March 26, 2013
Improving Potato Nematicide Application
Greater consistency and precision in their most costly and important pesticide application will pay handsome dividends for potato growers at planting, suggests Agrii regional roots development manager, Peter Jones. But achieving this will demand a much greater understanding of the limitations of current machinery and the need for extra care in its use.
“Modern planting equipment is doing a fantastic job of improving potato seedbeds,” he reports. “However, in many cases, it is failing dismally as far as nematicide application is concerned. Yet, at £400 to £650/ha, we’re talking about the crop’s single most expensive pesticide treatment. And less-than-ideal control of potato cyst nematode (PCN) and sprang (tobacco rattle virus) can be even more costly in both yield losses through early senescence – often mistaken for drought – and rejections.
“To effectively protect the crop, granular nematicides need to be incorporated at exactly the right concentration and in the right place within the seedbed. Where PCN is the problem even distribution in the soil surrounding the seed is the key, while a more localised but equally even in-furrow spread around the seed is required for free-living nematode reduction. The microscopic nature of both pests means they can gain access to the crop wherever the defensive nematicide barrier is either diluted in too much soil or too little.”
Despite this clear agronomic need, Peter Jones warns that most current seedbed preparation and planting equipment and practices are falling sadly short in both these respects.
In his experience nematicide application during either bed formation or stone-picking is far too inconsistent due to variations in soil type, depth of working and moisture content. Yet it is the norm for many.
Often too he finds in-furrow applicators giving very uneven granule distribution beneath and around the seed due physical interference from planter sides and considerable variations in planting depth. As well as under-dosing in some parts of the ridge, of course, this can also mean excessive pesticide levels in the vicinity of potatoes in others, and with it the risk of exceeding permitted maximum residue limits (MRLs).
“Remember, every slight change in soil type means a shift in tractor and machinery depth, changing the amount of soil being moved and with it granule concentration,” says Peter.
“That these inaccuracies matter is clearly illustrated by assessments of different machinery we made on a very high PCN site in the Midlands last season. Where a bed treatment nematicide applicator was incorporated on a new front-mounted tiller ahead of the planter we extended the growing period by three weeks. That’s an extra yield of around 7.5 t/ha with no other change, simply better placement of the nematicide.
“The kit wasn’t cheap, but it more than paid for itself in improved performance in the one year.”
While front-mounted tiller application provides an excellent way of improving bed treatment, Peter Jones is also concerned over in-furrow nematicide application. In particular, the fact that little or no work has been done on the design or placement of applicators to overcome the inaccuracies he invariably encounters in the field.
He sees a huge disconnect between machinery manufacture and agronomic needs in this critical area. What’s more, growers continue to buy expensive equipment without any thought about nematicide application. And working practices frequently make a bad situation worse.
“It’s nothing short of a tragedy that such a modern, vital and very expensive agrochemical is being applied in such an archaic way,” he stresses. “Accurate nematicide application has to be a far greater priority for growers. Which means they need to make it one for machinery manufacturers”
As well as being more discerning and demanding in their machinery purchasing, Peter Jones urges growers to be especially diligent in their equipment calibration and use – in particular, adjusting working depth with every change in soil condition for the most accurate planting.
“It’s essential everyone sharpens up their act with nematicide application because treatment ahead of planting is the only option we have,” he concludes. “Once our potatoes are in the ground we just have to live with the consequences.”