Lots of Insect Activity Still Out There

It’s been quite a week and it’s only Tuesday.  Many of you are calling about one of these pest issues so hopefully I can help answer all of your questions here.

Grass Sawfly in Wheat:  Once you start to see sawfly feeding (see previous blog for pics and details) the feeding damage is nearly done.  You only have about a 7 to 10 day window to do anything before the larvae finish their feeding.  That said, the grass sawfly infestations tend to be in pockets in the field, usually more focused along the fields edge.  A full field spray may not be necessary.  Plus make sure to follow the pre-harvest intervals for products registered in wheat since harvest is approaching.  See next paragraph for product info. Don’t confuse grass sawfly with wheat sawfly.  Some of you saw an article in CropPest this week regarding white heads in wheat and saw sawfly in the article.  That is wheat sawfly not grass sawfly.  Grass sawfly is very different and does not mine into the stalk of the plant.  It climbs up the plant from the outside and clips the stem as it sucks the sap from the plant. You will see clippings of stem and heads on the ground and may see the green larvae walking along the ground or stem of the plant.

Armyworm in Wheat–   The window is starting to close on the pre-harvest intervals (PHI) for some of the products available so keep that in mind when deciding whether to spray.  Also remember if the larvae are bigger than an inch, the control products don’t work as well.  Pre-harvest intervals can be found in Pub 812 at: http://bit.ly/jWpXjA One field was reported to have larvae that are naturally dying off from a virus that infected them.   It screws up their brain and sends them to the top of the plant to die there.  You can find shriveled up larvae stuck on the wheat heads.

Armyworm in Corn: As surprising as it seems, corn can grow out of armyworm damage.  They don’t feed on the growing point so the plant can start growing more new leaves once the feeding has stopped.  There may be a little yield drag but the cost of spray may not be economic.  The plants recovery does depend  a bit on the conditions the field goes through for the rest of the summer but pending no other stresses or lack of rain, they will pull through.  I only recommend seed corn or higher value corn fields to be sprayed if necessary.  But again, use the one inch rule.  If the larvae are bigger than an inch the control products may not be effective.

Black Cutworm in Corn:  Most of the pics I have received from growers and reps have been of larvae that were close to being full grown.  These not only are too difficult to control but should be finishing up their feeding soon.  Plus, the corn crop is advancing beyond the critical stage of 5 leaves.  These cutworm struggle to cut a corn stalk once they plant is at 5 leaf or beyond so focus your scouting in only those fields that were late planted and have not reached the 5 leaf stage yet.

Cereal Aphids: Twitter has been a new source of pest info from me.  Thanks everyone who are tweeting and retweeting info about what they are finding out there.  @KaptinKnapton found cereal aphids on spring wheat near Lanark above threshold levels.  Thresholds are 12 to 15 aphids per stem prior to head.  Scouting in that region is advised.  Natural enemies will be trying to move in to start feeding on them but they have to find the fields first.

I have info regarding soybean aphids too but I think I will wait to write another blog in the next few days to let you know what we are finding and what to expect this summer!