Common Landscape Plant Health Problems in Hawaii

Dr. Scot C. Nelson Associate Specialist (Plant Pathology)

University of Hawaii at Manoa College of Tropical Agriculture and Human Resources Cooperative Extension Service Hilo, Hawaii

October 22, 2009 1. General landscape problems

a. Site establishment b. Landscape installation c. Landscape maintenance 2. Disease and pest problems

▪ Nutrient deficiencies ▪ Fungal diseases ▪ Nematode diseases ▪ Insect pests ▪ Phytotoxicity ▪ Abiotic factors (lightning) ▪ Rats http://www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-67.pdf Visit our new website – “The Plant Doctor” http://plant-doctor.net General landscape problems General landscape problems a. Site establishment

1. Land preparation 2. Poor fill soils 3. Selecting wrong plants for site 4. Grass and shrubs in same irrigation zone 5. “Parking lot” diseases of trees 6. Brackish irrigation water as source of irrigation 1. Land preparation Bulldozer scraping can break up and remove large rocks, deepen the rooting zone level, and remove weed growth. It can have long-term, detrimental effects on plant growth.

Bulldozing near ‘ōhi‘a lehua trees can cause their death by crushing, breaking or damaging roots.

Scraping off topsoil with bulldozers can expose hardened, nutrient-poor subsoil layers. Plants do not grow well in clayey hardpans due to poor aeration or plant nutrient imbalances, and may die from root, stem disease, or nutritional deficiencies. 1. Land preparation Solutions:

- Keep bulldozers at least 10–20 feet away from ohia.

- Harrowing preserves soil structure and topsoil.

- Uptake of water and nutrients requires oxygen, so ensure good drainage during site preparation.

- Compost improves the properties of clay soils.

- Use herbicides rather than soil scraping. Land preparation - drainage problems

Good drainage Poor drainage 2. Poor fill soils Do not use heavy subsoils collected during the process of acquiring good topsoils. Heavy subsoil is usually high in clay, poorly drained, poorly aerated, and lacking nutrients.

The nutritional, physical (compaction, poorly draining), and disease problems associated with these poor subsoils used as topsoil can persist for many years.

Soils used to prepare and fill new landscapes can also be infested with plant root parasites known as root-knot nematodes (Meloidogyne species). 2. Poor fill soils Solutions:

- Use only topsoil for landscapes, no subsoil.

- Test and treat for plant-parasitic nematodes.

- Add gypsum and compost to improve soil structure, organic matter content, and plant nutrients.

- Because most topsoils and original soils do not drain well, one would save money by adding large amounts of compost to the original soil. Compost is best but is also required in large amounts. 3. Selecting the wrong plants for a site

Plants may not thrive where they are planted in microenvironments (consisting of various degrees of sun, shade, soil, pH, etc.) to which they are not well adapted.

They may grow weakly, decline, and die, resulting in “disposable landscapes” that must be replanted continually. 3. Selecting the wrong plants for a site

Solution:

- Match the plants intended for a landscape to the environments that are best suited for their growth.

Important factors:

Moisture / Rainfall Soil or growth medium (physio-chemical) Sunlight / temperature / shade level Elevation 4. Grass and shrubs in same irrigation zone

Shrubs tend to receive far too much irrigation water when placed on the same irrigation schedule as grasses. Grasses are more shallow-rooted than shrubs and may need more frequent watering in hot and sunny environments.

If plants with a wide range of moisture requirements occur in the same irrigation regime, the ones requiring the least amount of water may develop problems due to loss of soil structure, root suffocation, nutrient deficiencies, and root rot diseases. 4. Grass and shrubs in same irrigation zone

Solution:

- Keep grasses on a separate irrigation schedule from shrubs, where possible. 5. “Parking lot disease” of trees

Trees may suffer from what I refer to as “parking lot disease.” The problem usually occurs where trees are planted in relatively small openings within large paved areas.

Sometimes irrigation is not installed or trees are planted too deep. Roots can rot or suffocate or trees suffer from drought and nutritional deficiencies. Oil or gas leaks from vehicles also damage plants. 5. “Parking lot disease” of trees

Solutions:

- Allow a large enough opening in the asphalt for tree roots to breathe and receive sufficient rainwater, irrigation and fertilizer.

- Pave the lot before planting.

- Protect planting holes from oil or gas runoff from the parking lot. Protect trees from ramming by vehicles. Large space for root aeration and rain water reception

Soil cover for weed control

Barrier for runoff control and for foot and vehicle traffic management 6. Brackish irrigation water

The sodium in the rather brackish water in the North Kona district of the island of Hawai‘i can destroy soil structure by breaking down and dispersing soil materials into finer and finer sized particles.

This causes soils to eventually lose aeration, become hard packed and drain poorly. The salinity may also cause root rot. 6. Brackish irrigation water

Solutions:

- Do not over-irrigate plants with brackish water.

- Use mulch and compost to protect soil structure.

- Aerate soils periodically.

- Treat brackish water where possible before irrigating with it.

General landscape problems b. Landscape installation

1. Trees planted too deep 2. Plants placed in wrong growth medium 3. Planting pot-bound plants 4. Large plants too close to a structure 5. No compost or mulch installed 1. Trees planted too deep

If tree stems are planted too deep and then over- irrigated, their roots can suffocate and rot and the stem can decay and even girdle beneath the soil line, leading to plant decline.

This commonly can affect coffee, longan, monkeypod, shower trees, and other valuable woody plants in landscapes . 1. Trees planted too deep

Solutions:

- Make sure the hole is not too deep and fill it in with soil and pack the base slightly before transplanting. The proper depth to plant a tree is to place it in the soil so that the soil line is even with the top of the first lateral root connected to the stem;

- Do not place irrigation emitters immediately adjacent to stems for long, but place them at or near the tips of the roots (the drip line of the plant) Planting too deep 1. Trees planted too deep

Solutions (continued):

- If over time the new transplants sink vertically, dig soil away from the stem until you see the first lateral root.

Also: Use herbicide, mulch, or compost to keep a grass-free zone near the plants. However, do not allow contact between mulch and tree stems, because stem decay can occur when the mulch becomes hot during its composting. 2. Plants placed in wrong growth medium

When plants are grown in the wrong growth medium, they can develop root and stem diseases and have nutritional deficiencies that predispose them to unthrifty growth. 2. Plants placed in wrong growth medium 3. Planting pot-bound plants

A pot-bound plant is one whose roots encircle excessively within a pot, having grown for too long in the pot. The plant essentially becomes too large for the pot.

Pot-bound plants may eventually die or not grow well after they are transplanted into landscapes. The curling roots may not expand in the soils and may “choke” the stem of the plant. 3. Planting pot-bound plants

Solution:

- Avoid planting pot-bound plants in landscapes; inspect them before purchase or use and discard them.

- Some growers may choose to clip or loosen the pot-bound root systems with shears before planting to interrupt the root curls. Installing pot-bound plants No compost or mulch installed

Excessive irrigation that occurs in many professional landscapes can destroy soil structure and later its chemistry, making it very difficult to grow plants successfully.

Mulch or compost, considered to be unsightly by some people, can help preserve soil structure and improve nutrition. General landscape problems c. Landscape maintenance:

1. Excessive irrigation - root and stem rots - loss of soil structure 2. Nutrient management 3. Over reliance on pesticides 4. Soil pH problems 5. Irrigation emitters position left unaltered 6. Failure to recognize and treat problems early 7. Poor pruning 8. String trimmer injury 1. Excessive irrigation

Too much irrigation can cause root and stem rot and can destroy soil structure, creating a “disposable landscape” phenomenon.

Solution:

-Do not water on a schedule, but as needed by plant and weather factors.

- Avoid sprinkler irrigation impaction on woody plant stems and disease-susceptible foliage Xanthomonas bacterial leaf blight

A common disease where these plants receive overhead sprinkler irrigation. Irrigation problems with trees (impact)

Sprinkler irrigation impaction on woody plant stems or over-watering can cause stem bark diseases. Stem canker on shower tree – irrigation was excessive 2. Nutrient management Nutrient deficiencies are common in landscapes. Plant species differ in their nutritional requirements; hence it is important to supply important plants with the proper blend of macro and micro elements.

Some common deficiencies in Hawaii:

- Potassium - Iron - Boron - Nitrogen - Magnesium Nutrient Deficiencies for Palms

Potassium, boron magnesium & nitrogen are most common Potassium regulates the opening and closing of stomata

Potassium deficiency on Kentia Potassium deficiency Potassium deficiency Necrosis or scorching of leaf tips

Potassium deficiency Magnesium deficiency

Areca

Pritchardia Boron deficiency

Deformity of apical meristem Boron deficiency – palm

“Accordion leaf” Leaf trimming Boron deficiency

Deformity of apical meristem Leaf trimming Boron deficiency – Pritchardia “Accordion leaf” symptom Multiple nutrient deficiencies Recommended plant tissue levels for selected palms: sufficiency values and ranges.

Palm N P (%) K (%) Ca Mg S (%) B Fe Mn (%) (%) (%) (ppm) (ppm) (ppm)

Areca* 1.5- 0.1-0.8 0.7-4.0 0.8-2.5 0.2-0.8 0.21- 15-60 18-250 47-250 3.5 0.75 Seifritzii* 2.5- 0.15- 1.6-2.8 1.0-2.5 0.25- 0.21- 25-60 50-300 50-250 3.5 0.3 0.8 0.40

Rhapis 1.8- 0.15- 1.5-2.5 0.4-1.0 0.2-0.3 0.15- 16-75 80-300 50-250 2.8 0.8 0.75 Manila 1.95 0.24 0.81 0.55 0.34 0.34 15 26 48

*Container production. Source: Plant Nutrient Management in Hawaii Soils (2000)

Areca, Seifritzii, Rhapis - middle leaflets of most recently matured leaf

Manila - mid-section of most recently matured leaf Palm fertilizers

General – 2:1:2 (e.g., 12:6:12) or 3:1:3 plus minors

▪ Boron – Borax or Solubor. Dissolve about 4 oz of Solubor or Borax in 5 gallons of water and drench this into the soil under the palm canopy. Do not repeat this for at least 5 months, since it will take this long to see the results of the application

▪ Potassium – KCl, Potash

▪ Magnesium – Dolomite, green sand

▪ Ag lime or dolomite for pH adjustments

▪ Calcium nitrate Hint:

Trim the inflorescences of palms with deficiencies in elements such as boron 3. Over reliance on pesticides

Some landscapes require that a lot of pesticides be applied in order to maintain them. This can result in a loss of biodiversity and to unwanted human exposure to chemicals.

Solutions:

-Use plants that require fewer pesticides.

-Use specific-action pesticides.

- Use less deleterious pesticides. Some plants may be damaged by some pesticides such as herbicides, insecticides or fungicides. Vikane injury (termite control chemical) – Areca palm, foliar chlorosis Copper fungicide spray injury to fishtail palm

Leaf spot symptoms appear rapidly, but lesions do not expand in size over time as they would with a fungal disease. Switch fungicides. 4. Soil pH problems

The pH of landscape soils changes over time as rain and irrigation water and nutrients and other materials contact and move through the soil.

Solutions:

Monitor and treat soils yearly by submitting plant tissue and soil samples to the CTAHR Agricultural Diagnostic Service Center.

Understand the pH requirements for optimum growth of the plants in your landscape. 5. Irrigation emitters position left unaltered

People often leave the irrigation hoses or emitters in the same position, quite near to the plants, for at least a year and sometimes for several years. This can inhibit root growth and lead to stem and root rots (which cause leaf yellowing and plant dieback), especially where irrigation is excessive.

Solution: Move irrigation emitters away from transplanted plant stems after a couple of weeks, out to the root tip zone. 5. Irrigation emitters position left unaltered 6. Failure to recognize and treat problems early

If problems are detected early, they usually are more treatable and more easily rectified, and their spread to other plants in the landscape may be prevented.

However, significant pest or disease problem of roots or foliage often go undetected until it causes replanting to occur or to be necessary. 6. Failure to recognize and treat problems early

Solutions:

- Submit soil samples for analysis yearly.

- Fertilize plants at least 2–3 times each year.

- Scout or inspect plants.

- Submit suspect samples for analysis.

- Keep records on landscape maintenance and take photographs of periodically. http://www.ctahr.hawaii.edu/oc/freepubs/pdf/SCM-14.pdf 7. Poor pruning

Plants that are not pruned when they could be, or pruned poorly, may suffer disease and have an unthrifty appearance. Shrubs and trees should be pruned so that the apical growth is in balance with the root system.

Solution: Understand the principles of tree pruning in landscapes. 8. String trimmer injury

The bark of trees cannot re-grow once it is removed by string trimmers. Nutrients flow within tree bark, and when bark is removed in a circular pattern around a stem, the affected plant may eventually die.

Solution:

Use string trimmers carefully around young trees and consider wrapping exposed stems near ground level with trimmer-resistant materials such as rubber or plastic shields. Disease and pest problems Plant Diseases - The Disease Triangle

Conducive environment

Disease

Susceptible Virulent Host Pathogen Plant Diseases – causation

1. Fungi 2. Bacteria 3. Viruses and viroids 4. Nematodes 5. Phytoplasmas 6. Algae 7. Parasitic seed plants 8. Abiotic factors Coconut Heart Rot Phytophthora katsurae

Discolored nuts, internal stem necrosis (advanced symptoms).

Collapse of heart leaf (early symptom)

Young plant Mature plant Base Crown

Heart rot – Coconut palm Coconut Heart Rot

CONTROL: ▪ Pruning sanitation methods ▪ Destruction of diseased plants (buried or burned) ▪ Preventive applications of fungicides or phosphorous acid fertilizer ▪ Trim plants during dry weather Phytophthora diseases: root rot SYMPTOMS: plant stunting, chlorosis, wilting and death; black, soft and discolored roots; leaf scorch. CAUSE: Phytophthora spp.; Pythium spp. CONTROL: water management; good drainage; rogue diseased plants; fungicide sprays (copper products; Phytophthora root rot metalaxyl, phosphorous acid); clean on Howea forsterana plants and seed source; clean nursery sanitation.

Roots infected with Root cortex strips off P. palmivora easily Lightning injury – at Hilo golf course

Wilting and leaf necrosis Lightning injury – coconuts at Hilo golf course

Nut drop Lightning injury – coconuts at Hilo golf course

Pith explosion – see our free publication Severed stems

Breaking and toppling of triangle palm stems is common in high-rainfall areas Rat feeding injury

Manila palm de-fronding problem, Honomu – rat feeding Fungal diseases of palms in Hawaii

Fungal spores – light microscope Chalara (Thielaviopsis) Stem Bleeding HOSTS

Chalara (Thielaviopsis) Stem Bleeding

MANAGEMENT Is the cure worse than the disease? Bipolaris and Exserohilum leaf spots

SYMPTOMS: Leaf spots begin as tiny, water- soaked spots, which may be chlorotic to greenish brown, expand into circular to elliptical lesions (2-10 mm or more), becoming brown, reddish-brown, or dark-brown to black in color. May be chlorotic halo around lesions. Some palm species will have sunken, “eye spot” symptom. In severe cases, lesions coalesce and fronds become shredded. CAUSE: Exserohilum and Bipolaris spp. CONTROL: Reduce water splashing; reduce relative humidity in canopy; preventive fungicide applications; clean planting material; reduce excess moisture; reduce duration of leaf wetness; leaf spots

SYMPTOMS: leaf spots, starting as tiny black spots which enlarge to form approximately circular lesions up to 2 mm or more diameter; mature lesions are almost white with a black or dark colored border and a dark spot in the center; lesions form on leaf margins, blades, or rachis tissues.

CAUSE: Pestalotiopsis palmarum

CONTROL: Preventive applications of broad- spectrum fungicides; water and humidity management; promote leaf drying; plant spacing, etc. Pestalotiopsis leaf spots Fungal disease management

▪ Irrigation and moisture control ▪ Good plant nutrition ▪ Fungicides ▪ Plant spacing ▪ Sanitation ▪ Choice of planting location no brain head stylet no heart no lungs esophagus mouth and lips vulva egg anus

ovary

intestine NEMATODE ANATOMY tail Stained nematodes in root

Galling, knots on roots Nematode management in landscapes

1. Do not install infested soil at a site (test it first!)

2. If soil is infested, choose resistant plant material

3. Do not over-irrigate

4. Use composts, foliar fertilizer Insect Problems of Palms in Hawaii

Stinging nettle caterpillars Photos: S. Chun and A. Hara Darna pallivitta

Link to free brochure: http://www.ctahr.hawaii.edu/oc/freepubs/pdf/iP-22.pdf Source: Arnold Hara

Poison gland cell

The caterpillar’s stinging hairs release on contact a venom or irritant (mixture of histamines) produced by a poison gland causing a burning and itching sensation to the skin. Irritation by the venom have been reported to last for a week in most people. Nettle Caterpillar’s larval stage: (40-53 d); pupal stage (11-15 d) Life cycle (egg to egg-laying adult): 56 to 67 days, (avg. 62 days).

prepupa

pupa

adult Source: Arnold Hara Present Status of the Nettle Caterpillar in Hawaii

Infestation on mondo grass at a nursery Distribution: South Hilo district, upper and lower Puna, Kohala and around Kailua. Probably more widespread but that is what we realize.

HDoA has a parasitoid (wasp) it intends to release for biological control of the caterpillar. Coconut mealybugs (Nipaecoccus nipae)

▪ Male – white; Female – yellow ▪ May be tended by ants ▪ Create unsightly appearance and plant damage ▪ Associated with black sooty mold on foliage ▪ Control: imidacloprid (Merit) or soap/oil Scale insects – 11 species on palms in Hawaii

▪ Sap feeding insects

▪ May be tended by ants

▪ Create unsightly appearance and plant damage (yellowing)

▪ Associated with black sooty mold on foliage

▪ Control: imidacloprid (Merit) or soap/oil for soft-bodied scales Coconut scale (Aspidiotus destructor) colonies on leaves

Some scales have a wide host range, attacking may plant species Cycad scale (Aulacaspis yasumatsui) on sago palm Link to free article: http://www.ctahr.hawaii.edu/oc/freepubs/pdf/ip-23.pdf Biological control of cycad scale (Aulacaspis yasumatsui)

A tiny black beetle, Rhyzobius lophanthae, is a very effective biocontrol agent Cycad scale – “Queen sago” Eriophyid mites on Samoan coconut

SYMPTOMS: brown scarring and necrosis of nuts; cracking, nuts do not mature. CAUSE: Eriophyid mite, Aceria guerreronis feeding under the hard petals and sepals (tentative identification). CONTROL: Unknown. Sulfur?

Damage in Nanakuli associated with the Eriophyid mite, Aceria guerreronis. Kona Eriophyid mite damage to coconut in S. Kona Banana moth (Opogona sacchari)

SYMPTOMS: terminal necrosis and death, resembling coconut heart rot; internal necrosis. coconut CAUSE: Banana moth caterpillars. CONTROL: Approved insecticides such as BT (Bacillus thuringiensis) caterpillars Banana moth (Opogona sacchari)

- Has wide host range - Opportunist that can attack plants under stress - Can affect various palms (out-planted or nursery)

Link to free publication (banana moth on Pritchardia): http://www.ctahr.hawaii.edu/oc/freepubs/pdf/IP-24.pdf Whiteflies Sooty mold

▪ Black, non-parasitic fungal growth associated with honeydew produced by sap-feeding insects (whiteflies, scales, mealybugs, aphids) often tended by ants. It is very common.

▪ Control: imidacloprid (Merit) or soap/oil; do not over-fertilize; wash off mold with soapy water; control the ants

Click here for our free publication about sooty mold Mealybugs on residential palm in Wainaku Subterranean termites (Coptotermes formosanus)

Pritchardia palm on U.H. Hilo campus Necrotic heart of a Pritchardia palm at the Panaewa rainforest zoo. The sugarcane weevil was infesting the Pritchardia at the Panaewa rainforest zoo.

It was controlled with an insecticide drench. Coconut leaf roller

Pupae and larvae Coconut leaf roller Hedylepta blackburni

Mature caterpillars – make chewing holes in leaves (Hawi) Coconut leaf roller

Adult moth Miscellaneous problems Rose beetle feeding injury Hibiscus erineum mites Cypress roach Leaf hopper burn of ti Spiraling whitefly Spider mites Plumeria rust Plumeria rust http://www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-61.pdf

Ohia rust (Jaboticaba) Rust of beach heliotrope Black spot of rose Phytophthora blight of mock orange Cassytha filiformis and dodders Powdery mildews Hawaii Pesticide Information Retrieval System

http://state.ceris.purdue.edu/doc/hi/statehi.html For questions or further information:

Dr. Scot C. Nelson University of Hawaii at Manoa 875 Komohana St. Hilo, Hawaii 96720

Tel: 969-8265 Email: [email protected] http://plant-doctor.net

Mahalo!