Eradication of Orobanche/Phelipanche spp. seedbank by soil solarization and organic supplementation

Broomrapes are holoparasitic weeds responsible for high yield losses in tomato. The efficacy of available means to control them once they have attacked the crop is very limited. Due to this effective and environmental-friendly strategies to prevent these attacks on greenhouse tomato are needed. Both soil solarization and organic supplementation have been proposed to reduce broomrape attacks. However, a setup in their implementation, especially for eradicating broomrape seedbank from highly infested soils, is still needed before they can be widely adopted as a resolutive commercial practice. A set of two experiments was carried out in Southern Italy (37°03′N, 15°18′E, 10m a.s.l.) to study (i) the effect of repeated solarization (for 1–3 consecutive years) and (ii) a single cycle of soil solarization combined with three levels of organic supplementation (0, 0.35 and 0.70kgm−2), on broomrape seedbank dynamic and fruit yield of greenhouse tomato plants. Soil solarization alone during summer months increased mean maximum soil temperature by about 8.0–13.2°C (at 5cm depth) and 4.1–9.3°C (at 15cm depth). After one single cycle of soil solarization alone, seedbank mortality accounted for ∼99% of viable seeds, while induced seeds dormancy accounted for the remaining ∼1%. Complete seedbank eradication was achieved after the second year of solarization, while tomato fruit yield, starting from 3.43kgplant−1 in unheated soil, peaked after the third year of solarization (6.58kgFWplant−1). Organic supplementation prior to solarization further increased the temperature of solarized soil at both 5 and 15cm soil depths (by up to 4.3°C, on average) and enhanced the efficacy of solarization against broomrape seedbank. Indeed, total seeds mortality was induced after a single cycle of solarization combined with 0.35kgm−2 organic supplement, while tomato yield was enhanced up to 0,70kgm−2 supplement (9.44kgFWplant−1). Our results show that in Mediterranean climatic conditions at least two consecutive years of soil solarization are needed to completely eradicate broomrape seedbank from a highly infested soil. However, the efficacy of this technique may be improved when combined with organic supplementation, with positive effects on the yield of greenhouse tomato.