Archive Article: 1997/08/02

2 August 1997




WHAT the herbage seed business lacks in size, it makes up for in enthusiasm among growers and researchers alike.

Just as well, considering it attracts little funding, and agrochemical companies are loathe to pursue label recommendations for such a niche crop, believes Nick Poole, southern regional manager for the Arable Research Centre (ARC).

The ARCs herbage seed agronomy centre at Abbotts Ann near Andover in Hampshire attempts to redress this balance, and showcases its work at an open day every two years. This year the event, supported by Herbage Seed Services of East Stratton near Winchester and by WHD Seed Growers, focused on progress towards better use of inputs.

Nitrogen

Work on winter wheat in France and on herbage in New Zealand and Oregon, has established a correlation between tissue N at stem extension and final seed yield – the optimum N content for herbage seed being between 2 and 5%. This year, an ARC-funded trial is attempting to extend this relationship to chlorophyll content in the leaf measured with the N tester chlorophyll meter.

Using Anaconda, an early heading perennial ryegrass, with seven different nitrogen application rates in the range 0-180kg/ha, tissue N content and chlorophyll content were assessed at three timings around stem extension, between the end of April and mid May. The correlation was reasonable for N rates up to 100kg/ha, and stronger under the higher application rates.

"With an instant feedback from the chlorophyll meter at stem extension (GS32), which is when the correlation with final yield happens to be strongest, its not too late for extra N where its indicated," says Mr Poole. "Having established the relationship, well now be looking to get some better quantification into the system, possibly with different calibrations for different varieties."

Sulphur

Atmospheric depositions of sulphur are naturally low in the Hampshire areas. Responses to sulphur fertilisers have been established in many crops – what about herbage seed?

Experiments at the herbage agronomy centre last year showed some promising yield responses. "In each case, yields from fertiliser treatments which included sulphur exceeded those without it. However, we struggled to find statistically significant differences," comments Mr Poole.

This year, the trial attempts to define the effects of different fertiliser timings pre and post defoliation in Italian ryegrass, and also any differences between liquid and solid products.

Plant growth regulators

"As its the first new growth regulator to hit the cereal market for about 12 years, weve been trying to establish what scope Moddus (trinexapac-ethyl) might have for herbage seed production," states Mr Poole.

Using a diploid and a tetraploid intermediate perennial ryegrass and nitrogen at 120kg/ha, Moddus was applied at early stem extension at 0.4 l/ha and 0.6 l/ha, the maximum total dose for winter wheat and winter barley respectively

Lodging was assessed on 29 May. "The differences were quite stunning," says Mr Poole. "The lower rate didnt have much effect, but the higher dose was significant. I know that other researchers have been experimenting with rates as high as 1.2 l/ha, but if were to persuade the manufacturers to back us, its best not to exceed the existing maximum dose.

Herbicides

Annual meadow grass is enemy number one for herbage seed growers, especially in the fine grasses, with blackgrass and winter wheat close runners up. Attempting to control any one grass within another is always going to be a case of establishing the cut off point where enough weed species is removed and sufficient crop species survives.

In an attempt to understand these cut-offs, the centre has been using a logarithmic sprayer which reduces output along the length of each plot from full down to 0.15 rate. "Its just a crude look-see, but its identifying some products where there may be more mileage than wed thought," says Mr Poole, though he stresses that many of the products currently have no approval in herbage seed.

Topik (clodinafop-propargyl) has been picked out as having potential. "While its generally held to be more damaging than Wildcat (fenoxaprop and P-ethyl) on perennial ryegrass, it may have some advantages for blackgrass control," he adds.

Falcon (propaquizafop) has shown some scope in removing volunteer wheat and barley, at quarter rate. But Mr Poole stressed that the trials were screening only, and could not advise on the basis of them.

The Centre is also evaluating the new branded product, Bolero (diflufenican and terbuthylazine) for the second year. Although it has no approval, it has given promising results in terms of control of broad-leaved weeds and some control of meadow grass in perennial ryegrass.

Fungicides

Four chemicals were assessed at two timings in fungicide trials in 1995 and 1996 at the centre. The most damaging diseases, according to Bill Welling, of Herbage Seed Services, are brown rust and stem rust. Mildew might look more dramatic during May and June but, because the plants are producing so much green matter, they can afford to lose a little, he adds.

Pressure from brown rust is usually highest in the last two weeks of June, while stem rust generally peaks in the first two weeks of July under higher temperatures. This would account for the better control recorded from the later applications – the third week of May rather than the third week of April.

The problem with later applications is that some of the newer fungicides keep the crop so green that there was a risk of a two-tier maturity.

"By the time its fit to harvest, much of the seed has been shed," he explains. This was most notable in intermediate ryegrass varieties, with the intermediate tetraploids particularly uneven in development, but also most susceptible to crown rust. Mr Welling maintains there is a strong case for double combining in these cases.

He also believes that the strobilurins, if the persistency which they exhibit in cereals transfers to grass, could pave the way for an early April treatment which should hold disease right through the season.

They might also overcome the need for double combining since they should encourage a uniform crop in its early stages.

Growing herbage seed is more challenging than most. Tia Rund cuts a swath through the tangle of inputs.


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