OF CITRUS METHODS FOR CONTROLLING MATURITY (ACIDITY. W. C. Wilson. Florida Department of Citrus. 700 Experiment Station Road. Lake Alfred, FL 33850

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1 METHODS FOR OTROLLIG MATRITY (AIDITY OF ITRS W Wilson Florida Department of itrus 7 Experiment Station Road Lake Alfred, FL 3385

2 2 METHODS FOR OTROLLIG MATRITY (AIDITY) OF ITRS Table of ontents Introduction Arsanilic Acid (AA) as a Replacement for LA for Grapefruit Other itrus Acidity Adjustment hemicals IO Triacontanol Observations and se References itrus Ten Brix Plus

3 3 ITRODTIO lead arsenate (LA) has been the only plant growth regulator (PGR) chemical legally available for increasing Ratio of citrus fruits {red and white grapefruit only) Its history and use are summarized in the attached publication by Wilson (3) LA was a "grandther clause" chemical which was the property of no particular commercial company In addition, no toxicology data is available for LA Therefore, the Federal Environmental Protection Agency (EPA) did not renew registration of LA The cancellation does not affect stocks of the PGR manuctured before the cancellation date, hence, it is legal for growers to use up their existing stocks For a number of years, the Florida Department of itrus (FDO) has had a research project aimed at replacing LA Recently, a new natural product sold as ;trus Tentm (or Br;x Plustm) (I) has been available to Florida citrus growers to increase Ratio of most oranges and specialty fruits Arsanilic Acid (AA) as a Replacement for LA for Grapefruit The attached paper by Wilson (3) summarizes research studies with AA It is an effective LA substitute for grapefruit acidity reduction Application rates and timing are very similar to LA Additional (unpublished) data for the season indicate that AA is not as easily washed off by rains immediately following spraying as originally believed Also Red grapefruit respond to increased concentrations similarly to that observed for White

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5 5 Observations and se S;nce these or;g;nal tests w;th IO add;t;onal exper;ments were conducted during the ll of 1987 These are summarized in Table 2 first In the series of tests conducted at the Shinn Grove, north of Lake Alfred, the :1 results produced only a 5 point increase in Ratio when Hamlin oranges were sprayed 4 times with a FM Speed Sprayer However, a hand spray (dilute applicatidn) produced almost a full point Ratio increase Single triacontanol TRI) sprays also produced Ratio increases TRI was furnished by Michigan State niversity Results of experiments conducted at LaBelle showed that 4 applications of IO applied by fixedwing aircraft increases of more than 3 points or hands pray or both produced Ratio The single sprays of TRI also substantially increased Ratio particularly the higher level (l33 ppb) which increased Ratio by 456 points 1 applied to 'Marsh' grapefruit produced only a slight (if any) increase in Ratio In its present form, IO does not appear to be effective for use on grapefruit TRI has not been tested on grapefruit at this time Although the actual mechanism of action of these chemicals is unknown I reduced % acid significantly Tables 1,3) and can significantly increase Brix (Table 3), but did not do so in all tests (Table 1) TRI appears to affect these properties in a similar manner Table 3), but experiments with it have, so r, been limited Most of the effect of increasing Ratio by both chemicals is, however, their ability to reduce fruit acidity Except for grapefruit, the use of itrus Ten on most orange and tangelos or tangerine hybrids will probably result in a Ratio increase of 1 to 2 points (Although the FOO has not tested IO on this latter group of cultivars number of growers have reported excellent results from its use a However, IO

6 6 is not an inexpensive chemical to use, particularly as it requires 4 applications A copy of "General Instructions" prepared by BioOrganics, Inc for use of itrus Ten Brix Plus is attached (Table 4) In addition the company now recommends that spray tank ph be adjusted to between 6 and 7 for maximum chemical effectiveness Our own experience measuring spray water ph has shown most to be from ph 81, although this may vary greatly with location Aircraft application is as effective as a hand spray References 1 Knapp, J L, D P H Tucker, J W Holing, and V V Vandriver, Jr 1987 Florida itrus Spray Guide Florida ooperative Extension Service (Revised Annually) 2 R;es, S, V Wert and J B;ernbaum 1982 Factors altering the efficacy of tr1acontanol applications to plants Proceedings of the Plant Growth Regulator Society of America 9: 8 3 Wilson, W 1987 Results of experiments using arsanilic acid to reduce acidity of grapefruit in Florida Proceedings of the Plant Growth Regulator Society of America 14: 4952

7 TABLE 1 SMMARY OF BIOAGRO RESLTS: VALEIA ORAGES Fruit tested 4/23/87 Ratio 7 ontrol Very High (1 ml/l gal) (2 ml/l gal) (4 ml/l gal) Brix Acid % o 85 O O 97 O 91 O Three sprays applied, Orangeo, Ft Pierce (Block B2) April 6,1987 (1 12 am) April 8,1987 (1 12 am) April 9,1987 (1 12 am) Harvest April 2,1987 Fruit held at 4F until run on ADril 23

8 a GI II) S " < GI \ S o r e r S " GI II) oo S (!J or oro S or 't GI Il) S II) \ GI t o " II) r s GI 2: 't II) " GI r r II) GI QJ r o I I c V) og +oj IG Q: " or QI X, f, r c( c r +» I J, X) \ 4 Q) fo Q >, fo ' o V) s fg > +» r " fg +» c QI e +» IQ QI s I O\DO\ \D \, in ") ḠJ S o) Ia r Ia ) S GJ Ia S a V') ' GJ GJ a V') «««JJJJJJ pf +t \ ( ) +t o a V) +t +t +t +1 +t +1 \OMO\ r to ') ) ) ) ) r ) \ +' QI a >, to S o In a c to X ') \ 1 V') QI QI IG IG S S o cn cn ' ' IG IG \ \ +I +I a a D D tv) \D tv),, )\u)4 u)u) MOin\O, < < X :l: IGIG < 8:( X,:I:, I I +'+' I I I " or I 11 r r 'r or ' ' QJ ' p "" rca: " ) c >, or IG ' I " II) QJ " )(, IG :c J J ;J J J \ \D M ll Q Q Q Q Q Q (V') \ (V') c c :I: :I: c :I: c c +oj +oj :1:' :I: OO+J1a1a OJ OJ +oj +oj >, >, IG IG ' ' o o VI VI " " IG IG :I: :I: \ \ +> +> u u L an q an \ q \ \ Ln GI GI +» +» roo or og roo orog, Ln +oj Do GJ V) c t: c or or OLL () () () or or " " to to S S o /) /) og og c to to o L& o L& t: S O Y""4 u u I/) c I/) OJ +J ca 'r > +J " ca ca s ca Q It ' OJ OJ V "1/) > V QO I/) ca ca O>,+J or ca Q c +J ' OJ OV) ca QO VI/) OJ OJOc"o I/) ) +J Q OJ Q ca orca+j S<:J:a: ' ca ' s >, +J It OJ OJ OJ I V >,s ca+jcavc It or ' ca ca ' Q +J 'V)OV) V) OJ " I r OJ u ' r OJ OJ I Q1t >< OV) >, ca or J O+J cca S"O It +J r OJ s >Oc OOJ I I/) 'r I/) I/) " ca s s '" OJ OJ ca OJ It >+J"O+J ocai/)oi/) s ca OJ or ca +J>+J It V) ' ca 1/) cav""' lc'r ' a: V)caOOJQ ) V) ' Q a OJcaO) It ca, s It 'r " +J'r I/) "Oor ca I O Ia S ca s )J It s < \ OJ 'r QOJ I ca I OJ +J OJ s " s ca OJ O)OJ+J >, J )( +J " OJ +J OJ OJ c 'r +J or I/) " or +J ' OJ " OJ s Q OJ > It Q+JLn >,or _ I Ica < I/) "O OJ '=:) Q OJ ca +J It I/) OJ I/)OJO +J ca > oca J 'r"") +J OJ"O'S IV) It'ca I/) I/) ca It ca 'ca"o ) 'O) +J c or or:j: 'r ca V OJ Q ) or > \ X '"O ca 'OJ I+JO vcaooj ' ' OJI/) V or>, " S +J or ca OJ OJ c '+J'O V) 'QI/)VV +J I/) OJ I 'r I > OJ+J s ' s <It ca ca OJ J I o 1 :I:

9 9 Table 3 Effect of Sprays ontaining ;trus Ten (IO) and Tr;contanol ( TRY) on Br;x, % Ac;d, and Ratio of 'Hamlin' Oranges at LaBelle, FLz Treatment IO IO ontrol TRI (O6J r ppb) TRI (13 I ppb) Application Method Fixedwing Aircraft Hand Spray Hand Spray Hand Spray Brlx + SO % Acid + SO Ratio + SO «+ «+ «+ «+ « z Additional information concerning concentration, spray dates etc are shown in Table 2 footnote

10 1 Table 4 Manucturers Instructions for the se of IO ITRS TE BRIX PLS General Instructions Storage: A B Timing: A B Mixing: A B c D Application: A B c itrus Ten is very sensitive to extreme temperatures, store between 45 degrees F and 85 degrees F Do not store in direct sunlight Do not leave in a vehicle without proper cooling Start spraying 6 weeks prior to normal harvest Spray every 3 to 4 days for 4 applications Shake packet well before opening Mix 2 ml with 1 gallons of water per acre per 5 gallons) (One packet se 1/2 to 1 Pt of a onionic Surctant per 1 gallons of spray mix Injection by irrigation (microjets or drip) mix one packet per 2 gallons of water Spray between 6: AM and 11: AM Injection through irrigation between 6: AM and 11: AM (Inject during last of irrigation cycle leaving 1/2 hour for flushing) Material should be used within 3 hours of mixing Harvesting: A Do not harvest earlier than 1 days after last application for maximum benefit