Beet to be lifted later could benefit from T2

By Martin Rickatson

24/08/2010

Beet crops to be lifted from late November onwards should benefit from a second (T2) fungicide spray applied in the first half of September.

Broom’s Barn’s Dr Mark Stevens says: “Following T1 sprays in mid to late July, T2 sprays applied by mid September should benefit later lifted crops in two ways. They keep canopies clean and green into autumn, so crops can keep on building yield for longer, and maintain canopies better into winter so crowns are protected from frost damage.”

With powdery mildew levels currently looking relatively low in untreated crops at Broom’s Barn, rust pressure from here on is now Dr Stevens’ main concern. “Crops that get infected during September or October are likely to suffer leaf loss that will reduce yield potential whereas a healthy crop should still be gaining approximately 3 t/ha of yield per week during October.”

Agrovista technical manager Mark Hemmant says that with greater rust pressure in recent autumns more growers have been trying T2 sprays. In his experience crops lifted six weeks or more after application should gain an economic yield benefit, providing a fungicide is used that will control all four diseases and give a physiological yield boost.

Trials by Broom’s Barn, British Sugar and Bayer CropScience have studied the effects of one and two fungicide sprays. Across nine trials, a T1 spray of Escolta (cyproconazole + trifloxystrobin) has increased yield by an average of 9% and a T2 spray has added a further 5%. At T1 it has also consistently outperformed all other products and delivered 3.4 t/ha over Spyrale (difenoconazole + fenpropidin).

Mark Hemmant attributes this to Escolta’s broad-spectrum activity and combined strobilurin + triazole physiological effects. “Just one extra tonne of beet pays for an Escolta spray and everything above that goes on the bottom line. Growers lifting beet in February and March this year also found T2 sprays made crops less vulnerable to frost damage,” he notes.

Over the last two years of BBRO variety trials Dr Stevens has seen a relationship between rust leaf cover in late September and subsequent frost damage to the canopy; in January 2010 this extended to root damage. “From fungicide trials we also know that controlling rust in autumn maintains a healthy canopy into winter. Together these observations suggest fungicides can help avoid frost damage,” he says.

A new BBRO project is underway to better understand the relationship. This will assess yield and frost damage at a range of lifting dates following one and two spray fungicide sprays with different products and application rates. Initial findings will be discussed at the 2011 BBRO winter meetings.