Pandanus Tectorius Palms

Plant Health Care project.

This presents a research and monitoring trial implemented by HTC and the City Of Gold Coast since April 2020.

State of the art: April 2020

For the past few years, severe decline had spread across costal populations of Pandanus palms in Southeast QLD. As reported in the FINIA (Fraser Island Natural Integrity Alliance), up to 50% of the island east coast’s Pandanus had perished (circa~ 50,000 plants). Pandanus Dieback is a disease found in Pandanus trees (Pandanus tectorius) largely caused by an infestation of leaf hopper insects (Jamella australiae)

Pandanus provide a wide range of environmental services including control of coastal erosion, windbreak, improvement of soil fertility and organic matter levels, shade for humans, nesting sites for birds, habitat for wildlife.

They are exceptionally tolerant to salt winds, tolerant to strong winds, tolerant of moderately long droughts, and can possibly survive up to 6 months of waterlogging (Thomson et al, 2006).

Despite all these strengths and heavy resistance to abiotic stress factors, several pests and diseases of pandanus have been recorded.

Diseases and pest

The most important pests in the Central Pacific are sap sucking mealybugs that may weaken plants. Rats and hermit crabs may feed on green and ripe fruits. In general, Pandanus appears to suffer only minor damage from pests and diseases. There is a serious scale affecting Pandanus forests in Hana and the entire Maui region in Hawai’I; this pest was first noticed in the early 1990s and is spreading along the coast. Leaves yellow and trees were in very poor health in 2006 (Thomson et al, 2006).

Several arthropod pests have been recorded (Thomson et al, 2006).

In Northern New South Wales, dieback of Pandanus species is caused by an infestation of the pandanus plant hopper (Jamella australiae). The insects produce a sticky substance called honeydew, which encourages mold growth. This makes leaves drop and kills the tree’s growing points, eventually causing death of the palm. In its native habitats in North QLD, Jamalla is controlled by natural predators, including wasps.

Several fungal species have been recorded on pandanus. A bacterial disease of Pandanus has been recorded (Erwinia carotovora subsp. Carotovora).

Pandanus dieback management

The City of Gold Coast then started the implementation of a pandanus dieback management program. Several treatments were implemented by the council, notably the injection of systemic pesticides (an imidacloprid-based insecticide via stem injection or foliar methods). Heritage Tree Care was then hired to try and implement natural treatments focusing on soil health and microbiology to build plant’s immune system, resistance to pest and disease, and resilience. Indeed, certain beneficial soil organisms perform interactions with plant roots and help them mitigate stress factors (biotic and abiotic).

The Pandanus trial on the Gold Coast coastline was initiated in January 2020 when Pandanus palms were showing severe decline following pest infestation (Jamella australiae) and required urgent investigation.

Jamella australiae Pandanus Leaf Hopper is a pest of the native Pandanus; Pandanus tectorius var. pedunculatus (Smith and Smith, 2000). Please see previous reports for details and literature review.

Several years of below than average rainfall with increasing annual mean temperature (see chart below) might have weakened the palm’s health on the Gold Coast.

In North Queensland the native wasp Aphanomerus pusillus parasitises the eggs (Smith and Smith, 2000) and controls the disease. In the early 1990’s Pandanus trees were observed to be declining and dying on the Sunshine Coast. Pandanus Leaf Hopper was identified as the pest causing the disease (Smith and Smith, 2000).

Options to assist Pandanus recovery

Pandanus dieback can be controlled in the long term with the introduction of the predatory wasp (Aphanomerus nr. pusillus) that controls the Jamella insect outbreaks, which is already showing excellent results. Other options for the short term are treating the Pandanus trees infected with an imidacloprid-based insecticide via stem injection or foliar methods. Also the use of leaf stripping is being incorporated to assist with Pandanus recovery, which involves the removal of the old deceased leaves from the trees to remove the insect and decaying material from the Pandanus tree to allow a recovery of the tree.

Other several treatments of interest, which have previously been proven of high efficiency on sick palms in previous projects, were trialed on site on selected palm samples. These treatments are to support the plant natural immune system.

The initial objectives of the trial were the following:

• Trialing remediation options to improve Pandanus health and presumably build their systemic induced plant defense 
• Investigate stressors that are impacting palm’s general health (at the initial assessment and in the preliminary report) 
• Build a 3-month plant health program for 6 sites 

The outcomes of the 3 months’ trial allowed to define a long-term plant health care program (part of a one year program). 

It was of great importance to highlight the possible differences in soil parameters (please see Stage 1 completion report for soil tests) that would have impacted the palms’ growth, health and defenses such as abiotic (nutrient deficiency, drought) stresses and soil physical and chemical properties.

Following the completion of Stage 2, it was decided to continue the treatments for a final stage from August 2021 to January 2022, to try and understand better all the parameters affecting the palm’s health.

The trial consisted of 7 sites: 5 sites showing decline and pest presence with treatments to be tested, one site not showing severe dieback hence left untreated as a control. Lastly, an extra healthy site without pest presence which is used as a model to set guidelines.

Several plant health care treatments have been tested individually, as biocontrol to control leafhopper populations and to improve palm health and disease resistance (please see previous reports for treatments specifications):

Seven pandanus sites were selected among which 6 sites in advanced decline and one healthy site used as a benchmark.

The programs implemented on the diseased sites included:

• Visual site, soil and plant assessment. Palm health and pest levels were visually assessed. Plant tissues were sampled for analysis and assessed for their nutrient profile and chemical status.
• Soil testing for mineral (routine agricultural soil test)
• Plant tissue testing for nutrient content
• Treatments with natural products:
  • Aerated compost tea with indigenous microbes
  • Organic pesticides (eco-oil)
  • Entomopathogenic fungi
  • Palm health care
  • Combine treatments

The plant health care treatments have been tested individually, to improve palm health and resistance against the infestation of sap sucking insects.

Treatments have been applied fortnightly during the 4 phases of the trial as follows:

• January 2020 to June 2020: stage 1
• August 2020 to December 2020: stage 2
• January 2021 to June 2021: stage 2 continued
• August 2021 to January 2022: Final stage

Plant and soil conditions have been assessed at the start and then on a monthly basis to monitor plants’ reactions and possibly adjust treatments if necessary.

The first completion report, following the first stage of the trial, was released mid-2020.

In July 2021, the report following the completion of Stage 2 continuation was presented.

This report hereby covers the completion of the last and final stage of the trial

Palm Health Care treatment.

This includes:

• Soil drenches, dry mineral blend injections and foliar spray of custom blends of nutrients. This is to give palms the energy to fight diseases and strengthen their cell wall to reduce infection.
• Watering: plant under biotic and abiotic stress release stress oxidative molecules and transpire more hence water is the primary remedy to apply to compensate for the loss of plant moisture.
• Compost teas: brews containing beneficial soil microorganisms such as protozoa’s, beneficial bacteria and mycorrhizal fungi along with molasses and fish kelp, help to rebuild the soil biology and stimulates plants’ natural defences.

Entomopathogenic fungi treatment:

this is to repopulate with naturally occurring, beneficial fungal species  which are parasites of targeted pests. The product is a talc-based formulation containing the beneficial fungal species Beauveria bassiana, Metarhizium anisopliae, and Lecanicillium lecanii.  It is an Australian Certified Organic (ACO) registered input as it is based upon naturally occurring  fungi and is a powerful probiotic. Beauveria sp. is a filamentous fungus, belonging to the class

Deuteromycetes. Beauveria bassiana is a fungus that grows naturally in soil throughout the world and acts as a pathogen on various insect species, causing white muscardine disease; therefore, it belongs to the entomopathogenic fungi.

Foliar sprays and soil injection of natural oil treatment:

natural plant oils commonly used as pesticides and or/fungicides will be sprayed on aerial plant parts (including aerial feeder roots) and injected into the root ball. This is to allow the natural oils to be absorbed by the palms via the stomata so they can have a systemic effect after translocation in the phloem and via systemic uptake via the root system. The oils will then be present in the sap when the leafhopper sucks on it.

Inoculation of indigenous soil microbiology treatment.

This is to allow the indigenous populations of beneficial soil microbes, especially mycorrhiza, to repopulate the root zone, activate the plant’s resistance genes, help in the uptake of nutrients, maintain adequate moisture level in the rootzone and support the plant’s immune system. Coastal areas accumulated with sand are deficient in organic matter and consequently their fertility is low. Arbuscular mycorrhizal (AM) fungi help in establishment of plant cover, thereby improving the fertility of sand dunes.

Combined treatment trial.

This treatment is a multiprong attack strategy combining the application of the Palm care treatment program (1.), the Entomopathogenic fungi treatment (2.) and the Organic pesticide treatments (3.) into one trial treatment. This is to see if a muliti level approach weakens the pest population greater than the individual treatment.

Plant and soil conditions have been assessed at the start and then on a monthly basis to monitor plants’ reactions and possibly adjust treatments if necessary.

Material and Methods

Canopy aspect: density and dieback assessment

One palm crown is to be compared to a pie (as in a pie chart).

Full canopy is 100% crown circle (as pictured below as a pie) filled with live fronds in every pie slice. This equals to 0% dieback.

50% canopy is 5 pie slices filled with live fronds. Equals to 50% dieback.

0% canopy = 0 pie slice filled with live fronts = 100% dieback.

For Pandanus, several crowns, representative of the whole palm, are estimated. The results are averaged for the general assessment of the palm.

Dieback is the result of defoliation. Dieback gives the % of dead or missing leaves from non-natural normal senescing process.

Leaf color assessment reflects the health. A sick palm can show a full crown of 100% canopy density and 0% dieback but abnormal color.

Studies of palm physiology have shown that palms normally redraw nutrients from old senescing leaves and translocate it to the new growth. Once this process achieved, old leaves normally fall off the palms (Broschat TK, 1997). This is why dead leaves cannot always be considered as dieback, and should not be stripped off before the end of the natural process.

Visual canopy assessments were performed at the start of the trial before first treatment application, then on a monthly basis.

Leaf sampling

Leaves are sampled monthly from the inner rings of the frond, from mature leaves located close to new growth, when possible. Mineral content is analysed by an external lab.

Pest counts

Jamella australiae infestation levels

J. australiae presence is virtually certain in all areas not chemically treated, monitoring requires an assessment of relative infestation levels:

• Light; if the presence of Jamella is low density per leaf and confined to only a few leaves.
• Moderate; if the presence of Jamella is low density per leaf but extended to many leaves in the tree; OR the presence of Jamella was medium to high density but confined to only a small percentage of leaf heads.
• Heavy; if the presence of Jamella was medium to high density per leaf and extended over a significant percentage of the tree.

Key findings and outcome summary

Palms were reported to be in a rapid declining phase before the trial started. Following almost twenty-four months of treatments, the last canopy assessment attests a general increase in average canopy density percentage at all sites, but 5 sites showed more than 40% increase in canopy density since January 2020. Dieback progression has decreased at all sites, with the most important decrease observed at the site treated with entomopathogenic fungi.

Pest levels in January 2022 were all down to low or very low levels (see details in Pest Levels section) except for the site treated with indigenous aerated compost teas (medium levels).

Plant tissue testing across the two years of trial now allow for timed and adjusted fertilisation program according to palm physiological development calendar and customed guidelines.

Most soil nutrients are still below guidelines and would require seasonal applications of composted slow-release fertilisers.

Soil microbiology was rated OK at the end of the trial on average across treated sites.

A strong correlation has been observed between soil microbiology diversity and activity, and palm development. The site which received all combined treatments showed the most outstanding results for soil microbiology. The site treated with Palm health care is the only site which showed a “below OK” level of microbiology, correlated with the low active carbon content.

Weather events (high rainfall) can possibly have impacted nutrient content (leaching of applied products).

Certain sites are in heavy trafficked areas which do not favour building of soil organic matter (Carbon) levels.

The site used as a benchmark was still showing dense canopy and absence of dieback at the end of trial. This suggests that the configuration of the site where pandanus forms a dense stand favours good soil and plant health with natural element cycling (nitrogen, carbon) as well as active and diverse microbial populations.