USA
June 16, 2014
The benefits of a tactical approach to grassweed control, including ploughing, crop rotation and a full herbicide programme are being clearly demonstrated in a Dow AgroSciences rotational grassweed trial in Warwickshire.
The trial, now in its fourth year, assesses the difference that rotating cultivation practices and crops, along with herbicide programmes makes to blackgrass, ryegrass and brome control in winter wheat and oilseed rape (OSR).
The crop plots have been sub-divided into four distinct cultivation rotations; continuous min-till (MT), continuous plough, MT-MT-plough, and plough-plough-MT.
“After three cropping cycles results are beginning to emerge,” says Stuart Jackson, Herbicide Specialist at Dow AgroSciences. “Winter wheat plots established using minimum tillage continuously over the past three years have seen levels of blackgrass control reduce by around 40%.”
Mr Jackson continues: “In the continuous plough plots, the population of blackgrass has dramatically declined and by year three 100% control was achieved in all but one plot. You can see to a line the difference between the plough and min-till plots – in the min-till plots the grassweeds are clearly visible and the crop is less vigorous due to weed competition.”
The benefits of ploughing can soon be reduced. Just one year of min-till after two years ploughing saw levels of control reduce. Although this reduction may not be visible on a field scale.
“The quality of ploughing is important,” says Mr Jackson “Go too fast, too shallow or fail to properly invert the soil and bury all the trash will risk achieving a result more akin to min-till,” warns Mr Jackson. “Ploughing properly can be a slow and expensive business but the results appear to pay off.”
The trial shows that an oilseed rape break crop will improve weed control compared to cropping continuous cereals.
Establishing oilseed rape after wheat gives the opportunity to use different chemistry and establishment methods; particularly important if the preceding cereal had a high blackgrass population. Preparing the ground with min-till techniques will keep most grass weed seeds in the top 5cm ‘kill-zone’ of the soil profile where herbicides can be most effective.
No stale seedbeds were used, so the trial showcases the worst case scenario for autumn drilled crops. Each year the herbicide programmes have been: oilseed rape received 1.7 L/ha Kerb Flo 500 (propyzamide) in November; while winter wheat crops received a pre-emergence application of Crystal (flufenacet + pendimethalin) at 4 L/ha followed by a post-emergence application of UNITE (pyroxsulam) + Stomp Aqua (pendimethalin) at 270g + 1.75 L/ha.
In autumn 2013 one wheat plot did not receive the post-emergence treatment and the very high population of grassweeds, clearly showed the importance of a full herbicide programme.
The results for other grassweeds in the trial; sterile brome and ryegrass, are similar. For brome, ploughing offers a very effective control method. Continuous plough plots are giving the best result and continuous min-till the worst.
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