Weeds and Weed Management in Tomato - a review

The EWRS Working Group "Weed Management Systems in Vegetables" was established with the tasks of collecting and disseminating information and results on weeds and weed control strategies in vegetables, identifying gaps in knowledge and focusing new research projects. Information about key weeds, new weeds or species that have recently began to spread, critical period of competition, Integrated Weed Management programmes, authorised and under registration herbicides in tomatoes grown in the field conditions in Croatia (HR), France (F), Israel (IL), Italy (I), Morocco (MA), Poland (PL), Portugal (P), Spain (E) and Switzerland (CH) was collected. The weed communities are commonly very rich of species (both grasses and broad-leaved weeds) but they are made up by a small group of common species throughout the Mediterranean area (Echinochloa crus-galli, Amaranthus spp., Chenopodium album, Polygonum aviculare, Portulaca oleracea and Solanum nigrum). Crops are mostly transplanted. In early direct sown crops, early-emergence weeds (Alopecurus myosuroides, Avena spp., Lolium spp., and several species of Cruciferae and Compositae) are frequent. Solanum nigrum (plus S. sarrachoides and S. physalifolium in E) is the key weed in all the countries but the following species are becoming an increasing problem: Galinsoga parviflora in PL; Ambrosia artemisiifolia, Cirsium arvense and triazine-resistant Amaranthus hybridus in F; Euphorbia chamaesyce, Cynodon dactylon, Cyperus spp. and Sorghum halepense in E; Datura stramonium, C. dactylon, Paspalum paspaloides and Cyperus spp. in P; Abutilon theophrasti, Convolvulus arvensis, Calystegia sepium, Xanthium spp. and Cyperus spp. in I; A. theophrasti, A. artemisiifolia and D. stramonium in HR; C. arvensis, D. stramonium, Malva parviflora and C. dactylon in MA; triazine-resistant Amaranthus blitoides, C. arvensis, Euphorbia spp. and Polygonum arenastrum in IL. Among parasitic plants, Orobanche spp. is a problem in E, P, MA, I and IL while Cuscuta campestris in E and IL. Threshold density of S. nigrum in I and F is about 1 plant per linear meter in transplanted crops and close to zero in direct seeded crops. A S. nigrum management system should be based on: 1) chemical control in the previous crops where it is easier (i.e. sugar beet, carrot, celery, fennel, maize, soyabean, spinach, tobacco); 2) preferring transplanted than direct seeded tomatoes; 3) early soil preparation and chemical control of first emergence fluxes of Solanum before tomato planting; 4) row localisation of residual herbicides at planting (metribuzin, pendimethalin, napropamide, trifluralin, oxadiazon, oxyfluorfen, oxadiargyl…) integrated by inter-row hoeing and/or by split low-dose treatments with metribuzin+rimsulfuron against S. nigrum at very early growth stage (cotyledons-2 true leaves). Rimsulfuron is not yet authorised in F, HR, MA and PL. The number of authorised herbicides in MA and CH is quite low. Further and more detailed information can be found in the WG Newsletter (available on request) and in the WG web site (http:/www.unipg.it/~agronomy/ewrsveg/).