1. Micheal D. K. Owen Iowa State University Ames, IA 50011 USA
Weed management in 2008 – new opportunities, existing issues and anticipated problem
Micheal D. K. Owen Iowa State University Ames, IA USA

2. Introduction The discussion will focus on four topics
New herbicide resistant traits
New herbicides, premixes and formulations
Weed shifts in response to current crop systems
Managing traited volunteer corn
A “survey/field assessment” of weed shifts is also planned for the future

3. Introduction Continuing misperceptions about simplicity of glyphosate
Increased adoption in corn will result in greater selection pressure resulting in “new” weed management issues
The bioeconomy will have a dramatic impact on weed communities
Weed shifts and the evolution of glyphosate resistant weeds continues to escalate

4. Stewardship
Stewardship of pesticides, but glyphosate specifically, must become a primary focus of our production systems
Stewardship reflects management decisions that will enhance and preserve a particular crop trait and are economically rewarding
Appropriate stewardship strategies are also environmentally sustainable

5. New herbicide resistance traits
LL soybean
15,000 acres in Iowa for 2008
Full launch in 2009
Dicamba resistant soybean
Metabolism based resistance (Univ. Nebraska)
2012 or 2013 launch
Optimum GAT
Glyphosate and ALS resistance
Metabolism-based glyphosate resistance
2009 soybean; 2010 corn

6. New herbicide resistance traits
SmartStax
Collaboration between Monsanto and Dow AgroSciences
New traited hybrids will have 8 genes that code for resistance to multiple insect pests and 2 herbicides
DHT (Dow Herbicide Trait)
2,4-D and AOPP (Assure, Poast)
2012 for corn; for soybean

7. New herbicides, premixes and formulations: DuPont
Two products for burndown and short residual
30 days before planting until emergence
Enlite : Valor + Harmony + Classic
2.8 oz = 2 oz Valor + 1/3 oz Harmony + 1/3 oz Classic
Envive : Valor + Harmony + Classic
5.3 oz = 3 oz Valor oz Harmony oz Classic

8. New herbicides, premixes and formulations: FMC
Authority MTZ: 12 to 20 oz/A
16 oz = 3.8 oz Authority lb metribuzin
Preplant or preemergence
Do not use on soils with pH > 7.5
Rage D-Tech
16 oz = 1 oz Aim EC lb 2,4-D LVE
Soybean: 8-24 oz/A burndown, 7 to 14 day planting interval
Corn Preplant: 8 to 24 oz, 3 to 14 day planting interval
Post: 8 oz broadcast; 12 oz post-directed

9. New herbicides, premixes and formulations: Dow AgroSciences
SureStart SE
2 pt = 1.2 pt Surpass 6.4E + approx. 2.5 oz Hornet
Only for use on herbicide resistant corn (RR or LL)
Preplant, PRE or early POST
Sonic
3 oz/A = 1.86 oz Authority oz FirstRate
Apply 3 oz Preplant or PRE (within 3 days after planting) in GR soybeans
Use 6.45 – 8 oz/A in conventional soybeans

10. New herbicides, premixes and formulations: Bayer Crop Protection
Laudis (tembotrione + isoxadifen)
HPPD inhibitor (bleacher)
Postemergence broadleaf and grass (small - <3”)
3 oz + COC/MSO + UAN
0.5 lb atrazine recommended for improved activity
Will be labeled for seed, sweet and popcorn

11. New herbicides, premixes and formulations: Syngenta
Halex GT
3.6 pt = 1 pt Dual Mag + 3 oz Callisto +24 oz Touchdown HiTech
No safener, not recommended for PRE
NIS + AMS required
Up to 30” or 8-leaf corn
Apply before weeds exceed 4”
Lumax, Lexar, and Camix
Application of “solo” HPPD herbicides are not allowed POST following these products
Deleted description of 2,4-D combinations with Lumax and Lexar

12. New herbicides, premixes and formulations: Valent
Valor XLT: 2.5 to 5 oz/A
5 oz = 3 oz Valor +2 oz Classic
Fall, EPP or PRE in soybean
Do not exceed 2.5 oz on soils with pH > 6.8
Do not use on fields treated with an amide herbicide

13. Weed population shifts
Understanding selection pressure (as an ecological principle) is the key to understanding weed shifts in GRCs
All agronomic practices exert selection pressure
As a general statement, the differences for different herbicides are less than the similarities as they relate to selection pressure – all result inevitably in changes in the weed community
Given the adoption of GRCs, stewardship for this trait is critically important

14. Most Problematic Weeds by State
Cropping System IA IL IN NE
Continuous GR soybean
Common waterhemp
Ragweed spp.
Velvetleaf
Johnsongrass
Shattercane
Horseweed
Grass (general)
GR corn/GR soybean
Foxtail spp.
Bur cucumber
Woolly cupgrass
Common cocklebur
Most of the weeds listed as the most problematic are either species with reported glyphosate resistant populations (olive blocks) or known historically as “tolerant” (green blocks). It is obvious that these weeds are likely to increase in the future and given the selection pressure imposed by the grower (using glyphosate), the evolution of glyphosate resistant populations within the study area is inevitable. Note that there is commonality between rotations. Note that common waterhemp appears to be the most consistent problem in most states but is listed in one of the rotations in all states. Note that common waterhemp has already evolved wide spread resistance to ALS inhibitor herbicides and has populations that are resistant to triazines and PPO inhibitor herbicides and in at least one instance, resistant to all three.

15. Most Problematic Weeds by State
Cropping System IA IL IN NE
GR soybean/non-GR crop
Common waterhemp
Ragweed spp.
Foxtail spp.
Velvetleaf
Dandelion
Sunflower
GR corn/non-GR crop
Johnsongrass
Horseweed
Pigweed spp.
Morningglory spp. -
See previous comments

16. Weed shift or biomess?
Johnson, Purdue

17. Managing traited volunteer corn
2007 planting season not ideal – issues with replanting
Wind caused harvest issues later in the season
The “Bioeconomy” has resulted in more corn/corn rotations
Is managing volunteer corn in corn more difficult now? No.
Is the elimination of a corn stand for replanting more difficult now? No.
Is controlling volunteer corn in soybeans more difficult now? Maybe
Does volunteer corn in corn represent an economic issue? Yes

18. Influence of volunteer corn on corn yield (Ames, 2007)x
y = x
r2 = 0.97
Control yield = 190 bu/A
Data from Dr. Bob Hartzler

19. Conclusions
New herbicide resistant crops are under development – opportunities?
While companies continue to develop new products, no new MOA have been discovered – stewardship continues to be critically important
GR crops contribute to changes in weed populations
Weed population shifts
Evolution of herbicide resistant biotypes
Management of volunteer corn is important and may be easier now, but not necessarily
While consistency, simplicity and convenience are attributes desired by agriculture, they have concomitant and potentially negative economic/ecological impact –
Protect crop yields!