IWMPRAISE

Choosing cultivars that compete with weeds

It is possible to choose varieties that are more, or less, competitive to weeds particularly for annual crops. This measure consists of planting varieties with high covering power in order to limit the impact and development of weeds.

Planting intermediate crops with a negative allelopathic or biocidal effect: biofumigation

Biofumigation is a biological method aimed at controlling the development of pests (pathogens and pests of the soil, germinating weeds) in the soil by the use of any plants with allelopathic effects.

IWMTOOL: one factsheet considers cultivar choice

Suppressive crop varieties will reduce the fitness of the weeds, while tolerant varieties will maintain high yield levels under weed pressure, but will not necessarily reduce weed densities and therefore could result in a build-up of the weed population. The choice of cultivar is an important way to prevent high yield losses due to occurring weeds and to reduce the build-up of weed populations.

IWMGAME [arable crops]: One card represents this measure. It has limited preventative effects, competing weeds for light and space. You can play it at the first stage period and this method have benefit side effects. This method is no effective on perennial weeds. Allelopathy can be used in complement of cover crops (at intercropping period) to have more additional beneficial effects.

Practicing direct sowing, on bare soil or under cover

Direct sowing involves sowing the crops without any prior tillage, turning, decompacting or preparing the seedbed. This technique can be carried out on bare ground, or under dead or living plant cover. As a simplified cultivation technique, direct sowing has the advantage of preventing soil erosion and the development of weeds.

Adapting the implantation date according to the sanitary risks

Adjusting the sowing date can help avoid periods of greater susceptibility to attacks from certain pests. This must therefore consider the biology of the problem but also the capacity of the cultivated plant to tolerate the new sowing date depending on its biology and the soil on which it is planted.

IWMTOOL: Three factsheets are dedicating on describing sowing methods

Sowing date

Weeds thrive best in crops that are most similar to them. Among other relationships, specific weeds relate to the sowing date of a crop because they are sown during their germination period. By varying autumn and spring sown crops in a rotation, or by altering the sowing date of crops (e.g. choosing early or late varieties), the preferred germination period of specific weed species can be avoided. When sowing early varieties, the crop can have an advantage over the weeds because of an earlier soil cover or canopy closure, and by choosing (trans)planted crops, the crop has a greater competitive ability. Primed seeds can reduce time between seeding and crop emergence with a few days and may provide crops an advantage over weeds. Planted crops can give crops a head start and reduce the impact of weed competition. Knowledge of the germination periods of weeds can therefore help deciding which varieties to grow or determine an early or delayed sowing date to control specific weed species.

Sowing depth

By adjusting the sowing depth, the crop can have a competitive advantage over the weeds or the options for mechanical weeding can be optimized. Furthermore, the sowing depth interacts with water and nutrient availability. The optimal range for sowing depth varies between crops.

Sowing pattern

The sowing pattern is the spatial arrangement of a crop on the field. Most crops are sown on rows, with varying row widths and plant distances. Often the row width is determined by choices in machinery (e.g. potato ridges).

Alternative to sowing on rows, crops may be sown in a uniform grid or zig-zag pattern.

Crops like onion are some times sown in double rows or may be sown on clusters with 5-7 seeds.

IWMPRAISE Inspiration Sheet : Our French colleague presented the efficiency of “sowing date delay” technic in winter wheat. He averts on the limits of this measure.

IWMGAME [arable crops]: Four cards represent agronomic measures at implantation period. It mainly has preventative effects affecting weeds emergence. You can play it during the intercropping or first stage periods depending on the approach being taken. These methods may have some benefit or neutral side effects. These methods are not effective on perennial weeds.

Two presentations from NIAB on the effects of adjusting drilling date on weed management are presented below.

Adapting the sowing or planting density according to the sanitary risks

The modulation of the sowing or planting density can be considered in both ways (low or high density), but only following a risk analysis because negative effects may result from this technique.

IWMTOOL: There are two factsheets are describing sowing characteristics

Seed rate

Altering the seed rate and thus crop density can increase the competitive strength of crops, resulting in reduced weed growth and in the long-term reduced build-up of weed populations.

Seed vigour

An important component of the performance of crop seeds, including suppressiveness of the crop against weeds, is the complex trait of seed vigour. Using vigorous seeds promotes the competitive ability of the crop against weeds. “Seed vigour is the sum of those properties that determine the activity and performance of seed lots of acceptable germination in a wide range of environments”. It is not a single measurable property, but associated with seed performance aspects, including: the emergence ability of seeds under unfavourable conditions, rate and uniformity of seed germination and seedling growth; and performance after storage, especially the retention of the ability to germinate.

IWMTOOL: One factsheet considers transplanting technics

If economically feasible, crops such as onions and cabbage can be transplanted to give the crop a head start on the weeds. By transplanting, the crop becomes more competitive and the critical period in which crop-weed competition is very important is shortened.