Figure 1. Grub damage in Ontario forages, 2008
Photo Credit: Robert Moloney, FS Partners

Which Type Of Grub?

Though the most common grub in field crops is European chafer, other grubs can cause damage as well. It is critical to determine which grub you have and the level of infestation. Dig in the bare or dying areas of your fields and look for grubs. Examining the rasters or anal hairs at the butt end of the larvae will determine the type of grub. To more easily handle the grub either:

• cut the grub in half so that it stops squirming, leaving you with just the bottom half, or
• roll a piece of paper into a tube, let the grub crawl in, pinch the tube off so that the butt end still sticks out but the head and biting part does not.

Use a magnifying glass to get a good look at the rasters.

1. If the rasters have a Y- or deep, long V-shaped pattern (like an “open zipper”), it is a European chafer grub (Figure 2a).
2. If the rasters are in an oval-shaped pattern with the hairs running parallel to each other, it is a June beetle grub (Figure 2b).
3. If you live in the Niagara area, you may be dealing with Japanese beetle grubs, which have short V-shaped raster patterns (Figure 2c).

Figure 2a. European Chafer Grub – raster pattern. Note open “zipper”
Photo credit: Art Schaafsma, U of G, Ridgetown Campus

Figure 2b. June Beetle Grub Raster Pattern
Photo Credit Art Schaafsma, U of G, Ridgetown Campus

Figure 2c. Japanese beetle grub – raster pattern

Different Grubs Have Different Life Cycles & Feeding Patterns

1. European chafer is a one year grub (Figure 3). The larvae feed into late-fall and start feeding again in very early spring, until they pupate by mid-May. Then there is a summer break from larvae feeding. All of the feeding damage by chafer is done in late-fall and early-spring. This is why soybeans tend to escape chafer damage, because the crop is planted later and grows when the larvae are not actively feeding.
2.  June beetle grubs live in the soil for 3 years, making it the most troublesome. (Figure 4) Two of those years are spent as larvae that feed on the crop throughout the year. June beetle grubs can affect soybeans and most crops because the larvae are feeding all summer long, whenever the crops are growing.
3. Japanese beetle grubs are common in Niagara Region. They are a one year grub similar to the European chafer, except Japanese beetle grubs feed longer into the summer before pupating. (Figure 5) Feeding damage by Japanese beetle grubs can continue until early-June, until they pupate to become adults. Feeding begins again in late-summer, after the adults have laid their eggs and the new larvae hatch and begin feeding.

Figure 3. European Chafer – one year life cycle
Source: University of Nebraska

  Figure 4. June Beetle cycle – live for 3 years in soil
Source: University of Nebraska

 Figure 5. Japanese beetle life cycle
Source: University of Minnesota

Control Option – Rotate To Corn, Soybeans or Cereals?

There are no insecticides that will control grub damage in established forage crops. The best option in severely damaged fields is tillage (this exposes the grubs to predators) followed by replanting the field into a crop that has insecticide seed treatment options available (corn, soybeans, cereals). One year out of forages is required to reduce grub populations for chafer and Japanese beetle, and 3 years is usually required for June beetle control.

Neonicotinoid insecticides (Poncho, Cruiser) give protection in corn, cereals and soybeans. If you are finding 2 – 3 chafer grubs per square foot, an insecticide seed treatment is required. With very high infestations, a higher label rate of insecticide is necessary.

If your goal is to re-establish forage the following year in a field with European chafers, corn is the preferred rotation crop. Chafers will lay eggs in soybeans, but not in corn. Planting soybeans can result in grub injury to the newly seeded forage crop the following spring.

Scout for grubs again in early-fall to determine if numbers exist that require seed treatment the following spring, or a different crop to avoid injury.

Refer to the Field Crop Protection Guide, OMAFRA Publication 812.

http://www.omafra.gov.on.ca/english/crops/pub812/p812toc.html

Scouting for Weevil

If there is 40% leaf-tip feeding, with 2 or 3 active weevils per stem and there is more than 7-10 days to preferred harvest date, consider applying an insecticide. If you find less then 1 active larvae per stem no treatment is needed but keep monitoring the situation.  Action will be required if you find two larvae per stem and the alfalfa is less then 40 cm high.  If you find more than 3 larvae per stem, immediate action is needed.  For more information see check out the following link: http://www.omafra.gov.on.ca/english/crops/pub812/3weevil.htm

True Armyworm

There are some reports of true armyworm catches in Illinois and Pennsylvania so it looks like we should be seeing some adults soon if they are not already here.  Considering the weather conditions we’ve had this spring, it might be a good idea to start scouting for this pest soon.  More information on true army worm and scouting techniques can be found at: http://www.omafra.gov.on.ca/english/crops/pub811/13cereal.htm#tarmyworm

Don’t Forget!

If the corn is up, it is time to start scouting for black cutworm!

Reports from Michigan and Iowa indicate that alfalfa weevils were activity is early this year.  We’ve had some fairly warm weather earlier this spring and the weevils likely have had a bit of a head start. I was out in some fields in Oxford this week and I found some early instar larvae so the weevils are out there. Start your scouting program early this year. Check out the Agronomy Guide for Field Crops publication 812 for scouting tips and control thresholds.

Black Cutworm

Black cutworms were being caught in high numbers in Indiana over the last few weeks and Pennsylvania has reported minor activity with catches increasing in some areas.  These moths no not over winter in Ontariobut are brought in on strong storm systems that come up from the South. Black cutworm females will lay their eggs in low-growing green vegetation (particularly chick weed) and fields with weed growth are tempting places for these moths to land and lay eggs. Later planted corn is at a higher risk of damage from the cutworms since the insects are much larger when the corn seedlings emerge. Bt hybrids that contain Vip3A (Agrisure Viptera 3110 / 3111) provide good control and hybrids that contain Cry1F (Genutiy, SmartStax, Herculex I, Herculex XTRA, SmartStax and Optimum products) may only provide some suppression of younger larvae. Rescue treatments can be effective if infestations are found in time.

Considering that the migratory insects such as the red admiral butterfly are about 2 weeks early this year, storm fronts from the south are likely to bring up BCW a bit earlier. Expect to be scouting once the corn is up.  For more information on black cutworm visit the following link:  http://bit.ly/Jpxtw6

Other things to look for:

Cereal leaf beetle adults have been found in the Alliston area though the numbers are not at thresholds.

The Canadian Corn Refuge Hybrid Selector is a web-based tool that has been developed through collaboration of the Canadian Corn Pest Coalition, the Ontario Corn Committee, and the Canadian Seed Trade Association to provide all the information needed to follow up-to-date insect resistance management (IRM) requirements for all currently available Bt corn hybrids in Ontario.

Refuge Selector

Simply select the Bt hybrid or trait being planted and the field size and the Refuge Selector will provide a list of eligible refuge hybrids, the refuge size, placement and treatment options along with herbicide tolerance information.  The Refuge Selector can be accessed through the Canadian Corn Pest Coalition website http://www.cornpest.ca/ or through http://www.refugeselector.ca/.  It’s an excellent tool to help you place your 2012 seed order.

Though we know there were hot spots this year, including Bothwell to Strathroy and south of Tillsonburg, we encourage all corn producers to be scouting for ear damage over the next month.  Scouting will identify additional areas that had decent WBC pressure and are at risk of higher overwintering populations and therefore infestations again next year.  Scouting will also help in deciding whether to harvest the crop earlier, or to segregate grain from those fields to reduce risk of ear rot and vomitoxins.

Fields in the Bothwell area are seeing significant ear damage already.  Even fields planted to Herculex or SmartStax Bt corn that contain Cry1F are seeing greater amounts of damage than growers were expecting.  These Bt hybrids provide only approximately 70 to 80% control, so under heavier pressure, the damage can be significant.

Focus on later planted fields first.  Scout random areas of each field.  Look at 10 consecutive ears in a row.  You might see frass at the ear tip or a hole along the side of the husk where the larva entered. Peel back the husk and determine if larvae are present and make note of how extensive the feeding damage is.  Birds diving into fields is also a good indication that WBC is present and unfortunately they will also contribute to the ear damage.  Once the larvae reach the 6th and last instar, they drop to the soil and tunnel down deep to overwinter there.  If larvae are nowhere to be found in the field, it is a good indication that they have already started to get ready to overwinter.

Hopefully we experience a warm and reasonably dry fall to help mature the crop quickly and avoid ideal weather conditions that promote further ear rot development.

In dry beans, scouting 10 to 21 days after peak flight is the ideal time to determine if control is necessary.  Scout a field for 15 to 30 mins.  Select random plants in the field and take a good look at all of the pods on the plant.  If you can easily find pods with holes in them during that time, you need to spray.  If there is just surface feeding or scars on the pod, it may not be WBC damage. It could be from bean leaf beetles.  The only way to know for sure if it is western bean cutworm damage is if there are holes mining directly into the cavity of the pod.  Seed inside will also be fed on.  Open up the pod and see if anything is in there.  If you find a larvae, it is most likely European corn borer.  If nothing is in the pod, it is probably safe to blame the damage on WBC.  WBC larvae only feed at night in dry beans.  They drop out of the pods before sunrise and hang out in the soil or under crop debris during the day.  If in the time that you scout you are only finding a couple of pods with holes, it is not enough damage to warrant a spray.  But check again in another week to see if things have changed.  Matador and Coragen are both registered for dry beans.  Matador has a preharvest interval of 21 days.  Coragen has a preharvest interval of 1 day.

Pod feeding damage by WBC - Note the hole going into the pod

Surface feeding could be from other insects like bean leaf beetle

If a larva is present inside the pod during the day, it is more likely to be European corn borer

Q1.  With soybeans at $15, does that threshold change?  Answer:  No. The economic threshold of “250 aphids per plant and increasing on 80% of the plants in the field during R1-R5″, already takes into consideration a wide range of soybean prices.  The actual economic injury level (where the cost of control is equal to the damage they are causing) is around 660 aphids per plant.  So you have a large buffer area between the threshold and the economic injury level to determine if a spray is needed.

Q2.  Isn’t it getting late to spray for aphids?  Answer:  No. Soybeans are susceptible to aphid injury from R1 (first bloom) all the way until your crop reaches R6 (Full Seed – when the pods at the top of the plant have seeds filling the cavity of the pod).  Once it is in the R6 stage, you need a lot more aphids (over 1000/plant) to see any yield response.  And you need to be cautious as you approach R6 as you are also close to approaching the pre-harvest interval aka days to harvest limit for the products registered   But much of the soybean crop still has a ways to go before reaching R6 so please keep scouting.

Q3.  I have a field that has been fluctuating from 100 to 400/plant and back down over the last few weeks.  Do I need to spray?  Answer:  Most likely not -but keep watching. The fact that the aphid populations keep fluctuating in this fields is a good thing.  It indicates that the natural enemies are helping.  Plus the cooler night temps are not as ideal for the aphids so their development is going to slow down a bit, allowing for the natural enemies to keep up.  If the crop is not stressed (i.e.  it has been getting a decent amount of rain and is lush) you can hold off to closer to the ECONOMIC INJURY LEVEL before you need to spray.  So only if you see these fields hitting 500 or more and are staying at that level might it still be worth spraying.  Again, make sure the crop hasn’t reached R6 yet.  Any fields that are really stressed from lack of moisture (and I know there are some out there) need to stay closer to the 250 threshold and increasing  (but not below that number).  If populations keep fluctuating from 100 to 300 and back down, even these fields may not need to be sprayed.  As long as populations fluctuate, it is a sign that the aphids aren’t getting the upper hand.

Q4.  I am seeing 150 aphids per plant.  Should I get out and spray now and get ahead of them?  Answer:  Absolutely NOT. The threshold of 250 per plant and increasing is there for a reason.  You are not losing yield equivalent to the cost of the spray until closer to the 660 aphids per plant.  At 250 aphids per plant and below, there is a lot of opportunity for natural enemies to keep up with the aphid populations and provide you with free biological control.  If you spray too early, you kill these natural enemies off and give the aphids the freedom they need to build up more rapidly.  You will never get 99% control of the aphids but you are likely to get that good of control of the natural enemies.  Even if 10% of the aphids survived a spray, they will easily build up again in the absence of their enemies.

Q5.  I saw a Speed Scouting Aphid App recently launched out of the US.  Is it something we should use here?  Answer:  Unfortunately No. Nothing against my US counterparts who developed this concept.  But when we tested it here in Ontario in many field scenarios, when the aphid populations were building up rapidly, it did not tell us to spray soon enough and when the populations were building up very slowly, it often told us to spray when we didn’t need to.  So I don’t recommend its use in Ontario.  What I will recommend is the aphid app that we are developing here in Ontario (between UofG and OMAFRA).  I am not being biased here.  It is called the Aphid Advisor.  We are in the final testing phase this week.  Currently it is only for blackberries but if it is successful, we will be working on getting it for the other smartphones in use.  It does still require you to do the full plant counts on 10 random plants in the field but it also has you punch in the number of natural enemies hanging out on those plants.  Based on the forecast for your area (determined by the location you enter) and the ratio of aphids to natural enemies you are seeing, the app will tell you if you need to 1) Spray, 2) Wait and Watch or 3) Don’t spray.  It is based on the dynamic action threshold work that Rebecca Hallett et. al. did the last few years at U of G. We tested it in the field and it really does help to determine if the aphids are going to win the battle over what natural enemy population exists in that field.  It takes care of that grey area between the 250 to 500 aphids per plant range where you are uncertain as to whether you need to spray or not.  So keep an eye out for that launch expected in just a matter of days.  And we will be on display at the OMAFRA/OSCIA tent at the Outdoor Farm Show for all to try out.

If you want any more information on soybean aphids, here are a few helpful links:

Agronomy Guide for Field Crops – Soybean aphids: http://www.omafra.gov.on.ca/english/crops/pub811/13soybean.htm#soybean

Field Crop Protection Guide – Soybean aphids control options: http://www.omafra.gov.on.ca/english/crops/pub812/2aphid.htm

Soybean Aphid Scouting Cards:   English  http://bautebugblog.com/wp-content/Soybean-Aphid-Scouting-Card-ENGLISH.pdf French  Soybean Aphid Scouting Card – FRENCH

I’ve put together some slides to compare the look a likes to help you out in the field.   Any tiny first instars can not be identified by a photo and need to be sent in to me or my colleague Hannah Fraser (OMAFRA-Vineland) for ID.  If you think  you have BMSB, please contact us.

Click on the images below to view them in a larger format.

For more information on Brown Marmorated Stink Bug visit the OMAFRA BMSB webpage at: http://www.ontario.ca/stinkbug

Counties that appear to have peaked last week: Essex, Chatham-Kent, Lambton, Oxford, Haldimand/Norfolk, Waterloo, Wellington, Brant, Dufferin, Grey, Simcoe, Kawartha Lakes, Hastings, Ottawa

Counties still seeing an increase in moth catches: Elgin and Huron (both experienced only slight increases), Middlesex, Bruce, Perth, York, Peel, Durham (saw significant increase), Prince Edward, Northumberland, Lennox & Addington.  Quebec locations in general are still increasing.

Our Northern locations can not be determined as we did not receive trap counts last week from these locations.

What are we seeing in the fields? Some decent sized larvae are being found in ears in some fields.  Some reps are surprised at the amount of damage they have found already despite not finding significant eggmasses earlier on.  Even in fields that have Cry1F.  My concern is that we still have a long way to go before harvest.  Ear rots may have time to set in because of the damage the larvae are making, exposing the ear to potential disease infection.  I strongly advice everyone to scout their fields in September to determine if it needs to be harvested earlier to avoid ear rot.

Dry Bean Fields -Now that some counties have peaked I suggest we all start focusing our attention at looking for pod feeding.  10 days to 21 days after peak flight is the appropriate time for management if required.  If you have to spend more than 1/2 hr to find just a few pods with feeding damage then that field is not worth spraying.  Check back again a week later.

Scouting soybeans at least once a week from now until fields are into the R6 stage is advised.  Particularly since other pests are also active in the fields now including spider mites, defoliators like Japanese beetles, red-headed flea beetles and bean leaf beetle which the latter are also starting to feed on the pods and clip some pods off plants in some fields.

Besides…aren’t soybeans a lot easier to scout than corn fields this time of year?  Just saying….. 

I’ve also included an updated graph showing the counties that have been catching the highest average number moths per trap so far this year.  Counties with the Highest Trap Counts so Far

Many other counties are at risk too. Please make sure to visit the WBC Trap Network Website to see all of the trap catch maps for each region of the province.

Have a great weekend everyone!

So now what?  Well, this means we are still at risk of peak egg laying.  My crew has been running out to high trap count sites to look for eggs in fields but have not had much success outside of the original hot spot areas of Bothwell and south of Tillsonburg.  Does this mean that no other fields outside of these two areas have egg laying going on?  No.  It just means that the moths are more spread out now and scattered in ideal fields across the various counties catching moths in significant numbers.  We certainly can’t scout every field in the area of a trap site so it is up to you to be looking too.   Though the Bothwell and Tilsonburg locations were extreme with egg infestations ranging from 9 to 80% of the plants, other fields have got to be close to the 5% threshold too in other counties.  Scout late planted corn fields first that have not reached full pollen shed yet.  As long as you can feel a tassel in the whorl of the plant, the larvae can survive on it.  So target young fields first and move up from there.  Other host crops are also going to be at risk now as more corn fields starting to get beyond the more ideal egg laying stages.

Let us know too if you do find fields near or above threshold.  We want to make sure we document other locations of concern besides the heavy hot spots of Bothwell and Tillsonburg.  Even if it’s not until closer to harvest when damaged ears are spotted, we want to capture that information too.

Once we have all the data compiled from this week’s trap reports, I will make a graph comparing this year’s catch to the last two years just to show you how much higher our numbers are this year.  So..more to come tomorrow.

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.

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