Part 2, Section 1: Pest Management
Pest Management
Weed Control
Postemergence herbicide principles
Herbicide-resistant crops are available for use in crop production systems. Corn and soybean varieties are currently the only agronomic crops with herbicide resistance that can be grown in the Northeast. Herbicide resistance in crops results from two different procedures: tolerance selection and genetic engineering techniques.
Tolerance selection involves selecting naturally occurring herbicide-tolerant cells from a particular crop cultivar or cell culture and incorporating them into crop varieties and hybrids using traditional breeding techniques. Genetically engineering herbicide-resistant plants involves transferring a gene with a certain trait from one organism to another (e.g., from bacteria to plant) using complex technology. The transferred genetic trait(s) is then incorporated into crop varieties using breeding techniques. (The same genetic engineering technology is used to create crop resistance to insects -- e.g., Bt corn.) Several crop protection chemical companies and seed companies are involved in developing and marketing these crops.
Following is a brief summary of the herbicide-tolerant corn and soybean varieties currently available or soon to be released. See the corn and soybeans sections of this guide for detailed information on herbicide use for these crops.
IMI (IR/IT) or Clearfield (CL) corn was developed by tolerance selection to be resistant/tolerant to imidazolinone herbicides (e.g., Pursuit, Scepter). Although these hybrids initially were introduced to help manage herbicide carryover, Pursuit and Pursuit-containing products such as Lightning can be applied directly to the IMI corn hybrids as part of the weed-management program. Some IMI varieties (IR) also are tolerant of some sulfonylurea (e.g., Accent, Exceed) and sulfonamide (Broadstrike products) herbicides and are used to reduce injury potential from these products when they are applied alone or in combination with organophosphate (OP) insecticides.
LibertyLink/GR corn is genetically engineered to allow over-the-top applications of Liberty (glufosinate) herbicide. This program should provide broad-spectrum control of annual broadleafs and grasses of low to moderate pressure. Sequential applications or tank mixtures may be required for new weed flushes and perennials.
SR (sethoxydim resistant)/Poast Protected corn was developed using tolerance selection techniques to allow over-the-top applications of Poast (sethoxydim). This can provide control of annual grasses in a planned postemergence program or help manage escaped grasses.
Roundup Ready corn was developed using genetic engineering techniques. It allows postemergence applications of Roundup and some other glyphosate-type products directly to corn. This system should provide broad-spectrum annual and perennial weed control in corn.
The STS soybean/herbicide system enhances crop safety from certain sulfonylurea herbicides such as Pinnacle and Classic. Varieties were developed using tolerance selection methods to increase herbicide tolerance. The STS seed/herbicide system is designed to provide good weed control without crop injury. Although these varieties were developed to be used in combination with STS-labeled herbicides, they also provide greater safety from many of the ALS-type herbicides.
LibertyLink soybeans are genetically engineered to allow over-the-top applications of Liberty (glufosinate) herbicide. This program should provide broad-spectrum control of annual broadleafs and grasses of low to moderate pressure. Sequential applications or tank mixtures may be required for new weed flushes and for perennials.
Roundup Ready soybeans were developed using genetic engineering techniques. This system allows over-the-top applications of Roundup Ultra (glyphosate) and some other glyphosate-containing products to soybeans from cracking to flowering. The program allows timely application and provides broad-spectrum control of many annual and perennial grasses and broadleafs. Sequential applications may be required for harder-to-control perennials and wide row plantings.
Herbicide-resistant crop concerns
Several concerns are associated with the use of herbicide-tolerant crops. These include: (a) drift to nearby susceptible vegetation; (b) misapplication to normal crops; (c) herbicide-tolerant crops becoming weedy and difficult to control; (d) illegal use of bin run seed; (e) negative public reaction to genetic engineering; (f) commodity marketability issues; and (g) increased selection for resistant weed species or shifts in weed populations. Herbicide-resistant crops require greater management to prevent problems such as misapplication and weed resistance. Refer to the following section provides further information on the potential for herbicide-resistant weeds.