Baute Bug Blog

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!

Lots of reports are coming in of black cutworm and armyworm damage in Ontario.

Black cutworm has been found feeding in numerous corn fields and even an alfalfa field.  Locations that I know of so far include fields near: Parkhill, Watford, Embro (alfalfa field), Renfrew County, and parts of West Elgin.

True armyworm has also been found feeding at threshold levels in corn and wheat.  The corn field was near Little Britain (SW of Lindsay) and the wheat field was near Kerwood.

Larvae have been in a range of sizes.  If they are smaller than an inch the foliar insecticides will still work on them.  If the majority are bigger than that, then it is too late to do anything.

For Black cutworm Biology, ID and Thresholds: http://bit.ly/hbk52x For Management Options: http://bit.ly/m59Na0

For True armyworm Biology, ID and Thresholds: http://bit.ly/kqgWnl For Management Options in Corn: http://bit.ly/j34V7v and in Cereals: http://bit.ly/jWpXjA

Many of the reports coming in have been through twitter.  Reps have been doing great at informing followers and sending pics of what they are seeing.  If you are not on twitter yet, I suggest you give it a try.  You’d be amazed at the flurry of tweets taking place regarding these pests!

States to the south of us have been reporting intense black cutworm moth captures over the last few weeks.  The continuous storm fronts that keep moving across Ontario could be carrying some of these moths to us.  In addition, rain has kept us from getting into the fields to manage the annual weeds (especially chickweed) which the female moths are attracted to laying their eggs on.  The later we get into our fields and plant corn, the bigger the larvae may be once they start feeding on the tiny corn seedlings.  Also, don’t assume that all Bt corn protects from black cutworm.  Agrisure Viptera hybrids will provide good control, while hybrids containing Cry1F (Herculex I, Herculex Xtra, Genuity SmartStax, Optimum Intrasect, and SmartStax) may only give good control of younger larvae.  Rescue treatments can also be effective if infestations are spotted and controlled in time.  Expect to be scouting seedling corn fields to determine if control is needed.  More information on black cutworm scouting and management is available at: http://www.omafra.gov.on.ca/english/crops/pub811/13corn.htm#bcutworm

True armyworm could also be a risk this year.  We tend to see outbreaks following a cool, wet spring as this miserable weather impacts the parasites that help to control true armyworm.  Expect to start scouting wheat around mid May.  Examine plants from five locations in your field to determine the level of infestation. Winter cereals can be as attractive to moths as grassy weed borders so the field may be infested throughout. During the day, look for true armyworms under the crop residue and soil clods. Their frass will also be visible on the ground and lower foliage.  It is best to scout during the evening or very early morning (before sunrise) with a flashlight to observe the larvae feeding.   If there are reports of outbreaks, then corn fields will also need to be scouted.   Details on scouting, management strategies and control are available at: http://www.omafra.gov.on.ca/english/crops/pub811/13cereal.htm#tarmyworm

Calls continue to come in of feeding damage found even in corn larger than 5 leaf stage.  Some of the larger plants (6-7 leaf) are being mined into at the base of the plants and smaller plants are being cut off.   In most of the cases, the culprit is black cutworm.  Though it is odd to see plants larger than 5 leaf still experiencing feeding, I am not surprised given the year we have had.  Corn went in early and clearly got ahead of the cutworm larvae in terms of size.  The larger the plant, the harder it is for the cutworm to chew completely through the plant  and cut it off so instead they are mining into the stalk.

To identify black cutworm, use a handlens and look at the spots/warts or tubercles on the body of the larvae.  On each body segment there are a pair of tubercles, one always slightly smaller than the other.

Black Cutworm Larva Identification (Credit: University of Nebraska-Lincoln)

A couple of issues with trying to manage this damage now.

1)  Size of larvae:  From what I am seeing, the larvae so far in all of these cases are over 1 inch in size.  Foliar insecticides will not work well on these larger larvae.  Also, the larger the larvae, the more likely they are almost finished feeding.  So essentially the damage that they are going to do has already been done.

2)  Weather:  It is going to be difficult enough to get out and spray at night during this week’s rain events.  But the other key point to spraying them is to leave the soil undisturbed for 5 days so that the larvae that were not directly in contact with the spray, will come in contact with the residual product left on the soil when they do come out to feed.  Unfortunately if it rains during that time (especially the kind of downpours we’ve been having) this residual is washed away or diluted, reducing its effectiveness.

So before making the call to spray, check the size of the larvae to make sure it is worth the effort.

Thanks to Nick Zwambag for commenting on here that they are seeing cabbage seedpod weevil activity in winter canola near thamesville earlier this week.  But with this weather, little can be done about it and fortunately the cool temps should slow them down a bit.   Scout once this front goes through and see what infestations are like then.

Bean leaf beetles are not quite yet.  We’ve been sweeping in alfalfa fields and have not captured any.  We tend to see them emerging around this time so I expect if things warm up a bit, they will be making their way into alfalfa or newly emerging soybeans (if the soys escaped the frost).

These storms are also apt to be carrying in black cutworm and true armyworm moths.  States just to the south of us are reporting black cutworm flights and feeding activity.  Fields that had a decent weed mat this spring should be scouted.  There have been fewer armyworm reports but given the advanced wheat crop, those fields are going to look mighty appealing to the mother moths flying by.

And finally, Ohio is still reporting quite a lot of cereal leaf beetle activity, though I haven’t heard or found any yet here.  I do recommend that once this rain passes, we get out and look for armyworm and cereal leaf beetles.  This heavy moisture might be good for initiating entomopathogens but it needs to be a bit warmer for the fungus to get established.

Let’s hope we see the sunshine soon!