Today – sorry, alot of blabbing in this issue. 1) Walk a WBC field with Chris 2) Western bean cutworm update 3) SmartStax approval

Western bean cutworm – opportunity to scout a field with Chris

When: Monday July 27, 9 AM
Where: Oceana County near Hart, MI

Specific directions:

• Highway 31 to Polk Road exit (Hart, MI)
• Go east on Polk, towards Hart. Continue across State St. and Oceana Drive.
• Turn right on 84th Street = a dirt road
• 1/4 mile to corn field on your left

Sorry for the late notice, but we quickly arraneged this yesterday to give people a chance to learn to scout WBC eggs in the field. I haven’t seen the field yet but the local contact, Dave DeZwaan, is an experienced egg-mass-locator from 2008. We will spend 1/2-1 hour at the site, then I need to scout other fields plus collect egg masses, so it is a quick visit.

WESTERN BEAN CUTWORM

Update on trapping.

• Trap catch continues to increase – see attached power point maps or msuent.com
• Note the trap network shows that although moths are widespread, there are hot spots of concern in the state = western counties along the lake (Oceana), Montcalm Co, and southwestern counties.
• According to research in the western U.S., peak flight occurs at
  1422 degrees days (base 50, accumulated from May 1). In contrast, DD accumulations in our hot spots are much lower. The same thing has been found in Ontario. So we either reach peak catch at a lower DD number, or we still have several weeks more of flight.

929 in Traverse City
979 in Hart (Oceana)
1004 in Montcalm Co (Entrican)
1038 in Bath (Clinton co)
1118 in Hartford (VanBuren)

• There are trap catches now from as far east as Rochester NY. WBC moths are good fliers and they also fly at night, when they are likely to be picked up on winds from late afternoon/ evening rain events and moved long distances.

Update on Biology:

• We found, or have reports of, egg masses in NW, western and central counties. Egg masses are often reported on whorl-stage corn. This stage is not preferred by females, but if that’s all they have in the area, they’ll lay on whorl stage corn rather than explode.
• Early-laid egg masses in Montcalm Co were hatching on July 22.
• I think some larvae will survive on whorl-stage corn by feeding on leaf tissue in the whorl, then move into the tassel as it forms. Not sure how much ear damage occurs on plants infested early.

Updates on Management:

• Does a high trap catch = spray corn? NO, trapping is a scouting tool for corn. Certainly just a few moths (as in the Thumb) in a trap shows a low population. Higher numbers (I define as 25 and above in a
  week) indicate a higher population capable of causing problems, but damage to individual fields depends on where females choose to lay eggs. We certainly saw this last year in Oceana Co – despite many moths in traps, field infestations ranged widely from 0% to 30%.
  Research in the western U.S. shows females prefer late whorl /pre-tassel corn and irrigated fields. We don’t know if our crop diversity and humid conditions change preferences of the female.
  Bottom line – a higher trap catch alerts you to SCOUT, not spray.
• In corn, target the following for scouting first:
  - late whorl / pretassel stage corn (attractive)
  - irrigated fields (ditto)
  - non Bt corn and Yieldgard-type Bt corn
  - refuge corn in Herculex fields

• Does a high trap catch = spray dry beans? Not sure. I am very concerned about the high trap catches in Montcalm County around dry bean fields. But thus far we haven’t found any eggs on dry beans, and the neighboring corn is still mid- to late whorl stage because it is behind. Late corn may actually act as a trap crop and retain WBC moths, taking the brunt of the egg laying. But if moths continue to fly for many more weeks, we’ll have to reevaluate how attractive beans are in relation to the surrounding corn.

• Pyrethroids are preferred for control because of the long residual.
  If multiple fields need to be treated, there are bound to be some fields sprayed a bit too early. Pyrethroids will be a bit ‘forgiving’
  by providing 7-14 days residue that the critters will crawl over. One exception – if you have a SPIDER MITE infestation too, pyrethroids can flare mites. In this case, go back to the OPs such as Lorsban as a compromise to get WBC control without increasing mite pressure.

• For popcorn and sweet corn, reported thresholds are 4-5%. If you spray sweet corn routinely for other caterpillars, you are killing WBC. Also, corn earworms eat WBC.

SMARTSTAX

This week EPA and the Canadian government approved SmartStax corn, which has a combination of eight genes from Monsanto & Dow Agrosciences. News release.

The genes are: Herbicide tolerance: RR2 Roundup Ready and LL Liberty Link Bt for European corn borer: Cry 1F (Herculex 1), Cry 1A.105 and Cry 2Ab (Monsanto’s VT) Bt for rootworm: Cry 34 + Cry 35 (Herculex RW), Cry 3Bb (Yieldgard RW)

Like many other types of corn, SmartStax has stacked traits for herbicide tolerance and insect control. But it is unique in that it is the first case in corn of gene pyramiding = multiple, different Bt genes for corn borer and rootworm. A gene pyramid functions like a tank mix of insecticides with different modes of action, which in theory slows the formation of resistance. Because of this, pyramided crops are allowed to have a reduced refuge. This is the case in Bt cotton, and this will also be the case in SmartStax corn. The Smartstax refuge will be 5% instead of the current 20% for other types of Bt corn.

Dr. Christina DiFonzo
Field Crops Entomology Program
Michigan State University