9 June 1995

Making treatment choice

With several seed treatments available for next springs beet sowings, how should growers decide which to use? Andrew Blake relays the views of John Prince, British Sugars man who ensures seed orders are met

PROTECTING young beet against diseases and pests in 1995 cost from as little as £75/ha (£30/acre) to as much as much as £180/ha (£73/acre). Next year it will also be possible to spend nearly £13/ha (£5/acre) on a new steeping treatment aimed at increasing the flexibility of sowing dates.

Choosing the correct combination depends largely on the farms location and an assessment of the potential threats, says Mr Prince. Treatment costs are unlikely to change much for 1996, but the seed price is still unknown.

British Sugar offers three basic treatments. Extra for next year, the new Advantage priming will be generally available on some varieties. Estimated costs of each, and a comparison with the use of granules, are shown in table 1.

Growers so far fortunate to have escaped soil pests, such as millipedes, symphalids and springtails, and farming in "low risk" virus yellows areas, mainly north of Peterborough, need look no further than the Tachigaren (hymexazol) + thiram treatment, he suggests. This controls seed- and soil-borne fungi which cause black leg, damping off and other seedling diseases. "Our general advice in these cases is to use the standard seed treatment, check for aphids and spray as necessary."

Growers needing to control soil pests – other than the nematodes which cause docking disorder – have a choice between Force (tefluthrin) and Gaucho (imidacloprid). "They can, of course, rely on granules, but it is a more expensive strategy and the materials – aldicarb, carbofuran and oxamyl – are not particularly pleasant to handle and need specialist applicators."

Soil pests are most troublesome on silty and high organic matter land in Cambs and Lincs, says Mr Prince. "Growers usually know from experience where they have problems."

Docking disorder affects about 14% of the UK crop, mainly on light sands in North Norfolk, around Shifnal, Shropshire, and in parts of Notts and Yorks.

Affected growers have no alternative but to use the standard treatment and granules, the latter being the only means of control, he explains.

Up to 40% of the crop area has no soil pest problems. There the standard seed treatment and inspecting for aphids should prove the economic option.

Force first became available in 1992. "It does a very good job and is probably the most cost-effective method of controlling soil pests other than nematodes," says Mr Prince. However, Gaucho is steadily eating into its share of this growing market (see table 2). Already 85% of French and 65% of German sugar beet seed is treated with it, and it accounts for about half the Belgian and Dutch crops.

Extra protection

The big advantage of Gaucho over Force is the extra protection it gives against early aphids and hence virus yellows, he explains.

"Most people in most years need to spray at least once against aphids." Those having to spray twice and using Force will spend about £135/ha (£54.63/acre) – £11/ha (£4.45/acre) more than for Gaucho alone.

"Even the standard seed treatment plus two sprays works out at about £115/ha. We suggest that if they use Gaucho they wont need any spray." The added bonus of Gaucho is that it removes some of the pressure to monitor crops for aphids, he says.

Granules offer some protection against early aphids. But for growers in high risk areas, often associated with oilseed rape and set-aside, at least one spray is likely to be required as the effect of the granules wears off. The combined cost of standard seed treatment, granules and a single Aphox (pirimicarb) spray in these cases will be comparatively high – about £180/ha (£73/acre), he estimates.

"Our advice in these hot spots – like Bedfordshire, parts of Essex and the Suffolk coast – is that growers would do well to use Gaucho as their standard every year," says Mr Prince.

Naturally there is concern that over-dependence on a single chemical like imidacloprid could lead to pest, especially aphid, resistance. "We must continue to monitor and watch out for it," he concedes. Resistance to organo-phosphorous aphicides came about because they were used at reduced rates on a wide range of crops, he says.

"At the moment Gaucho is confined mainly to sugar beet." Its earlier and more extensive use on the Continent makes it likely that any problems would arise there first, he suggests. "By then, say in 5-10 years, I suspect well have virus-resistant varieties developed using the genes from wild beet."


Table 2: Force/Gaucho share of UK sugar beet seed treatment market (%)

ForceGaucho

199220Not available

199325Not available

19942012

19951625

Source: British Sugar.


Table 1: Cost of sugar beet seed treatments for 1995 crop £/ha (£/acre)

Tachigaren (hymexazol) + thiram74.60 (30.19)

Tachigaren (hymexazol) + thiram + granules140.00 (56.65)

Force (tefluthrin)106.00 (42.90)

Gaucho (imidacloprid)124.00 (50.18)

Advantage (at £11/unit)*extra12.65 (5.12)

* Seed priming available on Roberta, Triumph and Zulu only.

Source: British Sugar.

Virus yellows control with Gaucho in 1994. Treated fields (left foreground and centre right) compare well with the diseased field next to the farm buildings. Its a good choice for aphid hot-spots, says Mr Prince.