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One spray or two? “ The debate is always whether to put on a second treatment. ” Technical Sclerotinia Sclerotinia has the potential to decimate yields. CPM seeks advice from experts in a county where the threat is often highest. By Lucy de la Pasture It’s a sight that makes the heart sink. The oilseed rape crop has been looking full of promise all season, you’ve been feeling quietly confident that things have gone well and then you spot them –– patches of white stems, ‘rat-droppings’ and lodging –– the tell-tale signs of sclerotinia infection. Not many OSR diseases have the visual impact of sclerotinia and it’s high on the list of grower priorities when it comes to fungicide applications, says Dr Julie Smith, senior research scientist based at ADAS Rosemaund in Herefordshire. Although sclerotinia is a slightly sporadic disease and doesn’t occur in every season, it made an unwelcome return in 2016, catching some growers unawares. The question is why was this, and how can we guard better against a repeat performance? According to Julie Smith, weather data revealed more infection events than ‘normal’ took place last spring. For infection to occur, three factors have to happen simultaneously –– ascospore presence isn’t enough on its own, she explains. Relative humidity “For plants to become infected, a minimum temperature of 7 0 C, with relative humidity at 80% or above for at least a day is required. Petals need to be carrying ascospores, then the infected petals have to stick to the leaves of OSR plants to enable the fungus to infect the plant and for sclerotinia to become a problem in the crop.” And although the disease is widely associated with wet springs and moisture is required for infection to occur, it needs to be the right kind of moisture. “Heavy rain suppresses ascospore release and under these conditions, petals are often washed off the leaves and don’t have the opportunity to stick to them. In contrast, light rain or even just heavy dews offer perfect conditions for petals to stick and ascospore germination,” says Julie Smith. As petal fall is the main culprit when it comes to sclerotinia infection, apetalous or reduced petal varieties have been suggested as a way of circumventing disease spread. Defra-funded work carried out by ADAS has investigated this According to Julie Smith, sclerotinia control is more dependent on getting the timing right than the fungicide applied. by tracking flower opening and petal fall in apetalous specimens and found the sepals and stamens can also be a source of sclerotinia inoculum, rather blowing the theory. Further work revealed the leaf layers that were most likely to catch petals were situated between the bottom and mid-canopy, leaf layers 7-9. In the study, sclerotinia infection subsequently came in on the stem at the same level confirming the importance of petal-stick in the infection process, as well as the need for good fungicide coverage and penetration of the canopy. 18 crop production magazine arable extra march 2017
So do we really want varieties with big leaves at this level, asks David Lines, Herefordshire independent agronomist and AICC member. Although they provide a good source for photosynthesis, he reasons that retention of these leaves late in the season isn’t desirable in a sclerotinia-prone situation. Julie Smith agrees with the logic but suggests leaf size plays a much smaller role in sclerotinia infection than the weather during the flowering period so probably isn’t a major factor. “In 2016, first sclerotinia sprays were applied when 30-50% of flowers were open on the main stem, locally this was around 22 April on early flowering varieties and 3 May on later flowering types. One of the problems was that April was a cool month and crops stayed in flower for a long time, meaning a second spray was required. “Combined with the fact that minimum temperatures in May were slightly higher than the long-term average, this meant we saw an increased number of infection events,” she comments. David Lines nods his agreement and stresses the duration of flowering is all-important where sclerotinia is concerned. “Last season I saw more sclerotinia in Troy because it’s a later-flowering variety and this Bleached stems are a tell-tale sign that sclerotinia control was inadequate. Petals need to be carrying ascospores, then the infected petals have to stick to the leaves of OSR plants to enable the fungus to infect the plant. coincided with a period of weather that resulted in multiple infection events. For my crops, a fungicide application for sclerotinia control is a given –– the debate is always whether to put on a second treatment,” he adds. Agronomist and pathologist also agree that timing the sclerotinia application is the most important factor to get right, with product choice of secondary importance. Nothing to choose “There’s really nothing to choose between Proline (prothioconazole), Pictor (boscalid+ dimoxystrobin), Filan (boscalid) and prothioconazole (PTZ) plus Amistar (azoxystrobin),” says David Lines. “Last year I switched to PTZ during flowering because of the light leaf spot pressure (LLS) but I have tended to go down the Filan or Pictor route in the past. This season there’s not nearly as much LLS in crops and using chemistry from groups other than the azoles is good resistance management.” Julie Smith points out that some work done by ADAS found that fungicides from different groups affected the pathogen at slightly different stages of the life cycle. “SDHIs and strobilurins are more effective against spore germination and germ tube elongation so we often found clumps of un-germinated ascospores on petals, whereas azoles are more active against ▲
Page 1: In this issue... Hands-free hectare
Page 4: Am I wrapped up in a bubble? There
Page 8: Disease control Decision support to
Page 11 and 12: winter and new isolates -- Blue and
Page 14 and 15: Fungicide behaviour Bringing new cr
Page 16: Tech Talk According to Jonathan Bla
Page 22: Weed worries shouldn’t drive spri
Page 26 and 27: Weed control Colin Woodward was fac
Page 28 and 29: Liquid logic has a way with weeds I
Page 30 and 31: Innovation Insight Performance in m
Page 32: Spotlight on crop research “ The
Page 35 and 36: across the whole genome, making it
Page 37 and 38: Blackgrass Banbury blackgrass strat
Page 39 and 40: Precision agronomy helping farmers
Page 42: Precision agronomy The 40hp Iseki t
Page 45 and 46: Spring beans and OSR or spring bean
Page 47 and 48: Spring beans The crop’s given a p
Page 50 and 51: Conference grown, the weed control
Page 52 and 53: “ The domestic demand is predomin
Page 54: The new name for a farmer’s frien
Page 57 and 58: Insiders View Chris Guest notes Gra
Page 59 and 60: “ With sugar beet you’re not a
Page 62 and 63: Sugar beet weeds Weed control is on
Page 64: Potato weed control Herbicide treat
Page 67:
Opportunity in marginal gains Over
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