New Ways to Manage Weeds

Transcription

1 Newsletter of the Cotton Physiology Eduction Progrm Volume 8, Numer 1, 1997 New Wys to Mnge Weeds Weeds, the ne of every frmer, just never seem to go wy. Some, such s pririe sunflower, re tolernt of preplnt-incorported hericides nd hve ecome n incresing prolem (Figure 1). Fortuntely, new technologies re now ville tht mke controlling weeds lot esier. There re mny dvntges, some disdvntges, nd new costs ssocited with dopting these tools. Here we discuss typicl weed mngement progrms for ech of the four regions of the Cotton Belt nd give some insights s to how these new products cn est e used to complement existing prctices. Regionl Perspectives... 1 Conclusions On The Horizon The Cotton Physiology Eduction Progrm (CPEP) ws creted 9 yers go y grnt to the Cotton Foundtion from BASF, mkers of Pix, the originl plnt regultor. CPEP s mission is to discover nd communicte more profitle methods of producing cotton. Figure 1. Pririe sunflower. Regionl Perspectives West (AZ, CA) In Arizon, whether growers plnt into pre-irrigted eds or plnt shllow in dry soil nd then irrigte, preplnt-incorported hericides re used. They usully re pplied to flt ground nd incorported y discing or using field cultivtor with S-tine sweeps followed y listing (edding up). A dinitroniline hericide (Trefln, Prowl) is used lone or, when nnul morningglory is prolem, in comintion with rodlef hericide such s prometryn (Cprol, W Keeling Cotton-Pro). Occsionlly injury from preplnt pplictions of hericides is oserved (Figure 2). Once the crop hs emerged, cultivtion nd hnd weeding re used to control weeds until cotton reches the 6 to 8 inch stge, t which time the crop should e tller thn the weeds. Aout one-third of the growers then pply nonselective, post-directed hericides such s diuron (Krmex, Direx), prometryn (Cprol), or cynzine (Bldex, CyPro). Anne F. Wron, Ntionl Cotton Council; Pul Bumnn, Texs A&M University; John Bremer, Texs A&M University; Steve Brown, University of Georgi; John D. Byrd, Mississippi Stte University; Bo Hyes, University of Tennessee; Wyne Keeling, Texs A&M University; Bill McCloskey, University of Arizon; Ron N. Vrgs, University of Cliforni; Aln C. York, North Crolin Stte University 1

2 S Brown Figure 2. Cotton seedling injured y preemergence hericide ppliction. WB McCloskey Figure 4. Bd purple nutsedge infesttion. Sometimes these hericides re comined with MSMA s urndown postemergence tretments. These re the so-clled chemicl hoe tretments for smll weeds less thn 2 inches in dimeter. To void injury to the crop, these sprys must e directed t the se of the cotton plnts. Lyy pplictions re mde when the crop cnopy reches 20 to 24 inches in height efore equipment cn no longer e driven through the field without dmging the plnts. Some vritions in this generl weed control progrm exist. In fields infested with nutsedge, norflurzon (Zoril) my e used preplnt-incorported for shortterm suppression. If weed pressure is low, post-directed, rodlef hericide pplictions on 6 to 8 inch cotton my e eliminted. Selective postemergence grss hericides include fluzifop (Fusilde), sethoxydim (Post), nd clethodim (Prism, Select). These hericides re used to control weeds such s ermudgrss, johnsongrss nd nnul grss escpes. WB McCloskey Figure 3. Mid- () nd lte- () seson infesttions of morningglory. In Arizon, nnul morningglory (Figure 3) nd perennil nutsedge species (Figure 4) re mjor weeds difficult to control with trditionl prctices. Three new, selective postemergence hericides (Buctril, Roundup Ultr, nd Stple) hve een registered recently in Arizon. Buctril nd Roundup Ultr cn e used only on their complementry trnsgenic vrieties BXN from Stoneville Pedigreed Seed nd Roundup Redy cotton from Delt nd Pine Lnd, respectively. Stple cn e used on ll uplnd cotton vrieties. These new chemicls cn e pplied over-the-top to smll seedling cotton or post-directed on lrger cotton which hs more thn four true leves. One or two pplictions of these hericides llow growers to control rodlef weeds (pigweeds, Wright s groundcherry, nnul morningglories) in cotton from emergence until the cotton is over 8 inches high when trditionl weed control prctices cn e used. Roundup Ultr lso controls grss seedlings nd suppresses nutsedge (Figure 5). Use of Buctril, Roundup Ultr, nd Stple requires tht fields e scouted more frequently very erly in the seson (i.e. 2 weeks fter plnting). For them to e effective, it is importnt tht these hericides e pplied to smll, ctively growing weeds. Wter-stressed weeds will not e controlled. By plnting time, spry rigs need to e clirted nd redy to go. Usully hericide pplictions should e mde efore the first cultivtion following plnting. Successful use of these hericides cn reduce or eliminte the expense of hnd weeding. 2

3 Stndrd weed control strtegies in Cliforni s Sn Joquin Vlley include comintions of crop rottion, cultivtion, hnd hoeing, nd hericide ppliction. The most persistent weeds re tolernt of cotton hericides. Rottion of cotton with crops like tomtoes, which use the sme preplnt-incorported hericides (i.e. dinitroniline like Trefln or Prowl) lso hs selected for hericide-tolernt weeds. Weeds tolernt of dinitroniline hericides include the most prevlent nnuls, oth lck nd hiry nightshdes, the perennil silverlef nightshde (Figure 6), groundcherry, tolguch, nnul ufflour, nd Chinese thornpple. These weeds re ll memers of the Solncee, the sme fmily s tomto, pepper nd eggplnt. Additionl perennil weeds tht re prolems include oth yellow nd purple nutsedge, field indweed, ermudgrss, nd johnsongrss. Annul morningglory nd velvetlef re not controlled y dinitroniline hericides. Brnyrdgrss nd mny other nnul rodlef weeds re controlled effectively y the dinitronilines. R Vrgs Figure 6. Severe nightshde infesttion. Preplnt hericides such s Trefln or Prowl re pplied flt nd doule disced to incorporte. The field is then listed (edded up). If listing is done in the fll, cultivtion nd/or residul hericides (Bldex, Cprol, or Gol) re used to keep the fllow eds free of weeds until spring plnting. If residul hericide is not used, either Grmoxone or Roundup is pplied to control winter nnuls. Rolling cultivtors or ed mulchers re used to cultivte nd remove smll weed seedlings or weeds killed y previous hericide pplictions, just efore the eds re plnted. Nightshde nd nutsedge often emerge t the sme time s cotton. Fields hevily infested with either of these weeds re sometimes treted with metm sodium (Vpm). Two to 3 weeks efore plnting, the fumignt is pplied with spry ldes tht re pulled through the eds t plnting depth. Control of nightshde nd its reltives like Chinese thornpple hs een excellent (Figure 7). Growth of nutsedge is suppressed for 20 to 30 dys. R Vrgs Figure 7. Control of Chinese thornpple with Vpm (right); untreted check (left). WB McCloskey Figure 5. Nutsedge control in Roundup Redy cotton fter two sequentil pplictions of Roundup Ultr (); untreted (). 3

4 Nightshde usully grows fster thn cotton. Trditionlly, hnd hoeing, t costs of $50 to 200 per cre, ws one of the few options growers hd for erly seson nightshde control. Unfortuntely, post-directed sprys of residul hericides often dmge young cotton. However, with the registrtion of Stple in 1996, growers now hve nother effective mens of comting nightshde (Figure 8). When Stple is pplied erly seson to cotton (just emerging up to the 3 or 4 lef stge), this over-the-top hericide gives 95 to 100% control of nightshde t the 3 or 4 lef stge. Costly hnd hoeing cn e reduced. Becuse Stple persists in the soil, rottion-crop restrictions pply to numer of crops. Before lyy hericide (Bldex, Gol, Trefln) is pplied, cultivtion is used to supplement preplnt hericide pplictions nd to develop furrows for irrigtion. Postemergence grss hericides (Fusilde, Post, Prism) re used when nnul grsses such s rnyrdgrss or perennils such s johnsongrss re present (Figure 9). Roundup, pplied with hooded spryer, hs een used to successfully control field indweed. Weed-Seeker spryer technology hs een used for nutsedge control. This spryer only sprys hericide when it sees or senses the green chlorophyll of weeds in the furrows (Figure 10). When this technology is comined with hooded spryer, Roundup cn e spryed to control nutsedge nd other emerged weeds. A ig dvntge is the svings of hericides ecuse it only sprys when weeds re present. R. Vrgs Figure 10. Weed-seeker spryer, fitted with hood, pplying Roundup only to green weeds. R Vrgs Figure 8. Nightshde in untreted plot (); 100% controlled with Stple (). R Vrgs Figure 9. Johnsongrss infesting cotton (); fter ppliction of Prism (). At the finl cultivtion, lyy hericide is often pplied s the cotton cnopy closes over the furrow. This ppliction prevents the growth of nightshde, nnul morningglories nd ground cherry when it is no longer possile to cultivte. Breeders re developing Acl cotton vrieties with tolernce to Roundup nd Buctril. However, ecuse of the vriety testing nd relese progrm conducted y the Sn Joquin Vlley Cotton Bord, these new technologies will not e ville to growers until

5 Regionl Perspectives Southwest (NM, OK, TX) Although weed pressure throughout the growing seson is not s intense in the semi-rid Southwest s it is in res with higher rinfll, weeds compete with cotton for limited soil moisture, nutrients, nd light. The end result is reduced yields nd qulity. Common weed prolems include pigweed (Plmer mrnth), Russin thistle (tumleweed), devil s clw, nd perennils like silverlef nightshde (whiteweed), Texs lueweed, nd woollylef ursge. Weeds tht re ecoming prolem re yellow nd purple nutsedge, morningglory, lncelef sge, cockleur, pririe sunflower (Figure 1), lck nightshde, nd venice mllow. Severl of these weeds re shown in Figure 11. In the Southwest, preplntincorported dinitroniline hericides (Trefln, Prowl) re used on 85 to 90% of the cotton crege to control pigweed, Russin thistle, kochi, nd nnul grsses. Preemergence hericide tretments (Cprol, Krmex, Cotorn, or Dul) re pplied t plnting to control rodlef nnuls nd yellow nutsedge, which re not ffected y the preplnt hericides. Post-directed tretments for rodlef weeds re not commonly used, ut over-the-top grss hericides re pplied for the control of johnsongrss, ermudgrss nd escpes of nnul grsses. Fll tretments of Roundup nd Bnvel re widely used for perennil weed control. Spot spry tretments with Roundup re pplied in-seson for silverlef nightshde nd other weed escpes. Cultivtion is used for in-seson weed control. In the irrigted cotton grown in the Brzos river ottom, creful vigilnce is required to spot the first emergence of shrppod c e W Keeling & P Bumnn Figure 11. Common weeds of the Southwest include ) pigweed, Plmer mrnth, ) devil s clw, c) silverlef nightshde, d) Texs lueweed, e) shrppod morningglory, nd f) cockleur. morningglory, difficult-to-control pest (Figure 11 e). Preplnt nd preemergence hericides hve een used trditionlly to comt this nd other troulesome weeds. If weeds escpe these mesures, timely postdirected hericide pplictions, in conjunction with cultivtion, help provide control. d f 5

6 In the drylnd frming of the Blcklnds, weed pressure is not s intense. Use of post-directed sprys hs not een common. Brodlef weeds tht escpe preplnt or preemergence hericide pplictions re controlled y cultivtion or spot sprys of hericides. In South Texs, weeds grow well 12 months of the yer. A successful weed control progrm uses yer-round pproch. Offseson, winter tretments include cultivtion, urn-down, nd/or residul chemicl tretments (i.e. Bldex, Cprol, Prowl, or Trefln). These tretments re usully followed with stndrd preemergence tretment. This progrm provides dequte in-seson control of most nnul species. Although hooded spryers re gining fvor, in-seson directed sprying is normlly not ttempted ecuse high winds re typiclly present in the criticl spring tretment period. Escpes re removed y spot tretment or hnd weeding. For severl yers, producers used Commnd preemergence to control tough weeds like Texs croton, cockleur, pririe sunflower, nd lncelef sge. The potentil for off-trget drift limited the use of this technology, however. Appliction of Commnd lso required tht n orgnophosphte soil insecticide e used s sfening gent t plnting. Stple, the newly-registered, over-the-top, rodlef hericide, gives growers new options. Stple pplied postemergence controls pigweed escpes, morningglory, lncelef sge, nd other rodlef nnuls. However, ecuse of the severe drought experienced in much of South Texs in 1996, Stple received mixed review. For most effective ction, Stple needs to e pplied to smll, ctively growing weeds. Its potentil will e greter in yers with more rinfll. Trnsgenic cottons (BXN nd Roundup Redy) will e ville to producers in 1997 nd will e prticulrly useful where growers prctice minimum tillge, or where they hve tough-tocontrol species. Roundup Ultr pplied erly postemergence to Roundup Redy cotton in reserch plots showed excellent control (Figure 12). P Bumnn Figure 12. Untreted (); Roundup Ultr pplied erly postemergence to Roundup Redy cotton (). Buctril pplied to BXN cotton controls mny tough rodlef nnuls such s cockleur, devil s clw, nd morningglory (Figure 13). When used t higher rtes, it cn suppress perennil weeds. W Keeling Figure 13. Control of weeds with Buctril pplied postemergence to BXN cotton. Reserch to dte indictes tht Roundup nd Buctril should e integrted into complete weed mngement system tht includes use of soil-pplied hericides. Becuse products used to tret trnsgenic cotton will hve few, or no, restrictions s to which crops cn follow, their use will open up new crop rottion possiilities. 6

7 Regionl Perspectives Mid-South (AR, LA, MO, MS, TN) Cotton weed mngement in the Mid-South region egins with tillge (chiseling, discing, nd/or edding) or preplnt hericides to control vegettion efore plnting. Roundup or Grmoxone Extr lone, or in comintion with oxyfluorfen (Gol), cynzine (Bldex, CyPro), or prometryn (Cprol, Cotton Pro), is pplied in minimum nd notillge fields (Figure 14). Cynzine, prometryn, nd oxyfluorfen provide residul soil ctivity to reduce reinfesttion. In no-till, Prowl or Dul re surfcepplied in comintion with preemergence hericides (Cotorn, Commnd, Meturon, Zoril, etc.) for rodlef weed control. Grmoxone Extr is used if weeds hve emerged. In conventionl plnting, emerged weeds re destroyed y tillge with ed conditioner or field cultivtor. Dinitroniline hericides (Prowl, Trefln) re incorported t the sme time the field is tilled. Preemergence hericides (Cotorn/Meturon, Commnd, nd Zoril) re usully nded on less thn onehlf the row width. Almost ll the crege is treted with Cotorn/Meturon. W Keeling Figure 14. Conservtion tillge with terminted whet crop. Commnd is primrily used to improve control of velvetlef, morningglories, prickly sid nd spurred nod. The insecticides Di-Syston or Thimet re needed s sfeners t plnting to protect the cotton from Commnd injury. Zoril is one of the most effective tretments for prickly sid nd nutsedge. Whims of the wether cn further complicte weed control in this region. Excessive rinfll fter plnting my remove hericides from the effective zone in the soil. If this hppens, weeds escpe. On the other hnd, sometimes not enough rin flls to ctivte preemergence hericides. Agin, weeds escpe. Cool growing conditions promote the growth of some weeds like johnsongrss, velvetlef nd common cockleur. At cool tempertures, these weeds grow fster thn cotton. Weeds tller thn cotton re not esy to control with postdirected hericides. Selective over-the-top hericides (Post, Fusilde, Assure, Fusion, Select) replced DSMA for johnsongrss control. DSMA is still eing used for post control of rodlef weed escpes, especilly common cockleur. However, rsenicl-resistnt common cockleur is widespred throughout the region. In 1996, Stple pplied postemergence on smll, ctively growing rodlef weeds ws n effective new mens of control even of cockleur. In ddition to cockleur, morningglory, pigweed, nd hemp sesni ll succumed. Growers hve een stisfied with Stple s performnce when it is used with sound preemergence progrm nd timely post-directed sprys. Prickly sid, spotted spurge, velvetlef, nd sicklepod (Figure 15) re ll etter controlled y pre- rther thn postemergence pplictions of Stple. Tke the weed history of field into ccount when deciding whether to use Stple in preemergence ppliction. A mximum of 2.4 oz/a cn e pplied during seson. S Brown Figure 15. Hevy sicklepod pressure in cotton. 7

8 Geneticlly-engineered BXN cotton, resistnt to Buctril hericide, will e nother tool ville to growers in Buctril pplied to BXN 47 is prticulrly effective on common cockleur nd morningglory. Growers no longer hve to push preemergence hericides to the point where some cotton injury occurs in order to control these two weeds. However, Buctril must e pplied only to BXN cotton. It very effectively kills conventionl vrieties. Buctril is est used s one component of wellplnned totl weed mngement progrm which includes pproprite preemergence nd postdirected hericides. Roundup Redy cotton will e commercilly ville for the first time in For the North Delt, Pymster vrieties PM1215RR, PM 1220RR, nd PM 1244RR, long with Deltpine 5415RR, re similr to their ckcross prent with the sme numericl designtion. These vrieties tolerte Roundup Ultr postemergence overtop through the four-lef stge. After tht, ppliction should e directed to the se of the plnt. Appliction cn lso e mde overtop once the crop reches 20% open olls. Roundup rtes should e selected ccording to weed species nd size tles on the lel. Growers considering Roundup Redy cotton my e le to eliminte some preemergence hericides which re now pplied to the soil t plnting. However, if these t-plnting hericides re eliminted, creful mngement will e required to ssure the proper timing of the Roundup Ultr ppliction to control erlyemerging weeds. Wht other course of ction cn e tken if prolonged riny period prevents timely ppliction of Roundup nd no preemergence products hve een used? Some residul hericide t plnting, or s post-directed spry, my e eneficil. Grower greements, n $8 per cre technology chrge, nd seed premiums must e included in totling costs of the Roundup Redy progrm. Budgets suggest tht the totl progrm costs re equl to or elow tht currently eing spent. 8

9 Regionl Perspectives Southest (AL, FL, GA, NC, SC, VA) In the Southest, growers use n hericide ppliction progrm similr to the following: 1) preplnt incorported ppliction of dinitroniline hericide (Trefln, Prowl); 2) preemergence pplictions of fluometuron (Cotorn, Meturon) lone or in comintion with other products such s Zoril or, more recently, Commnd; 3) erly postemergencedirected pplictions of fluometuron plus MSMA (sometimes just MSMA); 4) one, or possily two, directed pplictions of cynzine (Bldex or Cy-Pro) plus MSMA to finish out the seson; 5) over-the-top pplictions of grminicides (Post Plus, Fusilde, Select, Fusion nd Assure) to control escped grsses (nnuls, ermudgrss or johnsongrss). Conventionl tillge systems typiclly include couple of mechnicl cultivtions (Figure 16) which re often ccompnied y post-directed hericide tretments. Use of hooded spryers hs incresed in the pst hlf dozen yers in oth conventionl nd conservtion tillge (Figure 17). Grmoxone Extr or Roundup re commonly used lone, or in comintion with diuron (Krmex, Direx) or cynzine (Bldex). The comintions increse the types of weeds ffected. S Brown Figure 17. Hooded spryer with postdirected nozzles. Zoril cn e included for sicklepod, tropic croton, prickly sid nd sometimes nutsedge control. Results re generlly etter when it is pplied preplnt-incorported or t lest hlf of the Zoril is preplnt-incorported. Zoril lone will not give dequte control of hevy infesttions of nutsedge. Directed pplictions contining MSMA re needed to complete the jo. A preemergence spry including Commnd effectively stops Pennsylvni smrtweed. It lso improves effectiveness on prickly sid, spurred nod, velvetlef, tropic croton, cockleur, rgweed, jimsonweed, lmsqurters nd sicklepod. Growers used ll the Stple they could cquire in Stisfction vried gretly. Growers who pplied Stple in timely fshion, when weeds re ctively growing nd of the right size, nd followed up with directed ppliction, such s Bldex plus MSMA, were quite plesed. Without question, Stple works well on pigweed tht escpes residul tretments. It lso hs good to excellent folir ctivity on mny other rodlef weeds including morningglories, coffee senn, wild poinsetti (Figure 18), nd citron. S Brown Figure 18. Wild poinsetti, one rodlef weed trgeted y Stple. S Brown Figure 16. Erly () nd lter () seson cultivtions re effective components of weed control progrms in the Southest. 9

10 Although post pplictions of Stple re errtic on sicklepod, reserch in the southern extremes of the Costl Plin indictes tht the ddition of low rtes (2/3 to 1 pt/a) of MSMA to Stple improves control. Erly over-thetop pplictions of MSMA or Stple with MSMA pose miniml risks. These erly pplictions must e mde to smll weeds nd cotton of one or two true leves. In some sttes, DuPont hs pplied for n over-the-top lel for the Stple/MSMA comintion with reduced rtes of MSMA. The Stple lel ws recently expnded to llow preemergence pplictions in comintion with fluometuron. Much etter sicklepod control is chieved when Stple is pplied preemergence. In 1995, BXN cotton, trnsgenic cotton with immunity to the post-emergence hericide, Buctril, ws introduced on limited crege. Although rodlef weed control ws super, the vriety BXN 58 did not stnd up to August het. Yields were s much s 30% lower thn those of other vrieties. However, this yer s reserch trils showed high yields nd good weed control in BXN 47, new trnsgenic developed from the recurrent prent, Stoneville 474. In 1997, limited quntities of BXN 47 will e ville for growers to dd to their rsenl of weed control strtegies. Another trnsgenic, Roundup Redy cotton with folir tolernce to Roundup, will e ville in limited supply in Over-the-top pplictions of Roundup cuse no visile injury such s stunting, yellowing, or lef crinkling. However, over-thetop pplictions of Roundup fter squre initition hve resulted in occsionl fruit loss nd yield reduction. This unpredictle response is elieved to e ssocited with pollen steriliztion. Becuse of the potentil for fruit loss, the Roundup Ultr lel for Roundup Redy cotton permits over-the-top pplictions up through the fourth lef stge nd post-directed sprys therefter. Applictions of Roundup to stressed weeds re not effective. Other weeds presenting chllenge re those more thn few inches in height nd troulesome weeds such s Florid pusley, yellow nd purple nutsedge, volunteer penuts, nd possily morningglories. How is the Roundup Redy technology est used? Growers committed to using Roundup Redy cotton will need to eliminte something from their stndrd weed control progrm in order to offset the technology costs. One possiility deted y weed scientists is not using the stndrd preemergence hericides. In order to eliminte them, erly post-roundup pplictions must cler the field of weeds s effectively s the pre- nd erly post-emergence hericide tretments. Rrely will single post tretment deliver seson-long weed control. Follow-up pplictions re routine. In the Southest, the stndrd, directed ppliction of cynzine plus MSMA, or similr tretment, is logicl ecuse it should e more effective on nutsedge nd morningglories nd it lso provides residul weed control. 10 S Brown Figure 19. Misppliction of dinitroniline hericide results in strip of escped grss.

11 With or without Roundup Redy technology, the economy nd effectiveness of the incorported dinitroniline hericides mke them irreplcele. Like ny other hericide, they must e pplied correctly to e effective (Figure 19). For mny of the smll-seeded rodlef nd nnul grss weeds which these products eliminte, postemergence tretments re fr less effective. Trefln nd Prowl deliver remrkly consistent weed control for just few dollrs per cre. More studies of the Roundup Redy cultivrs re needed to etter determine their yield potentil. Conclusions Using these vlule new technologies is ut one prt of n integrted weed mngement system. Determining which tools to use nd how est to pply them is the chllenge presented to growers everywhere. Insights gined from nswering these questions my help in deciding the est mngement options for your field. 1) Wht is your norml weed inventory? Which products re leled for controlling them? Answers to these two questions should help you decide if you need to keep pre-plnt nd preemergence progrms in plce. 2) Is your ppliction equipment up to the tsk? For exmple, will you e le to successfully post-direct mid-seson Roundup Ultr ppliction or ensure complete coverge with n ppliction of Buctril? 3) Will postemergence products lone hndle your weed prolems? Some erly seson wether ptterns cn keep equipment out of the field. Would such n event interfere with the crucil timeliness of n ppliction? 4) Wht re your crop rottion plns? 5) Cn you use these new technologies to cut costs nd increse yields? New weeds nd developing hericide-resistnt weeds re likely to occur if producers rely solely on ny single hericide. As new hericide-tolernt cotton vrieties ecome ville, weed mngement systems will continue to chnge nd evolve. 11

12 On the Horizon Technologicl dvnces in precision, or site-specific, frming will chnge weed mngement in cotton in severl wys. Equipment tht sees nd sprys weeds s it moves through the field will reduce hericide costs while more effectively controlling weeds (Figure 10). Quickhitch precision guidnce systems comined with in-row cultivtion tools will remove rodlef weeds in the seed line without using chemicls (Figure 20). Sensors tht see the crop row, rther thn physiclly touch it with ntenne, promise to mke these systems even etter. Mny weeds, especilly perennils, re not evenly distriuted throughout the field. By using glol positioning systems (GPS), growers will e le to mp weed infesttions nd soil textures in their fields nd downlod these dt to GPS computer-controlled spryers tht will pply hericides to only those loctions requiring tretment. Rtes of soil-pplied hericides will e djusted to reflect different soil textures ppering in field. WB McCloskey Figure 20. Antenne of precision g cultivtor (A) sense cotton stems nd keep cultivtor centered on crop row. Spring-hoes uproot weeds nd leve cotton unscthed (B). Mention of specific product does not imply endorsement of it over ny other product. 12