"Pollen drift is important - especially if your conventional neighbors are planting Bt corn, but please don't underestimate the potential for pollen drift in your own 'non-GM' field - because most of the corn seed we are planting this year is contaminated with 'Adventitious transgenic presence' at a low level.
...there is probably no way to buffer totally against pollen drift, especially if you live in an area where Bt/RR corn is grown and if you are buying hybrid corn seed that is coming to your farm and onto your fields pre-contaminated. "
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"Pollen Movement"
SANET Post
Mary-Howell Martens
April 22, 2001
http://www.biotech-info.net/MH_pollen_movement2.html
Pollen drift is important - especially if your conventional neighbors are planting Bt corn, but please don't underestimate the potential for pollen drift in your own 'non-GM' field - because most of the corn seed we are planting this year is contaminated with 'Adventitious transgenic presence' at a low level.
In a cross-pollinated/wind-pollinated plant like corn, the pollen is designed to travel - it is lightweight, plentiful and is shed up in the air currents where it can easily be picked up and carried.
There are many factors involved in determining the degree of potential pollen drift and contamination potential. These include biological considerations -
whether the crop is cross or self pollinating
whether it is bee (canola, cucurbits) or wind pollinated (corn)
where/how the pollen is produced on the plant
And environmental and geographical considerations
the wind direction and speed
the lay of the land
the specific weather conditions during pollination especially moisture and localized wind conditions during pollen shed (even a brief high wind can greatly increase pollen travel)
the proximity and direction of sexually compatible plants.
In other words, it is hard to generalize how far pollen can travel - it depends on many factors that can change momentarily, and are very localized.
Dr. Allison Snow at Ohio State University states that, in general, bees can spread a greater quantity of pollen away from the parent plant, possibly up to several miles, while wind can spread a smaller amount of pollen remarkably far from the parent plant. In either case, it is inevitable that some pollen will travel out of the field.
Studies using Vaseline-coated microscope slides have detected over 2500 corn pollen grains per square meter at a distance of 60 meters from the parent plant.
Studies from the John Innes Institute in England ("Organic Farming and Gene Transfer from Genetically Modified Crops" by Catherine Moyes and Philip Dale, 1999) has shown that pollen from clover has been detected more than 1,600m (about 1 mile) from its source, from plants in the cabbage family over 1,500m (0.93 miles) away, and from beets and grasses at more than 1,000m (0.62 miles). Other studies have documented corn pollen drift up to 150km (93 miles) from its source, other research has shown that the distance may be much greater under certain weather conditions.
In the Midwest, some experts feel that there is a virtual umbrella of corn pollen over the whole area at corn pollination time, much of it Bt corn. This is not enough to effectively pollinate a crop for even kernel production, but it is enough to skew the genetics - and enough to make any kind of buffer virtually ineffective.
Dale Wilson has done some work with pollen drift patterns and distances - maybe he can help out here with additional information. He did give me one useful bit of information earlier this year -
** On an ear of corn, the silks connected to the middle-of-the-ear kernels tend to emerge first, pretty much simultaneously, and because of this, they are most likely to be pollinated by whatever the intended male parent is. These will then produce what is called in the trade, the 'flat' seed.
The silks emerging later - connected to the tip and butt kernels - are more likely to be 'adventitiously pollinated' by other pollen that is in the air. These will produce the 'round' seed - small rounds from the tip, large rounds from the butt. It has been sometimes shown that round seed tend to have lower vigor during germination - the small rounds due to incomplete maturity or damage and the large rounds due to slower water imbibition during germination and possibly a greater potential for mechanical damage during harvest.
** What does that mean to farmers wanting to avoid buying contaminated corn seed? Ask for medium flat seed. In doing this, you will get corn that is least likely to be contaminated, and will also get the seed that is usually most vigorous and fastest to germinate too!
Hope this helps a little - if nothing else but to say, there is probably no way to buffer totally against pollen drift, especially if you live in an area where Bt/RR corn is grown and if you are buying hybrid corn seed that is coming to your farm and onto your fields pre-contaminated.
Mary-Howell