Slugs that are present this fall will also be the same ones that overwinter and start up again in the spring in that same field.  So knowing what the slug population is like in each field in the fall will indicate what will be present in the spring.  Higher-risk fields include fields with considerable crop residue including no-till corn, soybeans and canola, wheat fields underseeded with red clover, newly
seeded alfalfa and fields following forages, especially grasses.

Fall scouting for slugs is not that labor intensive.  If scouting during the day, look for shiney silver trails left on the soil or plant surface as a result of their mucous trails.  To determine population levels take small pieces of plywood (approximately 2-3 feet long) or roofing shingles and position them on the soil surface in fields that have been harvested. 10 to 15 boards randomly scattered across the field will provide a good indication of population levels. These boards will act as shelters for the slugs. Visit the boards every 5 days for about a month, counting the number of slugs present under the boards. Morning is the best time to look since slugs will still be hanging out in their shelters.

If slugs are commonly found under monitored boards described above, that field should be considered at high risk for slug injury.  In these high risk fields, planting into conditions that help the crop grow quickly can avoid heavy slug damage.  Any form of tillage that helps remove the crop residue that slugs hide and live in can help. Even moving trash away from the seed bed can help to reduce feeding damage.  If this fall continues to be cool and moist, expect more feeding than usual.

Most at risk at this time of year would be mixed forages where both grass and alfalfa could be defoliated by the caterpillars.  Very late planted corn or very early planted wheat could also be somewhat at risk.  These crops should be monitored for any FAW feeding activity.  If you find an infestation, please contact me.  Fall armyworm has already been found in some corn ears at low levels but these are from past moth flights and not at levels of concern yet.   We are more concerned with the outcome of these larger anticipated masses of migrant moths expected to arrive from Kentucky.

WBC pod feeding from Dublin

Pod Mined by WBC

Seed inside pod fed on by WBC

I recognize that it is a challenge to figure out if it is actually WBC feeding or not.  I am finding more European corn borer in beans then expected.  But the good thing is that ECB tends to leave a lot of frass just outside of the hole they made to enter the pod and you can sometimes even find them inside the pod.  Corn earworm is also doing some of the pod feeding.  The important thing to do is to open up pods that have holes going directly into the pod and look for feeding on the seeds.  If there is some seed feeding and no culprit present to point the finger at, it COULD be WBC.  WBC feed at night in dry beans so you are not likely to ever get a chance to see the WBC larvae.

If you are finding pods with holes in them on more than just a few plants in the field, we do recommend spraying if the crop is less than 21 days to harvest.  If it takes you an hour to find just a couple of pods with feeding, then that field is probably safe but scout it again later that week to see if pod feeding has increased.  Matador is registered for control.  Don’t spray at the heat of the day as temps above 25 degrees can decrease the products efficacy.  Days to harvest interval for Matador on dry beans is 21 days and for snaps and green beans it is 7 days to harvest.

Severe spider mite damage near London

Travelling the country side yesterday,  I saw too much spider mite damage going out of control in soybean fields that were easy to spot from my car.  Too many fields that still have some time to mature are seeing sure signs of spider mite activity.  Some are already too late to control, as the mites have already started to kill off the plants (picture provided).  But some are still at a stage of infestation that could make a world of difference if they were sprayed.

Spider mites are very hard on the soybean plant.  Their feeding eventually causes the plant to drop its leaves and prematurly die.  When infestations first start, individual leaves begin to look sandblasted or “dusty” on the underside of the leaf.  Infested plants start to take on a grey appearance in patches in the field.  If the infestation is allowed to continue, these patches eventually turn brown as leaves drop off the plant and the plants shut down and die.

Dimethoate (Cygon and Lagon) is the only product that will work on spider mites.  Do NOT use Matador as it does NOT control spider mites and can actually cause the mite population to build up more quickly.  However, the days to harvest interval for the dimethoate products is 30 days so if spider mites are active in your field, control will need to take place in the next week or two.

What is making it difficult is that there are a lot of defoliating insects out there this year that are making holes in the leaves and even scars on the surface of the pods.  This makes it tough to truly identify what is WBC feeding and what is from the others.  So you really can’t rely on foliar feeding to ID plants with WBC on them.  I am glad I had a sweep net with me to help me sort out some of the issues.  Both green cloverworm and redheaded flea beetles are in high numbers this year and are hacking at the leaves.

Defoliation by slugs, redheaded flea beetles and green cloverworm in dry beans

As for pod feeding, well that is not cut and dry either.  Bean leaf beetle in particular is doing some of the pod feeding.  Their holes rarely penetrate the pod though.

Bean leaf beetle feeding on dry bean pod

Make sure to look around in the canopy for BLB adults before assuming you have found WBC feeding.    There seems to be a lot of pods out there that had BLB or grasshopper feeding early on and the holes have dried up or even healed over.

I even found a field so full of slugs in areas that I am convinced that the big holes going directly through the pods were from the slugs and not WBC.  (Sorry Ron, I know you are pretty sure slugs don’t feed on pods but every time I found a big hole going through both sides of the pod, I found slime trails on the plant and big fat juicy slugs nearby on the ground).

WBC pod feeding tends to mine directly into the pod.  Once you open up the pod you may see some feeding on the seeds.  Here are some photos from pods that were on plants that were artificially infested and caged with WBC.  Note the one pod that actually still had WBC inside it, though this is rare to find in naturally infested fields.

Pod damage on WBC infested dry bean plant

WBC inside dry bean pod on artificially infested plants

There is one more insect that I came across that can mine into the pod though.   I found European corn borer feeding on the inside of one pod.

ECB feeding inside dry bean pod

Luckly it was still in the pod making it easy to peg as the culprit.  Unfortunately WBC is usually not inside the pod or on the plant during the day so you don’t get the satisfaction of being 100% confident in your judgement.

One final thing I learned this week.  I know I told you about how the first few instars of WBC looks sort of like ECB but with obvious dark warts and hairs coming out of them on their body.  Well, the second to third instars looks completely different.

2nd to 3rd WBC instar

They still lack the broad bands behind the head but they lose the hairy warts/spots that the very young instars have and actually start to look like true armyworm without the bands on the prolegs.  Until they get a bit bigger and start to get the broad bands behind the head, it can fool you into questioning what it is.  Those stripes certainly don’t remain on the body later in their development.

If it isn’t already obvious, there is a lot still to learn about WBC.  And it doesn’t seem to be an easy insect to scout for..especially in dry beans.  I didn’t think I’d ever say this, but I like scouting for soybean aphids much more!  Those I can find and count.