Cliforni Avocdo Society 27 Yerook 9: 131-148 Mry Lu Arpi Deprtment of Botny nd Plnt Sciences University of Cliforni, Riverside Muricio Tpi ACW Frm Fllrook, Cliforni Reuen Hofshi vocdosource.com Fllrook, Cliforni The Use of Nphthlenecetic Acid (NAA) to Control Vegettive Vigor in Avocdo Trees Introduction The Cliforni vocdo industry exists on the interfce of the urn griculture complex of southern Cliforni where wter vilility, lor issues, exotic pests, nd lnd prices threten the continued sustinility of the stte s vocdo production. This is especilly true when trees re plnted on steep hillsides. Additionlly, the Cliforni grower must compete with imported Hss fruit from Mexico, Chile, Dominicn Repulic nd New Zelnd. Growers in mny of these countries hve ccess to plnt growth regultors tht help them mnge tree vigor following pruning nd overll growth. In order to sustin the viility of the vocdo industry in such chllenging environment, Cliforni growers must develop the necessry tools to mximize productivity while minimizing inputs into the griculturl system. Nphthlenecetic cid (NAA), plnt growth regultor, hs the potentil to e such tool. It is synthetic uxin
tht is used for rooting, fruit thinning, reducing prehrvest fruit drop nd controlling the growth of wtershoots nd root suckers following pruning or topworking. NAA is registered for use in Cliforni on severl commodities including citrus (oth s fruit thinning gent nd for sucker regrowth), olives (s fruit thinning gent), s well s sucker regrowth for pples, pers nd nectrines. NAA hs een previously evluted for use in vocdos. Boswell et l. (1976), reported promising results using NAA to control rootstock suckers in vocdos. They found tht trunk ppliction pplied to topworked trees effectively controlled rootstock suckers for up to 7 months. Prompted y the work of Boswell et l. (1976) we initited study in 22 to re-evlute the potentil use of NAA on vocdos. Our hope ws to ultimtely gin registrtion of this mteril to control vegettive growth nd vigor of stumped nd pruned vocdo trees nd thus provide the Cliforni vocdo grower with mngement tool tht will ssist in cnopy mngement of this perennil sutropicl tree grown primrily on steep hillsides. Our results, descried elow, suggest tht the use of NAA s vegettive mngement tool could help sustin the continued viility of the Cliforni vocdo industry. We hope tht NAA will hve severl uses in the typicl Cliforni vocdo grove. First, it will e extremely helpful to the grower who wishes to rejuvente their grove through stumping, which is cutting mture tree ck down to height of 3 to 5 feet. The nturl dissters experienced y mny growers during 27 (freeze nd fire), s well s wter shortges, hve prompted mny to consider tree stumping. Experience hs shown tht when the vocdo tree is cut ck in this mnner, vigorous growth results ll over the tree stump including unwnted growth from the rootstock nd lower portions of the stump. A second use of NAA will e to control tree height when grower chooses to mintin trees t specific height. Tree height control nd the susequent reduction of ldder work re crucil for continued viility of hillside plntings from the perspective of hrvesting nd pest monitoring nd mngement. We foresee in the next 3 to 5 yers, s more growers move towrd high density plntings nd tree height control, tht the use of NAA will hve plce in this type of mngement strtegy.
The finl use of NAA would e for shoot tipping when grower is doing mintennce pruning either in high density or hedgerow setting. Successfully controlling vegettive vigor of the side rnches will reduce susequent lor inputs nd will lso increse sunlight penetrtion into the tree interior, thus reducing the dieck of interior rnches due to the lck of sunlight. We conducted 3 trils to evlute the use of NAA for these purposes using mteril mnufctured y Amvc Chemicl Corportion, Tre-Hold A-112. The results of these trils re summrized elow. The use of NAA s trunk sprout inhiitor For this portion of the project we sked the following questions: Does ppliction of NAA to stumped trees inhiit the numer nd vigor of rootstock suckers nd regrowth ner the soil re? Does NAA ppliction to the rootstock nd lower portion of the tree inhiit growth nd vigor ove the ud union? Mture Hss trees on seedling Mexicn rootstock (pproximtely 18 yers old) were stumped to pproximtely 1.5 meters (5 feet) in mid-my 23. Forty-two trees were selected nd divided into 21 locks of 2 trees ech. The stump of one tree ws whitewshed to the ground level nd served s the control. The second tree ws pinted with n ppliction concentrtion of 1.15% NAA (Tre-Hold A-112 diluted in wter nd ltex pint; Amvc Chemicl Corportion) to height of pproximtely 9 cm (35.4 inches) ove the soil line. The reminder of the stumped tree ws whitewshed similr to the control tree. A nd of rown pint ws pplied t the interfce of the treted re to ssist in susequent evlution (Figure 1). Tretments were pplied on June 2, 23. The numer of suckers in the treted re, the numer of shoots ove the treted re nd the vigor of the regrowth ws evluted on Septemer 24, 23. At the time of evlution, the numer nd reltive vigor of shoots rising elow nd ove the treted re were ssessed. Shoot vigor ws rted using the following scle: = no growth or sprouting; -1 = sprouted ut died ck; 1 = some growth, not vigorous (growth < 25 cm; 1 inches); 2 = moderte growth (growth 25-5 cm; 1 2 inches); nd 3 = vigorous growth (growth > 5 cm; >2 inches). All dt ws nlyzed using CoStt version 6.24 (CoHort Softwre, Monterey, CA).
Figure 1. View of stumped tree just fter ppliction of 1.15% NAA (TreHold A-112 diluted in wter nd ltex pint; Amvc Chemicl Corportion). Note control tree in ckground. Tle 1 reports the results of this prt of the study. The results corroorte those reported y Boswell et l (1976). We oserved fewer nd less vigorous regrowth shoots in treted trees s compred to the controls. Shoot regrowth nd vigor ove the treted re ws not impired. This portion of the study demonstrtes tht n ppliction of NAA to the lower portion of the stump successfully reduced oth the numer nd vigor of shoot regrowth without negtively impcting regrowth of the upper portion of the tree. The use of NAA to control regrowth on topped trees For this portion of the project we were interested in nswering the following questions. Does treting cut rnches with NAA inhiit the numer of shoots nd vigor or the susequent regrowth? Does the treted surfce re of wood influence this response?
Tle Tle 1. The 1. numer The numer of shoots of nd shoots nd vigor shoot within vigor the NAA within treted the re NAA or ove for stumped Hss vocdo trees (N = 21). NAA pplied to trunk from treted soil line re to 9 cm or height. ove Trees for stumped treted 6/2/3 Hss nd vocdo evluted trees 9/24/3. (N = 2). Trees treted 6/2/3 nd evluted 9/24/3. Treted Are Aove Treted Are Treted Shoot Are numer Aove Treted Shoot vigor Are Shoot numer Shoot Vigor Shoot numer Shoot vigor ( ( 3) 3) z Shoot numer Shoot vigor ( 3) ( 3) Control 3.95 1.3 1.55 2.35 Control 3.95 1.3 1.55 2.35 Treted Treted.75.75.4.4 1.5 1.5 2.2 2.2 Proility...27.3.7492.4194 z Shoot vigor rtes s = no growth or sprouting; -1 = sprouted ut died ck; 1 = some Men growth, seprtion not vigorous using (growth Lest < 25 Significnt cm; 1 inches); Difference 2 = moderte test (LSD) growth t (growth P <.5. 25-5 cm; 1 2 inches); nd 3 = vigorous growth (growth > 5 cm; >2 inches). Men seprtion using Lest Significnt Difference test (LSD) t P <.5. Mture Hss trees on seedling Mexicn rootstock (pproximtely 18 yers old) were topped to pproximtely 4.85 meters (16 feet) in mid-my 23. Sixty-three trees were selected nd roken into 7 locks of 9 trees ech. Within ech lock the trees were further divided into 3 sets of 3 trees. Ech set ws rndomly ssigned one of 3 tretments: 1) control (no tretment, whitewshed); 2) ech scffold pinted with n ppliction concentrtion of 1.15% NAA (Tre-Hold A-112 diluted in wter nd ltex pint; Amvc Chemicl Corportion) from 3 cm ( 12 inches) from the cut surfce; nd 3) ech scffold pinted with NAA from 6 cm ( 24 inches) from the cut surfce. The NAA ws mixed in light rown pint in order to esily identify the treted trees. Tretments were pplied on My 22, 23 (Figure 2). Growth of the topped trees ws evluted on Septemer 3, 23 (Figures 3 nd 4). At the time of evlution, the following mesurements were mde: rnch dimeter (cm); the numer nd reltive vigor of shoots rising within the treted re (tretments 2, 3); nd the numer nd reltive vigor of shoots in non-treted re (.5,.5 1. meter; 1.6; 1.6 3.3 feet) sutending the treted re. In the cse of the control trees, this ws from the cut surfce of the rnch. For tretments 2 nd 3, these mesurements were tken elow the treted re. Vigor ws rted s descried ove using -1 to 3 scle. Dt ws nlyzed using CoStt version 6.24 (CoHort Softwre, Monterey, CA). Tle 2 presents the results from this portion of the study. There ws no significnt difference etween the verge rnch dimeter
due to tretment. If we compre the numer of shoots nd the vigor of these shoots which rose in the NAA treted re of Tretments 2 nd 3, there ws significnt difference etween the numer of shoots due to tretment. This is not surprising, however, since the treted re for tretment 3 ( 6 cm) ws twice s lrge s the treted re of tretment 2 ( 3 cm). There ws no sttisticl difference, however, in regrowth vigor, which ws rted overll s not vigorous. Shoot regrowth nd vigor elow the treted re (or elow the cut surfce for the control) ws influenced y tretment. There were no significnt differences etween the control or either tretment for the first.5 meter elow the treted re. The results for the second.5 meter elow the treted re, however, show tht the -6 cm tretment hd sttisticlly significnt influence on regrowth nd shoot vigor elow the treted re. The -3 cm tretment ws not sttisticlly different from the control in either mesurement. If the growth nd shoot vigor for the entire meter elow the treted re is nlyzed, one sees tht the -6 cm tretment results in significntly fewer nd less vigorous regrowth. This suggests tht the length of the treted re elow cut is importnt to ssure good results with NAA. Further work is needed to finlize the reltionship etween shoot dimeter nd the mount of wood to tret to reduce regrowth. Figure 2. Generl view of treted trees in My 23 following tretment.
Figure 3. Regrowth in Jnury 24 Control. Note the vigorous regrowth especilly ner the cut surfce. Our work demonstrtes tht NAA pplied to topped trees successfully reduced oth the mount nd vigor of picl growth tht occurred in the months following tree pruning. This reduction will llow for etter regrowth of the tree in the lower cnopy. An dditionl vlue of controlling tree size will e tht it should llow for more efficient ppliction of pesticides to control the exotic pests which hve een introduced into Cliforni recent yers. Figure 4. Regrowth in Jnury 24 Tretment 3 (-6-cm; -24-in.). Note tht there re no new shoots within treted re (pinted rown). In the picture on the right, the treted rnch hs no new growth in the treted re; rther, the new growth is occurring well elow the cut.
Tle Tle 2. 2. The The 2. numer The of numer of shoots shoots nd of nd shoots vigor nd vigor within shoot within the vigor NAA the NAA treted within treted re the or re elow NAA or for elow topped for Hss topped vocdo Hss vocdo trees. Trees trees. treted NAA 6/2/3 treted nd re evluted either 9/24/3. 3 cm or treted 6 cm elow re lim or elow cut. Trees for treted topped Hss vocdo trees. Trees treted 6/2/3.5 meters nd evluted.5 1. meters 9/24/3. 1. meters 6/2/3 nd evluted Within treted 9/24/3. elow treted elow treted elow treted re z.5 meters.5 1. meters 1. meters Within re re.5 meters elow re treted re z re Within treted elow treted elow treted elow.5 treted 1. meters elow Brnch treted Shoot re re Shoot 1. meters Shoot elow re Shoot z treted Shoot re re Shoot Shoot re Shoot dimeter numer vigor numer vigor numer vigor numer vigor Brnch dimeter Shoot (cm) Shoot Shoot numer Shoot Shoot Shoot Shoot vigor ( Shoot 3) S hshoot (cm) o o t dimeter numer ( vigor 3) numer ( vigor 3) numer ( vigor 3) numer ( vigor 3) numer Shoot (cm) vigor ( 3) Shoot ( 3) numer Shoot vigor ( 3) Shoot numer y ( 3) ( 3) ( 3) Shoot Control vigor (9.37 3) - - 4.24 2.3 3.71 1.68 7.95 1.86 Control 3 Control cm 11.25 9.37.65-9.37.64 - - 5.24 4.24-2.29 2.3 4.24 2.69 3.71 2.3 1.6 1.68 3.717.93 7.95 1.68 1.95 1.86 7.95 6 3 cm cm 1.86 1.11 11.25 1.73.65.78.64 3.16 5.24 1.75 2.29 1.81 2.69.83 1.6 4.9 7.93 1.27 1.95 Proility 6 cm 3.511 cm 1.11 11.25.199 1.73.5333.65.78.39 3.16.64.29 1.75 5.24.28 1.812.29.2.83 2.69.4 4.9 1.6. 1.27 7.93 z Proility For control 1.95 elow.51 the cut surfce..2.533.39.21.3... Men z For control seprtion 6 elow cm using the cut 1.11 Lest surfce. Significnt 1.73 Difference.78 test (LSD) 3.16 t P <.5. 1.75 1.81.83 4.9 y Shoot vigor 1.27 rtes s = no growth or sprouting; -1 = sprouted ut died ck; 1 = some growth, not vigorous (growth < 25 cm; 1 inches); 2 = moderte growth (growth 25-5 cm; 1 inches); nd 3 = vigorous growth Proility (growth > 5 cm;.511 >2 inches)..199.5333.39.29.28.2.4 Men seprtion. using Lest Significnt Difference test (LSD) t P <.5. The use of NAA fter shoot tip pruning The following questions were posed for this study. Does ppliction of NAA to shoot tips fter pruning impct the pttern of vegettive re-growth? Cn NAA e used to help shpe nd mintin tree structure in hedgerow mngement scheme? Mture Hss trees on Mexicn seedling rootstock (plnted in 1975) were stumped to pproximtely 1.8 meters (6 ft.) in 21, nd llowed to regrow. Selective shoots on the trees were pruned in mid-april 23, to lterl rnch (Figures 5A, 5B, 6A, 6B) in n effort to trin the trees into hedgerow plnting design. Following pruning, the trees were divided into 2 groups. In one group, the pruned shoots were pinted with n ppliction concentrtion of 1.15% NAA (TreHold A-112 diluted in wter nd ltex pint; Amvc Chemicl Corportion). In the other group, the pruned shoots were pinted with white ltex pint. Following pinting, 1 to 5 shoots per tree were selected for monitoring. Shoots were selected sed on pproximte dimeter. Seventy-three shoots were selected from the NAA treted trees (36 trees), nd 7 shoots from 3 trees were used s control shoots. Tretments were pplied within week of pruning. Regrowth ws evluted on June 3, 23. The following prmeters were visully evluted t the time of evlution (Figures 5A, 5B, 6A, 6B). Shoots on the primry shoot xis (treted rnch) were ctegorized s follows:
No growth, Just strting; wek, Only t tips of xillry shoots, Multiple ud rek on primry xis, Vigorous shoot growth with xillry uds growing, Growth on primry nd secondry xis. Shoots on the secondry shoot xis (within.5 meter of tretment) were likewise evluted: No growth, Just strting; wek, Only t tips of xillry shoots, Multiple ud rek on primry xis, Vigorous shoot growth with xillry uds growing, Growth on primry nd secondry xis. The verge length of new growth on the primry nd secondry shoots were estimted nd ctegorized s follows: > to 15 cm, 15 3 cm, 3 6 cm, >6 cm (> to 6, 6 12, 12 24, >24 ). The numer of shoots with new growth on the primry nd secondry shoots were estimted nd ctegorized s follows:, 1 to 5, 5 to 1, 1 to 15, >15. In the cse of the NAA treted shoots, we oserved tht growth ws inhiited t the point of pruning. Ech shoot (control nd treted) ws rted for the length long the primry xis where growth ws inhiited s follows: > to 15 cm, 15 3 cm, 3 6 cm, >6 cm (> to 6, 6 12, 12 24, >24 ). Ctegoriztion of shoot growth Figure 7 shows the reltive growth on the primry shoot xis (the shoot treted). Note tht in the NAA treted shoots, virtully no growth hs occurred. In the control shoots, extensive regrowth hs occurred; clerly, ppliction of NAA slows regrowth of the shoots. Figure 8 illustrtes the type of regrowth present on the secondry shoot xis tht were present t the time of pruning. Note tht the NAA tretment delys shoot development of sutending rnches. Shoot length Figure 9 presents the rnge in verge shoot length on the primry xis pproximtely 3 months fter tretment. Note tht the untreted control hs much higher percentge of shoots tht re longer. Additionlly, the smple size in the NAA treted rnches is gretly reduced (only 2 of the 73 shoots hving noticele growth). Figure 1 presents similr dt with the exception tht this is rt-
ing of length of growth on the secondry shoot xes. A similr trend is oserved with the mount of growth reduced on the NAA treted rnches. Note the multiple ud reks long the primry shoot xis Figure 5A. Control shoots. Note the vigorous regrowth on oth the primry xis nd xillry shoots sutending the pruning cut.
Secondry shoot xis with multiple new shoots occurring ner pruning cut Primry shoot xis Figure 5B. Control shoots. Note the vigorous regrowth on oth the primry xis nd xillry shoots sutending the pruning cut.
Primry shoot xis Figure 6A. NAA-treted rnches. Note the inhiition of growth especilly ner the pruning cuts especilly on the primry shoot xis. The growth on the secondry shoots is lso inhiited nd occurs minly t the shoot tips.
Note the lck of new growth ner the pruning cut Note tht the growth on the secondry growth xis is occurring primrily t the shoot tips Figure 6B. NAA-treted rnches. Note the inhiition of growth especilly ner the pruning cuts especilly on the primry shoot xis. The growth on the secondry shoots is lso inhiited nd occurs minly t the shoot tips.
Shoot numer Figure 11 depicts the pproximte numer of shoots on the primry xis t the time of evlution. Note tht there re no new shoots on the primry xis in the NAA treted shoots. Figure 12 shows similr trend for growth on the secondry shoots sutending the treted shoot; the numer of shoots is gretly reduced in the NAA tretment. Zone of growth inhiition Figure 13 presents the pproximte zone of vegettive inhiition due to NAA tretment. NAA tretment of the pruned rnch resulted in zone of inhiition for vegettive growth elow the treted re. In only 1% of the shoots did growth occur within 6 inches of the pruning cut. In contrst, in the control shoots, no inhiition occurred nd growth ws oserved close to the pruning cut. Our results with NAA demonstrted tht this mteril cn e used for the purpose of controlling regrowth following shoot tip pruning. We were le to show tht y pinting the tip of the clipped stem, we could shift the growth of the rnch to lower rnches s well s to the secondry shoot xes. 1 9 8 7 % of totl shoots oserved 6 5 4 3 2 1 Control (n=69) NAA (n=73) NONE Only t tips of xillry shoots Vigorous shoot growth with xillry uds growing Just strting; wek Multiple ud rek on primry xis Growth on primry nd secondry xis Figure 7. Ctegoriztion of shoot growth on the primry shoot xis pproximtely 3 months following shoot tip pruning.
1 9 8 7 % of totl shoots oserved 6 5 4 3 2 1 Control (n=69) NAA (n=73) NONE Only t tips of xillry shoots Vigorous shoot growth with xillry uds growing Just strting; wek Multiple ud rek on primry xis Growth on primry nd secondry xis Figure 8. Ctegoriztion of shoot growth on the secondry shoot xis pproximtely 3 months following shoot tip pruning. 1 9 8 7 % of totl shoots oserved 6 5 4 > 6 cm 3 to 6 cm 15 to 3 cm > to 15 cm 3 2 1 Control (n=41) NAA (n=2) Figure 9. Averge shoot length for the primry shoot xis pproximtely 3 months following shoot tip pruning.
1 9 8 7 6 % of totl shoots 5 oserved 4 > 6 cm 3 to 6 cm 15 to 3 cm > to 15 cm 3 2 1 Control (n=64) NAA (n=5) Figure 1. Averge shoot length for the secondry shoot xis pproximtely Figure 1. 3 Averge months shoot following length shoot for the tip pruning. secondry shoot xis pproximtely 3 months following shoot tip pruning. 1 9 8 7 % of totl shoots oserved 6 5 4 >15 1 to 15 5 to 1 1 to 5 3 2 1 Control (n=69) NAA (n=73) Figure 11. The pproximte numer of shoots on the primry shoot xis pproximtely 3 months following shoot tip pruning. 1 9 8 7 6 % of totl shoots 5 oserved 4 >15 1 to 15 5 to 1 1 to 5 3 2 1 Control (n=69) NAA (n=73) Figure 12. The pproximte numer of shoots on the secondry shoot xis pproximtely 3 months following shoot tip pruning.
1 9 8 7 % of totl shoots os erved 6 5 4 > 6 cm 3 to 6 cm 15 to 3 cm > to 15 cm 3 2 1 NAA (n=65) Figure 13. The pproximte zone of vegettive inhiition due to the NAA tretment pproximtely 3 months following shoot tip pruning. Concluding Remrks In this study we hve demonstrted 3 potentil uses of NAA (Tre- Hold A-112) for controlling the vegettive vigor of Hss vocdo following tree stumping, tree topping nd shoot tip pruning. This reserch led to the vocdo industry nd the registrnt (Amvc Chemicl Corportion) to request further work under the IR-4 progrm. This work hs een completed, nd registrtion hs een requested so tht ll Cliforni growers cn use NAA for these purposes. Once TreHold A-112 is registered nd ville for use, it will e of utmost importnce tht the lel e closely followed. Non-lel usge could result in unexpected nd undesirle effects on tree growth, flowering, nd fruit set. This product, s is true for ll plnt growth regultors, will e est utilized y growers who closely monitor their orchrds nd understnd how tree performnce is influenced y differing mngement strtegies. References Boswell, S.B., B.O. Bergh nd R.H. Whitsell. 1976. Control of sprouts on topworked vocdo stumps with NAA formultions. HortScience. 11(2):113-114.