Assess the winterisation of your organic winter oilseed rape

Plant numbers, damaged head shoots, oilseed rape flea beetle and large tuber beetle fungus are the things to assess in your organic oilseed rape field.

By Sven Hermansen

Below are some tips on how to check in early spring whether the conditions in your oilseed rape field are good enough for the rape to survive. If the rape is too weak, it may be better to plough it down as a catch crop and plant a new crop.

Late summer and autumn 2025 provided good conditions for establishing winter oilseed rape in most places. Depending on the variety and field conditions, this can mean that the oilseed rape has developed strongly with soft stems and lifted head shoots. The hard frost and snow cover is usually not a big problem for the varieties used. However, you should still pay attention to the condition of the plants, as it has been some time since we last had real winter weather.

Therefore, the fields need to be inspected now. This can be a difficult decision, so consider whether you need a second opinion from your organic consultant who sees many winter rape fields.

The size and distribution of plants, weed pressure and the condition of the field should be included in the winter oilseed rape assessment to be made in early spring.

Below you can read about 4 points on how to assess your organic winter oilseed rape field in the spring.

1: Count the number of oilseed rape plants in the field

The first thing to check is the number of plants in your oilseed rape field. Ideally, there should be more than 30 evenly distributed plants per^{square metre} in your canola field to have a robust and competitive crop. In a field with a thin plant population, weeds will easily gain too much power and this will cost yields.

The optimal number of plants is around 30-60 ^plants/m2 when growth starts in the spring. However, we know that a winter oilseed rape plant in good growth has an amazing ability to compensate for low plant numbers by forming side shoots. So all guides require an overall assessment of the field to be made.

To get an idea of the plant count, count the number of plants per running metre in a row and multiply by the number of rows you have per metre in the field. If you have a row spacing of 50 cm, then there are 2 m rows per^m2 and you need a minimum of 15 plants per metre in a row to reach 30 plants per^m2. It's important that you do the count in several different places in the field to get an idea of the condition of the field.

At a row spacing of 12.5 cm, the number of plants is 4 - per running metre at 30 plants per^m2
At a row spacing of 25 cm, the number of plants is 8 - per running metre at 30 plants per^m2
For row spacing 50 cm, the number of plants is 15 - per running metre at 30 plants per^m2

A thin rapeseed field that should be assessed to see if the plant count is ok.

2: What does the oilseed rape plant look like?

It's also important to examine how the individual plants look, especially if the main shoot is intact. If the main shoot has been damaged by frost or pests, then it is necessary to look at the quality of the side shoots and weed pressure, as it will take longer for the oilseed rape to provide the necessary weed competition.

Rapeseed field with varying number of main shoots. Assess the entire field.

3: Check for canola flea beetle infestation

A third thing you should check is how badly your winter oilseed rape plants are infested with oilseed rape flea beetles. To check this, make an oblique cut just above the growing point in the stem of a oilseed rape plant and count the number of oilseed rape flea larvae. Again, it's important to walk around the field and carry out the test in several different places.

The oilseed rape flea beetle larva can do a lot of damage with its gnawing in the stem, but vigorous plants in good growth can withstand the damage of up to 3-5 larvae. In contrast, 2 larvae in a small plant can be critical.

As a rule of thumb, a stem with a diameter of more than 8 mm is a strong plant. If the stem is weaker, it will be more vulnerable all else being equal. That's why it's important to cover the entire field. However, how many oilseed rape flea beetle larvae the plants can survive and produce good yields also depends on the number of plants, row spacing and weed pressure.

Decision support tools have been created for use in counselling. These include the most important parameters for assessing the field. Ask your advisor if you are in doubt.

Larvae of oilseed rape flea beetles in a cut leaf stalk of oilseed rape.

4: Remember to deal with infestations of large-leaved knotweed

Later in the spring, after flowering has finished, damage caused by big head blight can be found. It's important to assess any infestation because it affects how oilseed rape cultivation can function in crop rotation in the future.