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Canopy management essential this year
Date added: 22/03/10 |
For the first time in three years, the majority of oilseed rape crops would benefit from the use of a PGR fungicide and growers should be assessing this need now by measuring the crop’s GAI (Green Area Index), says Dr. Dave Ellerton of ProCam.
Through use of nitrogen and PGR fungicide such as Juventus (metconazole) or Toledo (tebuconazole), the canopy structure can be optimised making it more open and able to intercept the maximum amount of light, resulting in better yields, he says.
“Large canopies, as we may well see this year once the weather warms up, need reining back as over-large canopies will lodge and light penetration will be poor. This will result in pod abortion, fewer seeds per pod and less efficient seed filling.
“With many early drilled crops and a warm and wet November, many crops were well advanced pre-Christmas. The cold winter has taken off a few leaves and pigeons have inflicted further damage, but many crops are still more advanced than they were last year and the year before.”
Growth regulating fungicides work in a number of ways – they decrease crop height and reduce the risk of lodging, Dr. Ellerton explains.
“Lodging can be underestimated in oilseed rape, but it will affect yield, quality and harvestability. Yield loss due to lodging can be in the range of 13% to 50% and so with rape at £250/tonne this can be in excess of £350/ha. Every 5cm height reduction means 10% less lodging.
“A lodged crop can also be more vulnerable to disease. Harvest is more difficult, more time-consuming and so more costly in a badly lodged crop. Seed loss due to pod shatter will mean more volunteers to contend with in following crops – lodging can be an expensive business.
“Metconazole is able to improve root length density by 25% which is important for nutrient and water uptake, particularly when it is dry at pod filling. This can add another 0.34t/ha,” he explains.
But Dave Ellerton warns growers to use PGR fungicides only when necessary.
“Crops with a GAI of more than 1 in mid March or over 2 in April will give an economic response to PGR fungicides of up to 0.5t/ha. But if crops are less advanced, say with a GAI of less than 1, they run the risk of yield penalty.
“In 14 trials an application of metconazole to crops with a GAI of less than 0.8 in mid-March resulted in a yield loss of 0.13t/ha, whereas in 18 trials an application of this effective PGR fungicide on crops with a GAI over 1 gave an average yield increase of over 0.2t/ha.”
Dr. Ellerton concludes that last year oilseed rape yields were good, 9% above the five year average, and this can be explained by a combination of factors including naturally small canopies, high radiation levels in April, adequate moisture in May and June and lower disease levels.
An ADAS survey last year showed that 43% of crops in March 2009 had a GAI (Green Area Index) of between 0.4 and 0.8 with 38% of crops being between 0.8 and 1.2 GAI. The average in March 2008 was 0.8, below the level that would normally require a PGR but would in itself lead to an optimum sized canopy, he explains.
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