1. 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

2. 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

3. 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.

4. 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.

5. 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

6. 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

7. 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

8. 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.

9. 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

10. 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

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

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

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

14. 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

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

16. 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

17. 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

18. 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

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

20. 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

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

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

23. 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

24. 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

25. 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

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

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

28. 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 ” corn; 4 oz on ” corn
6 oz = lb ai dicamba per acre

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