HORT 250 - Biotechnology in Agriculture

Lecture 14 - Controversies surrounding the development of herbicide tolerant crops

Now, I would like to consider some of the controversies that development of herbicide tolerant crops (HTCs) has raised. Remember first that HTCs are not new. All crops where herbicides are used are, by definition, herbicide tolerant. If they were not tolerant to the herbicides that are used, they would be killed along with the weeds when herbicides were applied. So the first point to make is that it is interesting to hear the vocal discussion about this issue now, but it has not been such a contentious issue in the past. I do not want you to think that there are not important new questions raised by this technology, but this debate should have been going on for a long time.

Herbicides are the favored method of weed control for most farmers. Listed below are a number of points of concern that have been raised by various individuals and groups who are concerned about the consequences of this technology, and some comments that address these.

1. HTCs will result in an increase in the acreage that is treated with herbicides by farmers and growers.

• 97% of agronomic production acreage is already treated with herbicides, so there is essentially no room to increase this figure, unless herbicides can be applied in situations, such as forestry or golf courses, where herbicides are not currently used.

2. HTCs will lead to increased use of herbicides.

• if the HTCs are extremely tolerant, the farmer might be encouraged to use herbicides more frequently, safe in the knowledge that his/her transgenic crops are extremely resistant and will not suffer any stress from repeated application of the herbicide. However, each herbicide application is an additional expense, reducing potential profit. I think it unlikely that farmers will incur extra costs for the sake of a really clean field.
• on the other hand, this development might actually decrease overall herbicide use. The farmer could plant without using any pre-emergence herbicide, and take a wait-and-see position to see where and when weeds will grow. Herbicides might only need to be applied to selected areas rather than throughout the field in the preemptive, precautionary strategy that is currently in use.

3. HTCs will become weeds - a weed is any plant that is growing in the wrong place at the wrong time, from the grower's point of view.

• It is interesting that this concern has not been raised previously with non-engineered crops. However, there are some special circumstances created here that are worthy of commen. There is always some carryover of seed from year to year in a field. You have all seen "volunteer corn" in a field of soybeans. If that corn was Rounup Ready and resistant to glyphosate, what happens in the next year when you plant Roundup Ready soybeans? The volunteer corn comes up but cannot be controlled with Roundup, so you have to find an alternative herbicide just to control the volunteer corn. This indicates that there may be a need for greater planning and selection of appropriate crop rotations.

4. HTCs will lead to a reliance on herbicides for weed control and abandonment, or failure to develop alternative techniques.

• this is certainly possible, but it does depend on how HTCs are accepted, the share of the market they take, and the pressures (or lack of them) to move away from pesticide use. But it is hard to see how this is very different from the current situation. While there may be problems with a reliance on herbicides for weed control (a point for debate!) it is not the development of HTCs that have led to this situation.
• HTCs may allow, for the first time, a chemical method to control pests like parasitic weeds, where at the moment killing the weed would also kill the host.

5. There will be increased use of particular herbicides on HTCs.

• this is obviously the hope of Monsanto for glyphosate, and similarly for other herbicide companies. While Monsanto has clearly got the head start in this area, other companies are not just sitting on their hands watching Monsanto grab a huge share of the herbicide market. Other companies are developing similar products, and I think it unlikely for several reasons that in 5 years time we will see the majority of the corn and soybean acreage planted to Roundup Ready crops.
• however, HTCs will also allow new combinations of crops and herbicides to be tested. Correct management of these combinations could also lead to development of methods to reduce the chances that weeds will develop resistance, by rotating herbicide use.

6. Some HTCs may be developed for herbicides that are regarded as more damaging to the environment.

• while this is certainly possible, and is being pursued for some crops, herbicides will still be regulated by Environmental Protection Agency (EPA), Food and Drug Administration (FDA) and Department of Agriculture (USDA) regulations. It is unlikely that herbicides that are more toxic than those currently in use would be developed as a result of HTC developments.

7. HTCs will reduce the level of biological diversity.

• after all, that is the whole point of using herbicides, to produce a field of corn, soybean, whatever, without any other plants growing in the field.
• a possible problem is that weeds that, for whatever reason, survive herbicide treatment will have greatly reduced competition and be able to rapidly propagate. Overall, I am not sure how different this is from the current situation.
• whenever cultural practices are changed, there is the potential for new weed species to develop and endure. HTCs might provide new niches for new weeds to fill.

8. Herbicide resistance genes will be transferred from HTCs to wild relatives of the crops.

• potential to develop "superweeds". This has the potential to be a serious problem. One of the most widely quoted examples is shattercane. This is the same species as sorghum, and the two are quite cross-fertile. If sorghum was developed with resistance to glyphosate, it is almost certain that the resistance gene would be transferred to the wild shattercane weed. Depending on the selective advantage this gene would provide, you could predict how this gene might (or not) spread through the population. This would lead to shattercane that could no longer be controlled with glyphosate. Depending on the selective advantage provided by this glyphosate resistance gene, this gene might spread very quickly throughout the population.
• most US crops (corn, soybeans especially) do not have wild relatives growing here. Therefore there is no recipient species available. In most cases in the US this will not pose a major problem. But what happens when the seeds are transferred to other countries which were the sites of origin of these species, e.g. China for soybeans, and Central America for maize?

9. HTCs, by promoting increased herbicide use (see No. 5), will lead to increased pesticide residues in foods.

• this will still be regulated strictly by the FDA, and they are unlikely to make these standards any less stringent than they currently are.
• there is the potential for new, potentially toxic, metabolites of these herbicides, but again if you have faith in the regulatory agencies, it is hard to see how this is significantly different from the current situation.

10. HTCs will result in the development of new varieties of herbicide resistant weeds

• the most serious threat of increasing use of one, or a small number of, herbicide is that this will promote development of herbicide resistance in weed populations. Almost without exception, introduction of any new pesticide, for weeds, insects, etc., has eventually led to the development of resistance to that pesticide. Continual use of the same herbicide in the same location, perhaps with more than one application per year, will accelerate the development of resistant weeds - guaranteed! Darwin was correct about the process of evolution. So, while I have used the argument that HTCs are not new to indicate that these will not lead to a significant change in many aspects of weed control, I have to say that herbicide use in non-transgenic crops has led to the selection of herbicide resistant weeds, and the same thing will happen here. In fact, continued use of the same herbicide on the same acreage will accelerate this selection process. Monsanto in particular has been downplaying this with glyphosate, but it is clear from Australia that weeds with resistance to glyphosate can be selected.

As I have said before, these products are now starting to enter the marketplace. There are may unanswered questions about their utility, acceptability, and profitability. It will be extremely interesting to see how this, one of the first major product groups in agricultural biotechnology, develops.

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