True grassweeds penalty quantified
By Andrew Blake
BLACKGRASS MAY be hitting wheat yields harder than some growers believe, says Masstock.
On average, each crop-competing blackgrass plant a square metre left uncontrolled in spring cuts output by about 44kg/ha (0.35cwt/acre).
That is the finding from the firm”s fully randomised and replicated 2004 trials at Rookery Farm, Stow Longa, Cambs.
“A population of 12 blackgrass plants a sq m is generating a yield loss of over 0.5t/ha,” says the firm”s agrochemical trials manager David Newton.
With wheat at 66/t, that typical level of infestation is well worth treating with Atlantis (mesosulfuron-methyl + iodosulfuron-methyl-sodium) for the yield return alone, provided spraying is not too late, he stresses.
“It”s a level which growers often regard as borderline for spraying.”
Higher value milling wheats and a reduced seed return to be dealt with in following years justify treatment at even lower levels, adds Dr Newton.
Blackgrass plant counts in the trials on Hereward taken to yield were done on Feb 4 and ear counts were assessed on June 9. Top yield, 11.4 t/ha (4.6t/acre), came from 98.5% control achieved by timely Atlantis treatment leaving a minimal 9.3 blackgrass ears a sq m. Delaying spraying until mid-April gave nearly 1t/ha (0.4t/acre) less, he notes.
Untreated, the crop lost 5.1t/ha (2t/acre) and autumn-only blackgrass treatment lost 1.6t/ha (0.6t/acre). The respective spring blackgrass plant counts, of 117 and 36/sq m, confirm that the loss per plant is surprisingly consistent. “The figures are very similar,” says Dr Newton.
“This simple blackgrass truth underlines the real value to farmers of Masstock”s commitment to practical, economic trials in these times of continuing downward pressure on cereal returns.”
