7 April 2000

Wider choice of canopy control for OSR growers

By Andrew Blake

OILSEED rape growers still have time to use a growth regulating fungicide spray to boost yield and reduce lodging, with a new product extending the range on offer this spring.

But more independent trials are required to find the most cost-effective approach to modifying canopies, says ADAS.

"It is well worthwhile using a growth regulator if you have a large crop," says John Spink of ADAS Rosemaund. The average yield response from correcting over-large canopies has been 0.5t/ha (4cwt/acre). "On very large crops we have seen up to 1t/ha extra. The best time to spray is in early April."

Determining which stands merit treatment remains largely subjective, so some HGCA work this year is concentrating on improving precision in this area.

The move to Autocasting and earlier sowing has encouraged excessive canopies which justify growth regulation, adds Mr Spink. "Any crop with over 30 large plants/sq m is likely to have too large a canopy."

With most nitrogen already applied the only option left to adjust crop development is a growth regulator, he says.

"The two front runners are tebuconazole (as in Folicur) and metconazole (Caramba). We have only one years work comparing them, and I am extremely cautious about saying which is better at the moment. But both seem significantly better than anything else." Prochloraz and most other triazole fungicides affect crop growth to some extent.

5C Cycocel (chlormequat) is no longer recommended on oilseed rape, because the market did not justify further approval work, confirms BASF. But there is a two-year "use-up" period for existing stocks.

In the absence of further data, choice will depend largely on relative prices, says Mr Spink. "Of the two Caramba may have a slightly stronger growth regulatory effect based on the shortening effect we saw last year."

Folicur is expected to cost about £23/litre and Caramba about £18/litre. Full doses are 1 litre/ha and 1.2 litres/ha, respectively, making field costs similar.

Cyanamids Mike Barrett says that in Germany, where Caramba took 30% of the oilseed rape fungicide market last year, 1 litre/ha produced 0.6t/ha (4.8cwt/acre) more yield than 0.75 litres/ha of Folicur over seven trial sites in 1998.

Bayers Tim Nicholson says that Apex sprayed at late green bud with full dose Folicur outyielded the full dose Caramba-treated crop by 0.35t/ha (2.8cwt/acre) in the ADAS trials. "In Pronto the difference in yield terms was a lot less."

"In general you get the biggest responses on largest crops treated early," says Mr Spink. "This year I expect the responses to be even better than last season."

Both Folicur and Caramba are said to offer useful control of sclerotinia and alternaria. &#42

OSRREGULATION

&#8226 Worthwhile on large crops.

&#8226 Shorter plants and less lodging.

&#8226 Caramba and Folicur main options.

&#8226 More independent trials needed.

A growth regulator fungicide spray could boost yields of well-grown crops. New product Caramba extends options.