Rapid stem extension, after a slow start to spring, islikely to create splits in oilseed rape plant stems that could increase therisk of Sclerotinia infection, warnsSyngenta Field Technical Manager, Simon Roberts. Furthermore, high levels ofCabbage Stem Flea Beetle larvae emergence now being seen will also create aneasy entry point for disease.
Some trial plots on the Syngenta Innovation Centre inHampshire have put on over 60cm of height and more than doubled their greenarea index (GAI) in less than two weeks, he reported. Typically such rapidgrowth results in weak stems with a greater frequency of splits and breakage atthe axial leaf joints.
In many crops we are also seeing large numbers of holesappearing in stems around the leaf axial joints, where Flea Beetle larvae areburrowing out from the stems to complete their life cycle. In some areas MrRoberts has found evidence of over 80% of plants affected and up to nine larvaein a single plant.
Any damage to the plant allows Sclerotinia to get in, especially if spore presence coincides withpetal fall; the pathogen uses the decaying petals as a food source to develop. Sclerotinia will exacerbate any weaknessin stems, leading to yield loss from extensive canopy collapse and early dieback.
Mr Roberts advocates growers ensure crops are protected frominfection early this season with Amistar Technology, either with a two-sprayAmistar programme, or using new Symetra as an initial application.
The added advantage of using Amistar or Symetra for theflowering spray fungicide programme is the additional physiological greeningeffects on the plant, leading to higher yields and increased oil content ofseed – even in the absence of disease.
In previous years extremely damaging high levels of Sclerotinia have been recorded inconditions that were considered low risk. Mr Roberts believes this may havebeen attributed to crops that were weakened and more susceptible to infection.
We will also use the Innovation Centre trials to assess theeffect of Toprex as a PGR to suppress crop height, and how that might impact onstem strength and preventing damage, he added.
Simon Roberts also points out that the high presence of CSFBlarvae in the crop highlights potential control issues last autumn, when adultswould have laid eggs around the base of plants. Even crops that escaped theworst effects of leaf shot-holing from adult beetle feeding in the autumn, arenow showing the damaging effects of larvae activity.
Itreinforces that, without the protection of Cruiser OSR seed treatment, growersand agronomists will need to be especially vigilant to control adult beetles nextseason, he advised.