Monday, August 19, 2019

Weather comes right for autumn treatment

November 1, 2018 by  
Filed under Crops

Mild weather means crops now in the ground need special attention, writes Richard Overthrow.

Conditions for cereal drilling were fairly benign well into last month and most land saw enough rainfall to provide good seedbeds while not seriously interrupting fieldwork.

Most cereals have established well and with more growers needing to apply residual herbicides soon after sowing, much of the autumn spraying will have been completed.

Those who use ALS-inhibitor herbicides for post-emergence treatment of blackgrass or bromes, for example, should look for opportunities to treat in the next few weeks, our own trials have shown consistently that autumn treatment is better – the exception being soft or meadow bromes which are largely spring germinating.

Annual meadow grass

This also applies to annual meadow grass which should also be considered for autumn treatment. It is a weed that is often underestimated, however it is very difficult to control it in spring if it has started to tiller.

In fact, the most effective products against annual meadow grass are the pre-emergence residuals used for blackgrass etc, so campaigns against meadow grass need early planning.

Cereal aphids were once again present in numbers and while they normally cease flying and colonising new fields in early November, if the weather around this time is mild then aphid activity can be extended and insecticide protection also needs to be. If aphids can be easily found in crops this month then further pyrethroid treatments to follow earlier ones or to top-up Deter seed treatments may be necessary.

Those crops drilled late, for grass weed management or other reasons, may not need any aphid treatment if the crop hasn’t emerged by the second week of November, but the comments on mild autumns also apply here.

Flea beetle

The condition of oilseed rape crops is extremely variable across the region. Cabbage stem flea beetle has caused many of these to turn into bean crops, while many of those that were ‘on probation’ and left to recover are still very backward.

The next problem is the potential for a larval infestation. Insecticide resistance means that there is no effective means of controlling the larvae so once again we have to suffer it and see if the crop can recover. If they attack the backward crops there is little hope for these.

Thankfully, we haven’t seen the early phoma infections we saw last autumn so decisions on further autumn inputs such as fungicides could be deferred. For the better crops, autumn treatment should be considered routine but if only targeting light leaf spot, timing is flexible and treatments can be applied with propyzamide, for example.

Soil temperature

Later this month, we should be able to apply propyzamide products. The general rule for these is not to apply until soil temperatures have fallen sufficiently but again if the crop is still struggling this treatment can be delayed further.

Even for the better crops, applying too early will achieve the required weed control but persistence will be affected and with continuous emergence of grass weeds now common, some long term efficacy is important.

Winter bean crops will have been sown last month. Ideally weed control would have been done or at least started pre-emergence as post-emergence options are few. Carbetamide is one post-emergence option, being a residual that can be applied post-emergence, but ideally before target weeds, especially grass weeds, become too large.

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

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