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New advice for the in-furrow application of Amistar during potato planting will achieve a more complete zone of protection around the mother tuber when...

• New nozzle technology investigated

• Good control of persistent black dot

• Seed and soil borne control needed

New advice for the in-furrow application of Amistar during potato planting will achieve a more complete zone of protection around the mother tuber when using high-speed belt planters.

Modern planters are capable of operating faster than traditional cup planters, says Syngenta application specialist Harry Fordham, who gave a special presentation to growers attending this season’s Potato Science Seed & Soil Pathogen webinar.

“That could compromise the consistent incorporation of spray in the soil target zone around the mother tuber with the original sprayer set up on the planter, along with potentially resulting in the risk of drift at the higher speed,” he warned.

With the essential role of Amistar for control of both black dot and Rhizoctonia pathogens in the soil, Syngenta has spent three years investigating new nozzle technology, water volume use and the set-up of nozzle orientation.

The original brass AZ in-furrow nozzle, which is no longer available, had a small orifice producing fine droplets susceptible to drift. Alternatives include hollow cone technology giving a wide band of application covering more soil faster, with a larger orifice less prone to blockage and drift.  

Trial results have shown the Lechler TR80 performs consistently well over successive seasons. The set-up recommended was with two nozzles, one at the front and a second at the rear of the planter shoe, to spray the soil as it falls back in to cover the planted tuber.

With the research repeatedly showing application at 100 l/ha producing the best results for both crop yield and tuber quality, compared to 50 l/ha, the TR80 was operated with an 015 nozzle in both situations.

Drift reduction

The other promising combination was a set-up instigated in Germany. It uses two Lechler FT90 nozzles, set up to deliver 33% of the spray at the front of the shoe, by fitting at 01 sized nozzle, and 66% at the rear on the closing soil, through an 02 nozzle.

“The relatively large nozzle orifice would be unlikely to block,” says Mr Fordham. “More interestingly it is a pre-orifice nozzle design, so offers some level of drift reduction and may be a combination to consider, especially with higher speed planters.”

Trials undertaken in a Norfolk field selected for the high risk of soil borne black dot saw Amistar reduce the incidence of severe infection on the harvested tubers. Disease control for silver scurf and greater marketable yield also improved from all the Amistar application techniques.

Persistent problem

Black dot is extremely persistent in soils, along with some indication that the pathogen is involved with the early die back complex that is being increasingly reported in potato crops.

“Microsclerotia of black dot can typically persist in the soil for eight years or more, which means that once established it can usually survive from one potato crop to the next in the rotation,” said Syngenta potato technical manager Michael Tait.

“We have seen very good results from Maxim seed tuber treatment, to prevent transfer of seed-borne pathogen onto the daughter tubers. But with this disease now so prevalent in soils, growers and agronomists need to be looking at the combination of both Maxim and Amistar.”

A combination of seed and soil borne controls was especially effective in countering Rhizoctonia black scurf – with better results achieved when they were used together as opposed to using either product individually.