Degree days can predict blueberry insect pest development, guide trap deployment during early spring

When might blueberry pests become active during this unusual season?

Degree days (DD) can be a very useful tool for blueberry scouts, consultants and growers, because they help predict when important stages of pests will occur. With this unusually warm spring, current and predicted degree days can also help provide a guide for how early pests might emerge, and how early to start deploying monitoring traps. We are in uncharted waters here, but historical timings from our monitoring of blueberry farms in recent years can be used to guide early deployment of monitoring traps and early checking of bushes.

For example, as shown in the table below, the first cherry fruitworm moths have started their flight on average at 262 degree days (base 50). This is before first bloom of Jersey which is predicted to start at 310 degree days. In a typical spring, we reach 262 degree days in mid-May. However, the hot days and warm nights so far this month mean that Enviro-weather stations are showing this may happen more than a month early in southwest Michigan. With the hot week ahead, the Benton Harbor Enviro-weather station is already at 140 degree days, and is predicted to reach 216 by Sunday (March 25). At that rate, cherry fruitworm flight may start in early April. A cool down in the weather would slow down development and delay the date of these events, but this example highlights the value of guides that can show how temperature drives pest (and crop) development.

The Enviro-weather system is a free service to Michigan residents that provides up-to-date weather information and predictive tools to support pest and crop management decisions. To access this weather information, go online to www.enviroweather.msu.edu. This keeps track of degree days for about 70 weather stations across Michigan at base 32, 40, 42, 45, and 50. To access these numbers, enter the website URL and click on the yellow dot nearest to your farm. Then, in the “Weather observations and summaries” box (see arrow in picture below), click on “Temperature, rainfall and degree day summary” (see circle in picture below). This will bring up the page of DD totals and you can scroll down to see the total for yesterday, plus the predictions for the coming week.

Enviroweather

The table below provides some DD predictions for key blueberry insect pests. This information was generated from MSU weather stations near six commercial blueberry farms that were scouted weekly for pest insects from 2003 to 2006. These were much more “typical” years in terms of crop development and spring temperatures, and so they will provide a useful comparison to 2012. Values presented here are the degree day values when specific pest events occurred, averaged across those farms and across the years. We suggest you print this table and keep it handy during this season.

With this table and the Enviro-weather station information, growers and consultants should be able to keep ahead of the pest development, even if it is unusually early this season. More blueberry pest information is available online at our updated website, www.blueberries.msu.edu.

We stress that these are predictions, and are not validated models. If you are trapping and also tracking DD in your area, your feedback on the accuracy of these values would be greatly appreciated. Please send comments to .(JavaScript must be enabled to view this email address).

Average date and degree days of blueberry insect pests (2003-6)


EVENT

Date first seen
Van Buren Ottawa

GDD 42

GDD 50

GROWTH STAGES




Bud break

April 17

April 18

224

108

Bloom

May 14

May 15

591

310

Petal fall

May 27

May 28

768

407

First harvest

July 15

July 15

2060

1313

Cherry Fruitworm moths




First

May 10

May 10

511

262

Peak

May 28

May 30

804

431

End

June 12

June 16

1180

683

CBFW eggs




First

June 1

June 2

872

472

peak

June 9

June 9

1074

612

End

June 21

June 18

1337

797

Cranberry Fruitworm moths




First

May 24

June 1

758

412

Peak

June 16

June 17

1267

747

End

July 17

July 11

2018

1285

CBFW Eggs




First

June 6

June 11

1235

732

Peak

June 9

June 13

1264

776

End

June 19

June 15

1401

856

Blueberry Aphid




First

June 5

June 4

949

525

Peak

July 4

July 4

1715

1062

End

Aug. 8

Aug. 13

2804

1853

Parasitized aphids




First

June 29

June 23

1503

904

Peak

Aug. 4

July 30

2571

1692

End

Aug. 28

Aug. 13

3314

2246

OBLR Generation 1




First

June 15

June 14

1208

695

Peak

July 1

June 28

1607

994

End

July 29

July 28

2434

1600

Obiquebanded leafroller moths


OBLR Generation 2




First

Aug. 18

Aug. 12

2968

1986

Peak

Sept. 6

Sept. 7

3574

2396

End

Sept. 27

Sept. 30

3980

2666

Japanese beetle adults




First

July 4

July 15

1908

1211

Peak

Aug. 14

Aug. 11

2738

1832

End

Sept. 4

Sept. 1

3452

2319

Dr. Isaacs’ work is funded in part by MSU‘s AgBioResearch.

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