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Damage assessment of the leafhopper Asymmetrasca decedens (Paoli, 1932) (Homoptera: Cicadellidae) on Salix spp. in Italy Allegro G.; Giorcelli A.; Deandrea G.; Bazzani R. CRA/PLF-Unità di Ricerca per le Produzioni Legnose Fuori Foresta, Casale Monferrato (AL), Italia
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[email protected] Abstract The damage caused by the leafhopper Asymmetrasca decedens was assessed over four different years (2001, 2002, 2005 and 2006) on 573 Salix genotypes belonging to different species and hybrids grown in a collection stand at Casale Monferrato (Italy). These genotypes were rated according to a four-level scale based on the ratio of curled leaves on 1 year-old shoots at the end of the growing season. Each genotype showed a quite constant level of susceptibility over the years. Most Salix alba genotypes and S. alba hybrids were heavily damaged; on the contrary, S. babylonica, S. matsudana and S. jessoensis genotypes together with their hybrids were generally resistant. During 2003, a control test with two insecticides (chlorpyrifos-methyl + cypermethrin and thiametoxam) was carried out in a nursery established in Casale Monferrato with the S. alba clone ‘SI 62.059’, rated as highly susceptible, in order to assess their effectiveness against A. decedens and to quantify growth reduction caused by the pest. Thiametoxam, a systemic insecticide, proved to be highly effective significantly reducing the pest damage. The plants in the control plots grew 50% less in height than those treated with thiametoxam, with 85% of wood volume loss. These results attest the risk of severe damage connected with A. decedens in Short Rotation Forestry (SRF) plantations established with susceptible Salix genotypes. Key words: Asymmetrasca decedens, Control test, Damage assessment, Salix spp., Susceptibility behaviour, Short Rotation Forestry Introduction Asymmetrasca decedens (Paoli, 1932) (Homoptera: Cicadellidae) (fig. 1) is a polyphagous pest occurring on herbaceous plants (Chenopodiaceae, Fabaceae, Solanaceae, Lamiaceae, etc.) and on tree or shrub species (Rosaceae, Salicaceae, Ulmaceae, etc.), that affects leaves and causes a severe growth reduction (Matthews, 1994). Typical symptoms, the so-called ‘hopperburn’, are leaves turning yellow and curling their edges downwards before drying-out and shedding (Atakan, 2009) (fig. 2). Moreover, A. decedens, together with a number of other leafhopper species, is able to transmit different phytoplasma groups, which can be highly injurious to plants (Pastore et al., 2003). A. decedens is widely spread in the Mediterranean area and Fig. 1 – Adult of the leafhopper since the end of the past century it was recorded in Italy mainly Asymmetrasca decedens from the Central and Southern Regions (Pollini, 1998). More recently, massive population outbreaks have been recorded in Northern Italy too, causing severe damage to peach-trees in Piedmont (Pansa et al., 2010) and to cultivated red raspberry in Trentino (Grassi & Dal Rì, 2006). During 2001-2006, the plants in a Salix collection stand grown in Casale Monferrato (NorthWestern Italy), including 573 genotypes belonging to different species (S. alba, S. bayilonica, Salix
jessoensis, S. matsudana, S. viminalis, S. fragilis, S. sachalinensis, S. dolychostila, S. daphnoides, S. koreensis, S. mongolica, S. smithiana, S. tetrasperma) as well as hybrids from intraspecific crosses and from crosses with S. alba, were heavily attacked by the pest (Allegro & Giorcelli, 2007). This paper illustrates the results of field surveys with the goal of assessing their susceptibility to A. decedens. Moreover, the damage caused by the leafhopper was evaluated by comparing the growth rate of attacked young plants of a highly susceptible genotype, the S. alba clone ‘SI 62.059’, with plants of the same genotype protected from damage by periodical insecticide sprayings. Two different insecticides were tested, showing different effictiveness against the pest.
Materials and methods
Fig. 2 – Symptoms of attack of Asymmetrasca decedens on Salix sp.
The 573 Salix genotypes grown in the collection stand (CRA/PLF experimental farm) at Casale Monferrato (5 plants per genotype) were checked at the end of the summer (September) 2001, 2002, 2005 and 2006 and rated according to the damage suffered from leafhopper attacks on 1 year-old shoots. The damage level was assessed according to a four-level scale based on symptom intensity and ratio of attacked leaves (table 1).
Table 1 – Scale for evaluation of the damage caused by the leafhopper Asymmetrasca decedens on Salix spp. Damage class Attacked leaves Symptoms (%) Curled leaves 1
