7 April 2000

Tiller killers out in force

By Charles Abel

HAVE you been a tiller killer this spring? Many cereal crops have needed dramatic thinning and none more than August-drilled wheat on Velcourts plots at the Cereals 2000 site near Lincoln.

In October, the Madrigal wheat sown on Aug 27 had 1100 tillers/sq m. With a top yield target of 600 ears/sq m that meant dramatic thinning was required.

A ruthless approach to nitrogen has seen massive tiller death, producing a thick mat of hay-like dead stems and leaves in the base of the crop. "We had to be brave, but we are now down to the 600-700 tillers/sq m we wanted," says technical director Keith Norman.

"Disease levels, especially mildew, are also lower, because cells do not contain such nitrogen rich sap and the disease-ridden lower leaves which usually act as an inoculum source have died right back."

The mild winter had little impact on tiller counts so first nitrogen on the brash site was delayed from late January to late February and rate dropped to 40kg/ha (32 units/acre). "We would usually use a small, early application on light soils to maintain crop growth and development, particularly of roots," says trials manager Ben Corbett.

5C Cycocel has been split two-thirds, one-third to boost lodging control. And second N rate was cut to 75kg/ha (60 units/acre) on Mar 22 when the crop reached GS31. "We are matching supply to demand and definitely not oversupplying it," says Mr Corbett.

It is an approach many other early drillers should have followed, says John Howie of PBIC. "There are a lot of very lush crops with lots of tillers and lots of mildew. Growers may not have appreciated how much management early drilled crops require."

To help in future PBIC is building a database showing how varieties respond to drilling date and rate. Differences in tiller development, tiller loss and growth stage progression will all help growers tailor inputs accordingly, he notes.

"At present it is a very crude science," Mr Norman says. "We know that varieties shed about 50% of tillers, and it looks like later drillings produce fewer tillers, which are harder to lose. We would like to know more about which crops will lose tillers more readily and any differences between varieties."

Growers can also exploit varietal differences to spread spring workloads, Dr Howie adds, ensuring varieties do not all arrive at key growth stages at the same time. "That could make a big difference to overhead costings for spraying and spreading," says Mr Corbett.

Root development in the early drilled plots is well ahead of the later sowings, which should help if conditions turn dry, Dr Howie adds.

In future, early drilling seed rates may be cut from 140 to 120 seeds/sq m, Mr Corbett even suggesting 90 may be feasible. "If you start low it is then a question of positively managing the population you have rather than trying to reduce it," he concludes. &#42

Plots drilled with a combined seed treatment of Evict (tefluthrin), Jockey (fluquinconazole) and Sibutol Secur (bitertanol + fuberidazole + imidacloprid) are significantly ahead of those treated with Beret Gold (fludioxonil) alone. "We would have thought that cocktail would slow growth, but it has done exactly the opposite," says Keith Norman. "We know that Evict can boost populations and vigour, so it is good to see there are no phytotoxic effects from combining the treatments."