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 50011 USA mdowen@iastate.edu www.weeds.iastate.edu

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

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

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

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

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; 2013-14 for soybean

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 + 0.2 oz Harmony + 1.9 oz Classic

New herbicides, premixes and formulations: FMC Authority MTZ: 12 to 20 oz/A 16 oz = 3.8 oz Authority + 0.25 lb metribuzin Preplant or preemergence Do not use on soils with pH > 7.5 Rage D-Tech 16 oz = 1 oz Aim EC + 0.5 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

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 + 0.24 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

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

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

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

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

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.

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

Weed shift or biomess? Johnson, Purdue

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

Influence of volunteer corn on corn yield (Ames, 2007) x y = 0.41 + 1.31x r2 = 0.97 Control yield = 190 bu/A Data from Dr. Bob Hartzler

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!