2008 Corn Weed Control Update Eric P. Prostko Extension Weed Specialist Dept. Crop & Soil Sciences UGA

Herbicide Resistance Concerns for Field Corn t glyphosate t ALS herbicides è Accent, Basis Gold, Beacon, Exceed, Lightning, Option, Permit, Steadfast t Atrazine

Glyphosate Resistance Around the World (13 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) t johnsongrass (2005) ** Can be found in the US

GA Confirmed Glyphosate-Resistant Palmer Sites Current Testing 2007

GA Confirmed ALS-Resistant Palmer Sites

Triazine Resistant Palmer Amaranth Macon County Atrazine 1 qt/A (PRE) fb Atrazine 1.5 qt/A + v/v (POST) (Photo 14 Days after POST) **15-20 year history of 2-3 atrazine applications/year

Cotton Herbicides/Corn Rotations tStaple: 9-10 months tEnvoke: 210 days tReflex: 10 months Reflex Staple

Burndown Control Options tglyphosate tparaquat tIgnite (glufosinate) t tank-mixes with? è 2,4-D è atrazine è others Aim, ET, Harmony Extra (14 DBP), Express (14 DBP), Clarity tNeed a clean seed- bed at planting

Ryegrass Control - Burndown tHard to kill with 1 shot tRyegrass is most susceptible to glyphosate when applied between boot and early flower stage of growth. tOption # lb ai/A + atrazine 3 pts/A tOption #2 è 0.47 lb ai/A – 2 WBP fb 0.47 lb ai/A + atrazine 3 pts/A – at planting tRR corn systems t Accent???? 1.50 lb ai/A = 35 oz/A of 5.5 lb/gal or 48 oz/A of 4 lb/gal 0.47 lb ai/A = 30 oz/A of 2L or 20 oz/A of 3L

Annual Ryegrass Control with Roundup WM Source: Lins et al Weed Technology 21:

Conventional or RR Systems?

Conventional Systems THE t Atrazine still THE major player in any system t Prowl in cheap but ……. t One of my favorites is Accent + Atrazine èIf Texas panicum is main problem t many Pre-mixes

Why do you not want to spend the money on an Accent + Atrazine treatment in field corn? Data from 21 comparisons from field trials conducted in Georgia from At $2.00 to $4.00/bu, it only takes a 6 to 13 Bu/A increase to pay for the treatment!!! +59 Bu/A

Corn Yield Response to Various POST Herbicide Treatments Average of 2 tests conducted in 2003 and 2004 (Tifton, Attapulgus) Where Texas panicum is the main weed problem Atrazine 1.5 qt/A e d ab a b a a a

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

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

U.S. Corn Acres Planted to Herbicide Resistant Hybrids Source: NASS Includes stacked

Should you use the RR corn system? t advantages 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 èGlyphosate price increases

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) Halex GT t Halex GT (mesotrione + s-metolachlor + glyphosate) t Do not forget to include extra seed costs/A in your budgets! 30,000/A = $6.00/A 18,000/A = $4.00/A

Corn Grain Yield As Influenced by Glyphosate Timing (35 locations) Gower et al., Weed Technology 17:

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

Preserving the Value of Glyphosate t tank-mix 2,4-D in burndown when glyphosate will be used in-crop è or consider paraquat or Ignite if appropriate t Alternate glyphosate use with other herbicide modes of action èTank-mix with atrazine tUse other practices such as cultivation tDo not allow weed escapes to produce seed

New Products that have been tested

tSyngenta tPOST t3 oz/A + COC + UAN or AMS ($12-13/A) tUp to 30” tall or 8-leaf corn tPalmer amaranth up to 5” tIf 2,4-D is undesirable or ALS- resistance tTank-mix with atrazine talso good on horsenettle tInteraction with OP’s tWeak on PANTE and CASOB

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.

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, Pioneer 33M Rebate Program * Up to $6.25/A

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

Morningglory Control in Corn t as 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) * 1 st application + atrazine

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

Corn Yield Losses Caused by Palmer Amaranth Plants When They Emerge with Crop Massinga et al Weed Sci. 49:

This is what a 2” pigweed looks like!!!!

Palmer Amaranth Control in Sorghum-Sudangrass Silage NTC 2,4-D 1 pt/A (3-4” tall pigweed) (27 DAT) GS-01-07

Palmer Amaranth Control in Field Corn (Photo 14 Days after POST) NTC Roundup 22 oz/A Applied EPOST (19 DAT) + POST (37 DAT) CN-01-07

GR-Palmer Amaranth Control in Field Corn May 31, 2007 (38 DAP) NTC Roundup Original Max (22 oz/A) Atrazine (2 qt/A) Prowl H 2 0 (2.1 pt/A) EPOST (18 DAP) CN-07-07

GR-Palmer Amaranth Control in Field Corn May 31, 2007 (38 DAP) NTC Callisto 4SC (3 oz/A) COC (1% v/v) (18 DAP) CN-12-07

GR-Palmer Amaranth Control in Field Corn May 31, 2007 (38 DAP) NTC Halex GT 4 pt/A 0.25% v/v 8.5 lbs/100 gals EPOST (18 DAP) CN-07-07

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

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

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 2004: 29 counties (light blue) 2005: 5 counties (black) 2006: 6 counties (dark blue) 2007: 2 counties (yellow)

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

Post-Harvest Control of Tropical Spiderwort 1.5 pt/A POST1 + POST 2 ($14.41/A) POST1: 8-10” tall COMBE POST2: 2 weeks later Photo 1 week after POST2

Post-Harvest Control of Tropical Spiderwort Untreated Gramoxone 1 qt/A + COC POST1 + POST2 ($25.40/A) POST1: 8-10” tall COMBE POST2: 2 weeks later Photo 1 week after POST2

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

Status 56WG t BASF t dicamba + diflufenzopyr + isoxadifen t “Super” Banvel + safener t POST t 5-10 oz/A ($2.20/oz) t broadleaf weed control

GR-Palmer Amaranth Control in Field Corn May 31, 2007 (38 DAP) NTC Status 56WG (5 oz/A) NIS (0.25% v/v) EPOST (18 DAP) CN-07-07