South: Think of the bees when spraying for bean pests

Despite some getting showers, what crops need now is rain followed by sunshine – both yield drivers that we can’t influence.

Bean herbicides were variable in efficacy. For me they worked best, contrary to received wisdom, following cover crops where preceding straw had not been removed for years – lots of surface “trash” and very little soil contact. Better moisture retention? Given the cost and often random performance, bentazone (eg Basagran) was only used where weed burden was severe.

Spraying insecticides on flowering beans causes ethical struggles. The scent change on worker bees sprayed, even with plain water, can lead to rejection from the hive by guard bees. I recommend pirimicarb for threshold levels of black bean aphid as it’s relatively bee safe. The need to go very early or late in the day if targeting bruchid beetles must be stressed.

Message for the week is “measure to manage.” Trials and open days allow assessment of varieties in untreated plots and generate surprises. Some Skyfall plots show significant rust, candidates show promise and the weakness of Solstice against disease is staggering. Selecting on agronomic performance can generate better margins than yield potential alone.

Fungicide treatments can be measured across varieties for margin over input costs – a key driver in choosing actives for next season. We aim to apply fungicide to best effect and improve the bottom line, but timing of applications is crucial. Where weather or farm logistics delays sprays, their performance reflects this. Review programmes used this season – has disease resistance in newer varieties led to a tailored approach? Dirtier varieties such as Solstice would need a far more robust programme than Skyfall, for example.

Grassweeds should be assessed, mapped and blackgrass seed should be sampled and resistance status measured to fine tune next season’s approach. This simple procedure can generate significant savings in weed management.


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