Cultivation Principles – Common chickweed
Superficial tillage will mix seeds into the soil which will place the freshly shed seeds into moisture but also into darkness, some seeds will germinate (15%) but it will also decrease predation. Buried seed will be exposed to light and will germinate. Leaving the soil uncultivated will result in more freshly shed seed germinating (c 85%) and increase the seed lost to predation. This shows that knowing how much seed is in the profile vs how much seed has been shed is crucial.
Repeated cultivations do not appear to be as effective as expected due to the law of diminishing returns but they are most effective when done in the autumn and spring when conditions are more conducive to emergence of seedlings.
Conventional, strip tillage and direct drilling are all appropriate when considering this weed. Note detailed comments on establishment.
Rotation has a low impact on chickweed control as it has the ability to germinate in almost every month of the year. The weed can be controlled by herbicides in most crops
Ensure even spread of residues across field and a good chop of straw to maximise herbicide efficacy and avoid unnecessary cultivations. Straw chopper knives need changing/reversing regularly – often three or more times a season.
Where appropriate (e.g. when direct drilling with appropriate drill into high residue levels) leave a longer stubble height. Stubble mulching of high stubbles can be used where straw needs time to become brittle after harvest.
Residue spreading and shallow stale seedbed cultivation by raking (passes followed by glyphosate as needed, although the law of diminishing returns applies to multiple passes) combined with surface rolling (for effective herbicide action, weed germination & slug management) or shallow discing/rolling is effective to manage residues, control slugs, and create the best conditions to stimulate weeds outside the crop. Depth to be only just greater than drilling depth of following crop, ideally ≤5cm. Consolidate after tillage to maintain moisture in the stale seedbed. Surface consolidation is essential after shallow tillage, and through to depth pressing plus surface consolidation is needed following deeper tillage. Timing of tillage ideally is later to allow surface predation of weed seeds, and is most effective when temperatures are sufficient for germination. Note seed heading can be as soon as 6 weeks after emergence.
NOTE: The law of diminishing returns applies to repeated shallow tillage in the case of this weed.
Ploughing is less preferred to shallow surface disturbance. This should preferably be done one year in 5 or more, and ideally ahead of a spring following crop. Effective burial by:
(i) Suitably narrow furrow width (30/35cm on heavier soils) and share width < furrow width;
(ii) Sensible forward speed;
(iii) Appropriately set skimmers;
(iv) Post plough pressing to close the surface;
(v) Pre-cultivation shallow if needed so soil/straw contact of the buried residues allows efficient breakdown and good rates of water movement through the profile.
Maintain seed bank horizons by controlled surface disturbance of all operations. Mixing weed seeds to variable depths reduces efficacy of residual herbicides and prolongs the germination period for weeds.
Loosening as needed by low rake angle winged tines with adequate lift height for conditions and depth worked. This controlled vertical fissuring also minimises disrupting the weed seed bank horizons. Aim to establish a following crop ASAP after loosening (cover crop if spring drilling the next main crop which is preferable) to stabilise the resulting structure created.
NOTE: Effective loosening is vital where structure is likely to reduce or inhibit moisture infiltration levels. Poor drainage reduces competitiveness of the following crop. Consider headlands and the main field areas separately where loosening is needed as in many cases loosening depths are different, or not required across the whole field.
AT ALL COSTS avoid:
- Deep non- inversion mixing
- Re-inversion before 5 or more years
- Lower depths of disturbance when cultivating than during follow-on spring drilling
- Failure to consolidate after soil disturbance as this will lose moisture and adversely affect germination potential of the weed seeds