22 October 1999

New tactics in take-all war

A SHROPSHIRE cereal grower hopes new chemistry, backed by slightly more early spring nitrogen, will soon provide an extra weapon in his on-going war against take-all.

Manager Andrew Lewis grows about 400ha (1000 acres) of winter wheat on Lord Barnards Raby Estate at Wellington.

"Over the past five or six years we have been slowly modifying our rotations and moving towards more continuous wheat on the heavier land," says Mr Lewis.

Some fields are through the take-all barrier, having grown wheat for up to 14 years. They now achieve 10t/ha (4t/acre). But take-all has taken a heavy toll in second and third crops in the past two seasons. "We have been getting only 2t/acre on the worst affected fields. We normally expect 65cwt."

Drilling date was rarely considered as a means of reducing take-all in the past. "We always used to sow all the difficult ground first. But about three years ago we began to drill second and third wheats after the first, usually around the first week in October to lessen the take-all risk. "Ironically the past two years have been so wet the disease has been a real problem."

Take-all also affects barley, a fact not always appreciated, he notes. "It is probably one of the reasons the crop has gone out of favour, because it often goes in as a second or third cereal."

On ADAS advice Mr Lewis tends to use specific varieties for the second/third wheat slot. Main choice is Rialto for its high stem carbohydrate reserves. But Equinox, heavily affected by take-all last season, has been dropped.

Second wheat seed normally receives Baytan (fuberidazole and triadimenol) dressing to help plants form better root clusters to counter the disease. Up to now his crops have also had early nitrogen, usually ammonium sulphate at 34-38kg/ha (27-30 units/acre), as soon as possible in February.

"I see that ARC trails suggest we use more, say 50-70 units, at that timing. On some fields we might go to 50, but I think 70 would be pushing it and asking for more growth regulator. We generally use 170-180 units in total for second wheats."

Monsantos seed treatment MON65500, now on sale in Ireland, has been tested in strips on second and third wheats at Raby. Take-all still had some effect on the treated areas, but he believes the dressing allowed ears to fill properly. "The difference wasnt particularly noticeable in the crop, but it certainly was when you looked at the combine yield monitor."

Brigadier tried as a supposedly more susceptible third wheat yielded about 5% more treated than untreated, even though there was no visual take-all.

At the Irish price of about £25/ha (£10/acre) MON65500 seems quite expensive, he says. "Its quite a lot of money when wheat is fetching only £65/t."

Monsantos David Leaper believes the cost, when the dressing eventually becomes available in the UK, should be compared with a foliar spray rather than other seed dressings.

"Its value is similar, so we are really talking about perceptions."

"I dont see the product as a ticket to an early planting slot," says Mr Lewis. "But it is another piece of insurance to be integrated with other controls." &#42

Effect of N rate & timing on Consort 2nd wheat at Wye, Kent (1998)

Nitrogen applied (kg/ha) Yield (t/ha) %

End Feb Mid-Apr

Total 160 32 128 7.78 100

" " 64 96 8.10 104

Total 200 40 160 8.06 104

" " 80 120 8.83 113

Total 240 48 192 8.63 111

" " 96 144 9.15 118

Source: ARC/HGCA

First line of defence

HGCA-funded trials, carried out by Arable Research Centres, show delaying second wheat drilling until mid-October is still the first line of defence against take-all.

"However, appropriate nitrogen management, in particular applying a large enough first dose, up to 60-80kg/ha, in early spring is also important," says ARC eastern regional manager Stuart Knight (see table).

Seed treatments such as Baytan have a role, especially if drilling has to take place earlier, he adds.

"MON65500 looks particularly useful, and when combined with delayed drilling and more early N, yield increases of up to 35% (1t/acre) were obtained in severely affected take-all trials last year."