Baute Bug Blog

Some scouts are starting to notice tiny WBC  larvae that have hatched that crawling in the whorl or making their way down to the ear of the plants.  To help you know whether they are WBC larvae, here are some photos.  You can click on them to enlarge them.

They start out with spots along their bodies (spots have tiny short hairs coming out of them).  You will need a handlens to really see the spots.

Newly hatched WBC Larvae (T. Baute, OMAFRA)

Closeup of newly hatched WBC larvae (Photo Credit: Chris DiFonzo, MSU)

Within a few days they start to develop stripes.

2nd or 3rd instar WBC larva (Photo Credit: T. Baute, OMAFRA)

To know for sure that they are WBC, watch how the way.  The itch their way along a leaf like an inchworm.  Click on video to see how they crawl.

Trap counts sent in to the network this week from last week’s moth catches indicate that moth flight increased dramatically.  And from tweets on Twitter and emails coming in from participants, even higher numbers are being caught this week in some traps.  So we haven’t quite reached peak moth flight yet here in Ontario.  The top counties that caught the most moths last week were Lambton (93/trap), Haldimand/Norfolk (88/trap) and Chatham-Kent (63/trap).  I’ve summarized the results for the top 9 counties so far this year in a graph below:

Top 9 County Trap Catches So Far

What does this mean?  We still have more scouting to do.  With moth counts still increasing, egg laying is also still on the rise.  Hot spot areas like Bothwell will start to be less ideal for the moths to lay eggs, as the corn starts to advance into full tassel/pollen shed.  Other counties with high trap counts and younger corn are at risk.  Though I suggest everyone scout their corn fields at least once or twice these next few weeks, even if trap counts are not that high.  Some of the original sites we found the most eggs in this year had very low trap counts initially.  Focus scouting efforts to corn fields that have plants with at least a tassel developing in the whorl of the plant to those fields with the tassel fully emerged but not fully shedding yet.  These are the fields that seem to be the most attractive for the moths.  And if fields have variable plant heights, we also noticed that there tends to be a higher concentration of eggs on what some tease about as “Baute” height corn.  No offense to my family members who are taller than me but those who have seen me know that I am a little vertically challenged.  So scout shorter corn in a field first before moving deep in.

Since peak flight has not happened yet, dry bean scouting is not quite necessary yet.  Most of the crop is still just starting to flower and develop pods.  Ideal management timing is when pod feeding can be easily found, which typically takes place 10 to 20 days after peak flight.

Despite the heat, western bean cutworm activity is increasing.  Trap catches over the past week have climbed significantly, indicating that peak flight is here or soon to be here.  The counties that have accumulated the most moth catches so far include Chatham-Kent (544), Lambton (256), Middlesex (244), Huron (206), Haldimand-Norfolk (138), Essex (155) and Elgin (105).  Click here to see the accumulated map catches for Southwestern Ontario. The Chatham-Kent trap sites with the highest catches are actually still in and around Bothwell which border the three counties of CK, Lambton and Middlesex.  Chatham-Kent and Lambton are both currently averaging 9 moths per trap, though some traps have caught 100s in just a few days.  To see trap catches for all of our trap sites, click here and view Week 6 maps.

Newly hatched WBC Larvae (T. Baute, OMAFRA)

More reps and scouts are finding corn fields with eggmasses at above threshold levels.   Though so far above threshold infestations have been mainly found in the greater Bothwell area and south of Tillsonburg, many more fields are going to be ideal now for moths to lay eggs in.  Those fields that were not planted with a Bt that protects against WBC need to be scouted.  Target fields that are in the early pre-tassel to early tassel emerged stages.  In this heat a freshly laid eggmasses can hatch in 4 to 5 days.  Remember you want to target a spray application just after egg hatch, if the 5% threshold is reached.  Young larvae will hang out in the whorl/tassel of the plant for a few days before heading down to the developing ear.

Don’t spray in the heat of the day during this heat wave.  Wait until the evening when temps are in the lower 20s to high teens.

I have been negligent in not mentioning the newest insecticide to be registered for WBC control in corn.  I have no excuse except that I been conveying product information through links to Publication 812, Field Crop Protection Guide and the product didn’t get registered for WBC control in time to make the printing deadline.  So it is going to get a special blog entry to make up for it.

Coragen Insecticide is now registered for WBC control in corn.  The active ingredient is chlorantraniliprole.  Rate would be 101-151 mL/acre or 250-375 mL/ha.  Use a minimum of 100 L/ha of water. 12 hr re-entry period.   Follow all label precautions which can be found the Coragen_en_2011.

Great to have more products to tackle this new pest.

Many questions are starting to come in regarding WBC.  Just to help clarify what the action thresholds for western bean cutworm are, here is a quick summary:

In Corn: Scout 10 plants in a row in 10 areas of the field.  In non-Bt corn or transgenic corn that does not provide any protection against WBC (click here to see corn trait list and insects they control), if 5% of those plants have eggmasses on them, a spray is warranted.  Time the spray application for just after egg hatch when small larvae are present at the top of the plant.  Egg hatch occurs a day or two after the eggmasses turn purple (typically 5-7 days after being freshly laid).  For a list of products registered in corn, click here.  In these extreme temperatures, insecticides should be applied in the evening when temps are below 24 degrees C.  I’d recommend waiting to spray until after Thursday of this week when nighttime temps start to go back down to low 20s, high teens.

Is there a threshold for Cry1F corn yet?  No.  As you have read in past blogs and articles, Cry1F (eg. Herculex, SmartStax) only provides approx 70 to 80% control for WBC.  So you can experience some damage in heavy infestations. Eventually we may set a much higher threshold for Cry1F corn but for now, we don’t know what that is.  The research is taking place right now.  Populations would have to be very high to justify spraying Cry1F corn.  70 to 80% control is still better than not planting a Bt hybrid that protects against WBC.  The Agrisure Viptera Bt corn does provide excellent control (nearly 100%) of WBC will not need a potential higher egg threshold.

In Dry Beans: There currently are no thresholds established for dry beans yet.  However, research suggests that insecticide applications are most effective when targeted as soon as pod feeding can be easily found in the field (ie..if after a half hour of scouting you only find a few pods with feeding it is not worth spraying).  Pod feeding typically takes place 10 to 21 days after peak moth flight so having a trap at the field location helps determine when moth peak occurs.  Ontario has not yet reached peak moth flight this year.  To see a  list of products registered in dry beans, click here.  If a corn field directly adjacent to the dry bean field has reached threshold, then the dry bean field should be considered at risk.  Plan to scout that field for pod feeding and spray if warranted.