Chemical control of root rot complex and stem rot of greenhouse cucumber in straw-bale culture

Experiments were conducted in three different commercial greenhouses wherein cucumber (Cucumis sativus L.) cv. Kalunga F1 (Long English type) were grown in composted straw bales, heavily infested with Fusarium oxysporum Schlechtend.:Fr. f.sp. radicis-cucumerinum Vakalounakis (FORC), the causal agent of Fusarium root and stem rot of cucumber. FORC was isolated from roots and stem bases of symptomatic plants either in single infections or simultaneously with other root infecting pathogens, including species of Phytophthora and Pythium and Rhizoctonia solani Kühn AG-4. Verticillium dahliae Kleb. was obtained from individual cucumber plants showing wilt symptoms. Fungicide applications started at the beginning of fruiting time when the first symptomatic plants occurred and followed at 45-day intervals. Three fungicides, either alone or as tank-mixed combinations of 0.1% Topsin M 70WP (thiophanate-methyl 700 g kg−1) plus 0.15% Previcur 607SL (607 g L−1 propamocarb hydrochloride), or 0.1% Benomyl 50WP (benomyl 50 g kg−1) plus 0.15% Previcur 607SL, were applied to the crown and root area of cucumber plants through drip irrigation systems as drenches at a rate of 0.25 L/plant. Plant mortality was reduced by 11.1%–84.8% and 23.8%–77.7% when plants were drenched with Topsin M 70WP in combination with Previcur 607SL or Benomyl 50WP plus Previcur 607SL, respectively. In comparison, significantly lower levels of disease control were achieved when these fungicides were applied individually. Three fungicide applications during the crop season increased the inhibitory effect of the fungicide regime on the disease incidence compared to one or two treatment.

► Various pathogenic fungi are associated with root and stem rot of greenhouse cucumbers grown in straw-bale culture.
► Fusarium oxysporum f.sp. radicis-cucumerinum is most frequently isolated from symptomatic plants.
► Root drenches with broad-spectrum fungicide mixtures decreases plant mortality.
► Increasing the number of applications from one to three in one crop season gradually improves the disease control.