Sunday, November 19, 2017

Use post-harvest management to manage blackgrass

June 30, 2017 by  
Filed under Crops

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As harvest nears, cereal crops are feeling the impact of lack of moisture earlier in the season, writes Richard Overthrow.

A long spell of wind and rain last month did little to rescue crops and made late season spraying very difficult.

Some barley crops stunted by drought had lodged by the end of June, and small flag leaves in drought-stressed wheat crops seem to stay that way despite ample water since. But whatever the outcome of harvest, we will carry on into next season as we have always done.

Pre-harvest farm tours or even views from the combine cab are a good opportunity to map any areas of surviving grass weeds. Blackgrass seeds became viable earlier than usual this season so there may be little to be done now. But this monitoring exercise will allow next season’s campaign to be planned.

There may also be broad leaved weeds which have come through herbicide treatment. Resistance in poppies and mayweeds in particularly, to some ALS-inhibitor herbicides, is spreading and any such cases should be noted to allow planning of future herbicide strategies.

Trash management

As ever, straw use will be an important decision to make. Many barley crops in particular lodged following the weather in June, and straw and trash management could be difficult.  Growers also need to be aware of the P and K value of crop residues, data for which are available in RB209.

Post-harvest cultivations are an important part of grass weed control programmes, both to encourage pre-sowing weed emergence and to prepare the best seedbeds possible for optimum residual herbicide performance.

Stale seedbeds, where the stubble is cultivated and rolled or pressed to encourage grass weed emergence, can be effective against black-grass and sterile and great bromes, and should be created as soon after harvest as possible.

If drilling is also delayed in the worst affected fields this should give ample time to get a good flush of grass weeds before sowing the next crop.

Stubble

Meadow and soft bromes have very different stubble management requirements. Seeds of these will be encouraged to germinate by leaving exposed on the surface, so if either of these is the main target leave stubbles untouched for as long as possible.

Where a stale seedbed follows an oilseed rape crop then if possible wait for shed rape seed to be wetted by rain before cultivating. Oilseed rape volunteers are becoming a widespread problem, particularly with the shorter rotations and seed shed during harvest can become dormant for several years if buried in dry conditions.

Stale seedbeds have less value prior to oilseed rape due to the shorter cultivation window but it is still worth trying where grass weed populations are high.

Glyphosate

The most common method of harvest management in winter rape is still glyphosate treatment. Check recommended timings carefully to avoid immature seed or delayed harvest.

Spring crops may still require management particularly for disease control. Fungicides may be needed for linseed, for seed crops at least, and in wet summers all crops can benefit from post-flowering fungicides.

Spring oat crops may succumb to late attacks of crown rust and need further fungicide treatment. Similarly some spring beans may still be prone to chocolate spot and rust, the latter can come into the crop quite late in the season. Both crops have been fairly clean this season and have coped with one fungicide treatment to date.

Richard Overthrow is a regional agronomist with NIAB TAG, the UK’s largest independent agronomy organisation with several research centres in East Anglia. For more details, call 01223 342495.

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