**Author details**

increase corn productivity growth over the last two decades. Despite these continual productivity gains, challenges still exist, chief among them are resistance and climate change.

The stellar productivity gains from commercially applying biotechnology in corn have focused on improving insect and weed management, which has created selection pressure on many pest species to evolve resistance to control. Even if farmers follow resistance management practices, pests have and will continue to evolve resistance—these practices only slow

Western corn rootworm (*Diabrotica virgifera virgifera*) evolved resistance to rootworm Bt corn within a few years of commercial release [35]. Rootworm Bt hybrids still have value to farmers, but their continued use requires that companies pyramid multiple rootworm traits together and that farmers use additional management practices such as crop rotation and conventional insecticides [36]. Companies have also responded by developing alternative GE traits to manage corn rootworm. Potentially the most promising is RNA interference (RNAi), which uses biotechnology so that crops create double-stranded RNA segments that interfere with transcription of specific segments of RNA found in only the target species [37–39]. The first US commercialization of RNAi in corn

proteins from non-Bt bacteria and shows excellent activity for control of corn rootworm larvae [40]. Weed control in corn (as with many crops) is important, with potential yield losses without control exceeding 50% [41]. Over the last few decades, herbicide resistant weed populations have continued to develop and spread globally [42]. HT seeds do not directly cause the development of herbicide resistant weeds, as herbicide resistant weeds have evolved in regions such as Western Australia where HT crops are not used [42]. Rather, HT crops contribute by encouraging farmers to rely on fewer herbicides modes of action and less tillage, which accelerate the development and spread of resistant weed populations [43, 44]. Problems with herbicide resistant weeds continue to develop and spread globally, which is worrisome because no new herbicide modes of action have become commercially available since the early 1990s and weed populations resistant to multiple modes of action having been documented [45, 46]. How weed control in corn and other crops will evolve over the next few decades to address herbicide resistant weeds and the possible role that GE hybrids and biotechnology will play is unclear. The race between insects and weeds and our ability to develop technologies and management schemes will continue to impact agricultural productivity. Maintaining our lead

in this race will require R&D investments and continued innovations in the future.

Climate change presents another challenge for agricultural productivity, with studies documenting impacts on corn yields [47]. Adaptation to climate change is a rising concern [48, 49]. Some regions will gain and some will lose productivity as climate patterns evolve and crop production shifts among regions. US farmers generally see agricultural adaptation to climate change as a private problem. They expect to respond with managerial changes, such as adjusting crops, using irrigation, modifying leases and using crop insurance, while seed companies will breed varieties and hybrids adapted to new climates [50, 51]. Breeding will certainly be important for corn, since hybrids must be adapted to new photoperiods when changing latitudes. Also, seed companies have commercialized drought-resistant corn hybrids, but these and other traits providing yield gains under extreme conditions tend to be quantitative or polygenic and can imply productivity tradeoffs [52–54].

Official US EPA news release: https://www.epa.gov/newsreleases/epa-registers-innovative-tool-control-corn-rootworm.

Also, corn has been genetically engineered to express insecticidal

the rate of resistance evolution, they do not stop it.

20 Corn - Production and Human Health in Changing Climate

received EPA approval in 2017.<sup>6</sup>

6

Jean-Paul Chavas1 \* and Paul D. Mitchell1,2

\*Address all correspondence to: jchavas@wisc.edu

1 Department of Agricultural and Applied Economics, University of Wisconsin, Madison, WI, USA

2 Renk Agribusiness Institute, University of Wisconsin, Madison, WI, USA
