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Unwanted environmental effects from growing GM corn

November 2013. Two varieties of genetically modified corn (GA 21 and NK 603) are being assessed against risks to biodiversity and the environment in Vietnam. Therefore, information of unwanted impacts are being gathered.

A member who lives in Indiana, USA, where glyphosate-resistant corn such as GA 21 and NK 603 are very widely grown, commonly rotated with glyphosate-resistant soybeans, replied as follows:

“I suspect that the biggest impact to biodiversity here over the last 15 years has been a decrease in biodiversity of non-crop plants in and around corn fields. It is easier for growers to achieve completely “clean” fields when a wide spectrum herbicide can be sprayed later in the season, directly over the crop. Also, it appears that growers are more likely to “clean up” weeds around fences and road edges with glyphosate when the crops are glyphosate-resistant. Glyphosate drift may also be affecting the populations of flowering plants near fields, but this is not being carefully monitored. In addition, some researchers think that weed management with glyphosate-resistant crops has facilitated larger farms with a trend towards removing hedgerows and other non-crop areas that are important for biodiversity”.
“As a result, important habitat for wild pollinators, birds, and other wildlife has been diminished”.
A clear example is the loss of milkweed within the agricultural landscape, with impacts on the population of monarch butterflies. See, for example, the following studies:

  • Pleasants JM & Oberhauser KS (2012) Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population. Insect Conservation and Diversity 6, 135–144.
  • Pleasants (in press), Monarch Butterflies and Agriculture, Ch. 14 in: “Monarchs in a Changing World: Biology and Conservation of an Iconic Insect” Cornell Univ. Press.
  • Hartzler RG (2010) Reduction in common milkweed (Asclepias syriaca) occurrence in Iowa cropland from 1999 to 2009. Crop Protection 29, 1542–1544.

Another member suggested that a good start might be the following website, which allows searches on many different events in multiple crops.