Technically, 2018 was a bad head rot year

The second year of research with neck rot trials has come to an end after the 2018/2019 storage season. While the conditions for neck rot were often still favorable in 2017, that is not the case at all in 2018.

The biggest challenge was to keep the onions growing through irrigation. Little or no crown rot was found in the test, except in the specially infected strips. Here the head rot percentage rose to 50%. Despite the unfavorable circumstances, 2018 still yielded interesting information.

Head rot control strategies
The goal of both the sector and the ministry is clear: effective management on the head rot. Effective also means that treatments are omitted if there is no need. The 2018 research year was mainly the year of the absence of infection chances. By infecting special strips themselves, the researchers ensured that there was a source of disease nearby. With that, each net field was even 3 meters from an infection strip center to center.

The control strategies ranged from 'doing nothing at all' to 'maximizing opportunities' to prevent head rot. However, it was mainly about the use of warning systems. The Decision Support Systems (BOS) of 3 providers were tested. For every BOS, the chance of infection determines the moment of spraying. In theory, a better timing of the spraying moment can ensure that head rot is combated more effectively. For comparison, reference objects were included in this test, such as an object with a flushing scheme with an effective plant protection product against crown rot.

Although such a schedule is not possible in practice due to the limitation on the number of sprays, it did provide information about the maximum achievable. Of course there was also a reference object where head rot was not combated. It was intended to find out how serious neck rot had wreaked havoc in the test. The third reference object focused on the maximum occurrence of head rot, with spraying based on a practical schedule. In the last reference object, only general diseases (such as leaf spots and downy mildew) were sprayed. There may be a side effect of these agents on neck rot.

Results
In 2018, the chances of infection for neck rot were awaited for a long time. It was only after the turn of the weather that there were some chances of infection, which was well overdue for the fungus to do any damage. The first spore flight was recorded from August 13 to 14. The first warning from a system came on August 13. At the end of the cultivation, spraying was nevertheless carried out in this object.

The second system issued a warning on August 14. Spraying was also carried out in that reference object. The third system reported no high probability of infection and was thus effectively equivalent to the untreated control. Note: the object 'untreated' was not completely without spraying, because spraying was done against downy mildew.

off country
The onions were dried off land, ensuring that top rot was given maximum chance. The degree of head rot in storage in January and April 2019 was therefore a result of what happened in the field and was not influenced by a good storage process. During the assessment in the month of January, no differences were found in the degree of head rot. For the various objects, it varied from 0,2% to 1,2%, based on weight.

What was striking was that the degree of infection in the infection strips was around 50%. At the second assessment in April, the degree of impairment ranged from 0,2% to 1,8%. Although this is still low, the degree of damage in the untreated control (and therefore also in system 3 and system 2) was significantly higher than in the other objects. Spraying about 1 day earlier gave 0,4% head rot and 1% 1,4 day later. If nothing was done, it was 1,8%. The purge schedule (0,2%) and both strategies (0,3% and 0,4%) gave similar results to System 1.

Conclusion after a dry year
The warning systems gave no warning during the hot summer. It was only after the turn of the weather that the warnings came from 2 of the 3 systems and that corresponded to the first trace flights. Spraying 1 day earlier still gave a significant (albeit small) reduction in the degree of head rot. All systems provide sufficient options and opportunities to further fine-tune them.

This article is from Ureka† Uireka is a unique chain project, where Hazera participates in. Its aim is to improve the quality, and thereby strengthen the export position, of the Dutch onion.