Timing MH spraying for optimum storage quality

The first MH spraying on seed onions has been carried out. Determining the right spraying moment is more difficult this year than in an average year. "Irregularities in the fields and dry conditions require extra attention," says Erwin Boogaard, cultivation specialist at Agrifirm.

According to him, the MH spraying is the most important spraying in the onions. A well-executed spraying (at the right time) ensures good dormancy and that largely determines the storability of the onions. "You don't want to be surprised by sprouts in your storage in January or February. Then you have an unsaleable product."

A successful MH spraying starts with allowing the crop to grow as evenly as possible. Then the ideal moment for spraying is easiest to determine. This year, however, there are many plots where the first corner of onions has already been completely ironed, while the rest of the plot is still standing. Such irregularities have various causes. The turnout may have been disappointing in places. A thinner setting ensures that the onions continue to grow for longer. Growth retardation can also be caused by a nematode infestation. "You can also cut up a plot with extremes," says Boogaard.

The first signal that the MH spraying is imminent is the ironing of the first onions. "The necks of the onions start to feel weaker, they no longer have the full strength they had before." Then it comes down to choosing the right moment. "Spraying too late does not mean maximum dormancy. For a good effect, the product has to get into the soil of the bulbs, for which the crop has to continue to grow for another two weeks. And if sprayed too early, the onions don't become hard. Then they remain void."

Find Leafless Skirt
The onion sector uses three different ways to determine the optimum spraying moment. "Overall, you are almost always good if 10 to 30 percent of the onions have been ironed," says Boogaard. It is important to make sure that the onions are really ironed. "Due to a shower or strong wind, the crop can also lie flat. Then ironing is no longer a good guideline for timing the spraying."

A second method for determining the spraying is to assess the relationship between bulb thickness and neck thickness. That ratio should be 3 to 1. "My experience is that in some years and with some varieties you can't handle that enough. Then you wait too long," says Boogaard.

The cultivation specialist prefers to cut onions. "See if the onion has a leafless skirt. That's the most reliable criterion." A leafless skirt is the skirt that does not grow upwards through the neck, but whose top, the nose, remains in the bulb. This ensures the bulging of the onion. If the onion has a leafless skirt, the onion will not remain dry. Moreover, the crop is then still vital enough to absorb the MH and transport it to the bulb bottom.

Good spraying conditions
For good absorption of MH, the crop must be growing well and must remain dry for 10 hours after spraying. "In changeable weather, the absorption is good, but it is sometimes exciting whether the agent has enough drying time. You can shorten that drying time by adding a bonding agent such as Bond."

If it is very dry, as is the case this year, the crop is not growing well enough. Irrigation prior to spraying is then a good option. Those who cannot irrigate must wait. "Under dry conditions you can also wait longer; until a maximum of 50% of the onions has been ironed," says Boogaard. "Try to spray in the evening before a dew night. Just before the dew sets in. The product then has a good chance to be absorbed before it is hot and dry again the next day."

Spray separately
Because the MH spraying is so decisive for the storage quality of the onions, Boogaard advises to always spray separately. "You don't want another agent, for example an insecticide, to get in the way of the absorption of your MH. It is too important a spray for that."

The product must be well absorbed and for this each onion tube must be given maximum coverage. That means: spray with a lot of water and a finer drop. Around 400 liters of water per hectare and a 03 or 04 nozzle with a standard sprayer give a good result.