In mechanical weed control, we typically think of spring and summer. However, there are many weeds that grow almost year-round. Chickweed and annual meadow grass are a couple of examples. True chamomile receives a significant germination boost after soil disturbance (such as sowing winter grains, harvesting vegetables, etc.) and can germinate late into the fall. These weeds are less susceptible to frost and thrive well in our warm and moist winters, which seem to be occurring more frequently in a changing climate. Towards the end of winter, we are increasingly surprised by these vigorously developed winter weeds.

In winter grains, these weeds are difficult to control in spring with a harrow. Often, the ground is too hard, and the weeds are too large for efficient control. Chickweed and annual meadow grass then grow invisibly beneath the crop, significantly enriching the seed bank. True chamomile grows alongside the grain, causing not only competition but also difficult harvesting.

We also see more and more problems with winter weeds emerging in vegetable cultivation. On late harvested and/or sparsely vegetated plots, these weeds have ample opportunity to develop during the winter period. In early spring, these weeds, even when small, are difficult to destroy. They uproot difficulty, and severed plant parts can easily re-root. In systems where plowing is not practiced, it is therefore difficult to create a weed-free seedbed in early spring. This was particularly evident in the wet spring of 2023.

In this project, we are investigating, based on seed bank samples from 50 organic plots spread across Flanders, whether relationships can be established between the seed bank size of the respective winter weeds on one hand, and the cultural and technical management practices on the involved farms on the other hand (including rotation, soil management, weed management). From this analysis, practical guidelines can be derived to better manage these problematic weeds in real-world situations.

This project aims 1)to identify   cropping systems and practices that can lower the incidence of these weeds, and 2) to evaluate combinations of cultural (sowing time,  cereal type, variety choice, plant density) and mechanical weed control  (precision flextine harrow: timings and number of passes) tactics for their effectiveness in controlling these weeds in winter cereals. The ultimate goal  is to provide tools and recommendations that  will help organic growers to keep these problematic annuals as low as possible.