Genetic engineering is a powerful new technology that makes possible rapid development of herbicide tolerances in superior crop varieties. Use of the technology will have a major impact on future agricultural practices and the agrichemical industry. Possible risks as well as significant likely benefits – to agricultural users, corporate suppliers, and the environment – are discussed. Increased product lifetimes, decreased costs, and increased usefulness of broad-spectrum, high-potency, environmentally safe herbicides and herbicide combinations are predicted.

The discipline of weed science is entering a critical period in its development. Decisions made in the next few years will determine if weed science will remain weed control technology oriented or develop into a broad-based scientific discipline. Over the last 30 yr the evolution of weed science has been based on the development of weed control methods. Currently, most crop production systems rely very heavily on one weed control technology, herbicides. Agriculture is now in a debate with society over how food and fiber should be produced. Society is asking weed science, because of food safety and water quality concerns, to develop new methods to control weeds. To do this, weed science must put more emphasis on principles-based research that can provide the basic knowledge required to develop new weed control technology. Weed scientists must join forces with private citizens and organizations concerned with the effect of current agricultural practices on the environment, to obtain, through the political process, new resources for weed science research. These resources are needed to develop the basic principles that will support the development of new weed control technologies with reduced environmental impact. Weed scientists must decide if they are going to lead the direction of weed science research or be led reluctantly by others.

The development of crop cultivars with resistance to selected herbicides has the potential to impact environmental quality, food safety, consumers, and crop producers in either a positive or negative manner. The technology that makes it possible to develop herbicide-resistant crops is neither good nor bad, it is rather how the products of this technology are used that will determine whether or not the introduction of herbicide-resistant crops is ultimately a good or bad decision. The introduction of herbicide-resistant crops will have diverse impacts leading to redundancy, diversity, and confusion in crop production systems. Often the introduction of herbicide-resistant cultivars will have the same impact on cropping systems as the introduction of a new herbicide that has the same mode-of-action and use pattern of herbicides already in use. This may add diversity of herbicide options for a given crop but will cause redundancy of product use over several years. This redundancy could lead to weed resistance and water quality concerns. Confusion at the user level will exist because not all cultivars of a crop will be resistant to the herbicide; this could be the major deterrent to widespread adoption of herbicide-resistant crops. Steps must be taken to provide information to crop producers that will insure that herbicide-resistant crops are used effectively and safely. Weed scientists will determine whether this technology will be used to improve food safety, water quality, crop production systems, and farmer profitability or have a negative impact on agriculture and the whole of society.

Phenmedipham was registered for use at 1.1 to 1.7 kg ai/ha in 1970 and desmedipham at 1.1 to 1.4 kg ai/ha in 1974 for postemergence control of broadleaf weeds in sugarbeet. Phenmedipham was sold from 1970 through 1981 and desmedipham plus phenmedipham (1:1), as a premixed product, has been sold since 1982. Development of multiple applications of reduced rates began in 1972 primarily to reduce sugarbeet injury. The technique was promoted to farmers after 1976. Ahalf-rate of phenmedipham and/or desmedipham applied twice at a 5- to 7-d interval controlled weeds better and caused less sugarbeet injury than a single full-rate application, and allowed application to smaller than four-leaf sugarbeet. Suggested sugarbeet size for the first application changed from 4-leaf in 1970 to cotyledon to two-leaf in 1992. Earlier application to more susceptible small weeds allowed a further rate reduction. The use of soil-applied herbicides prior to phenmedipham and/or desmedipham increased weed control and sugarbeet injury. Application to small weeds and sugarbeet by air or by ground sprayers at spray pressures over 1040 kPa controlled weeds better and injured sugarbeet more than when applied by ground sprayers at 280 kPa. Desmedipham and phenmedipham rates presently are adjusted for sugarbeet size, application method, soil-applied herbicide, and environment. The suggested initial application rate of phenmedipham and/or desmedipham in 1992 was 0.13 to 0.28 kg/ha as compared with 1.1 to 1.7 kg/ha in 1970. A typical rate of desmedipham or desmedipham plus phenmedipham applied in 1992, including multiple application, was approximately 0.7 kg/ha less than typical rates from 1970 through 1977.

We monitored pollen-mediated transgene dissemination from commercial transgenic squash CZW-3 into its wild relative Cucurbita pepo ssp. ovifera var. texana (C. texana). Transgenic squash CZW-3 expresses the neomycin phosphotransferase II (nptII) gene and the coat protein (CP) genes of Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV), and Watermelon mosaic virus (WMV); thereby, it is resistant to these three aphid-borne viruses. The rate of NPT II and CP transgene introgression increased with overlapping flowering patterns and a high ratio of transgenic F1 hybrids (C. texana × CZW-3) to C. texana. Transgene transfer also readily occurred from transgenic F1 hybrids into C. texana over three generations in field settings where test plants grew sympatrically and viruses were not severely limiting the growth, and fruit and seed production of C. texana. In contrast, introgression of the transgenes into C. texana was not sustained under conditions of high viral disease pressure. As expected, C. texana progeny that acquired the CP transgenes exhibited resistance to CMV, ZYMV, and WMV. This is the first report on transgene dissemination from a transgenic crop that exhibits disease resistance and hybridizes with a wild plant species without loss of fertility.