Sign up for our daily Newsletter and stay up to date with all the latest news!

Subscribe I am already a subscriber

You are using software which is blocking our advertisements (adblocker).

As we provide the news for free, we are relying on revenues from our banners. So please disable your adblocker and reload the page to continue using this site.
Thanks!

Click here for a guide on disabling your adblocker.

Sign up for our daily Newsletter and stay up to date with all the latest news!

Subscribe I am already a subscriber
Screening cucumber:

Effective green agent against Botrytis cinerea or mycosphaerella not yet found

Getting new effective agents available against fungal diseases is a key wish expressed by entrepreneurs from Glastuinbouw Nederland's Plant Health network. Jeannette Vriend, on behalf of Glastuinbouw Nederland, gives an update on screening research conducted in October 2024, focusing on the diseases Mycosphaerella cucumis and Botrytis cinerea, which lead to major production losses in the cucumber crop group, among others.

Because it is not well possible to properly inoculate two fungal diseases simultaneously in the cucumber plant and allow them to develop equally in a crop, two separate screening studies were conducted by Vertify. In both studies, five different fungicides based on natural active ingredients were tested.

Preventive and curative sprays
In both studies, one preventive spray was used, after which the cucumber plant was inoculated with the pathogen. The remaining sprays were applied curatively. A total of four to six applications, according to the label, were deployed, often in combination with an adjuvant.

Mycosphaerella flies through the crop
At the time when at the fruits the flowers were drying down, a preventive treatment with the pesticides was carried out. Three days after this, a spore suspension with Mycosphaerella was sprayed. And already nineteen days after infection, the first infected fruits were observed. At the end of the study, as many as 35% of the fruits in the control treatment were infected.

Despite the preventive and multiple curative applications, no significant reduction in infected fruits was observed in any of the treatments. However, a trend is visible. The object Ravibis with the adjuvant Elasto G5 had the lowest percentage of infected fruits at each observation time and the object under code (+ Silwet Gold) resulted in a significantly higher percentage of infected fruits.

Botrytis infection strikes well
Stem stubs were created by cutting off leaves. Preventive spraying was done once, and three days later, it was inoculated with Botrytis cinerea. Ten days after inoculation with botrytis, the first stumps with a so-called botrytis lesion larger than 3 cm appeared. Another week later, there was a sharp increase in infection pressure. And on almost all 40 stumps per field a lesion larger than 3 cm could be found. In the trial, botrytis did not penetrate further into the stem, as the stumps were already falling off or drying in earlier trials. None of the treatments resulted in a significantly lower number of stumps infected by botrytis.

Search for an explanation
In this study, only agents based on contact action were tested. When spores of botrytis germs grow on a wound and into the plant, contact-based agents can no longer reach the fungus and are ineffective.

Mycosphaerella infections occur mainly when the flower falls from the fruit. This creates a wound in which spores of mycosphaerella can germinate. A mycosphaerella infection can also occur on the fruit when crop work causes wounds. Spores present on the fruit before they have germinated in a wound can be controlled with contact fungicides. Once an infection has occurred and the mycosphaerella is in the fruit, contact-based fungicides are no longer effective.

There are actually two conceivable explanations why no action of the agents was demonstrated in this trial. Either the wounds were not well enough colonised with the micro-organisms after application, or the micro-organisms are not effective enough against the fungi.

Cucumber is a sensitive crop
Two of the tested agents were tested in combination with the adjuvant Silwet Gold. Both treatments produced a crop reaction. It is a given that cucumber is more susceptible to a crop reaction during the low-light period of the year than at other times of the year. Neither can it be said with certainty whether the combination of the agent without or with another adjuvant would also have given a crop reaction. What is clear is that no spray residue was observed in any of the treatments.

Trials have been visited by the authorization holders
Cooperation with authorization holders and various other stakeholders is important in arriving at good solutions for bottlenecks such as botrytis and mycosphaerella. The resource base of synthetic crop protection products in particular is shrinking rapidly. Unfortunately, the researchers have to conclude that this study has not yet found 1-2-3 an effective green agent with robust action on Botrytis cinerea or mycosphaerella for cucumber cultivation.

Source: Glastuinbouw Nederland

Publication date: