Important Important PestsPests of of KavaKava in Hawaii and in Hawaii and Their Integrated ManagementTheir Integrated Management

Scot NelsonAssociate Plant PathologistUH-CTAHRCooperative Extension Service, Hilosnelson@hawaii.edu

MeloidogyneMeloidogyne sp.sp.

CMVCMV

Aphis gossypiiAphis gossypii Phoma Phoma sp.sp.

PythiumPythium

Cropping system impactsCROPPING SYSTEM Monoculture,

MonocroppingPolyculture,Intercropping,Polycropping

Agroforestry

PEST RISK High intermediate LowINPUTS, COSTS High LowBIODIVERSITY Low HighEROSION Likely UnlikelyREEF SEDIMENTATION Yes NoYIELD AND PROFIT Higher (near

term)Lower (near

term)SUSTAINABILITY 5 years Hundreds of

years

Monocropping of kava is a not a logical choice unless the only goal is to achievethe highest yields possible per unit land area.

With the emergence of large-scale kava monocropping in Hawaii in the late 1990’s and early 2000’s, a number of severe plant disease problems developed.

This presentation covers the 4 most important of these diseases.

Major Pests of Kava*• Kava dieback

(virus/insect: Cucumber mosaic virus / Aphis gossypii)

• Pythium root rot(pseudofungus: Pythium splendens)

• Root-knot nematodes(nematodes: Meloidogyne spp.)

• Phoma shot hole• (fungus: Phoma/Didymella sp.)

* Pest attack can result in plant death or severely decreased plant growth and yield.

Kava dieback, North Kona

Minor or Other Pests of Kava*• Node rot• Stump rot• Spider mites• Melon aphids (Note: a major pest when in conjunction

with CMV) • Nutritional deficiencies (Fe, K)• Whiteflies (various species)• Slugs, snails, minor insects such as rose beetles,

katydids, scales, mealybugs, loopers and caterpillars• Weeds: Glycine, honohono grass• Rats, Pigs

* Minor pests do not usually cause large amounts of damage, but under some circumstances can cause significant injury to kava plants.

Root knot

Disease: Root knotPathogen: Meloidogyne sp. (several)Symptoms: Yellowing foliage, plant stunting, galled and knotted roots, root rot.Effect: Reduced yield and kavalactone contentManagement: Avoidance and preventive measures such as using nematode-free potting or growth medium; on-time or early harvest; crop rotation .Notes: All kava varieties are susceptible to infection by Meloidogyne spp.

Yellowing foliage of root-knot-infected kava plant

Kava root-knot diseaseEffects upon yield and quality of roots and stump can be significant

HEALTHY DISEASED

A Meloidogyne-infected kava root system has fewer later roots and has swollen, galled, rotting discolored roots.

A healthy kava root system has a prolific number of light-colored lateral roots with maximum yield potential.

Roots are swollen, knotty, galled, Roots are swollen, knotty, galled, distorted, cracked and necroticdistorted, cracked and necrotic

Root knot disease Root knot disease

Adequate nutrient and moisture level in soil

Nutrient deficiency symptoms (yellowing, necrosis), wilting, defoliation, & plant death due to decreased respiration and transpiration

Decreased uptake of water and nutrients; weak stems

Root galling, splitting and rotting

nematodes attack roots

How nematodesHow nematodesaffect plantsaffect plants

Adult femaleAdult female

Egg mass

root

Life cycle

Day 1

Day 7 - 12

Day 24 – 36* (estimated)

stained in rootstained in root Stylet acts as spearStylet acts as spear

MeloidogyneMeloidogyne sp.sp. generalized life cycle on Kavageneralized life cycle on Kava

juvenilesjuveniles

adult femalesadult females

headhead

Lips and mouthLips and mouth

styletstylet

Kava roots infected by Meloidogyne sp. (root-knot nematodes) can crack open, allowing fungi and bacteria to rot the root tissues.

White fungal mycelia White fungal mycelia growing on necrotic,growing on necrotic,galled kava root.galled kava root.

Rotting nematodeRotting nematode--infected kava infected kava ““laterallateral”” root, and transverse root, and transverse section showing internal section showing internal Root necrosis (right)Root necrosis (right)

Tip: Processing of nematode-infected kava roots results an a foul tasting and discolored product with a reduced phytomedicinal effect.

Kava diebackDisease: Kava diebackPathogen: Cucumber mosaic virus (CMV)Vector: The melon aphid (Aphis gossypii)Symptoms: Foliar mosaic and yellowing, leaf wrinkling and puckering, necrotic veins in leaf and stem, ringspots on leaves, stunting, plant death.Effect: Reduced yieldManagement: Avoidance and preventive measures such as using disease-free cuttings; rogue infected plants or stems; aphid control measuresNotes: Varieties such as ‘ISA’ and ‘IW’I seem to be resistant or even immune to CMV.Typical foliar mosaic of CMV-

infected kava plant

Leaf mosaic, ringspot, decline and dieback in Kailua-Kona (June, 2002)

Vein necrosisVein necrosis

Stem lesionsStem lesions

Plant diebackPlant dieback Leaf mosaicLeaf mosaic

Leaf mosaicLeaf mosaic Drooping petiolesDrooping petioles

PuckeringPuckering

RingspotsRingspots

‘‘AWA DIEBACK SYMPTOMS (CMV)AWA DIEBACK SYMPTOMS (CMV)

Basal stem rotBasal stem rot

Leaf rugosityLeaf rugosity Stem necrosisStem necrosis

Witling, yellowingWitling, yellowing

A. gossypiiA. gossypii colonizing colonizing ‘‘awa leafawa leaf

‘‘AWA DIEBACK SYMPTOMS (CMV)AWA DIEBACK SYMPTOMS (CMV)Aphis gossypiiAphis gossypii, , vector of CMVvector of CMV

‘‘Awa fieldAwa field

CMVCMV--infected CMVinfected CMV--free free

honohono grass w/ CMVhonohono grass w/ CMV

‘‘Awa stump: complex tissueAwa stump: complex tissue

IPM for IPM for ‘‘Awa DiebackAwa DiebackDiseaseDisease--free planting material free planting material Good nursery practicesGood nursery practicesEradicate alternate hosts Eradicate alternate hosts WindbreaksWindbreaksProtect young plants Protect young plants Rogue infected plants when youngRogue infected plants when youngMonitor ants/aphid populations Monitor ants/aphid populations Rogue diseased stems when > 9 mo. oldRogue diseased stems when > 9 mo. oldIntercroppingIntercropping Minimize plant stressesMinimize plant stressesHost resistanceHost resistance Aphid controlAphid control

Rapid wilt of young plantsRapid wilt of young plants

Wilted plantWilted plant

When rogueing CMV-infected stems, cut at the 1st or 2nd knuckle to lessen the chance of stump rot developing (see arrow above).

Shot holeDisease: Shot holePathogen: Phoma sp. / Didymella sp.Symptoms: Leaf spots in which tan-colored centers fall out; spots on stems; chlorosis.Effects: Defoliation, premature death of stems, reduced plant yield, plant decline and death.Management: Humidity and moisture management; intercropping; agroforestry; variety selection; choice of planting location; sanitation. Notes: Varieties such as ‘ISA’ and ‘IWI’ seem to be somewhat resistant shot hole; Hawaiian green-stemmed variety “Puna emerald green”is very susceptible). Triazole fungicides, although not registered for use on kava, provide excellent disease control. “Mahakea”performed very well in Hilo.

Shot hole symptoms

Shot hole lesions are about 1/16” to 1/8”-diameter. Lesions usually develop a whitish to tan-colored center with a well-defined or distinct border to the lesions.

Rather than simply expanding, the lesions tend to remain about the same size and the centers eventually fall out. Leaves turn yellow before falling to the ground.

Severe defoliation and stem diebackof affected kava plants can occur veryrapidly.

The fungal life cycle is completed in about 18 days on kava (time from inoculation to symptom expression and fungal reproduction).... 40 generations in 2 years.

Pythium root rot

Disease: Pythium root rotPathogen: Pythium splendensSymptoms: Blackened, rotting roots; plant yellowing and wilting.Effects: Plant death; reduced yield.Management: Choice of planting location and medium; ensure adequate soil drainage; avoid burning plant roots with fertilizer. Notes: As disease progresses, plant death can ensue quite rapidly.

Pythium root rot

Pythium root rot: wilting plants

Hilo Kona

Pythium root rot: necrotic roots

Summary of integrated management practices Summary of integrated management practices for kava pest controlfor kava pest control

MAJOR RECOMMENDATIONS FOR KAVA PEST CONTROLMAJOR RECOMMENDATIONS FOR KAVA PEST CONTROL

1.Avoid kava monocropping2.Choose your location and varieties wisely3.Exclude pests from nurseries4.Use disease-free planting material5.Scout fields weekly for symptom development6.Field sanitation7.Control weeds and alternate hosts for CMV and melon aphids

MAJOR RECOMMENDATIONS FOR KAVA PEST CONTROLMAJOR RECOMMENDATIONS FOR KAVA PEST CONTROL

1.Avoid kava monocropping2.Avoid plant stress: grow under shade/cover!3.Choose your location and varieties wisely4.Exclude pests from nurseries5.Use disease-free planting material6.Scout fields weekly for symptom development7.Field sanitation8.Control weeds and alternate hosts for CMV and melon aphids9.Do not over-fertilize (kava is very sensitive to salts and

over-fertilizing attracts whiteflies and aphids)

INFORMATION RESOURCES

http://www.ctahr.hawaii.edu/nelsons/kava/kava.html

www.ctahr.hawaii.edu “free publications”

For questions or more information:For questions or more information:

Scot NelsonAssociate Plant PathologistUH-CTAHRCooperative Extension Service, Hilosnelson@hawaii.edu

Mail: 875 Komohana St., Hilo, HI 96720 USAPhone: 808-981-8265