Northwest Michigan fruit update - July 3, 2018

Fruit is ripening quickly in hot temperatures; growers have concerns about making spray applications in the hot weather.

Weather report

There is little need to report the recent warm temperatures, but conditions have been hot across the region. The daytime high recorded at the NWMHRC Enviroweather station on Saturday, June 30 was 94.5 degrees F. Sunday was also a warm one, and the temperature hit a high of 92.6 degrees F. Monday, July 2 seemed cool comparatively when the daytime high was only 83.7 degrees. We have accumulated 1514GDD base 42 and 983GDD base 50. We did receive variable amounts of rainfall on Sunday evening into Monday (July 1); the NWMHRC Enviroweather recorded 0.33” of rain. Most other stations in the region received less rainfall. Rain is needed, particularly with the hot conditions.

Crop report

Crop ripening has hastened with the recent hot temperatures. The hot weather has also brought windy and stormy conditions. Some wind whip has been observed in tart cherries. The hot weather has contributed to small cherry size. Growers have inquired if there are potential options to increase fruit size, and irrigation is the best option at this point in the season. Growers will begin hand harvesting some early varieties of sweet cherries, and local cherries are available at the National Cherry Festival. Growers are also weighing decisions to start ethephon applications with the recent heat wave. Many growers anticipate beginning sweet cherry harvest in the next week. Tart cherry harvest is likely two+ weeks away, but fruit seems to be coloring quickly.

Apples are sizing, and some growers have been hand thinning. Many growers seem pleased with crop load as a result of natural thinning and chemical thinning strategies this season. The apple crop is looking good at this point in the season.

Pest report

In anticipation of harvest, growers have been challenged with deciding when to apply ethrel in recent hot temperatures in conjunction with protecting fruit from pests and diseases. Additionally, growers have been cautious with applications of some products and formulations in these hot conditions (please refer to article: Concerns about High Temperatures and Spray-Induced Phytotoxicity). Conditions have been mostly dry with the exception of Sunday’s storm; in some areas, wet weather continued into Monday. Many areas seemed to dry quickly following the rain, but several Enviroweather stations: Bear Lake, Benzonia, East Leland, and Kewadin remained wet long enough for disease infection periods.

In areas that received stormy weather, trauma blight caused by the fire blight pathogen was a concern, particularly in orchards that have ongoing fire blight infections. Growers with infected blocks have continued efforts to mitigate the spread of this disease. At the station, Honeycrisp are almost at terminal bud set – hence, disease progress should be slowing down. We received results from our first set of samples that were tested for streptomycin resistance. New detections of streptomycin resistant fire blight bacteria were found in Benzie and Grand Traverse counties.

Codling moth was flying again this week, and we found an average of one moth per trap in our apple blocks. We have accumulated 651 GDD base 50 degrees F since our initial biofix on May 28 and second generation moths are estimated to begin flying ~1000 GDD base 50 after biofix. However, in past seasons, distinct codling moth generations have been difficult to differentiate at the station due to relatively low pressure. Apple maggot traps were deployed at the station this week.

Cherry harvest is fast approaching, and cherry diseases have been a concern as fruit are ripe and we have had some wet weather. Cherry leaf spot infection periods were a possibility in some areas during rain events Sunday-Monday. Although leaf spot incidence has continued to remain low in most orchards, some orchards under minimal management programs have noticeable leaf chlorosis and some defoliation at this time.  We have received reports of active American brown rot in commercial sweet cherry orchards. Wet weather in the forecast could be conducive for cherry diseases, particularly brown rot, if we receive consecutive days of rain and if the relative humidity remains high.

Obliquebanded leafroller (OBLR) activity is ongoing. Since biofix June 18, we have accumulated ~430 growing degree-days base 42 and egg hatch is underway. Although several growers have counted on organophosphate or pyrethroid materials for OBLR control, we remind growers that previous data suggest that OBLR have reduced sensitivity to organophosphate and pyrethroid insecticides.

We are cautiously optimistic that spotted wing drosophila (SWD) numbers have remained low since our first detection nearly a month ago. Last week, we detected a total of six flies in our trap line, and three of the flies were in traps at the station. We anticipated that we would see an increase in detections within the last week; it is possible that hot temperatures slowed SWD activity. Because cherries are susceptible, many growers have started SWD management despite low catches. For recent applications, growers have chosen material(s) to target multiple insect pests that may have been active within the last week (i.e. scale crawlers, late plum curculio, etc.). We encourage growers to recover following rain events to ensure that the fruit are protected from this challenging pest.

It has been three weeks since the end of the first flight of San Jose scale males, and crawlers are active in both sweet cherry and apples at the station. Many yellow crawlers were noticeable on trunks, limbs, and spurs of trees with heavy infestations. Some of the crawlers had already selected new locations and adhered to the trees while others were mobile. We hypothesize that crawlers likely began emerging at the station in low numbers last week and that activity will continue through the week. After removing waxy covers on some female scales, we were able to find some crawlers that had emerged from their mother, but remained under the waxy cover. We have also received reports that lecanium scale crawlers are emerging in the region at this time. Lecanium scale crawlers are lighter and beige in color compared with the bright yellow San Jose scale crawlers; adult lecanium scales are substantially larger, raised brown bumps on limbs and are more distinctive compared with San Jose scale adults. We often see lecanium scale in sweet cherry blocks adjacent to woodlots with maple trees.

Rose chafer activity is ongoing and it has been a surprisingly long period of chafer activity this season. Cherry fruit fly has not been detected at this time.

Table 1. Avg. number of cherry and apple pests in the NWMHRC trap line by date.

Cherry - NWMRHC

7-May

14-May

21-May

28-May

4-June

11-June

18-June

25-June

2-July

GFW

5

2

1

0

0

0

0

0

0

APB

0

0

5

6

7

7

6

0

1

LPTB

   

Set

4

11

11

3

1

12

GPTB

     

Set

1

0

1

0

0

SJS (sweet cherry)

 

Set

0

6

73

10

0

0

0

OBLR

       

Set

0

8

19

10

CFF

       

Set

0

0

0

0

                   

Apple - NWMHRC

7-May

14-May

21-May

28-May

4-June

11-June

18-June

25-June

2-July

OFM

Set

0

0

0

0

0

0

0

0

STLM

Set

13

18

32

25

1

1

4

5

CM

 

Set

0

1

8

1

3

0

1

SJS

 

Set

0

6

24

1

0

0

0

OBLR

       

Set

0

2

3

1

AM

               

Set

 

APB = American Plum Borer

LPTB = Lesser Peachtree Borer

GPTB = Greater Peachtree Borer

SJS = San Jose Scale Adults

CFF = Cherry Fruit Fly

OFM = Oriental Fruit Moth

STLM = Spotted Tentiform Leafminer

CM = Codling Moth

AM = Apple Maggot

 

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