Leeks: White tip control (Phytophthora porri)

Summary: White Tip caused by Phytophthora porri develops from spores splashing onto leaves from soil and is hence prevalent in overwintering crops. Sporangia dispersal from lesions also leads to epidemics.  Inoculation tests have shown differences in varietal susceptibility to P. porri and this technique will be used to compare ten UK varieties. Fungicide products for White Tip control are limited and a review will seek potential novel conventional and biological products from those with efficacy against other oomycete pathogens. Non-conventional and conventional products will be applied as drenches in propagation to a potentially resistant and a susceptible variety before inoculation, to seek to increase plants’ resistance to infection. Another trial will evaluate products that could be soil incorporated. Two fields with a history of White Tip will be used to evaluate novel conventional products for foliar application in straight programmes. Information on conditions for disease spread in the literature and from field observations will be used to assess the feasibility of using weather data to aid growers’ decisions on if, when and what to spray. Leek growers and the supply industry will be consulted in the selection of test varieties and products and information exchanged on optimising control measures.

Aims:

      To identify leek varieties, plant protection products and treatment practices for improved sustainable management of White Tip.

     Objectives:

     To carry out studies to investigate potential mechanisms for the improved control of Phytophthora porri, the cause of White Tip in leeks:

     1. To determine by inoculated tests if there are differences in leek cultivar susceptibility to infection by P. porri

     2. To review the novel conventional fungicides, biological control products and elicitors which may be of benefit against P. porri

     3. To determine by inoculated tests whether treatments applied during propagation can lead to a subsequent reduction in White Tip on the plants

     4. To determine by inoculated tests whether treatments applied to soil may lead to subsequent reduction in White Tip on the plants

     5. To carry out a field trial in the west of the UK to evaluate the efficacy of foliar applied novel plant protection products against P. porri.

     6. To carry out a field trial in the east of the UK to evaluate the efficacy of foliar applied novel plant protection products against P. porri.

     7. To explore the potential for weather-based disease forecasting to assist spray application timing for White Tip

     8. To communicate results, and carry out further knowledge exchange, of White Tip control with growers in order to improve sustainable control of the              disease

     9. To prepare a factsheet to give grower-focused information on the lifecycle, epidemiology and cultural and chemical control measures of P. porri