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of spores a year, and the risk ofinfection is present right from thestart of the growing period (“greentips” stage) through to the end ofthe season. It should thereforecome as no surprise to learn that inthe year 2000, around US$150 millionwas spent worldwide on fungicidesfor use in spraying programmesto control scab.Growers already have a choice ofseveral fungicides to combat scabdiseases. But Flint, Bayer's newhigh-performance fungicide, setsnew standards. Several comparativefield trials, some of which were conductedby independent researchers,found that Flint was clearly worthyof its leading position. Initial experiencein practice has emphaticallyconfirmed this. Producers of highqualityfruit, especially in areasvulnerable to scab, will therefore bedelighted to have access to this newfungicide.Flint normally inhibits the earlystages of fungal pathogen development,particularly spore germinationand germ-tube growth. For thisreason, it is best applied early as aprophylactic treatment. However,apple scab is slightly different inthat the powerful intrinsic action ofFlint enables it to control laterstages of the fungus (such as thegrowth of the subcuticular stroma)as well. This offers added flexibilityin spraying programmes designed toFlint – Spectrum of Efficacy●●●● = excellent ●●● = good ●● = moderate ● = poorcombat this disease.In view of its excellent potentialefficacy, Flint is normally includedin anti-scab spraying programmeswhen weather conditions arefavourable to fungal reproductionand the infection pressure isstrongest. This can occur during thepre-blossom stage, but in mostyears, the principal infection periodcoincides with the time when pomefruit trees are in bloom. Mistakes inscab control during this phase cannotbe subsequently corrected. Thisis why the fungicidal treatment usedin spring is so important to successfuldisease control.Flint is most effective against scabwhen used preventively. Applicationrate recommendations varyfrom country to country, dependingon the local conditions, and rangefrom 7.5–15 g product/100 l 1 . Theinterval between applicationsshould not exceed 10 days whenspraying Flint during the principalinfection period or in orchards withstrong shoot growth. Intervals maybe extended to 10–12 days when theproduct is used later, or in generalwhen the risk of infection is lower.Multi-talented and versatileOne of the greatest strengths ofFlint is that it controls or at leastsuppresses many other importantdiseases of pome fruit alongsidescab; the level of success dependson the application volume used.For example, the application ratesPathosystem / DisorderActivitypreventive curativeVenturia spp. (scap on apple and pear) ●●●● ●●●●Podosphaera leucotricha (powdery mildew) ●●● ●Schizothyrium pomi (flyspeck)●●●●Gloeodes pomigena (sooty bloth)●●●●Gymnosporangium juniperi-virginianae (cedar apple rust)●●●Alternaria mali (alternaria leaf spot)●●●Stemphylium spp. (leaf spot in pear)●●●Botryosphaeria dothidea (white rot on apple)●●Glomerella cingulata (leaf spot and bitter rot)●●Gloeosporium spp. (leaf spot and bitter rot)●●●Jonathan spotno increaseLenticel red spotno increaseFruit russetingno increaseBitter pitpositive effectmentioned above for scab alsocontrol powdery mildew. The sameis true of typical summer diseases ofapples such as flyspeck (Schizothyriumpomi) and sooty blotch(Gloeodes pomigena), as well as leafspots in pears (Stemphylium spp.).Flint is also effective against storagediseases of pome fruit, a differentcategory of disease problem. It isvery difficult to choose the righttime to administer fungicides tocontrol these diseases. Finalpre-harvest applications are often asuccessful way of drastically reducingthe severity of these types ofinfection. The most common parasiticstorage diseases of apples arethe gloeosporium rots (Gloeosporiumspp.). Field trials with Flint onthese and other diseases showedthat the incidence of rot in storagecan be greatly reduced and that theresults are at least as good as thoseobtained from contact fungicides.These results have since beenconfirmed in practice.Responsible resistancemanagementThe build-up of resistance tofungicides in populations of fungalpathogens is a quite normal evolutionaryprocess. Just one change inthe genetic make-up of a pathogenpopulation, involving a spontaneously-occurringmutation, can setthis in train. The most widelyacceptedand well-founded theoryassumes that mutant genes controllinga specific resistance mechanismare already present in a naturalpopulation before a new fungicidecomes into common use. However,individual pathogens carrying thismutation do not necessarily benefitfrom it, but often lose out, in termsof growth and development in theabsence of the fungicide. That iswhy they would probably be quiterare in the population at first. Butfrequent use of the fungicide would1As Asian countries are also severely affectedby other pome fruit diseases which requirehigher application rates, anti-scab sprayingprogrammes in these countries sometimes useup to 25 g product/100 l.14Courier 1/2002
Preventive control of apple scap% efficacy10080usually lead to targeted selection ofpathogens carrying resistance to it.Resistance development is quite acommon phenomenon amongmodern fungicides. However, it hasin all cases proved possible tomaintain the efficacy of these fungicidesin many segments and uses bytaking responsible, appropriatecounter-measures at the right time.This brings us back to the beginningof the story of strobilurins and scabcontrol.The first signs of resistance tostrobilurins were noticed in somecrops after several years of widespreaduse had started. Some strainsof scab that are resistant to strobilurinshave been found. However,these strains have as yet beenobserved only in a small number ofregions with intensive pome fruitgrowing or on trial sites where theprinciples of preventive resistancemanagement have been deliberatelyviolated. In contrast to strobilurinresistance in powdery mildew inwheat (Erysiphe graminis sp. tritici),which is traceable to a pointmutation, four different resistancemechanisms have already beendescribed for apple scab. We mustbe aware of this distinction, andrealise that the situation with applescab will not necessarily become asdramatic as that with powderymildew in wheat. Nevertheless, it isimportant that the recommendationsfor strobilurin use set out below arealways considered as part of aresponsible, preventive resistancemanagement programme if thishighly effective substance class is toremain available for use in pomefruit growing in the long term:Flint or other fungicides containingstrobilurins should never be usedmore than 3 or 4 times a season tocontrol pome fruit diseases. Ofcourse, this also applies when Flintis being used to control storage diseases.In this case, it is advisable tomake the last treatment in the programmewith a contact fungicidesuch as Euparen ® M (tolylfluanid)rather than with Flint. Another6040200Foliar scapFruit scapField trials in Europe, under very heavy disease pressurePreventive control of powdery mildew on apple leaves% efficacy100806040200Infected leaves* Infected branches**Field trials in Europe, 1998* No. of infected leaves (untreated): 42%** No. of infected branches (untreated): 47%aspect of preventive resistance managementis that the recommendedintervals between applications arerespected and that ideally thetreatment programme should notcomprise more than two strobilurinapplications in succession. It hasproven beneficial to apply Flint in atank-mix, together with other specificscab fungicides or broad-actingcontact agents, particularly in casesof severe infestation. Possiblepartners in the mix are Euparen Mand Folicur ® (tebuconazole).Detailed national recommendationssuggesting tank-mixes with othercrop protection products can beobtained in Bayer recommendationbrochures or from advisors inindividual countries. If you areinterested in this topic, you can alsosee the latest recommendations onthe use of strobilurins in pome fruitcontained in the guidelines issuedby the FRAC (Fungicide ResistanceAction Committee; homepage:www.gcpf.org/frac).For pome fruit throughoutthe worldMany users who have incorporatedFlint into their spraying programmeto control scab and other pome fruitdiseases in the past growing seasonTrifloxystrobin7.5 g/100 lKresoxim-methyl10 g/100 lCaptan150 g/100 lTrifloxystrobin5 g/100 lTrifloxystrobin7.5 g/100 lKresoxim-methyl10 g/100 lPenconazole2.5 g/100 lare already convinced of the manybenefits offered by this fungicide.As it becomes registered for use infurther areas of the world, theproduct will go on sale in otherimportant pome-fruit-producingcountries in 2002: Italy, France,Chile, Japan and Korea are just afew. From 2003, Flint will be availablein all countries that producesignificant quantities of pome fruit.Two other important points:• In some Asian countries, Flint willbe sold not as an extrusion granulatebut in liquid form as a 250 SC(suspension concentrate). Othercountries have opted for the tradenames Zato ® or Aepul ® rather thanFlint.• Anyone who would like to findout more about Flint can visit thehome page of Bayer CropScience atwww.bayercropscience.com. Thiscontains a range of information,including a video with other interestingfacts that you can downloadfree of charge. ■Courier 1/200215
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