Managing OSR 08-Feb-2019

Carefully tailored  winter OSR management will be more essential than ever this spring to cope with massive differences in crop growth and development following an extremely challenging autumn for many.

 

Some crops established reasonably while others recovered from cabbage stem flea beetle attack courtesy of another kind early winter to come into the spring in decent shape. However, serious flea beetle problems and a bone dry September mean many others are decidedly backward.

 

“Thankfully, most crops haven’t sat in water so far this season so their root development should be quite sufficient to support productive canopies, “ reasoned Agrii oilseed rape specialist, David Leaper. “At the same time, we know how well OSR, in general, and fast-developing hybrids, in particular, can compensate for even quite substantial setbacks.

“This means that for the best performance at the least cost and risk we need to manage every crop for its genetic abilities as well as its current status. More forward crops, for instance, will need less early nitrogen plus a specialist PGR like Toprex or Caryx at stem extension to maximise their standing ability; especially if they’re inherently tall varieties with less-than-ideal levels of lodging resistance or stem stiffness. Our trials underline the importance of partnering this with a good prothioconazole/tebconazole co-formulation for sufficient light leaf spot control.

“On the other hand, struggling crops can really profit from a good early nitrogen boost, and the last thing they need is any check as they come into spring growth,” he pointed out.  “So, delaying the PGR until green bud or taking advantage of the less stressful growth-regulating effect of extra tebuconazole in the LLS spray might be a better bet.

“To prevent light leaf spot taking off it’s important not to hold back the fungicide to accompany any later PGR here. Otherwise, the disease could have devastating consequences for already struggling crops.”

 

David Leaper suggests a similar spring management approach for crops that look reasonable but are likely to be carrying significant burdens of flea beetle larvae. These are recognised as reducing OSR yields by an average of over 0.5t/ha. But crop compensation means the level of loss doesn’t appear to correlate well to larvae numbers.

Recent research in badly-infested trials, for instance, indicates that varieties like DK Exalte and DK Expedient which grow away earliest in the spring suffer noticeably less loss of main stems and stunting than later developing hybrids and conventional varieties (Figure).

“This makes the type of varieties we’re growing an important consideration here too,” he said. “We must give crops with the best ability to compensate all the help they can get to do so. Effectively writing them off because they’re carrying a sizeable larval burden is about the worst thing we can do. It just makes poor performance a self-fulfilling prophecy.

“These crops require greater spring management attention to stimulate canopy development and structuring, as well as the most effective protection against both leaf and stem diseases. After all, it has taken us considerable investment to get them this far.”

Matching canopy N applications closely to actual GAIs is crucial, in David Leaper’s experience. Because they can change so rapidly, he’s equally adamant that applications are based on GAIs measured only once growth has really started rather than too early in the season.

In addition to nitrogen, he stresses that OSR is highly susceptible to shortages of sulphur, magnesium and boron, and moderately susceptible to molybdenum and manganese, making it important to avoid imbalances of these nutrients.  Agrii tissue testing trial work also shows a clear shortfall of potash in higher yield crops from stem extension.

“Actively stimulating the growth of backward crops or those infested with CSFB so they can better withstand the effects of larval damage is also important,” David Leaper added. “Six years of our R&D has shown the ability of the growth stimulant, Nutri-Phite PGA  to increase OSR canopy size, greenness and yields.  In the absence of an autumn application, in particular, we recommend including it with the stem extension spray at 1.0 l/ha.”