WBC Management in Dry Beans
We are nearing or at peak flight for WBC. This is nearly 3 weeks ahead
of last year. Much of the corn crop is starting to be less attractive
for them. Late planted fields not in tassel yet will still be their target
but if those are not available, then they will move on to dry beans and
snap beans. WBC will continue to lay eggs over the next two to three weeks
so scouting in both corn and beans must continue. However, scouting and
monitoring in dry beans is a little more complicated.
WBC eggs and larvae are nearly impossible to find in dry beans. They do
the exact opposite of what they do in corn. They like to lay their eggs
on the underside of dry bean leaves and tend to do this on leaves that
are deeper in the canopy. Larvae do a little bit of leaf feeding but as
they grow, they start to only feed at night and go after the pods to feed
and mine into. So trying to scout for these critters in dry beans is frustrating
to say the least. And thresholds established in Nebraska and other western
states do not seem to work properly for dry beans grown in the great lakes
region.
Instead, we recommend you take a 3 step approach.
Figure 1. WBC Hole Close-up (Photo Credit to Chris DiFonzo
- MSU)
Step 1. Monitor traps to determine peak flight for your area
Having two traps in each dry bean field will give you an idea of when
peak flight will take place. We know that you should expect pod feeding
10-20 days after peak moth flight. If you don't have traps directly in
your own field, at least get an idea of when traps in your area have reached
peak moth flight. Over 400 traps are monitored through the WBC trap network
for Ontario and Quebec. Trap count maps are available at:
http://www.cornpest.ca/default/index.cfm/wbc-trap-network/weekly-maps-of-wbc-trap-catches/
Step 2. Scout neighbouring corn fields that are not in full tassel yet
As mentioned, WBC is a completely different beast in corn than in dry
beans. It is much easier to scout for WBC eggs in corn as they are quite
visible and are laid on the top leaves of the plant. If there is a corn
field near the dry bean field that hasn't fully tasseled yet, scout it
instead. Go out and scout these fields now. Walk in 5 areas of the corn
field and slowly walk by 20 plants.
Follow the helpful tips that I posted on the previous blog entries titled
WBC
Eggs Found in Fields in Ontario and Facts
You Need to Know to Scout and Manage WBC in Corn. If 5% of the plants
inspected have egg masses on them, know that your dry bean field is also
at risk. But you still need to scout for pod feeding to accurately time
your spray application (see Step 3).
Step 3. Scout for Pod Feeding in Dry Bean Field
You can effectively manage WBC in dry beans once you have found pod feeding
in your field. Pod feeding should start 10 to 20 days after peak moth
flight has been observed (Step 1). But again, ensure that pod feeding
is taking place to avoid a misapplication of insecticide in your field.
Some growers in Michigan are trying to spray for WBC in their dry bean
fields now, before they even have pods present on the plants which is
not the correct timing to effectively control WBC in dry beans. Wait until
there are pods present for WBC to feed on. Spraying once pods are present,
ensures that you are maximizing your chances of effectively controlling
the larvae when they are about to do economic damage. Spraying too early
when pods are not present is a premature application and will result in
you needing to spray again when pods need protecting. Spraying at the
correct time when feeding is present ensures there is a decent amount
of residual to protect the crop for a week or so during the critical time.
Scout 20 plants in 5 areas of the dry bean field. Leaf feeding may be
evident but is not economic. Inspect pods for surface feeding and entry
holes. Don't confuse the surface feeding caused by bean leaf beetle adults.
If the bean leaf beetles are doing the damage, you should be able to easily
find them in the crop. If no bean leaf beetles are present, it is most
likely WBC feeding.
Spray the crop once pod feeding has been found. Matador is registered
for WBC control in dry beans. See the 2010
Supplement for the OMAFRA Field Crop Protection Guide for rates and
recommendations.
Figure 2. Eastern Ontario WBC Trap Counts (July 18-24,
2010)
Figure 3. Southwestern Ontario WBC Trap Counts (July
18-24, 2010)
