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

I was sent a message today from Deb Campbell of Syngenta Seeds, that they are finding fall armyworm in corn in Grey, Perth, Oxford, Huron and Simcoe counties.  Infestations are low and the larvae are small but it is something to keep an eye on.  There could be fields with heavier infestations.

Also, both Michigan and Ohio are reporting finding incredibly heavy infestations of second generation true armyworm in mixed forages.  In Michigan it is a combination of true armyworm and variegated cutworm.  Grasses in these fields are being eaten down to the midrib of the plant.   Haven’t heard of any infestations like this in Ontario this year but keep an eye out for this.

There have been a number of reports of heads being clipped in wheat.  Some of it can be blamed on armyworm, but some cases (at least in Rodney) have been due to larvae known as grass sawflies.  These larvae are green to green-yellow in colour with a yellow brown head.  They look like caterpillars but are actually larvae from the order Hymenoptera or wasp group.  Unlike armyworm, they do not have stripes along their body but do have 8 pairs of chubby prolegs starting directly after their 3 pairs of true legs all the way to their last body segment.

Chris DiFonzo from Michigan State University is also starting to see heads being clipped there.  She put together a great infosheet this weekend on which critters could be blamed for the clipping and how to tell them apart.

Sawfly larvae feed during the day so they should be easier to spot, though they do blend in well with the colour of the crop.  They can actually do more damage, according to the literature, than armyworm if in high enough numbers.  Thresholds are hard to peg down since this is a rare occurence but Delaware has a threshold of 2 larvae per 5 feet of row.  If significant head clipping is noticed I feel that control is necessary.  Treat them as you would armyworm, but spraying can take place during the day since that is when they are feeding.

As for the armyworm populations, larvae are still reasonably small in size (most at 1/2 inch to some at 1 inch) and populations do not seem as high as usual.  But given that they are still small, they have a lot more feeding to do.  So scouting this week is VERY IMPORTANT. The armyworm larvae seem to be more green and orange in colour than the darker brown versions we are accustomed to seeing.  Again, use the infosheet provided above to help confirm your ID.

Keep the comments coming in so that we can get a good sense of what the head clipping situation is like out there.