The costs of Bt

April 2011

Bt-crops have huge direct and indirect costs attached.

Monsanto spends millions of dollars on PR to persuade maize farmers that their crops, and profits, will be eaten to oblivion by the European Corn Borer (ECB)

As its name indicates, ECB is a very expensive mistake introduced to America in 1910 on imported broom handles. It is an especially problematic pest because it produces three generations during the May to September corn-growing season, and the larval form buries itself inside the plant within 7 to 10 days, after which it is inaccessible to any conventional insecticide applications.

The ECB-weakened stem is prone to breakage and the disruption to the plant's vascular system inhibits plant growth and seed production.

Agronomists, entomologists and plant breeders have accordingly devoted tremendous efforts to combat the pest.

Chemical control is only feasible with intensive scouting and monitoring to identify the windows of opportunity when the larvae have moved to positions where they're exposed on the leaves, followed by a highly directed spray or by a powder poured onto the leaf-stalk to catch the grubs as they are about to start burrowing. More cost-effective methods involve crop rotation and adjusting planting dates to reduce the pests' opportunities to infest. The most important form of control is the selection of resistant hybrids, of which Bt-toxin generating GM varieties are, hands down, the most successful.

However, Bt maize comes at a cost, and many questions about its true value remain to be answered.

Amidst the host of commercial comparisons between Bt maize and other, conventional, maize strains in use, there are remarkably little controlled scientific data.

When one relevant study was published in 2005, some interesting results emerged. Several Bt maize lines were grown side-by-side with their isogenic (closest non-GM genome) equivalents. Measurements showed:
  • Bt maize produced a similar, or up to 12% lower, yield (suggestive of an inherent energy drain)
  • Bt maize had a similar or lower nitrogen content in the grain (suggestive of a lower nutritional value)
  • Bt maize had similar or higher nitrogen content in the plant residues (suggestive of plants directing effort into vegetative growth rather than seed production)
  • Bt maize took three days longer to reach maturity (suggestive of an inherent energy drain)
  • Bt maize had a 3-5% higher moisture content at maturity, representing a significant post-harvest drying cost (also suggestive of an increasing susceptibility to fungal attack)
  • Bt maize leaves and stalks stay green and more succulent when the cobs reach physiological maturity (suggestive of a diversion of effort away from the natural development of the seed and towards maintaining the rest of the plant).

There is no doubt that, in areas prone to high and frequent ECB infestations, Bt maize can be grown cost effectively when otherwise maize-cultivation would have to be abandoned. However, in areas of infrequent, low- to moderate- attack, the extra cost of GM seed is not justified.

Interestingly, the author of the study commented that the slower drying and maturation of Bt crops “was probably due to the fact that, unlike non-Bt hybrids, there was no cavity caused by ECB in the Bt-hybrids”.

The use of a low (natural) level of 'pests'-infestation as an aid to creating healthy seed by helping the plant to dry-out once its reproduction is complete, seems a much more efficient system than using fossil fuels to achieve the same result. However, monoculture, lack of crop rotation and reduced tillage all preserve a man-made environment which converts a useful 'pest' into a devastating nuisance.

Other, longer-term costs must always be added into the equation.

Bt crops do not reduce the need for vigilance and costly chemical treatments for other serious pests, and may even increase these in the long-term.

Natural Bt-toxin in Bt-bacteria is known to be allergenic to humans: the potential for artificial formats of Bt to be immunogenic is obviously present but hasn't been tested. Ill-health represents a huge cost which is never factored in to the Bt maize costs and benefits equation.

  • Ma and Subedi, 2005, Development, yield, grain moisture and nitrogen uptake of Bt corn hybrids and their conventional near-isolines, Field Crops Research 93 Issue 2-3, September
  • Krupke et al., European corn borer in field corn, Field Crops, Purdue University, Purdue extension E-17-W
  • Nielsen and Colville, Stalk Lodging in Corn: Guidelines for Preventive Management, Purdue University Co-operative Extension service Agronomy Guided AY-262

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