Weed Shifts in RR Crops Two types of shifts Tolerant species Nutsedge, waterhemp, velvetleaf Resistant biotypes Rate that shifts occur will be dependent on how the technology is used

Shifts to tolerant weeds Several common weed species can survive label rates of Roundup These species will increase in prevalence with continued use of Roundup Ready crops

Effect of Plant Tolerance on Roundup Ultra Consistency % of applications that provide acceptable control1 100 80 60 40 20 Foxtail Sunflower Cocklebur Waterhemp Y. nutsedge Tolerance 1Hypothetical data. Hartzler. ISU.

Effect of Plant Tolerance on Roundup Ultra Consistency % of applications that provide acceptable control1 100 80 60 40 20 Foxtail Sunflower Cocklebur Waterhemp Y. nutsedge Tolerance 1Hypothetical data. Hartzler. ISU.

Time of application Does time of day effect control? Many cases in 1998 of reduced efficacy with treatments after dusk No clear explanation of why May not be a consistent effect Does dew have an effect? Light dew should not When to the point of “run-off” there may be reduced efficacy

Temperature effects Herbicides perform best when weeds are actively growing Lower temperatures = slower plant processes = slower herbicide action Limited ability to predict when performance will begin to be affected

Waterhemp in RR Crops Two mechanisms for escape Relatively high tolerance Late emergence Both characteristics influenced strongly by environment Problems will vary from year to year

Waterhemp Tolerance to Roundup Numerous cases of control failures Everly, IA situation 3 applications - total of 108 oz/A (28, 32, 48) Everly biotype no more tolerant than biotype from different field in greenhouse Factors influencing tolerance Temperature, moisture, weed size, time of day, spray coverage, etc.

Late emerging weeds Late emergence allows weeds to escape Roundup applications Initial emergence of waterhemp 1-3 weeks later than giant foxtail Late emergence places weeds at competitive disadvantage

Waterhemp time of emergence study Four Roundup application timings At planting, 2, 4 or 6 trifoliate stage Waterhemp plants emerging within one week of applic. flagged Waterhemp survival, growth and seed production determined Soybean yields within 1 m radius Sponsored by ISPB

Influence of emergence date on waterhemp survival and growth 3 lb Hartzler and Battles. 1998. ISU.

Relationship between waterhemp and soybean yields Waterhemp biomass (g/plant) Soybean yield (bu/A)

Waterhemp time of emergence study Similar studies conducted in 1997 Waterhemp emerging after 2nd trifoliate failed to survive May-June rainfall 1997 7.1” 1998 17.3”

Potential for resistance to Roundup Evidence supports view that risk for resistance is very low History of use without resistance Difficulty in developing RR crops However, several examples of selection of resistant biotypes

Resistance to Roundup Controlled selection studies Perennial ryegrass - 5X increase in tolerance Birdsfoot trefoil - 3X increase in tolerance Rigid ryegrass - Australia Resistance confirmed at two locations 7 to 11X resistance

Roundup tank partners Many products promoted as partners with Roundup If you can’t beat ‘em, join ‘em Strategy Better control of ‘tolerant’ species Provide residual for one pass program

Roundup tank partners for residual control May lengthen control period from a single application Concerns applying during peak weed emergence rain is critical for optimum residual effectiveness interception by foliage interferes with distribution on soil surface

Development of weed management programs Goals of weed management full-season weed control protect yield potential economically feasible No single tactic, regardless of product(s), will consistently achieve these goals

Effect of application timing on soybean yield and weed control Pringnitz and Hartzler, Kanawha, 1998.

New Products for 1999 Aim - FMC Postemergence broadleaf control in corn Same family as Authority PPO inhibitor Fairly narrow spectrum of control Velvetleaf, lambsquarter, redroot pigweed, morningglory, nightshade

Product Update Authority Now marketed solely by DuPont Authority 75% DG 4 - 5.3 oz/A Canopy XL 3.6 - 8.8 oz/A Injury problems in Missouri Associated with poorly drained soils Tank-mixes with Prowl caused greatest problems

Product Update Axiom - Bayer New amide herbicide + metribuzin 54.4% FOE 5043 + 13.8% metribuzin 16 oz Axiom = 0.17 lb metribuzin Preemergence grass control corn: 13 to 23 oz/A soybean: 7 to 13 oz/A

New Products for 1999 Balance - Rhone Poulenc Preemergence broadleaf and woolly cupgrass in corn Registered in 16 corn-belt states No label in MN or WI EPA concerns Groundwater and surface water Off-target injury

New Products for 1999 Balance Good to excellent on most broadleaves Weaknesses - cocklebur, wild buckwheat Better on woolly cupgrass than amides Fair on foxtail Package mix with ai in Axiom is planned - tradename of Epic

New Products for 1999 Balance Bleaching herbicide Carotenoid inhibitor Different site of action than Command Crop injury potential Corn injury has been observed Normally short-term response

‘New’ Products for 1999 DuPont - BASF Marketing Project Celebrity 0.5 pt Banvel + 0.67 oz Accent LeadOff 2.33 lb Frontier + 2.67 lb atrazine/gal Same actives and ratio as Guardsman

‘New’ Products for 1999 NorthStar - Norvartis Post broadleaf control in corn Replacement for Exceed in Iowa Equivalent to: 0.5 oz Beacon + 0.23 pt Banvel 5 oz/A on 4 to 36” corn

New Products for 1999 Distinct - BASF Registration pending - February 1999? Premix of dicamba + diflufenzopyr New mode of action - antiauxin Good broadleaf control, provides some suppression of grasses 6 oz on 4 - 10” corn; 4 oz on10 - 24” corn 6 oz = 0.188 lb ai dicamba per acre

Drift Retardants Several products now available Reduce formation of small droplets Growth in RR has driven use Reduce drift potential, DO NOT eliminate drift