Chemical weed control in processing spinach

Processing spinach shows a good competitive ability and as a consequence yield losses due to weed competition are commonly low. Physical weed control gives reliable results (Tei et al., 2002) but weed management is still mainly chemical because: 1) the mechanical harvest needs a crop with an erect leaf posture favoured by a narrow row width (0.10 – 0.15 m) and that prevents the use of most post-emergence physical weed control methods; 2) processing industries demand harvested product without weeds, considered as “pollutant bodies” in industrial process. However, there are few herbicides registered for this crop. For the above mentioned reasons, chemical weed control field experiments on processing spinach were carried out in southern (Foggia, silty-clay soil, mid-October 2001 sowing) and central Italy (Latina, silty-sandy soil, mid-March 2002 sowing) to verify the efficacy and selectivity of authorised herbicides (i.e. lenacil, cycloate) and to evaluate the performance of potential “new” active ingredients (phenmedipham, metamitron, desmedipham) already used in sugar beets. Several different combinations of active ingredients and application timing were evaluated: pre-emergence treatments with lenacil or metolachlor; post-emergence treatments (at 2-4 crop leaf stage) with phenmedipham + lenacil, phenmedipham + desmedipham, phenmedipham + cycloate or phenmedipham + metamitron; pre-emergence application of lenacil or metolachlor followed by post-emergence application of phenmedipham + metamitron, phenmedipham + cycloate, phenmedipham + desmedipham or phenmedipham + quizalofop-ethyl. The most important weeds were Lolium multiflorum, Fumaria officinalis, Sinapis arvensis, Matricaria chamomilla, Veronica hederifolia in the southern Italy experiment and Chenopodium album, Stellaria media, Capsella bursa-pastoris, Amaranthus retroflexus and V. hederifolia in the central Italy experiment. Among pre-emergence treatments, metolachlor did not significantly affect the crop while lenacil caused a temporary leaf discoloration. Metamitron and the combination phenmedipham + metamitron applied post-emergence caused a reduction in growth, leaf bleaching and necroses. The other post-emergence treatments showed slight symptoms of phytotoxicity just after the application that disappeared one week later. Pre-emergence metolachlor controlled L. multiflorum, F. officinalis and V. hederifolia, but showed a low control of S. arvensis; lenacil sufficiently controlled only F. officinalis. Considering the efficacy of post-emergence applications, phenmedipham + lenacil and phenmedipham + metamitron exhibited good control of F. officinalis, but they were only partially effective toward L. multiflorum, S. arvensis, and C. album, and completely ineffective against V. hederifolia. Phenmedipham + desmedipham partially controlled all the weeds, while phenmedipham + cycloate showed a general good efficacy except on L. multiflorum. The results indicated that a pre-emergence herbicide application with metolachlor followed by a post-emergence treatment with phenmedipham + cycloate or phenmedipham + lenacil was the most suitable chemical weed management. However, spinach yield was not significantly affected by weed competition and herbicide efficacy but only by phytotoxicity due to post-emergence phemnmedipham + metamitron. Moreover, the presence of weeds, as “pollutant bodies” in harvested product, was always at very low level due to the possibility to regulate the harvest height in relation to crop and weed growth. Reference Tei F., Stagnari F. & Granier A. (2002) Preliminary results on physical weed control in processing spinach. 5th EWRS Workshop on Physical Weed Control. Pisa, Italy, 11-13 March 2002, 164-171 (http://www. EWRS-et.org/pwc/pdf/Pisa.pdf).