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Agrovista agronomist Craig Green provides some tips to help growers manage stressed maize crops this spring

Craig Green.

A long spell of cold nights, coupled with plenty of rain over the Easter weekend, means soils have been very slow to warm up over recent weeks. Ideally, maize needs to be drilled into a seedbed that remains at 10°C or above to avoid being stressed. At the time of writing (third week of April) readings were just 7–8°C, and the longrange forecast suggested the run of cold nights would continue. Much of the crop is sown by contractors who have large areas

to cover. Added to this, most maize varieties in the east tend to be the bigger and later ones with FAO values of 210 or more, so they need to be in the ground early to maximise their potential. Drilling therefore has been continuing apace over the past fortnight. These cool soils will put the crop under stress from the word go. Seedlings will expend more energy to emerge and establish and are very likely to suffer from cold shock. Many stands are likely to turn yellow soon after emerging, as roots struggle to grow and provide sufficient nutrition for the young plant. Work at our Great Ellingham trials last year, when conditions were even more stressful, showed a low-rate application (10-litres/ ha) of MZ28, a non-scorching foliar nitrogen product, gave these yellow crops the kick-start they needed. MZ28 is usually applied at 8–10 true leaves to aid cob production, but applying it at 10-litres/ha when the crop has 4-true leaves helped plants to green up and regrow, putting them in a much better

position once soils did warm up. This also helps keep herbicide programmes on track. Weeds are much less sensitive to soil temperatures, so in cool conditions pose even more of a threat than usual. However, stressed crops cannot be sprayed with herbicide as they are easily damaged.

Pre-emergence Pendimethalin applied preemergence will be critical this season. It provides good broad-spectrum control of most problem weeds and will optimise post-emergence herbicide performance. I’ll apply 1,200–1,400g/ha together with Remix, an adjuvant and application aid that keeps the active in the top few centimetres of soil where it does most good. I’ll also be advising adding N-Lock with the pre-emergence herbicide. This is a nitrogen stabiliser that slows the conversion by bacteria of ammonium bagged nitrogen for up to six weeks. This ensures enough nitrogen will remain near the soil surface to fill cobs – maize uses half of its total N requirement after flowering, and 60kg/ha can be lost between drilling

and that time. On average, we’ve seen a nine per cent yield increase at our Great Ellingham trials over the past three years. Post-emergence herbicide treatments are ideally applied at the 4-leaf stage. However, if crops are stressed you can hold off to six leaves in the case of Maister (foramsulfuron + iodosulfuron), or eight for other treatments. Product choice will depend on weed spectrum. For broadleaved weeds I’ll use Callisto (mesotrione) or Calaris (mesotrione and terbuthylazine), but be aware of following-crop restrictions, particularly sugar beet. Where broad-leaved weeds and grasses need controlling, Elumis (mesotrione + nicosulfuron) at 1.0–1.5-litres/ha provides exceptional broad-spectrum activity. An alternative that will control single R-resistant black-grass as well as a range of other grass weeds and broad-leaved weeds is Maister + Buctril (bromoxynil), at 150g/ha and 0.6-litres/ha respectively. *Craig Green is an agronomist with Agrovista, based at Great Ellingham, Norfolk ( ■

AGRONOMY UPDATE – SOUTH WEST Maintaining the pressure on septoria tritici will be key in winter wheat crops at the all-important T2 spraying timing, says Agrovista agronomist Esme Shephard.

Esme Shephard.

There was quite a bit of septoria to be found on the lower leaves of wheat crops at T1, and, while well-timed, robust sprays will have kept this in check it is important to keep up the pressure with the T2 application. Although disease spread is usually associated with rain splash and at the time of writing (third week of April) it remained very dry, the older leaves were rubbing against new

growth so septoria would have been able to spread by direct contact. Disease pressure may be reduced, but only of it stays dry through to, and beyond, the T2 timing will I be tempted to cut back on rates – and this should only be considered where a robust T1 has been used. The paybacks of a well-timed flag-leaf spray are well documented. You never know what the weather is going to do – even apparently clean crops can be harbouring latent disease, which can re-appear and spread very quickly in the right conditions if we let down our guard. With that in mind, I’ll be looking to apply Priaxor (fluxapyroxad + pyraclostrobin), Eclipse (epoxiconazole + fenpropimorph) and chlorothalonil, all at 1-litre/ha. This is an effective combination that will cover septoria, rusts and any mildew that may be present. It also provides several different modes of action to help prevent the build-up of resistance, particularly to

the SDHI component, which is now the key weapon against septoria. It has been a very “growy” season and some varieties, such as KWS Siskin, are looking leggy. If they look that way at T2 I’ll add Vivax (chlormequat chloride + ethephon) at 1.2-litres/ha to the T2 fungicide spray. I’ll also add magnesium on susceptible crops to boost chlorophyll production. Leaf tissue analysis is a very effective method of checking the need for this and other trace elements. Broadleaved-weeds have mostly been well controlled by pre-ems, but where they do need tidying I’ll also include some Gal-Gone (fluroxypyr) or Spitfire (florasulam + fluroxypyr), depending on species present.

Spring barley There is quite a lot more spring barley being grown this season, as black-grass pressure is now high in this area and people rightly see the crop as an aid to reducing the problem, giving them more time to control the weed between crops. However, the crop has had the worst possible start this season.

Most went in fairly late, at the end of March and into April, as the soil was too wet to go earlier. At the time of writing it hadn’t rained since, so much of it was desperate for a soaking to get it going, especially on lighter soils where it was drilled into dust. Pre-ems are unlikely to have worked that well so Axial (pinoxaden) + Adigor wetter makes a good alternative at early tillering, followed by SU herbicides at least a week later to take out remaining broad-leaved weeds, together with trace elements, particularly sulphur and manganese. Hopefully most spring barley crops, especially those on heavier soils that were drilled into moisture, will now be approaching T1 (GS30). Jaunt (fluoxastrobin + prothioconazole + trifloxystrobin) at 0.5-litres/ha plus chlorothalonil will be the main choice at this timing, probably with a growth regulator, such as Canopy (mepiquat + prohexadione) at 0.3-litres/ha. *Esme Shephard is an agronomist with Agrovista, based in Wiltshire (esme.shephard@ ■

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