Is variety a significant factor when it comes to take-all?

19 March 1999

Cut seed spud growth fillip

POTATO growers using cut seed to eke out supplies could benefit from applying an early carbohydrate-based growth stimulant, according to crop research specialist CMI.

A small replicated trial by the independent Lincs-based company last season showed a 17% yield response in mid-May planted cut Saturna which was treated with the recommended rate of Fulcrum. There was no apparent advantage in treating crop from uncut seed.

The 30litre/ha treatment applied on June 8 when most plants were 2-5cm (0.5-1in) high resulted in a hand-harvested yield equivalent to 47.4t/ha (19.2t/acre). The untreated plots delivered only 40.4t/ha (16.4t/acre).

Hand digs at 10-14 day intervals showed there were no differences in bulking rates. So the assumption must be that the stimulant helped the cut seed get away earlier by providing more readily available carbohydrate for the plants to draw on, explains CMI researcher Christine Jones.

"It is the crops that are checked which are showing the biggest responses," says Dr Jones.

Surfactant spin-off

SURFACTANT Slippa boosts eyespot control, claims manufacturer Interagro. It is believed to allow fungicides to pass between leaf sheaths and the stem, reaching normally inaccessible areas where severe lesions develop. Yield increases of 0.77t/ha (0.3t/acre) from its addition to Unix and a near doubling of eyespot control with flusilazole (eg, Sanction) and prochloraz (eg, Sportak) are reported. Cost is about £6/ha (£2.45/acre) in 200 litres of water.

Is variety a significant factor when it comes to take-all?

By Andrew Swallow

TAKE-ALL laid waste to some varieties last year, when others were barely touched.

But drawing conclusions about varietal tolerance from such observations could be hasty, warn experts.

At Saxham, near Bury St Edmunds, Crop Cares trials highlighted big differences. Nearly 80% of plants showed take-all symptoms in the worst hit variety, Rialto, compared with least hit Consort at 15%.

"Admittedly these trials need validating and repeating, but they reflect what we were seeing on farm with varieties such as Rialto and Hussar," says agronomy specialist Neal Boughton.

The Sept 26 sown plots, in three replicates a variety, were a second wheat on sandy clay loam.

"On a neighbouring wheat field spring barley had been the first cereal. There the farmer had time to repair soil structure and take-all was much less severe."

Whiteheads were visually assessed on July 14 and yields taken at harvest. While other stem base disease cannot be ruled out, flusilazole applied at GS31 to counter eyespot, and a 0.75t/ha (0.3t/acre) response where take-all seed treatment MON65500 was used, suggest take-all as the main factor.

"The whole crop was stunted, showing typical symptoms."

ADAS Rosemaunds John Spink urges caution interpreting such data. "Whatever is said about the uniformity of the disease, it is always very patchy in severity. Differences seen in one year can be completely different the next."

But rooting, tillering, speed of development, and stem sugar level could confer some tolerance to the disease, he says. "Varieties can all get the same level of disease but the amount of yield loss is dependent on their growth characters."

Take-all develops gradually on roots during the growing season. Varieties that develop earlier should be more tolerant of infection. "If grain-fill is early, and disease increases late, then grain-fill is less affected."

High reserves of soluble stem carbohydrate might also help varieties such as Rialto and Charger fill grain when nutrient supply from take-all damaged roots is limited.

That did not appear to help Rialto on the Crop Care site. "But last year was different. The disease developed very early and was very severe," notes Mr Spink.

It is a point echoed by PBICs John Howie. "We still back Rialto as a second wheat."

But Mr Boughton is taking no chances. "Riband and Consort can be grown anywhere in the rotation, but Rialto has to go as a first wheat. If it has done this one year, it is not worth risking again."

Fig: in creative-in as 102479 Targraph3.eps, reqs 2 line cap.


&#8226 Rialto worst, Consort best.

&#8226 Similar symptoms seen on farm.

&#8226 One-year, one site only.

&#8226 Tolerance not resistance.

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