Stemand root lodging pose the highest risk to winter wheat for many years, growersattending the first AgriiFocus Technology Centre agronomy day of the year nearMarlborough in Wiltshire this week (Thursday February 27) were warned, puttingthe onus firmly on the most effective plant growth regulation from the outsetthis spring.
Excellent early establishment and one of the mildest winters on record meansmany wheats are coming into the spring full of potential, pointed out Agriiregional technical adviser, Tim Horton. At the same time, though, Septemberand October-sown crops are generally thick, lush and well-grown.
Add to this poor anchorage support from very wet soils and the fact thatalmost two thirds of varieties on the Recommended List and over 75% of Group3 and 4 wheats are rated
7 or less for their inherent lodging resistance and the warnings bells soundloud and clear. Especially so for crops sown in or before mid-September whenratings can be reduced by two points at other than low seed rates and where soil mineral nitrogen levels havebeen more than adequate.
Even varieties with resistance ratings of 7 have shown as much as 90% lodgingin our trial work, he stressed. Sogood PGR management will be essential in forward crops if serious stem or rootlodging losses are to be avoided and canopy structures optimised.
For such crops, Tim Horton recommends a short split with low temperatureactive PGRs at both GS29/30 and GS31/32. Standard applications of Adjust, Meteor +/- Cutlass will, he explains,shorten internodes and reduce apical dominance as well as increasing root platelength and diameter, root fresh weight and stem thickness. He stresses, though,that it will be vital not to let yellow rust take hold while waiting for theright PGR timing.
Whilebackward crops will profit from a longer split with the first PGR applicationbrought forward to GS21-26, Mr Horton strongly advises against this with forwardcrops to avoid excessive tiller retention.
Regardless of crop condition, dont skimp on your early PGR application asthis will really improve anchorage to reduce the risk of root lodging, hesaid. Then go in with the second split to shorten the internodes andstrengthen the stem base.
A further application of Adjust + Cerone at GS37-39 will also be advisable torestrict stem elongation in particularly thick crops and varieties mostsusceptible to stem lodging. In all cases, our trials have shown the inclusionof Kantor improves PGR penetration and uptake to deliver valuable yieldbenefits.
Alongside effective PGR management, of course, it will be vital to timenitrogen applications carefully to both crop and soil nitrogen status, addedTim Horton. Our early N Min results suggest available soil nitrogen levels arelower than last season. But they can vary widely from site to site so westrongly advise specific assessments for the greatest precision.
Using Agriis N Planner, he recommends applications targeted at achieving aGreen Area Index of 6 ahead of flowering for the most productive canopies.Where less than 100 kg/ha of N is needed to achieve this, the majority shouldbe applied around two weeks before the terminal spikelet stage at GS30. Butwhere initial N requirements are higher two thirds of the amount required forthe canopy should be applied in two early season splits followed by a thirdbetween GS32 and GS37.
The last thing we need with thick stands is too much nitrogen too early, heinsisted. While our trials show more early N will increase both heads/m2and yields in thinner crops, in thicker ones this will restrict yields bycreating less efficient canopies.