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Mitigation Recommendations for European Corn Borer Resistance to Bt Corn (Cry1F) in the Maritimes

In 2018, field corn planted in Nova Scotia resulted in Unexpected damage (UXD) reports indicating the presence of populations of European corn borer (ECB) resistant to a single Bt product containing Cry1F (Herculex I).  Importantly, while Cry1F is also present in other hybrids containing multiple Bt traits that each target ECB, there have been no reports of UXD by ECB to any of these hybrids. ECB showing tolerance to Cry1F were collected from two separate locations in the major corn growing areas of the province.  Monitoring efforts are underway to determine if resistant ECB populations exist outside of Nova Scotia.  Regions perceived to be at increased risk of resistance may share some common characteristics: a) shorter growing season; b) few low CHU hybrids; c) single Bt products targeting lepitopteran pests, and d) inadequate implementation of required refuge (i.e. 20% non-Bt blocks or strips – 400 m from the Bt planting).

Some hybrids contain more than one Bt trait to control the same pest ECB (referred to as a pyramided hybrid).  The combination of multiple Bt traits in a single plant provides both improved efficacy over single Bt products and an effective approach for insect resistance management as it is significantly less likely that insects will develop resistance to two Bt traits at the same time.  If insects have developed resistance to one of the Bt traits in a pyramided hybrid, resistance can develop more rapidly to the second trait.  To prevent the spread of ECB resistant to Cry1F, we encourage growers to take steps to control the current resistant population and alert your seed company agronomist or sales representative, or provincial extension specialist of any field with unexpected damage by ECB in 2019.

Steps to Mitigate European Corn Borer Resistance

There are several measures that all growers should take to delay the development and spread of resistance in the European corn borer population:

1.  Scout for ECB activity. It is important to monitor for ECB damage in Bt and non-Bt fields.  ECB damage found in Bt fields (pictured below), should immediately be reported the seed company agronomist or sales representative, or provincial extension specialists (shown below).


Companies can also be contacted through the below central numbers:

       Syngenta Customer Interaction Centre:  1-87SYNGENTA (1-877-964-3682)

       Corteva:  1-800-667-3852

       Monsanto Technical Support Line: 1-800-667-4944


Provincial Specialists to Contact if ECB Damage is Found in Bt corn:





Nova Scotia

Angela Gourd

(902) 956-0981

New Brunswick

Chris Maund

(506) 453-3477


Sebastian Ibarra

(902) 314-0388


Julian Saquez

(450) 464-2715 ext. 249


Tracey Baute

(519) 360-7817


John Gavloski

(204) 745-5668


2.  Growers should know which Bt traits they are purchasing. A table of registered Bt corn products in Canada and refuge requirements, is available at: Growers are strongly encouraged to plant a two-mode of action Bt trait above ground product. 

3.  All corn growers must follow the refuge requirements of the hybrids they are planting.   For more details on proper refuge configuration, please go to:

4.  When possible, growers should plant a corn hybrid that expresses multiple Bt traits targeting ECB. Using a hybrid with multiple Bt traits that each target ECB is much more effective at delaying resistance and mitigating the current resistant population.  Growers should refer the trait table under point #2 above to identify multiple mode of action hybrids for ECB and contact their seed provider for additional information.

5. Growers who find damage in their Bt corn should take additional measures to control ECB to reduce the risk of resistance continuing in future ECB generations by reducing overwintering survivorship.  One of the most effective mechanical measures to control overwintering ECB populations includes mowing corn stalks to as close to the soil surface as possible after harvest, followed by burying the mowed stalks in the fall. Shredding and burial of corn stubble can also reduce the population. Tilling corn stubble under without mowing or shredding them first is not as effective.

Signs of ECB Feeding – Report if found on Bt Plants

ECB feeding found on Bt plants is a potential sign of resistance. Early season signs of feeding may include window-paning, pinholes and shotholes and are not considered unexpected. ECB larvae must feed on plant tissue to be exposed to the Bt proteins before dying. However, if damage continues to progress beyond pinholes and window-paning, this would be considered unexpected damage. See the link below for more information on signs of ECB damage to look for when scouting Bt corn fields

Signs of ECB activity and damage to scout for in Bt corn fields