Early appearance of late blight raises concerns for tomato growers

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A recent outbreak of Phytophthora infestans, or late blight, in UK tomato crops is likely to be a new strain of the disease, as symptoms have been seen early in the season on young plants.

Some existing plant protection controls are proving ineffective due to the apparent aggressiveness of this strain. The limited number of applications allowed for authorised protective and curative products for the disease during the growing season is also causing concern for growers, due to its early appearance.

AHDB’s crop protection programme, SCEPTREplus, has responded quickly to the outbreak and will be conducting a trial this year to identify new potential options to control the strain.

Cathryn Lambourne, AHDB crop protection scientist, said: ”We were alerted to the issue in young plants in late March, the disease was confirmed and the genotype identified by David Cooke at The James Hutton Institute. We are working quickly to raise awareness of the emerging problem and also to help with seeking approvals for crop protection products for growers.”

Introducing biosecurity measures and understanding cultural and environmental factors will also play an important role in helping growers to prevent and control the disease.

Gracie Emeny, AHDB knowledge exchange manager, said: “Conditions to avoid for disease development are a combination of 10-20˚C and high relative humidity. It’s important to prevent the development of standing water and surface wetness, and to remove all infected plant material from the glasshouse.”

Phytophthora are oomycetes, which are related to seaweeds and depend on free water for infection and spread. Symptoms of the new strain include brown stem lesions that start just above the graft union and spread along affected stems.

As part of an AHDB-funded project to develop on-site diagnostic testing for oomycetes, Tim Pettitt, senior research scientist at the University of Worcester, visited a nursery infected with P. infestans to help staff better understand the disease and minimise the risk of spread.

Information about the new strain, including symptoms, testing and diagnosis, biosecurity measures and cultural control options can be accessed here horticulture.ahdb.org.uk/phytophthora-infestans.

A free biosecurity guide for crops grown under protection is also available from horticulture.ahdb.org.uk/biosecurity-protected-edibles-guide.


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