Start SCOUTING for Western Bean Cutworm – egg masses being found

Contributed by Robert Moloney, NK Brand Seeds

 We are starting to see a high number of Western Bean Cutworm (WBC) moths in our monitoring traps from London through Windsor and along the east shore of Lake Huron. What does this mean to you? It’s time to start SCOUTING for egg masses. Kudo’s to Cole Cruikshank from Bluewater Agromart near Kincardine for being the first NK dealer to help OMAF researchers find egg masses. Egg masses have also been collected in Chatham-Kent. Since this is a new pest to Ontario and populations will be sporadic, OMAF is looking for any egg masses that they can collect and use to infest their research plots. These research plots are being used both to learn about this pests behavior and also to determine the proper threshold levels for spraying this pest in Ontario.


 In some ways scouting for egg masses is relatively simple. The egg masses range in size from the size of a penny to the size of a quarter. They are laid on the UPPER surface of the UPPER leaves of the plant. Most likely leaves are going to be the ones that are still upright on the plant. There seems to be a very strong preference for the moths lay eggs on plants that have not tasseled over those with exposed tassels. Within a field the first place to look for egg masses will be later maturing plants (i.e. areas with compaction or other issues that have delayed development) or look in later planted fields next to other earlier planted/tasseling corn. Ontario experience this year suggests the eggs tend to be laid nearer to the base of the leaf than the tip.

 The easiest way to scout for egg masses is to look up such that the sun is behind the leaves you are looking at. If you see a blotch-like shadow on the leaf, pull the leaf down and likely it will be an egg mass on the upper side. The eggs are laid in a mass of individual eggs. They are round and start off pearly white. As the eggs mature and get near hatching they become purple in colour. For more details on egg scouting and egg masses check out Tracey Baute’s (OMAF Field Crop Entomology Lead) blog at

If you find egg masses in your field (especially white, recently laid ones) please collect them, keep them cool and let your NK rep know. OMAF is still looking to collect egg masses for use in their research and they will come and pick egg masses up.


The threshold for spraying for WBC is 5% of plants in a field with egg masses. However, timing is the key to spraying for control of the WBC larva. There is a very small window between egg hatch/larva emergence and the point at which the larva are protected from spray under the cover of the husk on the cob to get control. Matador insecticide is registered for control of WBC (including aerial applications), but it requires contact with the larva to kill them and it will not control larva in unhatched eggs. This means that before spraying you at very least need to scout to see when eggs are hatching to get effectiveness from spraying, although you should also be scouting to determine if you are at threshold or you may be wasting your money anyway.


One Response

  1. In the past Syngenta researchers have noticed that if there is a residue of lambda-cylhalthrin on the egg mass, larvae will pick this up off the eggshell as they eat their way out and this is usually enough to kill the insect. This is particularly true with the moth family. Spray early rather than late.

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