Late blight of potato and tomato is a declared pest in WA
Late blight of potato is not known to occur in WA and must be reported to DPIRD if found or suspected to be present in WA.
Early detection is critical to help protect the Western Australian potato and tomato industries.
About late blight
Late blight (Phytophthora infestans) is considered the most serious and devastating diseases of potatoes worldwide.
It can affect tomatoes, and other closely related crops may be mildly affected.
Late blight is a fast-spreading fungal disease that can rot entire fields of potatoes and kill tomato crops. The disease caused the Irish potato famine of the 1840s.
- The main hosts of late blight are potato and tomato.
- Closely related crops such as capsicum and eggplant are also mildly affected.
- Other hosts are common garden petunia, Japanese morning glory (Ipomoea nil), tobacco and the weed blackberry nightshade (Solanum nigrum).
- Large, pale green areas on potato or tomato leaves which become water soaked and dark
- Lesions expand rapidly and the whole leaf can die.
- When conditions are wet and humid late blight produces spores which are easily seen on the underside of the lesion as a white fluffy “down”.
- Lesions and sporulation can also occur on the stems of plants.
- Firm dark brown lesions form on tomato fruit, and these can grow quickly and destroy the whole fruit.
- Potato tubers can be affected with a tan-brown, reddish or purplish rot that penetrates about 1.5 cm into the tuber.
- Other fungi and bacteria often invade tubers that are infected by late blight, and the whole tuber breaks down.
- Tubers that seem healthy when harvested can rot later in storage.
In favourable weather, late blight completely destroys potato foliage in a few days and infected tubers rot in storage.
There are two types of late blight, called mating type A1 and mating type A2. The combination of the A1 and A2 mating types has produced more aggressive strains of the pathogen and enables sexual reproduction to occur, helping the disease to survive better in the soil and become resistant to fungicides.
The A1 mating type is present in some states of Australia, but not in WA. The A2 mating type and new aggressive strains of the A1 mating type are not present in any part of Australia but are present in a number of neighbouring countries in southeast Asia.
- Late blight causes serious epidemics when the weather is suitable.
- Wet, humid weather coupled with temperatures around 21°C favour rapid development of late blight.
- Late blight is usually introduced to new areas with seed potatoes. It can be present even if the seed looks healthy.
- Spores form on infected leaves and these can be splashed by rain onto nearby plants or carried up to 20 km by wind.
- Tubers are infected when spores are washed down into the soil from infected foliage.
- Late blight can survive between crops on plant residues.
Legal duty to report
Late blight of potato and tomato is not known to occur in WA.
Phytophthora infestans is a declared pest under section 12 of the Biosecurity and Agriculture Management Act 2007.
This means that any person who finds or suspects the presence of late blight of potato and tomato must report it to DPIRD.
Report suspected late blight
Early detection and reporting will help protect WA’s agricultural and horticultural industries.
If you find or suspect the presence of late blight, report it in one of the following ways.
WA's freedom from late blight of potato and tomato is supported by general and specific surveillance, specific measures such as potato seed certification, and specific import requirements to prevent its entry.