7 November 1998

DONT PANIC IF YOURE LATE

Establishing a wheat crop becomes more risky the longer you leave it. Sarah Henly explains how to avoid the pitfalls of late drilling.

USUALLY by now, most winter wheat seeds are tucked up in bed. But the catchy, wet weather has severely delayed drilling progress in some areas.

Theres no need to panic. Beet and potato growers are used to establishing wheat as autumn comes to a close. Provided you know the potential risks and penalties of drilling late, you can find ways to adjust for them, says Doug Stevens, senior agronomist at Morley Research Centre in Norfolk.

"I have seen excellent crops following drilling in early December. The yield penalty may be in the order of 2t/ha, depending on the variety and the season, but you can usually offset that loss by saving on inputs. While seed rates will undoubtedly need to be increased to compensate for the lower tillering ability of late sown wheat, other inputs such as broad-spectrum seed treatments, grass weed herbicides and eyespot fungicides can be reduced in many cases," he explains.

The variety of wheat grown will determine the yield potential and the extent to which you can save on those inputs, so its important to choose carefully.

Varieties such as Charger, Harrier and Hussar have performed well in late sown trials at Morley, while Riband and Buster havent fared so well. Much depends on tillering ability and straw strength, which differ when crops are sown late, says Mr Stevens. He favours the milling group two type Charger for its consistency of yield and ability to attract a modest premium in most years.

"If you choose a high yielding variety that also has milling quality, you stand to make money on two counts. Then even if you dont get a milling premium, you havent lost out much. Varieties like Charger and Rialto give you that chance," he stresses.

If you already have seed in the barn to use up, you may have to make what you can of it. But some varieties, for example Savannah and Equinox, are best left in the bag, suggests Richard Fenwick, cereals specialist at NIAB in Cambridge.

"The yield potential falls markedly in wheats sown in November, so think quality rather than feed. While you may be safe with Hussar, its better to opt for a Rialto-type or indeed a spring wheat variety. Our trials suggest a spring milling variety such as Chablis or Imp is the best bet," he says.

Spring in November?

Theres no reason why you cant drill a spring wheat in late November. For example, Chablis was developed by CPB Twyford as an early-drilled spring wheat with no vernalisation requirement. It has yielded 106% of the controls in NIAB trials, which is comparable to Brigadier sown at the same time. NIAB produces a comprehensive list of the potential yield and quality of a range of both winter and spring wheats sown in the late autumn.

Although he recognises there may be a yield penalty to growing spring wheats, Mr Stevens believes they are the best option where drilling is delayed. However, he fears Chablis may not attract a breadmaking premium because it is a group 2 type. He favours Shiraz, which is unusually a soft milling variety with breadmaking qualities.

For those sticking with winter varieties, waiting for a weather window may be frustrating. But rushing the job of preparing a seedbed and drilling is foolhardy, warns Selwyn Richardson, soil scientist at ADAS Boxworth.

"Its wise to wait until the soil has dried out down to a depth of 6in before travelling, even with the lightest of cultivators. A wheeling that sinks by just 2in causes compaction to about four times that depth in wet seedbeds," he explains.

While the soil may appear dry on the surface, it can be plastic at cultivation depth. Mr Richardson recommends growers do the worm test to gauge the state of the seedbed before entering the field.

That involves digging down to 150mm (6in) with a spade and taking a handful of soil. Roll it out on your hand or on a plate of glass, and see if it can form a worm. Only if you cant form a 3mm thick worm without it crumbling is it safe to work.

Even then, do the least you can get away with, he advises. A light cultivator such as a Dutch harrow lifts and gently breaks up clods, and smears the soil less than a power harrow. Rolling consolidates the seedbed and aids slug control, but it can worsen compaction, so each field must be assessed individually.

Using wide wheels with low ground pressure tyres on the front and rear is the best option to minimise wheelings in wet seedbeds. Other suitable equipment includes dual wheels, cage wheels and crawlers with caterpillar tracks, explains Mr Richardson.

Quick turnaround

The same advice applies where ploughing is essential, such as after potatoes. But Mr Stevens warns growers to take extra care. Potatoes stop removing moisture from the seedbed well before harvest, so fields may well be wet already. A quick turnaround after harvest is advisable, particularly on unstable sandy loams.

Taking appropriate measures before or during late drilling can avoid seed losses to pests and diseases. It involves risk assessment, since the risk varies with soil type and seedbed conditions.

Seed dressings are important since soil- and seed-borne pathogens can become more aggressive in cold, wet seedbeds. Furthermore, there is potentially a high level of fusarium on wheat seed this year.

Perhaps the biggest pest threat to emerging seedlings in wet conditions after root crops is the slug. And this autumn is considered high risk – populations were above average in September, and Octobers wet, mild conditions allowed them to escalate, says David Green, entomologist at ADAS Wolverhampton.

"Although slugs are often less active and go down deeper when the weather turns colder, they quickly bounce back once it warms up. Peak activity has occurred as late as the end of November in wet seasons. And late-drilled crops will be slower to emerge, giving a greater potential for hollowing," he warns.

With a pressing need to establish crops, assessing the risk using traps before cultivating may not be feasible. Where the risk is expected to be high, Mr Green suggests applying slug pellets based on either metaldehyde, methiocarb or thiodicarb to the seedbed before, at or after drilling. The earlier the better usually applies, but not at the expense of undue delays in drilling.

BACK ON TRACK

DONT be concerned if you are behind with drilling, and the forecast looks grim. Already too many crops have gone in to unfavourable seedbeds, according to some independent agronomists.

Procrops Bryce Rham, who looks after 400ha (1,000 acres) of sugar beet and other crops in Shropshire, is used to seeing winter wheat drilled as late as Christmas without problem. He believes the promise of higher yields has pressurised growers to get on and dismiss the threat of seedbed compaction.

"Due to a protracted harvest, some growers were delayed from drilling early, then Octobers wet start held them up further. Perhaps that was a blessing in disguise, considering the sub-standard soil conditions, because the best yields come from mid-October sowings, and November-sown winter wheats are not far behind," he says.

In any case, it is the gross margin and not the yield which matters at the end of the day. Costs will generally be lower in late sown crops, remarks Mr Rham.

"The later you drill, the higher your seed rate should be, which increases the growing costs. Wet seedbeds, cold weather and crows can hinder emergence, and late sown crops wont compensate as well by tillering. I recommend adding 20 seeds/sq m to your 280 seeds/sq m calculations for every weeks delay after mid-October, which means potential seed rates of 200kg/ha are likely, depending on variety, thousand grain weight and seedbed conditions."

However, late sown crops after beet will require fewer herbicides, possibly fewer insecticides, no slug pellets and will be less prone to early spring diseases.

"Its usually not necessary to apply isoproturon or other autumn residual herbicides because grass weeds wont get a hold in time to cause a threat. A broad-spectrum spring treatment is often sufficient. And in disease-resistant varieties, for instance Charger, you can sometimes delay the first fungicide until flag-leaf emergence," he suggests.

But theres still a strong case for applying a growth regulator to most varieties, with the possible exception of short-strawed Equinox. Those commonly chosen for late drilling, for example Charger, have poor standing ability, stresses Mr Rham. Its also wise to watch your nitrogen fertiliser rates to avoid lodging problems.