A tickle and late seed unsettles the weeds

Trials show annual ryegrass gets a beating from autumn tickling, high seed rate, late seeding and cross-seeding of wheat.

Herbicide resistance to annual ryegrass now offers growers in WA and elsewhere an annual challenge. Widespread resistance to Groups A (Fops and Dims) and B (sulfonylurea, Imidazolinone and Sulfonamide) herbicides has narrowed the chemical arsenal available to growers in Western Australia and elsewhere. But a growing body of research is looking at non-chemical alternatives to weed management.

In Ground Cover 22 we introduced a four-year Western Australian trial, supported by growers through the GRDC, which is aiming for the most effective and profitable combination of methods to beat resistant annual ryegrass.

A parallel research effort, also supported by growers and conducted by Agriculture WA, is showing just how effective some of these methods can be. Tim Evans reports.

Research at Wongan Hills and Merredin has shown the amount of ryegrass in the crop can be reduced by as much as 70 per cent — with the right combination of methods.

Research is focusing on autumn tickling, high seed rate, late seeding and cross-seeding of wheat. Results show these methods can effectively reduce ryegrass soil-seed reserves, suppress ryegrass growth and increase wheat yield.

Autumn tickling and early emergence of weeds

Researchers Abul Hashem and Aik Cheam said last year's trials into autumn tickling induced emergence in a lot of ryegrass seedlings prior to seeding. "The experimental paddock was tickled to a depth of 2-3 cm by conventional scarifier with 10 cm-wide points on 1 May 1997 at Wongan Hills," Dr Hashem said.

"It was followed by 24 mm rainfall over the first three weeks of May which stimulated emergence of 1,717 seedlings/m2 (Fops-resistant) before seeding, compared to only 456 ryegrass seedlings/m2 in the untickled plot. Delay in seeding beyond the normal seeding time stimulated further emergence of ryegrass seedlings before seeding."

The ryegrass seedlings were killed by knockdown herbicides. Wheat was seeded on 31 May (normal seeding) and 20 June (late seeding). Ryegrass seedlings were counted in the crop, three weeks after crop emergence.

Tickling and late seeding a winner

Plots seeded at the normal time had ryegrass seedling density of 486/m2 in the tickled plots and 639 seedlings/m2 in untickled plots — a reduction of 24 per cent ryegrass in-crop.

In late seeding plots, ryegrass density was 184 seedlings/m2 in the tickled plots and 400/m2 in the untickled plots. Late seeding alone reduced ryegrass 37 per cent, and late seeding coupled with autumn tickling reduced ryegrass seedlings 71 per cent in the crop compared to untickled plots seeded at normal time.

Increase your wheat competition

"High seeding rates of wheat increase the competitive ability of the crop," Dr Hashem said. "It establishes a dense crop stand which utilises nutrients, water and light efficiently, depriving the ryegrass. High density can also compensate for any accidental crop damage caused by herbicides."

Autumn tickling and high seeding rate (120 kg/ha) of wheat increased wheat yield by 69 per cent in normal seeding and 51 per cent in the late seeding plots. It reduced the number of ryegrass heads by 28 per cent and increased wheat heads by 61 per cent, in the absence of any herbicide to control ryegrass, compared to untickled plots seeded at 60 kg/ha at normal time.

Double the yield without herbicide?

The yields from tickled plots seeded at 120 kg/ha with no herbicides were 11 per cent higher at normal seeding time and 100 per cent higher at late seeding time than yields in untickled plots seeded at 60 kg/ha and treated with three herbicides such as trifluralin, diuron and Fops.

Tickling and high seed rate with one herbicide (trifluralin) produced 16 per cent greater yield than the highest yield from an untickled plot with 60 kg/ha and two herbicides (sulfonylurea and Fops). Wheat screening and protein were the same for both standard seed rate and high seed rate.

In another trial at Merredin, higher seed rate (100-150 kg/ha) increased wheat yield 14-28 per cent compared with 50 kg/ha seed rate in the presence of 360 ryegrass seedling/m2. Cross-seeding of wheat increased wheat biomass, reduced ryegrass biomass by 23 per cent and ryegrass heads by 17 per cent.

Dr Hashem concluded that in paddocks where wind or water erosion is not a big problem, farmers can rid themselves of rich soil-seed reserves of ryegrass by autumn tickling and late seeding and can increase wheat yield by using a high seed rate.

However "to get more benefit from autumn tickling, it is necessary to tickle the paddock before season break. Some rain following tickling is necessary to stimulate ryegrass emergence."