Trapping for fruitworm pests as part of your blueberry IPM program

Monitoring can help identify optimal timing for fruitworm pests in blueberries.

The warm, spring weather heralds the start of blueberry integrated pest management (IPM) programs. Some of the most important early-season pest insects are cherry and cranberry fruitworms. These can cause fruit infestation that can reduce yield in severe cases and cause fruit contamination, especially in the earlier-harvested varieties. Future Michigan State University Extension articles will focus on the management of these with biological and chemical methods, but given the early phase of the season, this article will highlight use of monitoring traps to detect these pests and help growers know when to protect their crops.

All insects, and blueberry bushes, develop based on heat accumulation, and this can be tracked with growing degree days (GDD). The table below shows the approximate growing degree days for Van Buren and Ottawa counties in Michigan for when various crop growth stages occurred, as well as key fruitworm pest events. This also shows the average growing degree days at two different base temperatures (42 and 50 degrees Fahrenheit) when these events occurred. The information was summarized from a four-year research project in Michigan blueberries.

Approximate dates and growing degree day (GDD) timings for key activity events in the lifecycle of cherry and cranberry fruitworms in Michigan blueberries

 

Date first seen

 

 

Event

Van Buren County

Ottawa County

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

2,060

1,313

Cherry fruitworm moths

First

May 10

May 10

511

262

Peak

May 28

May 30

804

431

End

June 12

June 16

1,180

683

Cherry fruitworm eggs

First

June 1

June 2

872

472

Peak

June 9

June 9

1,074

612

End

June 21

June 18

1,337

797

Cranberry fruitworm moths

First

May 24

June 1

758

412

Peak

June 16

June 17

1,267

747

End

July 17

July 11

2,018

1,285

Cranberry fruitworm eggs

First

June 6

June 11

1,235

732

Peak

June 9

June 13

1,264

776

End

June 19

June 15

1,401

856

This information can help you time when it is appropriate to place monitoring traps for fruitworms into blueberry fields, and we recommend that traps for cherry fruitworm are placed in fields this week to be sure to get one or more zero counts before the moths emerge. This helps you identify the start of flight, and this can be used to time cherry fruitworm control treatments that should be started at 100 GDD (base 50) after the first moths are trapped. If this pest has been causing significant damage in recent years, an application of Intrepid at 8 ounces per acre timed to coincide with early egglaying is an effective way to reduce this pest. Intrepid, as well as B.t. formulations such as Dipel, Javelin, etc., can control fruitworms without any risk to bees.

Moths of cherry and cranberry fruitworm as seen trapped in monitoring traps. Note the contaminant moth pictured in the upper right that can be confused with these fruitworm pests. It is an early-active moth that is attracted to the cherry fruitworm traps, but causes no economic injury to blueberries.

Cherry fruitworms
Left, male cherry fruitworm moth on trap. Right, male cherry fruitworm moth on trop (top) with contaminant moth below. Moth = 8-10 mm long.

Cranberry fruitworms
Left, male cranberry fruitworm moth with wing opened. Right, male cranberry fruitworm moth on trap. Moth = 15-18 mm long.

To determine the start and activity periods of these two pests, each species can be monitored using a specific pheromone lure placed inside a monitoring trap. Use a pheromone trap with a sticky surface and place the lure inside the trap, ideally mounted on a pin to suspend it from the inside of the trap roof. Place the traps in the top third of the bushes and at field borders next to woods for the best chance of trapping the pests. Adding traps inside fields can help tell you whether they are abundant only at the field border. Traps of the two species should be placed at least three rows apart to separate the pheromones.

Check the traps weekly at a minimum and count and record the number of the target moth species detected. We typically keep records in a notebook, but the number and date can also be recorded on the bottom of the trap. During warm periods of the spring, more regular checking can help you get a more accurate handle on the first activity of the moths.

Lures and traps for these pests can be purchased from many suppliers, but a good local supply for these is Great Lakes IPM, 10220 E. Church Road, Vestaburg, MI 48891, telephone 1-800-235-0285.

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

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