MNGEMENT TECHNIQUES FOR WEE CONTROL IN LFLF Willim H. Isom. Extension gronomist University of Cliforni, Riverside Vern Le Mrle. Extension gronomist University of Cliforni. vis Poor irrigtion mngement nd improper hrvest schedules proly ccount for most of the weed prolems in lflf. Mrle (1974. In ddition to these two chief cuses of weediness in lflf. we my dd other fctors which involve mngement decisions or ction such s choice of lnd. seeded preprtion. use of high qulity seed. plnting. nd wise timing of most culturl prctices. Choice of Lnd lflf is est dpted to medium textured soils with good internl dringe nd low or no slinity prolems. Medium or slightly sic ph fvors the development nd growth of lflf nd the cteri which fix nitrogen on the roots. Fctors which fvor good lflf growth will tend to minimize weed prolems simply ecuse they mke lflf more cple of suppressing weeds y sheer crop competition. lnd should lso e chosen which is irrigle with minimum tendency for wter ccumultion when the crop is irrigted. If possile. the lnd should e leveled so there re no depressions to collect nd retin wter. lehmn nd Erwin (1974. lflf stnds decline rpidly if wter collects round the crowns of plnts nd remins there over prolonged periods. Erwin nd lehmn (1974. Furthermore. when lflf stnds decline. weeds move in nd econe so competitive tht lflf production econes unprofitle. third considertion for choice of lnd is to void those fields which hve d weed history. especilly if the weeds re the kinds which hve competitive dvntge over lflf either in stnd estlishment or in the estlished crop. Seeding lflf into fields hevily infested with such perennil weeds s ermudgrss. Johnsongrss. or field indweed is sure to detrct fr001 producti"iity of the lflf especilly if plnted in the lte spring of the yer. Lnd infested with seeds of fst-growing weeds is lso to e voided since lflf plnts re smll nd slow-growing in the seedling stge. Seeded Preprtion ny lnd preprtion ~sure which fvors good lflf growth will minimize weed prolems throughout the life of the stnd. If the lnd hs severe weed history. this should e tken into ccount nd steps e tken to reduce weed pressures on the new seeding. Perennil rodlef nd grssy weeds should e pre-treted nd eliminted with effective trnslocted hericides tht present no residue prolems for the lflf. nnul weeds cn e reduced y intermittent pre-irrigtions nd cultivtions efore the finl seeded preprtion. Lnd should e leveled to tke out low spots where wter will ccumulte nd cuse lflf stnd losses. The finl seeded preprtion should provide fine. firm. nd moist seeded into which lflf cn e seeded t uniformly shllow depth to insure rpid germintion nd emergence. uniformly dense lflf stnd is good competitor with weeds if growing conditions re right for the lflf. Fertilizers for new seedings of lflf should generlly e pplied during the seeded preprtion period. Usully. phosphorus is pplied prior to disking. Sometimes complete fertilizers re pplied nd do enhnce erly lflf gr011th ut nitrogen pplictions ove miniml rtes of 25 to 30 pounds of t4 per cre re not considered dvisle for they tend to promote excessive weedy growth. especilly grsses. -42-
Seeding nd Seeding Rtes There re pproximtely 210.000 seeds in pound of lflf seeds. t.'ture lflf seeds re out 2.5 X 1.5 X 1.1 mm in length. width. nd thickness. Gunn (1972. s n ssurnce for good emergence nd good stnd estlishment. the smll seeds of lflf should not e plnted deeper then 1/2 to 1 1/2 inches. depending on soil type nd conditions. The greter depths re for sndy soils or soils which do not crust or which hve tendency to dry out during the germintion period. In no cse should seed e plnted deeper thn is necessry to insure good stnd. The good stnd is essentil to hedge ginst weed estlishment. Seeding rtes ffect stnd estlishment ut not necessrily yields or stnd persistence. McClelln (1975 found tht t the end of the first seson. there were no differences in plnt popultions or yields of lflf seeded t 1.24.6. or 33.0 ls. of seed per cre. The higher seeding rtes my provide sollewht etter crop competition with weeds in the course of stnd estlishment. ut generlly 15 ls. of seed per cre is dequte if the seeded is properly prepred nd good plnting techniques re employed. Fifteen pounds of seed per cre would provide in excess of 72 lflf seeds per squre foot or 1 plnt in ech 2 squre inches if they ll germinted. Plnt High Qulity Seed iscolored or off-colored seed is usully of poor germinility or if it germintes, it produces seedlings poor in vigor. Weeds re permitted to estli$h ecuse of filure of lflf plnts to grow nd dominte. Clenliness of seeds is of even greter importnce ecuse poor vigor nd germintion cn e somewht corrected for y seeding t higher rtes wheres contminted seed lots only dd to the weed prolem. lflf seeds infested with dodder seeds hve een the mjor source of spred of this insidious weed. Some grssy weeds re virtully impossile to seprte from lflf seeds, consequently the est insurnce ginst creting weed prolem is to plnt weed-free seeds of known qulity. Time of Plnting lflf seeds will germinte t lower tempertures thn most summer nnul weeds. We hve oserved tht lf1f seeds will germinte nd seedlings wi11 ecome estlished when soi1 surfce tempertures pproch freezing in the erly mornings ut dytime tempertures rise to 60oF or 70oF. Furthermore. 1f1f seed1ings tend to survive frosts rther we1l fter the first trifo1iolte lef is est1ished. Using this s se of opertion. it is est to plnt lf1f in the fll of the yer or very erly spring to void excessive weed competition. If winter weeds do pper to e thret. they cn e controlled dequtely y postemergence hericides. Fll nd erly spring plntings lso provide the dvntges of more effective mngement of irrigtions for germintion nd stnd estlishment nd the slower growth of weed competition while lflf is ecoming estlished. Tillge nd Cropping Prctices voidnce or escpe from weed prolems in lflf cn e chieved through the use of good tillge nd cropping prctices. These prctices must egin efore the lflf is plnted nd continue throughout the rottion cycle. Sometimes "smother" crops re used to minimize perennil weed infesttions efore plnting lflf. Hericides cn sustitute for mechnicl fllow in the control of troulesome weeds. The use of proper crop rottions or cropping sequences ssists in freeing the lnd of weeds which could e prolem in lflf. ifferent crops re usully ssocited with specific weed prolems nd hve their OiIn rry of sfe hericides. These hericides ech control certin weed species. thus crop rottion ffords mens of getting t different weedy prolems nd provides wy to minimize certin weed prolems in lflf. Peters nd Peters (1972}. J -43-
Irrigtion Mngement Irrigtion mngement is extremely criticl oth s to times of ppliction. mounts. nd durtion. s direct result of poor irrigtion mngement. lflf stnd losses occur nd weeds invde. Erwin nd Lehmn (1974 showed tht lflf plnts died fter remining in sturted soils longer thn 24 hours. They lso found tht mowing lflf plnts just efore n irrigtion resulted in more plnts dying from over irrigtion thn if they irrigted first nd hrvested lter. These findings imply tht irrigtions should e of short durtion permitting the soil to drin to field cpcity or elow in less thn 24-hour period. Furthermore. in order to mintin good lflf stnd. irrigtions should e mde on growing lflf just efore hrvests insted of just fter hrvests. nother fctor to consider in this reltionship of hrvesting nd irrigtions is tht irrigting freshly hrvested fields provides perfect sitution for weeds to develop. The soil surfce is wetted nd sustined t sufficiently high moisture for weed seeds to germinte. t the sme time. sunlight reches the exposed surfces etween plnts nd weed seeds tht require light nd moisture to grow re fvored. lflf plnts re slower to strt regrowth nd some my hve died s result of the irrigtion fter cutting. consequently. weeds move in wi.ere the lflf stnd econes weker. Field Compction Mny lflf stnds decline nd weeds replce lflf plnts ecuse the lflf is used through excessive field trffic t hrvest time or during the dormnt seson. Hrvest equipment wheels run over s much s 75 percent of the surfce re of hy fields during ech hrvest. Sheesley et l.(l974. Repeted hrvests or repeted compction in the sme res hs sustntil dverse effect on lflf growth nd stnd survivl. Sheesley et l. (1974 lso found tht much of the initil lflf stnd loss occurred s result of wheel trffic in the first nd second hrvests of new lflf fields. They concluded tht where unimpeded soils permit good lflf root development. lflf roots on newly estlished stnds should e well developed into the 1 1/2 to 2-foot depths of the soil efore the first hrvest is mde. This would reduce stnd losses thus minimizing prospects for weed invsion into newly estlished stnds. Cutting Mngement The vigor of lflf plnts is miniml soon fter the forge is hrvested. Plnts egin to moilize nd trnsport root reserves to produce new top growth nd it is not until plnts rech out 1/10 loom tht root reserves hve een restored to the originl level. s consequence. cutting intervl hs decided impct on stnd persistence of lflf s shown in Tles 1 nd 3. Stnd persistence. in turn. ffects the rte of weed invsion of lflf fi'elds s shown in Tle 2. lflf vrieties. ecuse of their different growth chrcteristics must e hrvested differently in order to mintin dequte stnds. ifferences etween vrietl responses for the different cutting intervls etween the two loctions s shown in Tles 1 nd 3 my e. in prt. explined y different mngement prctices t vis nd Riverside. t vis. plots were flood irrigted nd no hericides were used for weed control. t Riverside. plots were sprinkler irrigted nd soil persistent hericides were used to control most weeds. Those vrieties most dversely ffected y frequent hrvests were proly lso more dversely ffected y weed competition t vis thn t Riverside. In the 4th yer of production t Riverside. however. weeds tolernt of iuron nd Triflurlin did invde thinned lflf stnds in the 3 nd 4-week cutting-intervl-plots ut not in plots where hrvest intervl ws greter thn 4 weeks., Most vrieties of lflf require t lest 4 weeks or more fter hrvest to rech 1/10 loom; dormnt vrieties my tke week or two longer even during hot wether. When wether is cool in the spring nd fll. six weeks or more my e required from hrvest to -44-
1110 loom for non-dormnt vrieties nd longer for dormnt vrieties. Hrvesting lflf efore 1110 loom depletes root reserves on most vrieties nd repeted hrvests ccentute the prolem. Therefore, cutting intervl should e djusted to fit the vriety nd tempertures to void loss of stnd from poor plnt root reserves. If stnds re mintined strong nd helthy, weeds hve difficulty competing with well mnged lflf. Literture Cited Lehmn. W. F. nd. C. Erwin. 1974. The Use of Lnd Leveling. Irrigtion. nd Vrieties In the Reduction of Sunlner Stnd ecline of lflf In esert res. Proc. Cliforni nd rizon Low esert lflf Symposium. pp. 49-57. Mrle. V. L. 1974. Optimizing lflf Production In esert res of The Southwestern United Sttes. Proc. Cliforni nd rizon Low esert lflf Symposium. pp. 75-91. McClelln. W.. 1975. Clif. gr. 29:13. lflf: Effects of Seeding Rtes nd Rhizoium Inocultions. Peters. E. J. nd R.. Peters. 1972. Weeds nd Weed Control. In: lflf Science nd Technology. mer. Soc. gron. Monogrph Series No.15. pp. ~5-573. Sheesley. R... W. Grimes. W.. McClelln. C. G. Summers. nd V. Mrle. 1974. Influence of Wheel Trffic on Yield nd Stnd Longevity of lflf. Clif. gr. 28:6-7. -45-
TLE 1 EFFECT OF CUTTING INTERVL ON STN PERSISTENCE OF LFLF VRIETIES T U.C. VIS lflf Persistence Rtings for -ifferent Cut tin Intervls.:.! 1/ 3 4 5 6 MO 69 K 131 Mens Men Seprtions* 5% & 1% Levels uc Slton Mop 69 6.6 4.6 6.2 5.0 2.6 2.6 c WL 512 2.4 1.6 7 N-78 5.6 6.4. 4.07 WL 318 2.4 0 Lhontn 3.0 1.2 1.6 1.8 1.4 2.07 ekl 131 5.8 5.2 3.8 3.8 4.6 3.0 4.37 wson 5.2 6.0 4.0 4.20 Cutting Intervl Mens 4.90 4.93 3 2.78 3.10 2.60 Men Seprtions* oth 5% & l~ Levels L.S.. for X Cutting Intervl 5% = 0.77 1% = 6 1/ Cutting intervls re equl to.5. nd 6-week. intervls. plus MO 69 = 1/10 -lo001 for Mop 69 nd K 131 = 1/10 loom for WL 318 nd ekl 131. Tulr vlues re visul estimtes of lflf stnds sed on 1 to 9 scle where 1 is perfect stnd nd 9 is no stnd. Rtings were mde Octoer 1977 t the end of the 3rd production yer. * ny two mens not ccompnied y the sme letter re significntly different t oth the 5% nd 1% levels of confidence. -46-
TLE 2 EFFECT OF CUTTING INTERVL ON CONTROL OF WEES IN LFLF VRIETIES GROWN T U.C. VIS lflf -Cuttinq IntervlJ - 3 4 5 6-MO 69 K 131 Mens Men Seprtions* 5% & 1% Levels uc S1ton Mop 69 WL 5'2 N-78 WL 318 Lhontn ekl 131 wson s. 4. 4. 6. 4. S. 6. 6.,6,6,2,2.6 2 8 2 1..8 1..6 1..8 4..4 3..8 3.,6 6.,4 7. 4 1.2 1.4 1.4 1.2 1.8 1.8 5.0 1.97 1.73 1.67 2.57 2.30 7 3.50 3.80 C C C Cutting Intervl Mens 5.43 3.85 1.22 2.35 Men Seprtions* 5% 1% c c L.S.. for X Cutting Intervl 5% = 9 1% = 1.48 1/ Cutting intervls re equl to.5. nd 6-week intervls. plus MO 69 = 1/10 -loom for Mop 69 nd K 131 = 1/10 loom for WL 318 nd ekl 131. * Tulr vlues re for degree of weed infesttion where 1 = no weeds nd 9 = hevy weed infesttion. -47-
TLE 3 EFFECT OF CUTTING INTERVL ON STN PERSISTENCE OF LFLF VRIETIES T U.C. RIVERSIE Percent Stnd for 1 Men lflf ifferent Cuttinc Interyls~ Seprtions* 3 4 5 6 MO 69 K 131 Mens 5% 1% Mexicn Sonor UC S1ton 18.8 32.5 32.5 58.8 46.2 53.8 63.8 75.0 48.8 58.8 53.8 67.5 44.0 57.7 E d c Mop 69 42.5 75.0 75.0 76.2 72.5 77.0 69.7 C S 13 21.2 78.8 86.2 87.5 80.0 8 7 C WL 508 60.0 77.5 87.5 84.2 77.5 80.0 77.8 h N-78 57.5 70.0 83.8 83.8 76.2 76.2 74.6 C Lhontn 72.5 81.2 92.5 90.0 87.5 93.8 86.2 ek1 131 18.8 70.0 90.8 91.2 81.2 85.0 7 C Cutting Intervl Mens 40.5 68.0 77.0 81.5 72.P' 77.1 Men Seprtions* 5% 1% c C c C cd C cd l.s.. for X Cutting Intervl 5% = 15.5% 1% = 20.5% 1/ Percent stnd is n.estimte of desirle stnd elieved necessry for mximum -production with 100% eing perfect. * ny two mens not cc001pnied y the sme letter re significntly different t the confidence level shown.