PRODUCTIVITY AND SEVERITY OF Cercospora longissima IN LETTUCE UNDER INCREASING DOSES OF ORGANIC COMPOST

Abstract

Lettuce (Lactuca sativa L.) is widely produced and consumed in Brazil. Its cultivation is carried out mainly by family farmers in both conventional and organic systems. However, the crop is affected by a range of foliar diseases, especially cercosporiosis, caused by the fungus Cercospora longissima, which results in necrotic leaf spots that compromise plant development and commercial quality. Thus, organic management combined with adequate nutrition is essential to reduce disease incidence, ensure consumer safety, and increase productivity. The present study aimed to evaluate the efficiency of increasing doses of organic compost on productivity and the control of cercosporiosis in lettuce under an organic production system. The experiment was conducted in Rio Branco, Acre, at Sítio Ecológico Seridó, in a protected environment. A randomized block design was used, with five treatments and four replications. Treatments consisted of organic compost doses of 0, 15, 30, 45, and 60 t ha⁻¹. The variables evaluated were total fresh mass (TFM), commercial fresh mass (CFM), commercial dry mass (CDM), total productivity (TPROD) and commercial productivity (CPROD), diseased leaves (%), and commercial loss (%). Data were subjected to ANOVA and regression analysis at a 5% probability level. The organic compost doses did not significantly influence the incidence of cercosporiosis or commercial biomass loss (p>0.05). However, a linear increase in TFM, CFM, CDM, TPROD, and CPROD was observed with increasing compost doses. Although the organic compost did not reduce disease incidence, the yield gains highlight its positive effect on lettuce cultivation. Nevertheless, its isolated use is not sufficient for phytosanitary control, making it necessary to adopt a more comprehensive and integrated management approach.