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