Solarization of soil in piles for the control of Meloidogyne incognita in olive nurseries in southern Spain

The potential of solarization to control Meloidogyne incognita in piles of soil used at olive nurseries in southern Spain was studied in 1999 and 2000. Kaolin and soil infested with free eggs and egg masses of the nematode in nylon bags were buried 20 and 40 cm deep inside conical piles of soil 80 cm high and with a base diameter of 1 m. Soil piles were solarized for 3 weeks in July and August. The effect of various periods of solarization was assessed by egg hatch bioassays in sterile water, and by infectivity to tomato plants. Maximum soil temperature at 20 cm depth in solarized piles was 47.4degreesC in 1999 and 48.2degreesC in 2000, compared with 32.9degreesC and 31.7degreesC in nonsolarized piles. Solarization reduced egg hatch by > 95% compared with nonsolarized samples, irrespective of type, burial depth and location of inocula in a soil pile. Egg hatch of egg mass-infested samples buried at 20 cm depth was higher than that of free eggs buried at the same depth. The differential effect associated with burial depth and type of inoculum was not found in solarized piles. In nonsolarized piles, hatch of free eggs from samples buried at 40 cm depth was higher than that from samples buried at 20 cm depth. Egg hatch in samples from solarized piles was lower than that from nonsolarized piles. A bioassay of tomato plants in 2000 confirmed the reduction in infectivity of free eggs buried in solarized soil piles. Under the conditions in southern Spain, solarization of 40 cm-high piles of soil for 3 weeks can therefore be used for the control of root-knot nematodes in potting soil for olive nursery production.