South: Pest and disease risk increases

Dry weather seems to be the order of the day. During May we have had about 10mm of rain, with the west faring a little better than the east of the region. Crops on the light land are suffering badly with flag leaf beginning to roll in the heat of the day and those on the parched sandy soils, are looking sickly and seem to have given up completely. There is some general rain forecast for Tuesday 1 June and this may just help regain some of the lost yield potential.

Winter wheat is at the ears emerging GS53 stage. Any flag sprays that have not been carried out should be completed soon as the risk of septoria has increased considerably since the 5mm of rain we had about a fortnight ago. At present the top leaves of the crop canopy are clean but there is septoria sitting in the bottom of the short crop canopy and it will not take long for it travel up to the flag leaf.

Yellow rust has been noticed in a crop of Oakley that was sprayed with a robust T1 fungicide some three weeks ago. Considering the high temperatures peaking at 26C, it is surprising to note the incidence of yellow rust. It goes to show how virulent this new strain of yellow rust is.

Most early varieties of oilseed rape, are about 70% podded and may have escaped the risk of sclerotinia attack. Late varieties such as ES Astrid are only 50% podded and may well be subject to a sclerotinia incidence if this week’s forecast rain arrives. If there is sufficient rain to stick the petals to the stem then a sclerotinia spray may be worthwhile and should be considered.

Those areas that had rain during the last two weeks could have orange blossom midge adults flying onto the emerging ears of wheat now. This is a sporadic but highly damaging pest of winter wheat. Two pheromone traps per field should be laid in those fields where there is a history of this pest and if 30 adults per trap are caught over 2-3 days, then it will be advisable to carry out in field monitoring. One adult per three ears in the case of feed wheat, and one adult per six ears in the case of milling wheat is the spray threshold. Orange Blossom Midge monitoring begins.

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