UNIVERSITY OF CALIFORNIA COOPERATIVE EXTENSION GLENN COUNTY P.O. Box 697 (821 E. South St.), Orland, CA (530) FAX (530)

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1 UNIVERSITY OF CALIFORNIA COOPERATIVE EXTENSION GLENN COUNTY P.O. Bx 697 (821 E. Suth St.), Orland, CA (530) FAX (530) March 27, 2008 Vl. IX, N. 3 In This Issue New Walnut Rtstcks and Pest Interactins Walnut Blight Cntrl Spring Fertilizatin fr Walnuts Managing Pistillate Flwer Abrtin in Walnut with ReTain Guidelines fr Care f Yung Walnuts Newsletters Available Electrnically Bill Krueger Farm Advisr In accrdance with applicable State and Federal laws and University plicy, the University f Califrnia des nt discriminate in any f its plicies, prcedures, r practices n the basis f race, religin, clr, natinal rigin, sex, marital status, sexual rientatin, veteran status, age, medical cnditin, r handicap. Inquiries regarding this plicy may be addressed t the Affirmative Actin Directr, University f Califrnia, Agriculture and Natural Resurces, 300 Lakeside Drive, 6th Flr, Oakland, CA (510) T simplify infrmatin, trade names f prducts have been used. N endrsement f named prducts is intended, nr is criticism implied f similar prducts which are nt mentined. Sacrament Valley Walnut Newsletter This is the first issue f a new walnut newsletter which is written and cmpiled by UC Sacrament Valley Walnut Farm Advisrs. It will be published peridically with the gal f prviding timely infrmatin t area walnut grwers. New Walnut Rtstcks and Pest Interactins Janine Hasey 1, Gale McGranahan 2, Michael McKenry 3, Greg Brwne 4, Dan Kluepfel 4 The standard walnut rtstcks are seedling Paradx and seedling black. Where tree death frm walnut blackline disease is a cncern, seedling English have been used. Paradx, which is a hybrid seedling between a black walnut species (usually nrthern Califrnia black) and English walnut, has been the rtstck f chice because f its vigr and greater tlerance f wet sil cnditins. Hwever, seedling Paradx is highly susceptible t crwn gall infectin caused by Agrbacterium tumefaciens. T determine the diversity between different surces f Paradx, UC and the Califrnia walnut nursery industry initiated a Paradx Diversity Study in Seedlings were planted in lng-term field trials and evaluated fr vigr, resistance t nematdes, crwn gall, and Phytphthra. Superir individuals were selected, micrprpagated (clned) and retested. Frm thse studies, tw clnal Paradx rtstcks, VX211 and RX1 were released in 2007 and will be available in The first Paradx clne t be micrprpagated was Vlach which came frm a vigrus Paradx tree in Stanislaus Cunty. Vlach has been available since 1999 and was als tested in these studies. Clnal Paradx rtstcks prvide ptins in selecting a rtstck t manage prblems r issues in a particular rchard. Althugh experiments are nging and data is tentative, the table belw is a guide fr selecting the mst apprpriate clnal Paradx rtstck fr each situatin. Cperative Extensin Wrk in Agriculture and Hme Ecnmics, U.S. Department f Agriculture, University f Califrnia and Cunty f Glenn Cperating

2 Respnses t Selected Nematde and Disease Pathgens by Clnal Paradx Walnut Rtstcks Available Based n UC and USDA-ARS Screening Tests t Date 1 Categry Vlach VX211 RX1 Inherent Rtstck Vigr Vigrus 2 Highly Mderately vigrus vigrus Phytphthra citricla LR MR MR P. cinnammi Agrbacterium tumefaciens (gall LR MR LR LR MR LR ccurrence/develpment) LR = lw resistance MR = mderate resistance Rt Knt Nematde S-? S-ST Rt Lesin Nematde HS-IT HS-ST (Pratylenchus vulnus) Nematde s ability t reprduce HS = highly susceptible S = susceptible Tree respnse t nematde ST = sme tree tlerance t nematde presence IT = tree intlerance t nematde presence 1 Data is tentative and trials are nging 2 Vlach ranked first in trunk circumference in 2006 in Paradx Diversity Study (PDS) acrss fur sites and ranked 4 th in prductin in 2007 in the San Jaquin Cunty PDS trial. In additin t clnal Paradx, wn-rted English walnut trees (English variety n its wn rts with n graft unin) have been available since 1999 and usually planted where walnut blackline is a severe prblem. Own-rted English trees have replaced seedling English in the nursery trade. Based n a statewide survey f grwer rchards and experimental plts cnducted in , wn-rted English walnut trees averaged less than 1 percent crwn gall infectin cmpared t seedling Paradx with 21 percent crwn gall. Own-rted English walnut trees shuld nly be cnsidered fr deep, well-drained lamy sils with n lesin nematdes. Fr mre infrmatin n walnuts in the nursery trade, hw they are prpagated and understanding the terminlgy, a handut is available at yur lcal UC Cperative Extensin ffice r n the web at r A list f nurseries licensed t sell clnal Paradx is als listed at 1 UC Farm Advisr Sutter/Yuba Cunties, 2 Pmlgist, UC Davis, 3 UC Extensin Nematlgist, Kearney Ag Center, 4 USDA-ARS Plant Pathlgists, UC Davis, respectively

3 Walnut Blight Cntrl Richard Buchner 1, Jim Adaskaveg 2 and Steve Lindw 3 Depending upn weather cnditins, pathgen ppulatin size and walnut variety, walnut blight caused by the bacterium Xanthmnas campestris can cause significant crp lss. During the 2007 seasn in Tehama Cunty, untreated trees under simulated plus natural rainfall had 32% blighted walnuts in the mid-canpy and almst 70% damage n walnuts reachable frm the grund. Research funded by the Califrnia Walnut Bard has resulted in a gd understanding f the disease and hw t prtect walnuts frm infectin. Walnut blight bacteria ver-winter n drmant buds primarily under the uter bud scales r cataphylls. Bud ppulatin evaluatins have shwn that the inner buds where the immature walnut flwers are lcated are relatively free f bacteria. When buds break in the spring, cataphylls pen and yung shts extend past them. During favrable weather cnditins, blight bacteria are splashed nt and can infect any green tissue. Early infectins usually ccur at the flwer end f develping walnuts. Once inside the walnut, bacteria grw tward the center f the nut, destrying the develping kernel resulting in nut abrtin. S-called end blight ccurs early in the seasn cmpared t later infectins that are randmly distributed ver the hull and are referred t as side blight. Side blight may r may nt result in kernel damage depending upn when infectin ccurs. Successful blight cntrl relies upn decreasing bacterial ppulatins and preventing new infectins. We have tested almst all f the available spray materials and mix cmbinatins and fund that cpper mixed with Manex is currently the mst effective spray chice. Tests have repeatedly shwn that any gd-quality cpper prduct mixed at the label rate with Manex will prvide gd prtectin. Pest Cntrl Advisrs (PCAs) can help select which cpper prduct t use. The sectin 18 registratin fr Manex has been apprved fr the 2008 seasn fr listed cunties and a PCA recmmendatin is required fr Manex use. We cntinue t seek full registratin f Manex and ther ethylene bisdithicarbamates (EBDCs) such as Manzate fr the cming seasns. Additinally, we are evaluating new bacteriacides that culd ptentially be used in future rtatin prgrams with cpper/ebdc bactericides t avid the ver-use f any ne single material. Once the material and rate have been selected, spray timing and cverage are the remaining tw elements in a successful walnut blight cntrl prgram. Timing the first spray when 40% f the buds are at the prayer stage has the greatest effect n reducing bacteria ppulatins and prtecting walnuts. A gd-quality adjuvant will wet cataphylls and encurage the cpper/manex mix t penetrate between bud scales and kill ver-wintering bacteria. Fllwing the first applicatin, decisins are made based upn weather cnditins and damage histry. Warm, wet (rainfall r leaf wetness frm dew) weather favrs disease epidemics and severe damage cmpared t relatively lw infectin risk if weather is dry. Under severe walnut blight pressure, a secnd applicatin 7-10 days fllwing the first spray will prtect any remaining shts that have emerged fllwing the first applicatin. Additinal spray applicatins are based upn the weather and the risk f infectin. Risk increases with warm wet weather. A disease predictin mdel, XanthCast, develped by Jim Adaskaveg at UC Riverside is available in sme areas. XanthCast can be fund at If XanthCast is nt an ptin, watch weather frecasts and treat befre rainfall. Blight treatments wrk by prtecting walnuts frm infectin and will nt cntrl the disease if applied after infectin has already ccurred. Cpper/Manex treatments result in a prtective barrier n the tissue surface. If cverage is pr r bacteria are expsed t a sub-lethal dse, sprays will nt wrk well. In additin, spray failures increase the risk f develping cpper/manex resistant bacteria. 1 Farm Advisr, Tehama Cunty, 2 Plant Pathlgy Prfessr, UC Riverside, 3 Plant Pathlgy Prfessr, UC Berkeley

4 Additinal walnut blight infrmatin is available at Examples f walnut shts at r clse t prayer stage. Blight incidence (percent infected walnuts) ver time n untreated Chandler walnuts in Tehama Cunty under envirnmental cnditins with natural and simulated rainfall. Disease symptms first ccurred after April 27 and increase until May 21. The graph represents a disease prgress curve ver the spring seasn and demnstrates the disease ptential under very favrable cnditins fr walnut blight % 90.0% 80.0% Walnut Blight Disease Prgress Curve, Tehama Cunty, % 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% 4/27 5/3 5/7 5/10 5/14 5/17 5/21 5/29 % BLIGHTED NUTS

5 Spring Fertilizatin fr Walnuts Carlyn DeBuse, UC Farm Advisr, Slan/Yl Cunties Many factrs affect tree grwth and prductivity. One f the mre imprtant factrs is tree nutrient status determined by nutrients stred in tree tissue r available in the sil. A gd spring fertilizatin prgram prmtes healthy vigrus trees and a gd crpping. The tw mst imprtant spring nutrients are the macrnutrient nitrgen (N) and the micrnutrient zinc (Zn). With the rising cst f fertilizer, determining a nitrgen budget fr yur rchard and the crrect timing f applicatin may save yu mney while benefiting yur rchard and yield. Nitrgen Symptms f deficiency- Nitrgen deficiency symptms are rarely seen because grwers apply large amunts f nitrgen annually. Symptms include pale leaves, nnvigrus sht grwth, and early fall leaf yellwing and drp. Surces f nitrgen- The mst cmmn surce f nitrgen are the synthetic fertilizers; urea (45%), ureaammnium nitrate (32%N), ammnium nitrate (34% N), ammnium sulfate (21%N), calcium-ammnium nitrate (17%N), and calcium nitrate (15%N). Organic surces might include manures, cver crps and/r rganic fertilizers. Nitrgen can be fund in frms ther than the applied surces and these surces shuld be cnsidered when budgeting N applicatin. The first is the amunt N stred in the tree itself. Tree nitrgen is estimated by taking leaf samples in July using analysis by an analytical lab. Leaf values belw 2.3% are cnsidered deficient requiring additinal N. Leaf values abve 3.0 % suggest additinal N will give little tree grwth imprvement. Secndly, irrigatin water can cntain a significant amunt f N. One ppm nitrate frm a water analysis equals 2.72 lbs. f N per acre-ft f water. Thirdly, rganic matter in the frm f manures, cmpst, and animal meals will add N within the year applied and in future years at a slwer release rate. First year N release estimates range frm 10-65% depending n the type f rganic matter used. If the rganic matter is applied annually ver many years then yu can estimate that the full N cntent f the material is released yearly. Cver crps add nitrgen hwever the amunt f N released is dependent n the bimass and the final N cntent f the cver crp. Leguminus cver crps that are incrprated int the sil have a 20% higher N recvery than if mwed. Nitrgen efficiency and lsses- Nt all f the applied nitrgen ends up in the rchard. Nitrgen fertilizers, rganic and synthetic, are vulnerable t leaching, vlatilizatin, and denitrificatin. Lsses vary with the type f fertilizer, methd f irrigatin, and sil type. The highest recvery is in clay lam sil applied by fertigatin thrugh micrsprinklers r drip. The lwest recvery ccurs in sandy lam sil with bradcast applicatin, n incrpratin and fld irrigatin. Budgeting - The best way t nitrgen budget is t fllw the guidelines in the publicatin Guide t Efficient Nitrgen Fertilizer Use in Walnut Orchards, by K. Andersn, J. Grant, S. Weinbaum, and S. Pettygrve ( ANR #21623). Their budgeting methds take in t accunt the amunt f N fund in irrigatin water, rganic surces, and cver crps. Estimated available N tgether with N remved by the crp is used t calculate rchard nitrgen needs.

6 Timing- Springtime is when N is taken up quickly and used readily as new grwth ccurs. Applying half t twthirds f the annual N right befre r during the first flush f grwth is recmmended. The remaining N shuld be applied by the end f August. Nitrgen applied in autumn and winter is discuraged because trees are nt able t uptake nitrgen efficiently and mst f the N is lst t leaching. The mst efficient way t apply N is in small amunts thrughut the grwing seasn. Fertigatin is a very efficient technique t accmplish that gal. This practice has been shwn t be very beneficial t the health f the tree with reduced N lsses. Zinc Symptms f deficiency- Zinc deficiency, depending upn severity, can delay spring bud grwth and result in small disclred terminal leaves with intervenal chlrsis (little leaf). Mild deficiencies may nt shw leaf damage but may affect the size and quality f the nuts. Severe deficiencies can cause terminal dieback and limb death. Surces f zinc- Many zinc frmulatins are available fr fliar applicatin. Studies have shwn that the tw frmulatins mst readily absrbed and used by the tree are zinc sulfate (ZnSO 4 36%Zn) and rganic chelated zinc (Zn-EDTA 15% Zn). Timing- The best timing is spring applicatins. The zinc shuld be applied just as the yung shts and leaves are turning frm pink tinged t full green. At this time, the ability t absrb Zn is highest and the leaf has the maximum surface area available befre it begins t harden and change t the mature leaf. Recmmendatins- Fliar applicatins f ZnSO 4, 36 % Zn, at 1-2 lbs. per 100 gallns f water buffered t a ph f 5.0, r zinc chelate ( Zn- EDTA) at 2 punds per 100 gallns f water with an additin f a surfactant have crrected zinc deficiencies. Severe deficiencies- If zinc deficiency is severe, a sil applicatin f ZnSO 4 either by trenching r sil injectin shuld be cnsidered. Anther ptin is t bradcast Zn chelate befre an irrigatin. Annual nitrgen replacement and zinc fertilizatin, where deficiencies ccur, shuld be an annual spring fertilizatin prgram t keep walnuts healthy and prfitable. Check ut the web site at UC Davis fr additinal infrmatin Managing Pistillate Flwer Abrtin (PFA) in Walnut with the Use f ReTain Rbert H. Beede 1, Je Grant 2, Kathy Kelley Andersn 3, Janine Hasey 4 What can we nw tell grwers abut the use f ReTain t manage pistillate flwer abrtin (PFA)? First, we knw that PFA is the result f t much pllen landing n the pistillate, r female, walnut flwers. We als knw that excess pllen triggers ethylene prductin, which causes flwer abrtin r PFA. ReTain is a plant grwth regulatr that blcks ethylene prductin, thus preventing the ccurrence f PFA n flwers treated befre they are expsed t excessive pllen. Statewide research by farm advisrs shws that the ecnmic value f ReTain applicatin is entirely dependent upn the level f PFA within the rchard and the number f flwers prtected frm PFA. Receiving benefit frm ReTain is purely a numbers game! Every researcher having studied walnut pllinatin and PFA will tell yu that it varies within the rchard and amng years. They will als tell yu that PFA is highly dependent upn the verlap f pllen shedding n the pistillate blm. Pllen surces include Serr, pllinizers in the rchard and frm adjacent rchards. An excellent example is 2007, in which the Serr catkins emerged well ahead f the female peak blm, thus reducing the amunt f pllen and making last year lw in PFA and generally high in Serr yield regardless f whether yu used ReTain r nt.

7 Previus research by Dr. Plit, Plant Sciences Department, UC Davis, and UC farm advisrs demnstrated the significant yield benefits f reducing pllen within Serr rchards by remving pllenizers and/r shaking catkins when they begin t elngate. Hwever, the limitatins f this apprach include tree remval, which may nt be fully cmpensated fr by expansin f the remaining trees, access t a shaker at the prper time, the pssibility f needing multiple shakes t adequately reduce the pllen density, the inability t access wet rchard flrs, and the inability t reduce pllen frm adjacent rchards. In 2007, a test was perfrmed in Kings Cunty t cmpare catkin remval against ReTain applicatin. The results suggest that ReTain imprves yield as well as catkin shaking fur times, which virtually eliminated all but a few catkins per tree. Cmbining catkin shaking with ReTain treatment did nt prvide any greater yield imprvement. A ReTain applicatin alne prvided a 20 pund per tree r 1000 lb/ac increase in dry yield ver the untreated and unshaken cntrls. Tests were als cnducted in Kings Cunty t determine the effect n efficacy f adding cpper t ReTain. Cmbining cpper and ReTain reduced fruit set by 20% cmpared t ReTain alne. If cpper is applied prir t a ReTain treatment, ne shuld wait at least tw and preferably three days befre applying ReTain. Cpper appeared t have n affect n ReTain perfrmance when ReTain was applied ne r three days befre the cpper treatment. The use f ReTain r any ther methd t reduce the effects f excessive pllen is nt a cure-all fr pr rchard perfrmance caused by pr water management, pest prblems, lw fertility, r shaded canpies. These factrs all reduce flwer number, which is the critical cmpnent fr high yields. D we nw knw everything abut ReTain and reducing PFA? By n means! Several walnut grwers reprt little benefit frm ReTain use. Additinal research wrk is needed t understand the varius factrs affecting prduct perfrmance and t further refine applicatin guidelines. In the meantime, ReTain seems t have rejuvenated the Serr variety in the suthern walnut districts t the pint that grwers are talking abut planting new rchards, especially when the grades sheets shw up t 59% edible yield! UC Guidelines Fr ReTain Applicatin 1) ReTain prevents walnut flwers frm falling ff due t excessive pllen. It is NOT a general enhancer f fruit set. It may nt wrk in sme rchards in sme years. 2) Fr maximum effect, apply 50 grams active ingredient per acre (ne bag f prduct) in 100 gallns f spray slutin. 3) Applicatin shuld be timed at an estimated 30% blm, r when the maximum number f flwers are present in the early stage f receptivity. 4) Cverage is critical! ReTain des NOT translcate. It must cntact the flwer t be effective. 5) Grund applicatins shuld be made with speed sprayers calibrated having 66% f the spray vlume in the upper half f the manifld. Travel n faster than 2 mph! Research shws 100 gallns f spray slutin per acre is sufficient t prvide gd cverage, prviding the prper applicatin speed is bserved. 6) Spray cncentratins less than 66 ppm (ne-half bag in 100 gallns f water) have been shwn less effective, especially under high PFA cnditins. 7) Aerial applicatin shuld nly be used when grund treatment is nt pssible. Fr ptimal cverage, apply ne-half bag f ReTain in 20 gal/ac, and fly in the directin f the tree rws. Then repeat the same applicatin rate, but fly perpendicular t the tree rws t minimize the shadw effect. 8) Applicatins made under cnditins f higher humidity, such as prir t dawn, may enhance prduct perfrmance due t extended absrptin time.

8 9) D nt cmbine ReTain with cpper-based fungicides, due t their adverse effect n ReTain perfrmance. If pssible, apply ReTain at least ne day prir t cpper treatment. Delay ReTain treatments fr three days fllwing cpper applicatin. 10) Read and fllw label instructins. UC Farm Advisrs 1 Kings/Tulare Cunties, 2 San Jaquin Cunty, 3 Stanislaus Cunty, 4 Sutter/Yuba Cunties, respectively Guidelines fr Care f Yung Walnuts Frm Planting Thrugh the First Seasn Bill Krueger, UCCE Glenn Cunty 1) Make the planting hle just deep and big enugh t accmmdate the rt system using an auger r shvel and plant the tree n deeper than it was in the nursery. Trees can be planted n a mund r a berm t insure gd water drainage away frm the crwn. This can be particularly useful n heavier and prly drained sils. 2) D nt allw the trees t dry ut while they are waiting t be planted. Stre them in the shade and cver with a mist blanket. 3) Prune brken rts r rts that wn t fit in the hle withut bending 4) If a crwn gall preventative spray is used with K-84 bacteria, it s success will depend n the resistance r susceptibility f the strains f crwn gall bacteria present in the rchard. 5) Spread rts and wrk sil arund rts, rient strngest rts in the prevailing wind directin and, t the extent pssible, avid leaving the bud crk (the flat side ppsite where the scin bud emerged) with a suthwest expsure. 6) D nt put fertilizer r rganic material int the hle. 7) If the sil is mist and friable it shuld nt be necessary t water the trees at planting time. Wrk the sil arund the rts t insure gd sil t rt cntact. If the sil is dry, water with ne at tw gallns t establish gd rt t sil cntact and eliminate air pckets. 8) Head the tree back t 3 t 5 buds abve the graft unin (usually 15 t 24 inches abve the grund) t insure vigrus grwth. 9) Paint trees with a 1:1 mixture f interir white latex paint r similar tree whitener that will nt peel r crumble t prevent sunburn. Avid paints which cntain mineral il r refined petrleum which may injure the tree. Make sure that the base f the trunk at the sil level is prtected. 10) Check trees after settling and pull up if necessary t make sure that they are nt t deep. 11) Stake trees with a stake that is 8 ft ut f the grund fr cnventinal plantings and 8-10 inches away frm the tree n the prevailing wind side s that the wind blws the tree away frm the stake. 12) Delay irrigatin until the nset f rapid sht grwth. Mnitr sil misture in the rt zne with a sil tube, auger r shvel and irrigate t the depth f rting when the sil begins t dry. Yung walnuts d best with light frequent irrigatins. Intervals will vary depending n envirnmental cnditins, sil type, and irrigatin system. Yung walnut trees stressed fr water stp grwing and will take several weeks t resume grwth nce water is reapplied. 13) Nitrgen is usually the nly nutrient that may be required the first year. Apply sparingly frm late spring t mid summer nce there is sufficient grwth. Avid applying near the trunk. Discntinue applicatins by end f August t reduce late seasn vigrus grwth which culd be susceptible t freeze injury. 14) The bjective f the first year is t grw ne strng sht t serve as the trunk. After 10 t 12 inches

9 f grwth, chse ne sht t be the trunk and start tying it lsely up the stake. Keep the side shts pinched back t encurage grwth f the main sht and remve suckers. D this frequently thrughut the summer. After the sht reaches a height f 9 feet r mre, if necessary, the sht can be pinched back, remving nly the grwing pint, t prevent it frm bending r breaking. 15) Slw grwth f vigrus trees t reduce the risk f freeze injury by reducing watering in September until the terminal bud sets n the main sht. Then, nrmal watering can usually be resumed withut stimulating new grwth. Newsletters Available Electrnically Yu can receive newletters frm Glenn Cunty Cperative Extensin electrnically. If yu sign up fr this service, yu will be ntified via when new editins are published. The will cntain a link which will take yu t ur website where the newsletter can be fund. The advantages f receiving yur newsletters this way include immediate delivery as yu dn't have t wait fr them t be delivered by mail, newsletters ften cntain reference links which will take yu directly t the referenced site and clr pictures can be printed ut n yur wn printer in clr rather appearing in black and white as they will if yu receive them by mail. Additinally, receiving them electrnically will save us the cst f printing and mailing them. If yu are interested, check ut ur website at Yu may sign up fr the cmmdities yu are interested in there r call ur ffice at and we can d it fr yu. Glenn Cunty Cperative Extensin P. O. Bx 697 Orland, CA Nnprfit Organizatin U.S. Pstage PAID Orland, CA Permit N. 63