In many onion fields, infections with fungal diseases have been found at the end of the season. These can affect the storability of the batch. Syngenta's onion experts discuss the dilemmas surrounding the harvest.
"I find it worrying what I'm seeing at the moment," says Kees Jacobs. "Downy mildew or leaf spot disease is detected in the onions on a lot of fields." Colleague Michiel van Mol adds: "And what you're seeing now are infections from 2 to 3 weeks ago. I'm dying to see what else we're going to see." According to the onion experts at Syngenta Seeds, many growers have been taken by surprise by the mold pressure. "In recent years, we have become accustomed to dry, hot summers without significant fungal problems. You could spray economically with impunity. And there is also a group of new growers who have probably never had to deal with outbreaks of fungal diseases like this season. That group knows and recognizes the diseases less well."
Fewer kilos
With the end of the season approaching, the question arises as to how any fungal infestations will affect harvest decisions. Jacobs: "Usually we recommend harvesting at about 50% green foliage. This normally gives a good compromise between yield and skin quality. This year there is a chance that the foliage will die faster due to fungal infestation and there may be a temptation to keep the plot longer. This does not have to be a problem for land delivery, but if you want to store the onions I would opt for less kilos.Although the fungi stop in storage, an infected onion offers entry ports for other attackers, such as head rot and bacterial disease. And the storage facility is not a hospital. A batch with a lot of sick and sore can simply be stored less well. And don't forget that this is really a rotten year."
MH passed?
The storability of a batch is not only influenced by the presence of fungal infestations. "You also have to be sure that the MH spraying was successful," says Van Mol. "In a plot with fungal disease, the affected onions may no longer have had the required 2 weeks of juice flow. And then the question is whether enough MH has entered the bulb. That is yet another reason to take a good look at how you can plot there. And keep in mind that downy mildew you see today was already infected two or three weeks ago." Van Mol also advises continuing the disease control until a maximum of 2 weeks before the harvest. "Or until at least 2 weeks after the MH spraying. Whichever applies."
Harvesting technique and the weather
Apart from fungi and MH, the weather conditions are of course also of great importance in determining the harvest moment. If the current weather type continues, onion growers should not wait until opportunities become available for a field period of 3 or 4 days, according to the Syngenta onion experts. "If significant amounts of precipitation are predicted and you see a chance to drive them in, I would certainly do that," advises Van Mol. "And if driving in doesn't work, I would dig them up," adds Jacobs. "That's better for skin quality than leaving them stuck."
The last point of attention is the harvesting technique. "There's no news to report here, but it is important," says Jacobs, "Heading damage is an entry point for head rot and bacteria, so you have to prevent that." Good folding work is also important towards storage. "No deeper than a fist above the last leaf split", advises Van Mol. "After all, you will need a large chimney for drying."