New strain of phytophthora infestans on tomato

Tomato growers have been put on alert that a recent outbreak of Phytophthora infestans, or late blight, in UK tomato crops is likely to be a new strain of the disease, with symptoms having been seen early in the season on young plants.

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

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.

AHDB stressed that its 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.

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, also visited a nursery infected withlate blightto help staff better understand the disease and minimise the risk of spread.

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, the levy body said.

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