A firm, preventive commitment to mildew control in rose cultivation is unavoidable. Resistance management and label limitations make it necessary to regularly alternate agents with different mechanisms of action. At the same time there is a growing need to work with less chemicals and more organically. Arend Roses from Maasland is well on its way, thanks to the experience with Karma last season.
Ferry van Rodijnen: "We now make smaller bundles so that the evaporation moisture dries up quickly, causing the crop to condense less in cold storage, where we now also apply dehumidification."
Rocket, Karma and Frupica are three strong tools against powdery mildew that Certis gives to rose growers. This is confirmed by Arjan Spaans Van Iperen, who supervises crop protection at Arend Roses. Along with cultivation manager Ferry van Rodijnen he closely followed the practical research conducted at their company by two students of HAS Hogeschool for twenty weeks (see also Glashelder no. 29, Spring 2015). The aim was to find out why roses treated with Karma experience condensation in cold storage sooner.
"We also wanted to know if this could be prevented," says Lianne van Wijk, who oversaw the project. "Karma is in fact a product of natural origin that works great. It would be a shame if growers have to avoid it from now on because of this side effect - which, incidentally, does not occur in all cultivars. Fortunately this is not necessary."
Apparently, the research has yielded results. Ferry van Rodijnen: "Yes, that's right. It works on the basis of potassium bicarbonate, which is a salt. Our suspicion that salt residue on the leafs attracts moisture from the ambient air has been confirmed by the students. That is the crux of the issue. Compliments for their work, they have worked very hard to get to the bottom of this.” The grower continues: “We actively pursue sustainable cultivation. The future lies in less chemistry and more organic products. If I can substitute chemicals with green alternatives such as Karma, I will certainly do so."
"In September/October, the risk of Botrytis is bigger and Frupica can be used to great effect," Arjan Spaans tells Lianne van Wijk. "My advice would be to use it twice then."
In consultation with his advisor, Van Rodijnen has introduced measures that enable the use of Karma. The first measure is taken during harvest, by forming smaller bundles. The roses are then less densely packed, allowing evaporation moisture to dry up quicker and not accumulate in the bundle.
Spaans: "The second measure is cooling down slowly. When you suddenly move 30ºC roses to a damp cold storage at 2ºC, condensation will occur for sure. Taking more time can prevent this. The third and most radical measure is active dehumidification in the cold stores. The cold store for finished products already has this, the remaining stores will follow.” Van Rodijnen: "This was already a wish of mine, because drier air gives Botrytis less chance. The study gave the final push to make that investment now."
The fourth and simplest measure the cultivation manager mentions is a limited application period. "Between April and September the weather is generally poorer," he explains. "The crop then condenses less anyway. I want to give Karma a permanent place during that time. Even then I will continue to alternate in order to avoid too much salt accumulating on the crop. I won’t rule out still doing some comparative tests myself. I'm always doing research, because it keeps me sharp and it is necessary to innovate in time. It has also been a pleasure collaborating on the project."
Karma therefore doesn’t make products like Rocket and Frupica unneccesary. Rocket in particular is valued in rose cultivation for its powerful curative and preventive effect. "Virtually all growers know it and regularly apply it throughout the year," says Spaans.
"Frupica is clearly less known in rose cultivation, while it is an excellent and gently preventive tool," says Van Wijk. "Is this because you can use it only twice a year?"
"That’s possible," the crop protection advisor replies. "It is easy to buy products that you already know and can apply more often. That sometimes makes you forget that there are other good products. Still, I think this product will be used more in rose cultivation. More and more products suffer restrictions that make frequent alternation necessary. And Frupica works well both against mildew and Botrytis. In September/October the probability of Botrytis increases, and this product can be applied to great effect. My advice would be to use it twice then."
Spaans suggests that his client makes a complete overview of all approved mildew and botrytis products, the chemical groups to which they belong and their possible limitations: "Maybe you can operate even more consciously and sustainably than you are already doing."
"That sounds good," Van Rodijnen reacts. "Most of it is in my head, but if you write it down you can’t miss anything. Other growers will also feel that need."