Stop the import of damaging pests and diseases that could devastate the Australian hop industry

Jun 30, 2020
The Australian hop industry is fortunate to be free from many damaging pests and diseases that affect hop production overseas. Protecting this enviable status should be an absolute priority since their import could cost growers millions in lost production, unacceptable brewing quality, control and containment programs. While federal, state and territory governments are responsible for all pre and post-border biosecurity measures, their personnel are generalists rather than experts. This means onus is on the hop industry to manage any risks associated with the import of hop propagation material. We need to work together to ensure all growers abide by the import conditions, know the key threats, remain vigilant and report suspected incursions.

Image: Hop leaves with severe powdery mildew caused by Podosphaera macularis in the United States Pacific Northwest (Plant Management Network).

Despite the fact there are prescribed pre and post-border biosecurity measures in place, it’s very difficult to import hop propagation material safely, even when the import conditions are followed to the letter. The import conditions for hop propagation material are available on the Biosecurity Import Conditions (BICON) system, and include a valid permit, virus-free certification, establishment and disease screening at a government owned quarantine facility. Failure to abide by these import conditions exposes all stakeholders in the hop industry to high levels of risk and may result in a hefty fine or even jail time.

The Australian hop industry is fortunate to be free from damaging pests and diseases that affect growers overseas, but two-spotted mites and other arthropod pests do occur. In the case of two-spotted mites biological control is sometimes possible with the resident population of predatory mites, such as Phytoseilis persimillis, and other beneficial insects that are available for purchase and release from Biological Services.

There are currently no antifungals registered or permitted for use on hops anywhere in Australia. The onus is on growers to take all necessary precautions to stop the import of key fungal, viral and viroid pathogens in Table 1.

Table 1. Key fungal, viral and viroid pathogens that present a threat to the Australian hop industry

PATHOGENSYMPTOMSOUTCOMESMANAGEMENT
Citrus Bark Cracking ViroidAlso referred to as severe hop stunt viroid due to its much shorter incubation period. Early season growth is delayed causing the length of internodes to be reduced by as much as two-thirds. The cones on the sparse and shortened laterals are smaller and development is slower. Visible symptoms only take up to one growing season to appear after initial infection. Caused severe mortality in hops in Slovenia. Can only be eradicated from the soil by long fallow periods prior to replanting, which would cause major problems since Australia has very limited land available for hop production.
Downy MildewStunted, brittle shoots with downward curling leaves. A distinctive yellowing beginning at the centre of infected leaves may be present before purple to black spores on their underside can be observed. Caused upheaval in the hop industry in the 1990s. Can result in severe crop damage, and in some cases complete crop failure if significant infection and crown rot occurs. Infected bines must be manually removed and healthy shoots retrained in their place. No single management tactic provides satisfactory control. Strict attention to growth, prudent irrigation management and timely antifungal applications are needed to manage the disease successfully. Some of these antifungals are copper-based, which presents a major threat as it can inhibit the development of fruit-forward flavours that are characteristic of Australian varieties. Copper is also one of the most widely reported heavy metal soil polutants
Hop Stunt ViroidEarly season growth is delayed causing the length of internodes to be reduced by as much as two-thirds. The cones on the sparse and shortened laterals are smaller and development is slower. Visible symptoms may take three to five growing seasons to appear after initial infection, which frequently leads to propagation and planting of infected material. Caused severe mortality of hops in Japan, Europe and North America. Can reduce alpha acid yield by 60-80%. Any infected bines should be removed promptly, including as much root tissue as possible. Because of the latent period, several adjacent plants should also be removed. Sites should be allowed to remain fallow for one season so that any remaining living roots produce shoots that can be treated with herbicide. Farm equipment should also be thoroughly sanitised to remove plant residue that may lead to further transmission.
Mosaic ViroidMosaic mottling between major leaf veins that can become necrotic. This is most severe when a period of cool weather is directly followed by a period of high temperatures. Plants can be infected for several seasons without visible symptoms until the appropriate environmental conditions occur. Infected plants may establish poorly, exhibit weak bines, and often fail to attach to the string. Varieties with Golding ancestry are particularly susceptible, and yield can be reduced by up to 60%. Use of herbicides rather than mechincal pruning to control basal growth. This may help to reduce transmission to adjacent plants. Application of insecticides to control aphid population may also help to reduce transmission to adjacent plants.
Powdery MildewPowdery white masses that develop on stems, leaves, buds and cones. During periods of rapid plant growth, raised blisters are often visible before sporulation can be observed. Infection of burrs can cause abortion or severe distortion as it develops. Caused upheaval in the hop industry in the 1990s. Can result in severe crop damage, and in some cases complete crop failure due to lost production and unacceptable cone quality. Breeding programs would also experience significant set backs.Integration of varietal resistance, crop sanitation, fertilization, irrigation and timely application of antifungals throughout the growing season. Some of these antifungals are copper-based, which presents a major threat as it can inhibit the development of fruit-forward flavours that are characteristic of Australian varieties. Copper is also one of the most widely reported heavy metal soil polutants in the world.
Verticillium WiltRange and severity vary depending on the aggressiveness of the pathogen. Yellowing of the lower leaves, death of tissue between major veins, and upward curling are common. Infected bines become noticeably swollen and tissue exhibits medium to dark brown discoloration when the plants near flowering. Caused significant damage in Europe. Plants affected by non-lethal strains in one season may fully recover and appear healthy the following season. In contrast, plants affected by lethal strains will experience a sudden collapse of leaves and laterals that will rapidly kill susceptible varieties.Can only be completely eradicated from the soil by long fallow periods prior to replanting, which would cause major problems since Australia has very limited land available for hop production.

Australian growers don’t need to look very far for examples of just how devastating the invasion of these key fungal, viral and viroid pathogens could be for the hop industry, particularly because their absence up until this point means that any varieties developed in Australia are possibly susceptible to an outbreak. For instance, it took 5 years and more than $26 million for the Australian banana industry to eradicate Banana Freckle in Cavendish Bananas. Similarly, it took 6 years and more than $1 billion for the New Zeland kiwi fruit industry to recover from Bacterial Canker infecting Golden Kiwi Fruit.

The primary means of importing the key fungal, viral and viroid pathogens is through infected hop plants, from which subsequent propagation can and does occur. If you’re seeking hop propagation material to grow on your farm, at your brewery, or in your backyard, be sure to use a reputable Australian supplier. In other countries, growers have developed programs like the National Clean Plant Network. There is currently no such program in Australia, so propagation should only be made from parent plants that are known to have good growth, yield and are free from pests and disease symptoms. Growers should discuss plant health status with their supplier, inspect parent plants in field, and access plant pathology services through their local Department of Primary Industries (DPI). If you can’t source the hop propagation material you need from an Australian supplier, it is essential that you import certified virus-free material while abiding by the strict import conditions.

Digital resources are also becoming increasingly important to plant biosecurity, providing fast access, download and analysis of information. See Table 2 for some of the online systems are used by stakeholders in the biosecurity system.

Table 2. Digital resources that aid plant biosecurity in Australia

RESOURCEORGANISATIONINFORMATION
Australian Biosecurity Import Conditions (BICON) for hop seed, hop tissue culture, and hop nursery stockDepartment of Agriculture, Water and Environment (DAWE)• Import conditions
• Fact sheets
• Contingency plans
• Diagnostic protocols
The Biosecurity PortalPlant Health Australia (PHA)• National plant surveillance reporting tool
• Knowledge bases and data libraries
• Shared spaces for committees and working groups
• Awareness and information resources
The Australian Plant Pest Database (APPD)Plant Health Australia (PHA)• Key reference system for plant pests and diseases
• Information on validated pests and diseases of plants with significance to agriculture, forestry, pasture or the environment
• Draws information from 18 databases throughout Australia
AUSPestCheck™Plant Health Australia (PHA)• Surveillance data on the presence or absence of exotic and established pests around Australia
• Maps generated in real time provide digital representation of pest status around the country, including during invasions

While the Australian Government is responsible for the majority of pre and post-border biosecurity measures, state and territory governments are responsible for the delivery of plant biosecurity operations and supporting legislation within their borders. Each state and territory has a different approach to preventing the spread of existing and exotic pests and diseases, primarily due to the varied climatic conditions and legislative frameworks across the country. See Table 3 for details regarding the department that is responsible for plant biosecurity in your state or territory.

Table 3. State and territory government departments responsible for plant biosecurity

STATE OR TERRITORYDEPARTMENT
ACTEnvironment Planning and Sustainable Development (EPSD) Directorate
NSWDepartment of Primary Industries (DPI)
NTDepartment of Primary Industry and Resources (DPIR)
QLDDepartment of Agriculture and Fisheries (DAF)
SADepartment of Primary Industries and Regions (DPIR)
TASDepartment of Primary Industries, Parks, Water and Environment (DPIPWE)
VICDepartment of Jobs, Precincts and Regions (DJPR)
WADepartment of Primary Industries and Regional Development (DPIRD)

It’s critically important that anyone who is not prepared to invest the time, money and effort required to abide by the import conditions simply make do with the hop propagation material available in Australia. It’s time to work together to ensure all growers abide by the import conditions, know the key threats, remain vigilant and report suspected incursions that could threaten hop production, the brewing industry, and a future full off delicious hop-forward beers.

 

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