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.However,in the case of SRC Willow, this is not considered a practical solution for a number ofreasons:" Economics - SRC Willow is a high volume low value crop and the necessary repeatedfungicide applications could not be sustained economically.Melampsora epiteaHeteroecious rust alternating on European larch (Larix decidua)Lifecycle of Melampsora epitea (AFBINI)" SRC Willow is seen as an environmentally acceptable crop and the intensive use offungicides would not be compatible." Practically, after the early stages of re-growth following coppicing, it is increasinglydifficult to achieve the necessary chemical coverage of the plant to effect adequatedisease control.As a result, an alternative non-chemical disease control strategy needed to be020developed and this has been the subject of ongoingresearch since the late 1980 s.If the major contributingfactor to the development of the disease was the lack ofgenetic diversity in the single variety plantations used inthe early plantations, it was argued that the introductionof diversity by planting mixed variety plantationswould be effective in control.This has proved to be asuccessful approach, with mixtures delaying the onsetof the disease and reducing its spread, so that at the endof the growing season, the disease although still presentwas not at levels where yield was affected.This wasconsidered to be a more sustainable approach and asa result of the work a number of conclusions and fromthese standard recommendations can be made:" Evidence clearly indicates that where disease pressureis high, as it is in Ireland, the planting of single varietyRust infected plantationplantations even where the variety is less susceptible orshowing premature leaf fallresistant to rust is a short term high risk strategy andand die-back (AFBINI)not to be recommended.There are examples where apreviously resistant variety has become susceptible asthe natural rust population has evolved, resulting in severe losses in single varietyplantations." The yield of the improved varieties from the breeding programmes in Sweden and theUK, together with their superior rust resistance, means that only they should be usedin commercial developments." Yield from diverse mixtures is greater than the equivalent yield of the mixturescomponents grown in monoculture even in the absence of the disease." Where less diverse mixtures have been planted e.g.mixtures of exclusively Salixviminalis varieties, these yield increases have not been recorded and the diseasesuppression aspects, whilst present, are not as marked.This is an important aspectsince many of the commercially available improved varieties are of Salix viminalisorigin.Yield (kg) from 100m2 of mixtures and component genotypesgrown in mono-plots350300250MIXTURE200150MONO10050X5 X10 X15 X20021kg 100m-2Short Rotation Coppice Willow - Best Practice Guidelines" Increasing diversity in mixtures can result in yield compensation.Where individualcomponents of the mixture become susceptible to the disease over time and makeincreasingly smaller contribution to yield, it has been shown that in a mixture of tenvarieties, the loss of up to 30% of component varieties can be fully compensated forand the potential yield loss avoided.This yieldcompensation occurs as a result of the remainingvarieties occupying the space left by those thathave become disease susceptible.Consequently,at least six and preferably ten varieties should beincluded in commercial plantations." Where varieties have been shown to have a highlevel of rust susceptibility, their inclusion inmixtures does not improve their productivity or Willow leaf beetle (Phratorasustainability.vulgatissima) and larvae (AFBINI)" Completely random planting of mixtures is the ideal configuration to maximize yieldcompensation.However, with the planting machinery used the short run, randommixtures achievable with the step planter would be an acceptable compromise." There are differences in how individual mixture components contribute to the overallyield of the mixture.Provided that individual components do not have a significantnegative effect, their inclusion is justified by the diversity they bring and the positiveeffect they have as a result on sustainability.PESTSWillow beetles (Chrysomelids): This group of beetles represents the major economic pestproblem in SRC in Ireland." There are three species of willow beetle involved - brassyor green (Phratora vitellinae), blue (Phratora vulgatissima)and brown (Galerucella lineola).The blue and brown speciesare more prevalent." Overwintering adults emerge from hibernation inApril and, after a short feeding period, begin tobreed.Egg-laying takes place between early Mayand late June.Larval stages are found from mid-Mayinto July and develop through three instarsbefore pupating.The new generation of adultbeetles appear in July/August and feed until hibernatingin the autumn.left: Giant willow aphis022(Pterocomma salicis) (Sligo IT)" There can be two generations per year  the first emerging from the eggs laid byoverwintering adults in May and a second generation in August." Adults feed on the upper leaf surface larvae whilst the larvae feed on the undersideof the leaf which eventually is skeletonised and turns brown.Unlike rust infections,skelotinised leaves usually remain attached." Economic damage has been recorded in UK.However, damage may visually appearsevere but defoliation experiments have shown if 50% to [ Pobierz całość w formacie PDF ]