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CONTENTS

PageIntroduction 1Problems with the SoU 1

How to Collect a Soil Sample 1Problems on Roots and Trunks 4

Macadamia Root Rot 41'runk Canker 7Inverted Bottleneck-shaped Trunks 8

Problems on Branches or Entire 1'rees 10Poor Tree Shape 10Dieback or Slow Decline 12Macadamia QUick Decline (MQD) 14

Problems on Leaves and Young Shoots 17How to Collect Leaves for Tissue Analysis 17Iron Chlorosis 20Magnesium (Mg) Deficiency 21Clyphosate (RoundupTM) Injury 22Macadamia Quick Decline (MQD] 14Black Citrus Aphid 23

Problems on Flowers 25Poor Flowering 25Flower Blights 26Black Citrus Aphid 23Broad Mite 28Katydid 30

Problems on Nuts and Kernels 31Premature Nut Drop 31Southern Green Stink Bug 33Koa Seed Worm 36Macadamia Shothole BoreL 38Broad Mite 28Rats and Pigs 40Stick-tights 42Poor Management of Harvest and

Postharvest Handling .43

COMM:ON PROBLEMS OF MACADAMIANUT IN HAWAII

H. C. Bittenbenderand Howard H. llirae

INTRODUCTIONMacadamia nut growers in Hawaii frequent­

ly see striking or odd things in their orchards.What's this? Is this a problem? Is my tree sick?Wlll this lower yield? Even the experiencedgrower might miss the less 0 bvlou s signs ofproblems that will seriously lower an orchard'sproductivity.

This bulletin responds to a spec1fic requestin Macadamia Industry Analysts Number 4,1988. action 1.4: "Publish a pictorIal chartshOWing 99% of the common macadamia prob­lems. despite cause. i.e., pest. disease, nutrientimbalance. improper pesticide and fertilizerapplication." Growers at the 28th Annual Meet­ing of the Hawaii Macadamia Nut Associationwere surveyed on their common macadamiaproblems. both minor and major. that newgrowers should know about. The problemsidentified by growers are the basis for thefollowing discussion of common macadamiaproblems in Hawaii.

Unlike most bulletins that deal withproblems and their causes. this one is organizedby symptoms and their location on the tree.Each problem is described briefly wIth accom­panying photographs. These show outstandingfeatures for l,"ecognizing the problem in theorchard. References for other publications andsolutions (if known) are given.

PROBLEMS WITH THE SOIL

How to Collect a Soil SampleSoil sampling is recommended before

planting an orchard and annually when collect­ing a leaf sample. It is important to collect thesample properly to avoid contaminating it withfertilizer on top of the 5011 or on your tools.FollOwing the fertilizer recommendations froma soil analysIs is the most important way toavoid nutritional problems.

1

SolutionSoil samples shou ld be taken from a zone 2

feet from the trunk out to the edge of the canopyor drip zone. Using a clean shovel that hasn'tbeen used for applying fertilizer. scrape away thesurface leaves and soil until you reach the smalland sometimes stubby macadamia roots (Fig. 1).Collect soil from this depth down another 4 to 6Inches using a clean plastic glove or bag overyour hand (Fig. 2). Put a cup or more of soil into aclean plastic bag (Fig. 3).

If you have just a few acres. samples fromthree or more trees throughout the orchardshould be collected and thoroughly mixed to­gether. The soil sample should weig;h at least apound for 1t to be analyzed for phosphorus,potassium. calcium, magnesium. and pH. If youhave an area that you suspect has nutIitionalproblems. collect two separate samples. onefrom this area and one where tree growth isnormaL

Label the sample bag and complete theinformation forms required by the analyticallaboratory. Check with your extension agent forcompanies that do soil analysis.

Fig. 1. Scrape away weeds. leaves, and topsoil down tomacadamia roots. H. C. Bittenbender photo.

2

Fig. 2. Loosen soU and rocks 4 to 6 lnches below the top of themacadamia root zone. lL C. Bittenbender photo.

Fig. 3. Put soil (not rocks) in a clean plastic bag. H. C.Bittenbender photo.

3

PROBLEMS ON ROOTS AND TRUNKS

Macadamia Root RotThis fungus, Kretzschmaria clavus, attacks

the roots and lower trunk of macadamia nuttrees, eventually killing the tree. Orchards inhigh rainfall areas near forests or on recentlycleared forest land are most susceptible to thisdisease. The disease doesn't spread rapidly orappear to be a major problem, however.

Besides poor growth and few leaves, theobvious symptom is a black fungus with asmooth or slightly knobby appearance on thelower trunks or exposed roots (Fig. 4). Youngshoots (suckers) growing around the trunk arealso a symptom (Fig. 5). If the tree is cut down,look for black lines and gray areas in thetrunk's cross and long secUons (Figs. 6 and 7).

SolutionNo fungiCides are registered nor likely to be

effective. Dead trees and roots should beremoved from the orchard. Don't plant in thesame hole or nearby until the diseased rootshave decomposed.

Remove forest trees completely whenpreparing new orchard sites in forested areas.Don't bury or chip trees in the orchard, as theymay be diseased and infect the orchard. Don'tleave large rocks near the base of a tree whenplanting. As trees grow, cuts and scrapes ontrunks and roots caused by rocks or othermechanical injuries provide entry for thisdisease.

4

Fig. 4. Spore-producing stage on the bark or surface-exposedroots. Photo courtesy oC Wayne NisblJima.

Fig. 5. An infected tree is slowly dying. Note typicalproduction of new sboots around base of tree. H. C.Bittenbender photo.

5

Fig. 6. Trunk of infected tree ~ut lengthwise shows graydiseased area. Howard H. Hiree photo.

Fij;!. 7. Infected roots cut crosswise show the edge of theinfected area as black lines. Photo courtesy ofWen Ko.

6

Trunk CankerThis is an uncommon disease. The fungus

Phytophihora cinnamomi can infect trunks ator near the ground, generally through a wound.The infected part of the trunk appears crackedand callused or flattened and produces a darkgummy sap (Fig. 8). Tree growth is reduced andthe tree may die.

SolutionNo fungicides are registered. Preventive

measures include planting on well-drained sites.not planting too deeply, and not cutting orwounding the trunk near the ground.

Fig. 8. Trunk of Phytophthora.infected trunk showsflattened canker areas with vertical cracking and darkgummy sap on bark. Pboto courtesy of Wayne Nishijirna.

7

Inverted Bottleneck-shaped TrunksThe inverted bottleneck becomes apparent

when the trunk of the scion (lop part of a graftedtree) grows wider than the rootstock below thegraft union (Fig. 9). This is primarily a problemin older orchards where smooth-shell cultivarsare grafted onto rough-shell rootstocks. Newerorchards have smooth-shell rootstocks, so theinverted bottleneck isn't a problem.

Biochemical incompatibility between thetwo species- the rough shell and the smoothshell- is the cause. Symptoms don't developimmediately. and not all trees with rough-shellrootstocks will develop symptoms.

Frequently, affected trees will break at thegraIt union or the yields will decrease over time.

SolutionNever plant trees grafted onto rough-shell

rootstocks. If your trees have this problem now,plant three or four smooth-shell seedlingsaround the tree. GraIt a 1/2-lnch-diameter orlarger seedling onto the smooth-shell section ofthe trunk (above the graft union) with anapproach graft (Fig. 10). Bond 23 producesvigorous seedlings, but any healthy smooth­shell seedlings will do. Alternatively. if the treehas severely declined, remove it and replant.

8

Fig. 9. Trunk shows rough-sbell rootstock overgrown bysmooth..heU scioD. H. C. Bittenbender photo_

Fig. 10. Inarched smooth-shell seedlings lltrengtben tbe tree.Photo courtesy of Lcng Chiao

9

PROBLEMS ON BRANCHES OR ENTIRE TREES

Poor Tree ShapeThis is a serious problem. A narrow angle

between the scaffold (main branch) and leader(trunk), called the crotch angle (Fig. 11), and toomany scaffold branches at the same placeweakened the tree (Fig. 12). These trees snap ofTor suffer severe limb breakage as they mature.partLcularly Ln wLndy areas.

SolutionDUring the first two to four years in the field.

prune trees to a single upright leader. Scaffoldbranches should be pruned to three per whorl,evenly spaced around the trunk (Fig. 13). Bypruning. space branches at intervals of 18 ormore inches up the trunk. Root or trunk suckersshould be removed as they emerge.

Fig. 11. Double trunk will split because branch angle Is toonarrow; one should have been removed. Drilling throuj;!hboth tronks and bolting them together with a 1/2-incn­diameter rod or cable may help. Photo courtesy of MikeNagao.

10

Fig. 12. Young tree before pruning to space branchesproperly. Photo courtesy of Mike Nagao.

Fig. 13. Same tree after pruning to space groups of branchesand reduce number pee group (whorl} to two or three. Photocourte1ly of Mike Nagao.

11

Dieback or Slow DeclineThis is a general term for trees with many

dead branches. Trees drop leaves at branch endsor older leaves drop too soon. so that only a fewleaves are left at the ends of branches (Fig. 14).The condition develops slowly, and there aremany causes for this type of dieback.

1. DiSease Infection in trunk or rootsystem.

2. Prolonged droughts.3. Anaerobic conditions caused by compac­

tion or poor drainage.4. Poor root structure caused by planting

root-bound trees.5. Toxic chemicals· from herbicides or over­

application or uneven application offertJIizers.

6. Nutritional problems.Dleback related to nutritional problems is

common on highly leached soils in high rainfallareas like the Hamakua coast. Acid soils (lessthan pH 5) interfere with nutrient uptake,partIcularly phosphorus. Other soils can bIndphosphorus so roots can't absorb it. Under theseconditions aluminIum levels in the leaves mayreach toxic levels [greater than 200 ppm).

SolutionTry to determine the cause of the problem by

the process of elimination. Proliferation of rootsuckers generally indicates root, collar, or trunkinJUry. Phosphorus defiCiency usually starts onthe main terminals first and works down.General loss of leaves of the entire tree, orconfined to particular branches but notnecessarily the top, is probably not phosphorusdeficiency.

Use soil and tissue analYSiS. and applyfertilizer and lime as recommended. Beforeplanting a new orchard. have the soil analyzed,and fertilize and lime as recommended.

12

Fig. 14. In a tree with dieback. upper bcaocheli may have fewor no leaves. Most new leaves are produced on Dew branchesat the center of the tree. Howard H. H1rae photo.

13

Macadamia Quick Decline (MQD)Leaves quickly turn brown and may stay on

the tree (Fig, 15) or all drop Immediately: deathof the tree is rapid. Currently this problem ismore prevalent in high rainfall areas.

Unknown stress factors are suspected toaffect the tree and increase Its susceptibility toambrosia beetle att.ack. Waterlogged soil, lowsoil pH, nutritional problems, and fungal rootand stem rots are suspected stress factors.Xylaria, a fungus with black pointed fruitingbodies (Fig. 16), and Neetria. a fungus with flatorange fruiting bodies that resemble lantanaflowers (Fig. 17), are commonly seen on thetrunk. .

The role of the ambrosia beetle. Xyleborusaffinis, is thought to hasten tree decline (Fig. 18).It bores matchstick-sized holes in the trunk,leaving a trail of white powdery wood (frass) onthe outside (Fig. 19).

SolutionDon't plant 'Ikaika' (333): it is more suscep­

tible than other cultivars. Dead and dying treesshould be removed from the orchard or bUITled.so that beetles and fungi from infested treesaren't able to reinfest other stressed trees.

Fig. 15. Tree ~firing," or dying 80 quickly that leaves turnbrown and don't drop. is a symptom of MQD. Howard H.Hime photo.

14

Fig. 16. Xylaria. arouscula fungUil is frequently associatedwith MgD. Photo courtesy of Wea Ko.

Fig. 17. Nectria rugulOlSO fung1ls is frequently associated withMQD. Photo courtesy o(Wen Ko.

15

Fig. 18. This adult ambrosia beetle is greatly magnified.Photo courtesy oC Arnold lIara.

Fig. 19. Trunk shows severe attack by ambrosia beetles. Notewhite powdered wood (Crass) on bark; this is produced by thebeetle. Photo courtesy of Ron MaIL

16

PROBLEMS ON LEAVES AND YOUNG SHOOTS

How to Collect Leaves for Tissue AnalysisSemiannual tissue analysis is recommended

to determine the best fertilizer practice for yourorchard and to prevent nulritional problems. Itis important to choose the correct leaves foranalYSiS and to understand the results on thelaboratory analYSiS report or "Elementalanalyses of plant tissue by ADSC, CTAHR" form.Symptoms of common nutrltlonal problems arediscussed later.

SolutionIf you've never taken a leaf or soil sample.

talk with your extension agent or fertilizerrepresentative before begi.nning. If your orchardappears normal, sampling one tree per acre isenough. Collect a leaf sample before treesproduce new leaves. generally dUrinp; Februaryand March or before feliilizing in September orOctober. Pick three to four branches when thebud at the tip of branch is Just opening andbeginning to grow. Don't be fooled by buds withlong, hard red scales called false flushes; theymay not open for months (Fig. 20). Buds at theproper stage will have three small. pale greenleaves 1/4 to 1/2 inch long; they look like a claw(Fig. 21). If you wait too long. the bud will opencompletely and tum green, and the new shootand leaves will be easy to see. Pick one healthyleaf from the second node (whorl) of leaves belowthe bud. Fifteen leaves from four to five trees areneeded for each sample submitted for analysis.Place the leaves in a plastic bag and label the bagwith your name, date of sampling. and samplenumber.

17

Element concentrations adequate for growth ofbearing macadamia trees

ElementNitrogenPhosphorusPotassiumCalciumMagnesiumSulfur

ManganeseIron

CopperZincBoronAluminum

SymbolNPKCaMgS

MnFe

CuZnBAl

ConcentratiOn (%)1.4S-2.000.08-0.110.4S-0.600.65-1.00.08-0.100.24 or a N:S ratio

between 9 and 14

ConcentratiOn (ppm *)50-1500SO or a Fe:P

ratio> 600"415-2040-100less than 200

·ppm means parts per mlllion or one ten-thousandth of 1%in oven -drIed leaves_

"As ppm/%. e.g. 50 ppm/O.08% =625.

18

Fig. 20. In a false flush, the tenninal bud isn't growing. Notehard red, lea1like scales. Photo courtesy of Mike Nagao.

Fig. 21. In a true flush, the tcnninal bud is growing. Note verysmall new leavcs are pale green. This is tfie proper stagc tosample leaves. Photo courtcay of Mike Nagao.

19

Iron ChlorosisThe typical symptom is new leaves that are

pale yellow to white: older leaves are green (Fig.22). ThiS problem Is common in 'a'a soils thathave pH greater than 6.5 or are overfertilizedwith phosphorus. Trees growing in other soilsunder similar conditions can develop thisproblem.

Nursery stock may develop symptoms whenexcessive amounts of high phosphorus fertilizersuch as 10-30-10 are used.

SolutionStop phosphorus fertilization until symp­

toms disappear. Semiannual leaf-tissueanalysiS can be used to monitor leaf phosphorus(P) and iron (Fe) levels. If the Fe:P ratio is lessthan 600, .iron chlorosis is present or willdevelop. For example, in the table on page 18. theFe;P ratio is 50 ppm divided by 0.08 percent. or625. (See Hue and Nakamura. 1988, Macadamiachlorosis by phosphorus and iron fertilization.Proceedings of the 28th Annual Meeting. HawaiiMacadamia Nut Association).

In nurseries, foliar application of a 1 to 3percent iron sulfate solution may relievesymptoms if plants are sprayed several times attwo-week intervals.

Fig. 22. YOUllgest leaves are pille yellow: mature leaves arenonnaI green color. H. C. Bittenbender photo

20

Magnesium (Mg) DeficiencyYellow older leaves with wide green veins

(interveinal chlorosis) are typical symptoms(Fig. 23). Leaf-tissue analysis shows Mg levelsless than 0.065 percent. Dry weather or 'a'a sonsunder high rainfall conditions favor this prob­lem. Overapplication of ca1ciu m or potassiumfertilizers may cause Mg deficiency.

Mg deficIency had no effect on the growth ofseedlings 26 months after symptoms appeared(Bowen. 1987. Micro-element nutrition of mac­adamia. Proceedings of the 27th AnnualMeeting. Hawaii Macadamia Nut Association).We think Its effect on yield is minimal.

SolutionUse tissue and soil analysis to confirm that a

deficiency exists. Apply dolomitic Hme ormagnesium sulfate according to soil analysisresults. Symptoms on affected leaves won't goaway. When the deficiency is elimInated. newgreen leaves will mask and replace affected olderleaves.

Fig. 23. Y0W1~e8t leaves have green veIns. but area betweenthem (lntervelllal.lls yellow. H. C. Bittenbender photo.

21

Glyphosate (RoundupTM) InjuryEarly symptoms are dead or yellow leaves;

the bark of green sterns may crack. New growthis quite unusual. Many shoots begin to grow atthe end of branches or tops of young trees (Fig.24). The tree or branch has a bushy appearance.New leaves may be stunted. narrow, and pale.InjUry 1s caused by spray drifting onto greenfoliage or heavy application in porous soils.

SolutionBranches or young trees generally survive

and return to normal growth. If the excessshoots stay and anew, single stem doesn't takeover within a year, prune off excess shoots.Severely affected young trees may stay stuntedfor months to years. and replanltng may benecessary. Be extremely cautious when applyingherbicides around young trees. Avoid sprayingon windy days or soaking weeds down in porousso11s. FOLLOW THE LABEL.

Fig. 24. New growth at end of' branch or top of' young tree isproducing many small shoots with narrow leaves instead ofnormal growth and leaves. Howard H. Rime photo.

22

Black Citrus AphidYoung and adult aphids suck the sap of young

leaves (Fig. 25) and Dowers (Fig. 26), causing adistortion or puckering of the leaves. Undernormal conditions. yields aren't reduced.

SolutionGenerally, enough natural predators are

present to prevent serious damage.

23

Fig. 25. Aphids feeding on leaves. Leavea are diatortedcompared to nonnalleaves. Photo courtesy oiRon Man.

Fig. 26. Aphids are feeding on raceme of unopened Dowers;the raceme below didn't set nuts. Howard H. Hirae photo.

24

PROBLEMS ON FLOWERS

Poor FloweringThe intensity of flowering isn't the same

every year. In years when the flowering period isquite long, with no distinct period of heavyDowering. growers call this a poor flowering.Growers commonly call a concentrated or heavyflowering period a good flowering (Fig. 27).

Research shows that tree yields are the samewhether flowering is "good," many nuts set. andmany drop prematurely, or whether flowering is·poor.- few nuts set, and few drop prematurely.

SolutionThis isn't really a problem. (See Nagao. 1988.

Flowering, nut set and premature nut drop ofmacadamia. Proceedings of the 28th AnnualMeeting, Hawaii Macadamia Nut Association.See also Premature Nut Drop on page 31.)

Fig. 27. "Snowball," or intense Oowerlng, doesn't mean yieldwill be as good as or better than a normal flowering scatteredover several weeks. Photo courtesy of Mike Nagao.

25

Flower BlightsA brown wilhering of the Dowers and

racemes is caused by two different fungi:Phy tophlhora caps lei causes phytoph thorablight (FIg. 28), and BotryUs cinerea causesbotryUs bllght (Fig. 29}. A third fungus.Cladosporium. is usually secondary or foundalTecling only the raceme tips. Heavy continualrain and cool temperatures during Oowering areIdeal conditions for development of thesediseases.

Infection is usually scatlered within the treeand stops when the weather becomes drier.Phytophthora blight is more conmlOO in closed­in orchards. attacking all Dower stages aodyoung developing nuts. while botrytis blight ismore common on opened nowers.

SolutionFungicides are available but seldom improve

yield. Dry weather or reduced rainfall generallyends the infection. If the problem persists.opening the orchard by pruning or removingtrees to improve air circulation may help. Don'tplant closer than 25 by 25 feeL in high rainfallareas.

26

Fig. 28. Phytophthora-killed racemes and young nuts aredark brown. Photo courtesy of Wayne NishlJima.

Fig. 29. Botrytis-infected racemes are light brown and cot­tony; healthy ones arc: pale green. Photo courtesy of WayneNishijima.

27

Broad MiteThe broad mite. Polyphagotarsonemus latus,

damages leaves (Fig. 30). flowers. and nuts.Flower buds and unopened flowers may tumbrown (Fig. 31) and young nuts drop. Husks oflarge nuts may be russetted or bronzed. but thisdoesn't affect the nut (Fig. 32). This pest has aWide host range that includes many weeds anddoesn't appear to affect macadamia yield undernormal mite populations.

SolutionMonitor Dower buds for damage every week

or two and spray wettable sulfur if you see arapid increase in mite damage. Eliminatingweed hosts around the orchard should also help.(See also Premature Nut Drop on page 31.)

Fig. 30. Broad mite damage i, visible OD leaf, while bl'llnch00 left I, Donnal. Photo cowtesy of ROD Mau,

28

Fig. 31. Broad mite damage is visible on Wlopened flowers.while those at top are noonaI. Photo courtesy ofRon Mau.

Fig. 32. Mites feeding on nuts cause a bronze russettlng ofhusk. but damage isn·t serious at this stage. Photo courtesyofRonMau.

29

------------------

KatydidTwo long-horned grasshoppers. Cono­

cephalus saltator and Elimaea punctifera,occasionally cause damage to macadamiablossoms. Normally. these katydids eat otherinsect pests, but they can damage unopenedmacadamia ilowers. young shoots. and leaves.Though only the tips of flowers look damaged.they won't set nu ts (Fig. 33).

Katydids eat at night and hide in macadamialeaves dUring the day. [f you rusUe the branches.they'll fly out.

SolutionWeed control around the trees will help.

Damage is usually not serious enough to warrantspraying. but malathion Is effective. FOLLOWTHE LABEL.

Fig. 33. Katydid feeding damage Is visible on unopenedmacadamia nowers: undamaged flowers are at the right.Photo courtesy of Hiroshi Ooka.

30

PROBLEMS ON NUTS .AND KERNELS

Premature Nut DropMost fruit and nut trees. including mac­

adamia. have a tendency to drop frults at almostany stage of development. The most commontime for premature nut drop is soon after nut setwhen nuts are generally pea sized or smaller(Fig. 34). In Hawaii, this is from March throughJune. In temperate frult- and nut-growing areasof the northern hemisphere. it occurs in June:hence, the term ~June drop."

Other nuts that are dropped prematurelyclose to harvest appear normal and are oftenharvested. During proceSSing these prematurekernels, called Mimmatures" or wshriveled nuts,"must be discarded. They may be wrinkled,spongy. or discolored (Fig. 35). These are poorquality: they sink in water. Low oil and highsugar content make the kernels dark coloredwhen roasted.

Many factors infiuence how many nuts willdrop. Drought. cold. heat. waterlogging, cloudi­ness. nutritional imbalance, injurieS, anddisease and pest infestation can increase pre­mature drop. Each tree regulates the Size of thecrop it can bear without damaging the tree bydropping nuts. even when no pests or diseasesare present.

SolutionMost premature drop is normal. Regularly

check development of the crop. Pests such asstink bug and koa seed worm shou Id becontrolled if possible. If you suspect that stress,such as poor nutrition or drought. is reducingyield. try to correct the condition.

31

Fig. 34. Small and medium premature nuts are on thegt'ound. A few lat'gel' prcmatul'es wiU continue to drop untilharvest. Photo courtesy of Mike Nagao.

Fig. 35. Dried premature kernels sink in water. They nulya.ppear wrinkled or leathery like these. H. C. Bittenbenderphoto.

32

Southern Green Stink BugThiS sucking insect. Nezara viridula. is a

serious pest that attacks young and mature nuts(Fig. 36). Symptoms aren't easily detected untilthe nuts are dried and cracked. Pits on thekernel are typical signs of sUnk bug damage (Fig.37). Damaged kernels may become moldy beforehaIVest. Early heavy infestation may increasepremature nut drop.

SolutionRemove host plants from the orchard.

particularly members of the bean family. Plantrattle pod (Crota[aria) on the borders of theorchard (Figs. 38 and 39). It provides a favoritefood for the sUnk bug -and encourages stink bugparasites. Don·t let the rattle pod die In the dryseason, however. Stink bugs will move from thedead rattle pod 111to the orchard and feed on thenuts.

Parasites of the stink bug have been releasedthroughout the state by the Hawaii Departmentof Agriculture. An egg parasite. Trissolcusbasalis. and an adult parasite. Trichopodapennipes. are the most common. If sUnk bugparasites are available. releaSing them in theborder areas and orchard may be effective if therelease is made before major damage is seen.Research is needed to determine whetherproperly timed release of stink bug parasites iscost eITective. MacadamIa trees can be sprayedwith endosulfan or malathion. FOLLOW THELABEL. (See also Insect Control on page 18 ofMacadamia Industry Analysis Number 4. 1988.)

33

Fig. 36. Adult Southern green stink bug is feeding on thekernel through the husk and sbell before harvest. Photocourtesy of Ron Mall.

Fig. 37. Dried kernels show typical pitting made when theDut was still OD the the tree. Kernel In center has mold andyeast growth introduced by stink bug during feeding. H. C.Bittenoender photo.

34

Fig. 38. Smooth rattle pod is growing outside the orchard.Howard H. Rirae photo.

Fig. 39. Closc;-up of flU~Y rattle pod in flower and fruit. Stinkbugs will feed here and parasItes will feed on them. HowardH. Hirae photo.

35

Koa Seed WormThe caterpillars (larvae) of this moth.

Cryptophlebia illepida (Fig. 40). and of a relatedspecies. C. ombrodeHa, the litchi fruIt moth (inAustralia called the macadamia nut borer), areserious pests. They eat through the husk andshell (Fig. 41) or enter the kernel throughnatural holes (the hilum and occasionally themicropyle) Ln the shell. Damaged kernels arerecognized by tunneling, frass, and webbing;they may become moldy before harvest (Fig. 42).Early infestation may increase premature nutdrop. (See also Insect Control on page 18 ofMacadamia Industry Analysis Number 4. 1988.)

SolutionNatural parasites provide some control.

Parasites from other countries are being studied.but Improvements in the degree of control maynot be cost effective. Spraying with endosulfanmust be timed accurately with the increasingpopulation, limiting its cost effectiveness. Aninsect attractant (Isomate-M®) has been regis­tered for use to trap and confuse male moths.Research is under way to determine its costeffectiveness alone and as a tool to predict whenspray app]jcations would be most effective.

Preventive measures include usIng cultlvarsthat have a short harvest season (tn your area),and better sanitation. such as removing infestednuts. husks. and prematures from the orchard.

Fig. 40. Adult koa seed worm moth. Photo courtesy of EmestYoshioka; original taken by Ron Mau.

36

Fig. 41. Koa seed worm larva feeding on husk in amacadamia nut. Photo courtesy of Ron Heu.

Fig. 42. Damage is visible on dried kernels. Note irregularlyshaped holes on the left kernel, and webbing, feces, mold,and yeast growth on the right. H. c. Bittenbender photo.

37

Macadamia Shothole BorerThis very small beetle, Hypoihenemus

obscurus. is a newly introduced pest and ispotentially serious in dry areas (Fig. 43).Macadamia shothole borer (MSB) commonlyattacks macadamia stick-tights in Costa Rica.Little is known of Its biology in Hawaii: it wasfIrst found in central Kana in 1988.

It bores a pinhole (smaller than that of thekoa seed worm) throu~h the shell and lays eggsin the kernel (Fig. 44). The larvae feed andbecome adult beetles, then eat pinhole-sizedtunnels in the kernel and through the shell (Fig.45). Nuts can be attacked on the tree. on theground. or during in-shell storage. Damagedkernels can become moldy before harvest. StJck­tights are frequently infested.

SolutionSanitation and frequent harvesting are im­

porlant to prevent MSB attack. Take harvestednuts to the processor as soon as pOSSible. Don'tsort and leave MSB-infested nuts in the orchardor near nut storage areas. because damaged nutsmay contain MS8. Take all harvested nuts to theprocessor. Just because a shell has MSB holes.that doesn't mean the kernel is damaged. If youdo sort out damaged nuts, either bury them atleast 3 feet below ground or burn them. NopestiCides are recommended at this time.

Fig. 43. Close-up of adult macadamia shothole borer. Photocourtesy of Jack Beardsley.

38

Fig. 44. Nut witb boles in shell e~ten by koa seed worm(larger) and macadamia aha thole borer (smaller two). Thehilum, a Dormal hole in shell through which iosects andmold can enter, is at upper right. H. C. Bittenbender photo.

Fig. 45. These dried kernels show pinhole damage; adultbeetle is small black speck on clean kernel (upper teft).Molds and yeasts carried by the beetle Clln also attack thekernel. H. C. Bittenbender photo.

39

Rats and PigsRats attack young nuts in the tree and nuts

on the ground. They chew holes 1/4 to 1/2 inchin diameter through the shell and eat the kernel(Pig. 46). Three species attack macadamla. Mostdamage is done by black rats, which spend muchof their time in trees.

Wild pigs consume the entire nut, leavingonly small pi.eces of shell and husk (Fig. 47).They're a problem in orchards near forestedareas.

solutionFor rats, remove brush piles in orchards and

borders; use rat bait staUons throughout theyear. especially if nests are spotted in the treesand you find damaged nuts. Don't let the bait gelwet; this reduces Its effectiveness. FOLLOW THELABEL. Encouraging owls may be of some ben­efit. but they will not eliminate a severe ratproblem.

For pigs. keeping dogs is helpful. Electricfencing and trapping may be necessary.

40

Fig. 46. Rats can chew holes through sheD. leaving tiny teethmarks and empty shells. H. C. Bittenbender photo.

Fig. 47. Crushed shells on orchard floor are a clear sign ofpig damage. H. C. Bittenbender photo.

41

Stick~tights

Nuts that don't drop when mature but hangon until knocked down are called stick-tights(Fig. 48). This is caused when a small layer ofcells called the abscission zone isn't produced asthe nut matures. Why some nuts don't producean abscission zone is unknown. Drought, otherenvironmental stresses. koa seed worm, an­thracnose, and red and black flat mites havebeen suggested as possible factors.

The cultivar 'Kakea' (508) produces morestick-tights than other cultivars. Despite thestick-tights, 508 has high yields. In areas wheremacadamIa shothole borer becomes common,stick-tights may lead to higher levels of damage.

SolutionNo solution is known. The problem of sUck­

tights does not appear to have an economic e1Tecton yield, however. If you want to knock themdown, do it at the end of harvest before theybecome too old and damaged by the macadamiashoLhole borer.

Fig. 48. Stick-tight nuts on tree. Howacd H. Hirae photo.

42

Poor Management of Harvest and PostharvestHandling

Nuts w1ll span or start to germinate ifthey're not picked up within a reasonable lengthof time after dropping. There are several stagesand ways in which nuts spoil after dropping. Thetime before harvest is longest for late and earlyseason nuts. These nuts remain on the groundlonger because growers walt for enough nuts todrop before picking. Every extra day a nut Is onthe ground increases the chance that a pig. rat,or shothole borer wilLa.Vack. Nuts lying on theground In wet shadeck'R,-reas will eventuallygerminate. begin to' rot;' ,qr become moldy (FIg.49). Fungi and bacteria, 'even ~mts, enter theshell through natural holes (the hilum andoccasionally the micropyle). Genninatlng nutsare bitter and undesirable for processing.

Another common mistake is storingunhusked nuts in bags or boxes for several daysbefore taking them to the processor (Fig. 50).Husks become moldy and the kernels fennent.Allhough the kernels may not look moldy,they'll begin to smell bad: these kernels can't beeaten. Stale kernels may look normal, but theywon't taste good.

SolutionKeep spoilage records each year. Each grower

must decide when losses resulting from moldy,germinating. and rat- and pig-damaged nuts costmore than the extra labor cost of picking morefrequently. The rule of thumb is to pick at leastevery four weeks in rainy weather and less oftenin dry weather.

Never store,.unhusked nuts more than oneday in a bag or box. If you don't want to take asmall load to the processor, and the rats and pigsaren't too bad, it's better to leave the nuts in theorchard. If the nuts were picked but can't bedelivered to the processor and you can't huskthem, then dry them. Spread the in-husk nuts todry on a wire or slotted rack out of the rain anddirect sun. It's best to husk nuts Immediatelyand air dry them or take them to the processorthe next day.

Don't mix old unhusked or husked nuts Withfreshly harvested nuts or ship them as the samelot to the processor. The poor quality of a singlebad bag might ruin the sampling for an entireload. Remember. when you lose quality you losemoney.

43

Fig. 49. Mold- and yeast-dama~edkernels left in the orchardtoo long after dropping, The In-husk nuts weren't moldy;they looked nonnal. H. C. Bittenbender photo.

Fig. 50. Fresh in-husk nuts are moldy after being in a closedbox Cor just a few days. The kernels look normal, but theysmell bad. H. C, Bittenbender photo.

44

The Library of Congress has catalogued this serial publicationas follows:

Research extellBion seriea I Hawaii Institute ofTropical Agri­culture and Human Resources.-O01-[Honolulu, Hawaii]:

The Instituic, [1980-v. : ilL ; 22 cm.

Irregular.Title from cover.Separately catalogued and classified in LC before and

including no. 044.ISSN 0271·9916 = Research extension series - Hawaii

Institute of Tropical Agriculture and Human Resources.1. Agriculturc-Hawaii-Collected works. 2. Agricul­

ture-Research-Hawaii-Collected works. 1. HawaiiInstitute of Tropical Agriculture and Human Resources.II. Tille: Research extension series· Hawaii Institute ofTropical Agriculture and Human Resources.852.5&47 630'.5-<lc19 85.045281

AACR 2 MARC-SLibrary of Congress [8506J

THE AUTHORSH. C. Bittenbender is an associate specialist inhorticulture. College of Tropical AgriCUlture andHuman Resources. University of Hawaii atManoa.

Howard H. Hlrae is an extension agent. HawaiiCounty.

DISCLAIMERReference to a company or product name doesnot imply approval or recommendatlon of theproduct by the College of Tropical Agricultureand Human Resources, University of Hawaii. orthe United States Department of Agriculture tothe exclusion of others that may be SUitable.

Issued in furtherance of Cooperative Extension work, Acts ofMay 8 and June 30, 1914, in cooperation with the U.S.Department 0 r Agriculture. Noel P. Kefford. Direc[()r andDean, Cooperative Extension Ser" icc, College 0 f TropicalAgnculture and Hum3J1 Resources, University of Hawaii atManoa. Honolulu, Hawaii 96&22. An Equal OpportunityEmployer providing programs and .~crvices to the citizens ofHawaii without regard (0 race, color, national origin, or sex.

RESEARCH EXTENSION SERrES I 12 05/90 CUM)