Corn Weed Management for “New” County Extension Agents Eric P. Prostko Extension Weed Specialist Department of Crop & Soil Sciences - UGA April 2007

Cultural Practices tPlanting Date tRow Spacing tFertility tgive the crop a competitive edge against weeds

Mechanical Cultivation tTime tDiesel fuel prices tStrip-tillage

Insecticide/Herbicide Interactions tInsecticides èOrganophosphates (OP’S) èCounter, Lorsban, Thimet tHerbicides èAccent, Beacon, Option, Callisto, Steadfast, Basis

Weed/Disease Interactions tMaize Dwarf Mosaic Virus (MDMV) tMaize Chlorotic Dwarf Virus (MCDV) t johnsongrass t aphid/leafhoppers t Accent/Beacon t hybrid tolerance

Corn Stages of Growth

Specific Herbicides t Atrazine t Prowl t Accent

Atrazine Use in Field Corn t Since 1958 t foundation t inexpensive t excellent crop tolerance t PPI, PRE, POST (12”) t broad-spectrum t up to 2.5 lb ai/A/year t easily tank-mixed t weak on T. panicum t does not last full season in SE

Conventional Weed Management Systems Many Pre-Mixes Available t Bicep II Magnum (atrazine + Dual II Magnum) t Lariat/Bullet (atrazine + Lasso) t Lexar (atrazine + Dual Magnum + Callisto) t many others t preemergence t a good choice if many different weed species are present t need 0.5” of rainfall or irrigation within 7-10 days for activation

Prowl Use in Field Corn t since 1975 t pendimethalin t DNA or “yellow” t inexpensive but…. t do not apply PRE t early-post (EPOST) è up to 30” tall or V8 t crop injury concerns èPlanting depth (1.5”) èFurrow closure

Optimum Prowl/Pendimax Timing Field Corn Prowl will not control emerged grasses!!!

Prowl Injury In Field Corn ProwlControl

Accent Use in Field Corn tsince 1991 tnicosulfuron t sulfonylurea t ALS-inhibitor t POST è up to 20” tall or V6 è 20-36” (PDIR) tPigweed, Texas panicum tWeak on crabgrass tHybrid sensitivity tOP interaction tTank-mix with atrazine tcost

Corn Hybrid/Herbicide Tolerance t Pioneer è gronomy/corn/herb_table.pdf

Why do you not want to spend the money on an Accent + Atrazine treatment in field corn? Data from 18 irrigated weed control trials conducted in Georgia from At $2.00 to 3.00/bu, it only takes a 9 to 14 bu/A increase to pay for the treatment!!!

Know Your Grasses large crabgrassjohnsongrassfall panicum broadleaf signalgrass Source: SWSS Weed ID Guide

Texas Panicum vs. Crabgrass WSSA Fringe of hairs membranous Texas panicum Southern crabgrass

Post-Directed Applications

Post-Directed Options for Field Corn tEvik tGramoxone Inteon/Firestorm (paraquat) tLorox/Linex tAim ètropical spiderwort èpigweeds èmorningglory

Herbicide Resistant Corn Technologies

Should you use the RR corn system? t advantages èInexpensive èeasy èBroad spectrum èReduced drift concerns èNo soil insecticide issues tdisadvantages èNo residual èover-reliance on a single product èHerbicide resistance concerns èVolunteer in other RR crops

How would I use RR corn systems? tIf you are unwilling to use a PRE application of atrazine or something else…. t2 applications of glyphosate è1 st application: DAP + atrazine ( qt/A) è2 nd application: DAP t Sequence t Sequence (s-metolachlor + glyphosate) Expert t Expert (s-metolachlor + atrazine + glyphosate) t Do not forget to include extra seed costs/A in your budgets! 30,000/A = $ /A 18,000/A = $7-8.00/A

Texas Panicum Control At Harvest with Single or Split Applications of Roundup WM - II CN (Attapulgus) Untreated Roundup 22 ozs/A 21 DAP Roundup 22 ozs/A DAP

Corn Yield Response to Single or Split Applications of glyphosate (4.5 lb 22 ozs/A. Average of 7 locations ( ) DKC67-60RR

What about Liberty-Link Corn? tGlufosinate èLiberty (corn) èIgnite (cotton) tNo tech fee tup to 24” tall corn or V7 tTank-mix with atrazine èLiberty ATZ t good on morningglory, Texas millet, sicklepod tHybrid performance??? èGarst 8353CB/LL, Hytest 7729Hx/LL 2007 Rebate Program * Buy 20 gals and get a $5-6/A rebate

Don’t Forget Liberty-Link Corn! UntreatedLiberty 32 ozs/A 1.0 lb/A 3 lbs/A Applied 26 DAP CN (Croplan Genetics 731 HX/LL) Ponder Farm 52 DAP 83 Bu/A114 Bu/A

Clearfield Corn Systems t Not used that much or at all in Georgia t Pursuit t Lightning èPursuit + Arsenal t POST t Non-GMO t ALS-resistance

Common Weed Problems tTexas panicum (Texas millet, buffalograss) tsicklepod (coffeeweed) tpigweeds tmorningglories tnutsedges tjohnsongrass tTropical spiderwort (Benghal dayflower)

Texas Panicum Control in Corn What works! t Prowl/Pendimax (DPRE/EPOST) t Accent (POST) t Option (POST) t RR or LL system t post-directed * Evik/Paraquat

Texas Panicum Control OR About 30% of the time, Accent has provided better control of Texas panicumAbout 30% of the time, Accent has provided better control of Texas panicum But, yields have not been different.But, yields have not been different.

Texas Panicum Control (104 DAT) - II Accent vs Option CN (Attapulgus) Applied 21 DAP PANTE = 1-2”, 2-4 leaf Untreated 0.67 ozs/A 1% v/v 1.5 ozs/A 1.25% v/v 3 lbs/A

Sicklepod Control in Corn tConventional Systems èAtrazine è2,4-D èClarity tHerbicide-Resistant èRR corn system èLL corn system

Pigweed Control in Corn tpreemergence èAtrazine èDual/generics èOutlook tpostemergence èAtrazine èAccent èCallisto è2,4-D èPermit èAim èglyphosate (RR corn) tTiming is critical!

Morningglory Control in Corn tas much atrazine as possible t 1.0 lb/A – PRE fb 1.5 lb/A – POST è small grain rotations è tank-mix with Aim (POST) t2,4-D, Clarity, Status tLiberty-Link Corn Systems tsplit applications of glyphosate (RR corn) è1 st application + atrazine tHarvest Aids è2,4-D, sodium chlorate, glyphosate, Aim, paraquat

Nutsedge Control t not very competitive è800 plants/100 row feet only reduce yields by 2% tEradicane or Sutan - PPI tDual II Magnum or generic – PRE t Glyphosate – RR corn èSplit applications t Basagran t Permit

Johnsongrass Control in Corn t Accent è no OP soil insecticide è hybrid tolerance to Accent è hybrid resistance to MDMV tGlyphosate in RR corn

Tropical spiderwort (a.k.a. Benghal dayflower) Commelina benghalensis ttropical Africa native tannual or perennial tseeds and rhizomes tabove and below ground flowers t1,600 seeds/plant talternate host of southern root-knot nematode tReservoir for southern stem blight (white mold)

TSW in Georgia * confirmed in 29 counties by GA Dept. of Ag and UGA in 2004 (light blue) * identified in 4 more counties in 2005 (black) *identified in 6 more counties in 2006 (dark blue)

TSW Control in Field Corn tDepends on planting date t2,4-D or Aim – POST tSequence or Expert in RR corn tAim/Gramoxone/Evik + Dual Magnum – layby tPost-harvest may be more important than in-crop èTillage è2 applications of 2,4-D, Gramoxone, or Aim

Reduced Tillage Systems

Burndown Control Options tglyphosate tParaquat tIgnite (glufosinate) t tank-mixes with? è 2,4-D è atrazine tNeed a clean seed- bed at planting

Ryegrass Control - Burndown tHard to kill with 1 shot tOption # lb ae/A + 3 pts/A tOption #2 èGramoxone 1.9 pts/A – 2 WBP fb Gramoxone 1.9 pts/A + 3 pts/A - planting t RR corn systems t Accent????

Herbicide-Resistant Weed Issues t Glyphosate t ALS

Herbicide Resistance Definition t inherited ability of a weed or crop biotype to survive a herbicide application to which the original population was susceptible. Biotype = a group of plants within a species that has biological traits that are not common to the population as a whole.

Glyphosate Resistance Around the World (12 species) t rigid ryegrass (1996) t goosegrass (1997) t horseweed (2000) t Italian ryegrass (2001) t hairy fleabane (2003) t buckhorn plantain (2003) t common ragweed (2004) t giant ragweed (2004) t Palmer amaranth (2005) t common waterhemp (2005) t johnsongrass (2005) t wild poinsettia (2005) ** Can be found in the US

** 3/15/2007

What does ALS mean? tAcetolactate synthase (ALS) tAcetohydroxyacid synthase (AHAS) tchloroplast enzyme needed to form certain amino acids èValine, leucine, isoleucine tHerbicide families èImidazolinones èSulfonylureas èSulfonanalides èbenzoates

Commonly Used ALS Herbicides t Accent t Ally/Cimarron t Beacon t Beyond t Cadre t Classic t Envoke t Exceed t Express t Finesse t FirstRate t Glean t Harmony Extra t Maverick Pro t Osprey t Peak t Permit t Pursuit t Python t Scepter t Staple t Strongarm

ALS-Resistant Palmer Amaranth Survey

Where to go for more information? tUGA Weed Science Web-Site è tUGA Pest Control Handbook tUGA Corn Production Guide