Baute Bug Blog

What Moths Prefer- Moths prefer laying their eggs in corn before it tassels.  After the crop is in tassel, it will prefer neighbouring fields that are less advanced in crop stage OR they move to dry beans and other host crops (like snap beans, sweet corn etc).  Pick the tallest and healthiest looking fields that are not quite tasseling yet.

Where Eggs are Laid- Eggs are laid on the top 4 or so leaves, especially on those leaves that stand erect or just have or are about to unfurl from the whorl.  Eggs are usually on the upper (hairy) surface of the leaf.

What WBC Eggs Look Like – Egg masses can range in size from smaller than a dime to bigger than a quarter.  Each individual egg is shaped like a tiny cantelope.  Initially they are pearly white when first laid but turn tan and then purple just before hatch.  Click here to see a picture of how an egg mass changes colour as it ages over time.

How to Scout – Select the appropriate fields based on information above.  Inspect 20 plants in a row.  Inspect the upper leaves for both egg masses and young larvae.  If any are found, make note of the age of the egg and when it might hatch.  If young larvae are found, make note of their location on the plant.  After scouting those 20 plants, cut across the field and pick another 20 plants in a row.  Continue this until you have inspected 20 plants in 5 areas of the field.  That gives you a total of 100 plants inspected per field.   Eggs will be laid in patches in the field so you may or may not come across one of these hotspots during your scouting attempts.  Change up the areas of the field you monitor so that you are more likely to hit one of these hotspots in one of your scouting trips.

Threshold in Corn – If 5% of the plants (or 5 plants if you have scouted all 100 as suggested above) have egg masses on them, the corn needs to be sprayed.  Spray may not be required in those fields containing Cry1F (Herculex or SmartStax) as this type of Bt provides the crop with some protection (similar to one spray of insecticide).   However if populations are high, Cry1F fields may also experience damage.

Spray Timing – Time the spray application to immediately after the majority of the eggs have just hatched.  This will be one or two days after the eggs have turned purple.  This will ensure that you are targeting the smallest larvae which are the easiest to control.  These small larvae will be close to the top of the plant near the tassel unless there are already silks on the plant.  If silks are present, then the larvae will be attracted to the silks and may be hanging around the ear.  You must control the larvae before they enter the ear and are protected from the spray.

Chemical Control Options: Both Matador and Decis are registered on corn for western bean cutworm control.  See the 2010 supplement for Pub 812 that is now available at  http://www.omafra.gov.on.ca/english/crops/pub812/sup/p812suptoc.htm for label rates and recommendations.

Next Blog:  Update on this weeks moth catches, when peak moth flight is expected and dry bean management recommendations.

Several wheat fields were found with grass sawfly north of London from Hyde Park to Kintore and St. Marys.  Damage averaged anywhere from 3 heads clipped per square meter to 30 heads clipped per square meter!  Reports have also come in from Rodney, Glencoe, Molesworth, Brussels and now northern Huron County.

Close up of Grass Sawfly Larva - T. Baute, OMAFRA

Scout fields to determine if sawfly is present.  All fields infested look fine until you part the wheat plants and look at the canopy floor.  Only then do you see the number of heads laying on the ground.  These larvae don’t seem to bother eating the leaves but instead climb the plant and clip the heads right off.

Wheat Heads Clipped by Grass Sawfly - T. Baute, OMAFRA

Side View of Grass Sawfly- Note the numerous chubby prolegs - T. Baute, OMAFRA

Finding the actual larvae is difficult.   They do feed during the day but blend in very well with the wheat.  Shake plants in a square meter to force the larvae to drop.  Then part the wheat plants and count the number larvae and clipped wheat heads laying on the ground.  The larvae curl into a C shaped when they first drop so look for a small green ball on the ground. Armyworm larvae may also be present (though they too are much greener than we are used to seeing them) but armyworm infestations seem to be low in general.  It appears that it really is the sawfly causing the majority of the clipping.

Thresholds based on the number of larvae per foot of row may be tough to determine.  Delaware’s threshold is 0.4 larvae per foot of row.  Taking into consideration the number of heads being clipped may be a safer assessment.  30 heads clipped per square meter or 3 per square foot should equal the cost of control.  Just make sure that the larvae are present still in the field.

We’re not sure how long the feeding will continue.  Most of the larvae I have seen are close to full size.  The larvae live for approx 30 days then burrow in the ground and stay in hibernation until next spring when they pupate and emerge as an adult sawfly.  So there will be an end in sight though I can’t exactly say when yet.

I have heard reports now from a few different locations of both wheat heads being clipped and leaf feeding taking place in corn in southwestern Ontario.  This is a good sign that true armyworm is present.

Both wheat and corn fields need to be scouted to determine if armyworm is present.  Here is an article from last year’s CropPest Newsletter that explains thresholds and management strategies.  Pay attention to the days to harvest intervals for wheat products!

I don’t have a good grasp yet as to how widespread this issue is.  What are you seeing?  I know you guys are out there looking too so please send in your comments!

More reports of WBC damage are coming in.  Here is an updated list of sites with damage and or larvae found in Ontario:

Chatham- Kent (Dover Centre, Bothwell)

Lambton (Petrolia)

Middlesex (Wardsville, Appin, Glencoe)

Elgin (Rodney)

Huron (Blyth, Clinton, Exeter, Dashwood, Holmesville, Belgrave)

Bruce (Walkerton, Kincardine)

Simcoe (Alliston, Barrie, Stayner)

Durham (Kinsale, Lindsay, Brooklin)

Victoria (Dunsford)

Peterborough (Millbrook)

Dundas (Chesterville)

I will be attending a meeting this week with my US counterparts where we will be discussing what each state/province has observed with regards to WBC and soybean aphids.  I will give an update next week on any new information from the meeting.