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  • From: Bill Shoemaker <wshoemak AT illinois.edu>
  • To: "Market Farming" <market-farming AT lists.ibiblio.org>
  • Subject: Re: [Market-farming] Bt Sweet Corn
  • Date: Mon, 25 Jan 2010 16:07:17 -0600 (CST)

Lots of good comments on this thread. I'll add a few. I've worked with sweet
corn for over 25 years and have done work with Bt sweet corn too, so I can
relate by experience to some of the issues raised.

First, corn earworm is a moth that lays eggs on corn silks. Worms hatch out
and crawl right into the eartip, where they aren't exposed to sprays. That;s
why they are hard to control, even with powerful pesticides.

One of the most important ways of dealing with them is monitoring with
pheremone traps. Do a search for Great Lakes IPM and they will have detailed
info on trapes and pheremone lures, and most importantly, how to use them. If
there are moths in the neighborhood, traps will catch them. If you don't
catch any, YOU DON"T NEED TO WORRY ABOUT THEM. They just aren't there. That's
how good the traps are. The traps don't reduce the population. They just
sample it, telling if the pest is present or not. Often its not.

In the Midwest these insects don't overwinter very well. They become pests
when populations build in the south and southwest on cotton. Storms carry
populations north, dumping them all along their paths. Then they start laying
eggs in corn. But traps will start catching them immediately. Then you know
you must do something. The zea-lator is a good tool, but as mentioned, labor
intensive. Entrust is OMRI approved so this is a good way for organic growers
to be sweet corn producers. And you might as well charge to cover the cost
because its worth it.

The good news is that corn earworm populations cycle. When females are
present and lay eggs, they do so for about 7-10 days. Then they stop because
they die out. The next generation comes from the eggs they laid, usually
about 3 weeks later. So in reality, for the whole growing season, even if you
plant successively and have corn planting silking for 3 months, you may only
need to control the pest off-and-on for a total of 4 weeks, depending on the
season. If you trap moths, you'll find significant periods where there are no
earworms to worry about. They just aren't there. No spraying and worm-free
corn. Trapping is the most important tool for adressing this problem.

One of the issues emerging from the widespread use of Bt corn and cotton is
the concern for resistance. It isn't clear its emerging yet, but it could. On
the other hand, there may be 100 million acres of Bt crops planted in the US
annually. Earworms feed on both cotton and corn. If resistance merges, it
will render Bt useless on both crops. However, it may not ruin Bt because the
resistance won't emerge in other susceptible species at the same time. So it
will still be an effective organic pesticide in cabbage, brocolli, collards,
etc. The pests in those crops won't become resistant because of Bt corn.

Regarding pollen drift, it really doesn't drift very far. Corn pollen is
large compared to other pollens. It tends to stay within a 50' zone. I'm
pretty clear on this because of a student project I supervised to test the
hypothesis of pollen drift. When yellow corn pollen falls on the silks of
white corn varieties, it will turn the white corn kernels yellow. Each silk
goes to an individual kernel. It is only pollinated by one pollen grain. So
we planted 4 rows of yellow corn then planted a bunch of white corn in rows
to either side of the yellow rows. We let the corn pollinate openly. When we
harvested, we found that the level of yellow kernels in the white corn
dropped dramatically as the rows got further from the yellow corn rows. By
the time you got to row 6 (about 20'), the incidence of yellow kernels was
almost negligible (<1%). Now, the problem is the scale of production of Bt
corn. Phil and I live in the leading corn production states, IL and IA, with
over 20 million !
ac!
res between the two of us. A big percentage of it is Bt corn. And
unfortunately, any Bt pollen contamination of organic corn is a violation of
certification. Plus, the seed from that corn is legally controlled by
Monsanto. You can't legally plant it. I suspect it would be a violation of
law to sell it if you hadn't paid for Bt seed. Its not moral, but it's the
law.

Bottom line, I don't think organic growers have to grow Bt corn to have
worm-free corn. Control with something like zea-lator when you need to but
trap to make sure you only make the effort when you need to. Be sure you know
how to use the trap properly. It isn't foolproof. And don't leave pheremone
lures in the field. Dispose of them properly so they don't confound your trap.

Last comment/ If you grow sweet corn varieties with high sugar genes (se or
sh2), you shouldn't have problems with starchy corn if you pick early in the
morning, keep it in the shade and cool it down. The market is so good for
corn, especially worm-free certified organic sweet corn, you shouldn't have
problems selling everything you harvest each day you pick it. If you are, get
some help with your marketing plan. By the way, in northern Illinois growers
often start the season selling at $6/doz. They finish at $4.50/doz.

Hope this helps out.

Bill



>You were wondering about growing Bt corn. Especially since you are in the
>Corn Belt, local experience may be really
>relevant. Have you talked to Purdue or a county extension agent about what
>they are seeing and hearing?
>
>
>From afar I took a look to see what Purdue is saying in its publications
>about ear worm and Bt corn. Other sources have
>said that the primary target pest of Bt corn is the borer, and ear worm
>control is more variable. Carla in OK is having
>what sounds like pretty good success. It may be slightly different in
>Indiana - see below.
>
>
>You didn't say what part of Indiana you are in. Purdue extension talks
>about carefully selecting planting time as a
>strategy to avoid corn ear worm damage:
>
>
>
>
>
>"CEW (corn ear worm) usually will not survive winters north of about
>Bloomington, Indiana. In southern Indiana, this
>insect may attack both early and late planted corn. In central and northern
>Indiana, CEW generally affects only the
>late-maturing crop. Following mild winters, CEW may survive further north,
>and early-planted sweet corn may be attacked.
>Throughout the state, corn maturing in mid-season is less likely to be
>injured, because CEW are between generations at
>that time, however monitoring populations is important."
>
>
>
>They also make it clear that in their experience, Bt corn is still not a
>substitute for at least some spraying. Here is a
>quote:
>
>
>
>
>
>"Bt SWEET CORN
>
>There are varieties of sweet corn available that have had a gene inserted in
>them that causes the plant to produce the
>same toxin as the bacterium, Bacillus thuringiensis, or Bt. This toxin will
>provide considerable control of corn earworm.
>
>
>However, planting Bt sweet corn will NOT eliminate the need to spray
>insecticides. Bt sweet corn will often have large
>numbers of small earworms in the tip of the ears, making those ears
>unacceptable in most markets. Particularly in late
>season sweet corn, it is advisable to plant Bt sweet corn if your market
>will accept it. Used in combination with
>insecticides, Bt sweet corn will allow production of high quality sweet
>corn, even when corn earworm populations are
>extremely high."
>
>
>
>One thing they don't say but I do wonder is whether Indiana is experiencing
>increases in populations of Bt resistant ear
>worms. The pest pressure Purdue describes sounds higher than what Carla in
>OK was reporting.
>
>
>Here is the Purdue piece:
>http://extension.entm.purdue.edu/publications/E-31.pdf
>
>
>
>I read a piece from the mid-80's that suggested the length of the corn
>wrappers can affect the ability of the ear worms to
>infest the top of the corn. I don't know if anyone regards using corn with
>longer wrappers as useful to do now or not.
>At the time, some seed companies were trying to find varieties of corn that
>had physical characteristics making them less
>susceptible.
>
>
>
>Widespread use of the same pesticide pretty inevitably leads to pesticide
>resistance. Some IPM fact sheets I looked at
>recommended specific planting patterns of Bt and non Bt corn and used e.g.
>30-40% NON-Bt corn for the purpose of making
>sure there was a group of non-BT resistant ear worms to mate with any
>survivors in the Bt corn. They are called
>refuges.
>
>
>
>Here is an example of that approach to avoiding developing resistant
>insects:
>http://www.ipni.net/ppiweb/ppibase.nsf/b369c6dbe705dd13852568e3000de93d/62f1f3f2f34e04e2852569db0032bbde/$FILE/SSMG-33.pdf
>
>
>
>
>
>You asked about organic methods. Johnny's sells a corn silk applicator that
>uses vegetable oil plus Bt. This may or may
>not be a viable alternative time-wise, depending on how much you are
>growing.
>
>
>http://www.johnnyseeds.com/Assets/Information/107945570431182.pdf
>
>
>
>Is there any price/competitive advantage of diversifying out of corn into a
>less common crop that also can be timed to
>get the max out of your market price? With so many corn pests around that
>make corn a challenge to grow, a series of
>vegetable crops that corn pests do not also attack might have pretty low
>pest pressure.
>
>
>
>
>Chris Reid
>
>Stamford, CT
>
>
>
>
>
>
>
>
>
>________________
>_______________________________________________
>Market-farming mailing list
>Market-farming AT lists.ibiblio.org
>http://lists.ibiblio.org/mailman/listinfo/market-farming
>
William H Shoemaker, UI-Crop Sciences
Sr Research Specialist, Food Crops
St Charles Horticulture Research Center
535 Randall Road St Charles, IL 60174
630-584-7254; FAX-584-4610




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