Farm Trials Shed Light On Second Wheat Variability

Second wheat yield losses from take-all this season have been almost as high as last year despite very much lower apparent levels of root infection, according to the second year of farm trials undertaken by merchant, T. Denne & Sons. To such an extent that the disease is likely to have been behind much of the extreme variability seen in 2003 second wheat crops.

"Across one hectare plots of five of the most commonly-grown second wheat varieties we recorded an average 0.78 t/ha response to specialist take-all seed treatment this year," reported the company's Andrew Bourne. On average, we harvested 8.1 t/ha from the plots treated with Latitude (silthiofam) compared with 7.32 t/ha from our controls.

"Root assessments over the growing season showed lower levels of take-all infection in the treated plots than in the controls, culminating in GS 52 take-all Indices of 12.8 and 22.2 respectively," he explained. "So we were expecting some yield response. But with overall infection levels less than half those we recorded last year, nothing like we actually saw."

In 2002 the trial field on Doug Wanstall's 1500 acre Bank Farm, Aldington near Ashford went into harvest with take-all Indices of over 72 on the 1-100 scale in the control plots and just over 20 where Latitude was used. The net result was an average yield response of 0.95t/ha.

Based on this experience, and the fact that they hadn't seen nearly so much evidence of take-all in the crop over the past season, Andrew was expecting yield responses from take-all protection of around half the level actually achieved.

"This underlines just how much more there is to take-all losses than simple infection levels," he pointed out. "There may have been a late season surge in disease levels this year, but I'm convinced the real factor was the weather.

"The drought we had throughout April and early May almost certainly prevented the high initial take-all levels we recorded on the roots developing. At the same time, we know from the huge loss of tillers we saw over this period just how much stress it put on the wheat crops. Then we had another prolonged dry period in June, topped-off by a baking week in July, leading many crops to literally die on their feet.

"Under these conditions, we can't be surprised that even the lower levels of root damage caused by take-all this season had such serious consequences for yields," Andrew Bourne observed. "I think it has to be a major factor in the extreme variability we've seen across 2003 second wheat performance, in particular."

The notably high impact of relatively modest take-all infection levels in the past season has been confirmed by the commercial performance of the 140 acres of second wheat grown by trial host, Doug Wanstall.

Following the impressive yield recoveries seen in the 2002 trials on his farm, Doug had all his second wheat seed treated with Latitude for 2003 harvest, leaving one field untreated as a control.

"Overall, at an average 7.9 t/ha, we've been well-pleased with our second wheat this year," he said. "But we didn't know how much we had to thank the take-all dressing for until we moved into the untreated patch and the yield monitor dropped like a stone - to just 6.1 t/ha."

Two year's of take-all trials leave Andrew Bourne convinced of the need to adopt a very careful second wheat growing strategy based firmly on risk minimisation. Not least because it's impossible to tell how challenging the season will prove to be in either take-all levels or impact.

"Go for a variety with a track-record of consistent second wheat performance," he advised. "Make sure you treat it with a specialist seed fungicide wherever you're growing it under a significant take-all risk. And do everything you can to provide a seedbed and soil structure that positively encourages root development."