Haulm destruction and blackleg in seed production

The advisory message that haulm pulverisation in seed crops with blackleg would lead to an increase in contamination and disease risk in subsequent crops was widely spread since research (Perombelon et al, 1979) first indicated the risk. Sulphuric acid was an effective alternative that ended tuber growth quickly.  However, since the message was first disseminated, there has been a gradual return to haulm pulverisation which has accelerated since it was known that sulphuric acid would be withdrawn as a haulm desiccant from 5^th June 2010 (2008/937/EC).

Collaboration

SAC, SCRI

Approach

The trials took place in two fields with high levels of blackleg: Elgin (61.3% blackleg) and Inchbare (27% blackleg). Within each field two replicates blocks of crop were identified for haulm pulverisation or haulm desiccation with diquat. Haulm destruction and comparison only took place at Inchbare owing to flooding at Elgin.

Key Findings

• At Inchbare, there was no evidence that haulm pulverisation resulted in increased tuber contamination over the diquat treatment. This may have been due to limited rainfall and a sustained period of dry weather after pulverisation. There is a suggestion from blackleg risk assessment tests that greater contamination was present where diquat was applied rather than with the flail treatment, although statistically inconclusive.
• P. atrosepticum was found to contaminate weeds in and around the potato crops studied. Weeds may be another potential source of contamination of high grade seed crops.
• There are situations where haulm pulverisation can be used even where blackleg is present in a crop. However, pulverisation of crops exhibiting blackleg may lead to contamination of nearby high grade seed crops.
• The haulm destruction method may influence diseases other than blackleg. Future R&D is proposed to understand the epidemiology of pathogens and changes in crop physiology that relate to increased disease risk as a result of haulm destruction methods.