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Copper (electrolytically generated or from cupric sulfate) is increasingly used to control diseases and algae in the greenhouse industry. However, there is a shortage of information regarding appropriate management strategies for Cu²⁺ (Cu) in greenhouse hydroponic production. Three greenhouse studies were conducted to examine the growth and yield responses of sweet pepper (Capsicum annuum L., Triple 4, red) to the application of Cu in hydroponic production systems. In the first two experiments, plants were grown on rockwool and irrigated with nutrient solutions containing Cu at concentrations of 0.05, 0.55, 1.05, 1.55, and 2.05 mg·L^–1. Copper treatments were started either when plants were 32 days old and continued for 4 weeks, or when plants were 11 weeks old and continued for 18 weeks, respectively. In the third experiment, roots of solution cultured pepper seedlings were exposed to Cu (1.0, 1.5, and 2.0 mg·L^–1) containing nutrient solutions for 2 hours per day for 3 weeks. Higher Cu treatment initialized when plants were 32 days old significantly reduced plant leaf number, leaf area, leaf biomass, specific leaf area, stem length and shoot biomass. The calculated Cu toxicity threshold was 0.19 mg·L^–1. However, when treatment initialized at plants were 11 weeks old, Cu did not have significant effects on leaf chlorophyll content, leaf area or specific leaf area. Copper started to show significant negative effects on leaf biomass and shoot biomass at 1.05 mg·L^–1 or higher levels. Copper treatments did not have any significant effect on fruit number, fresh weight or dry weight. Under all the Cu levels, fresh fruit copper contents were lower than 0.95 mg·kg^–1 which is below the drinking water standard of 1.3 mg·kg^–1. Seedling growth was significantly reduced by exposing roots to Cu (≥1.0 mg·L^–1) containing solutions even for only 2 h·d^–1.

Electrolytically generated copper is increasingly used to control diseases and algae in the greenhouse industry. However, there is a shortage of information regarding appropriate management strategies for copper in ornamental crop production. The objectives of this study were to characterize the response of three ornamental crops (Dendranthema ×grandiflorum L. `Fina', Rosa ×hybrida L. `Lavlinger', Pelargonium ×hortorum L. `Evening Glow') to different solution levels of Cu²⁺ (ranging from 0.4 to 40 μm) and to determine the critical levels above which toxic responses became apparent. The following measurements were used to assess the treatments: leaf chlorophyll fluorescence (F_v/F_m), leaf chlorophyll content, and visible injury of leaf and root. Excessive copper reduced plant root length, root dry weight, total dry weight, root to shoot ratio, leaf area, and specific leaf area in all three species. The critical solution level of Cu²⁺ that resulted in significantly reduced plant dry weight for chrysanthemum was 5 μm; for miniature rose, 2.4; and for geranium, 8 μm. Plant visible root injury was a more sensitive and reliable copper toxicity indicator than visible leaf injury, leaf chlorophyll content, F_v/F_m, or leaf and stem copper content. Generally, all the species exhibited some sensitivity to Cu²⁺ in solution culture, with chrysanthemum and miniature rose being most sensitive and geranium being least sensitive. Caution should be taken when applying copper in solution culture production systems.

To determine the nutrient solution copper (Cu²⁺) level above which Cucumis sativus L. (cucumber, cv. LOGICA F1) plant growth and fruit yield will be negatively affected, plants were grown on rockwool and irrigated with nutrient solutions containing Cu²⁺ at 0.05, 0.55, 1.05, 1.55, and 2.05 mg·L⁻¹. Copper treatment began when plants were 4 weeks old and lasted for 10 weeks. During this 10-week period, plants were harvested at 3 weeks (short-term) and 10 weeks (long-term) after the start of Cu²⁺ treatment. Neither visible leaf injury nor negative Cu²⁺ effect was observed on plant growth (leaf number, leaf area, leaf dry weight, and stem dry weight) after 3 weeks of continuous Cu²⁺ treatment. However, after 10 weeks of continuous Cu²⁺ application, cucumber leaf dry weight was significantly reduced by Cu²⁺ levels 1.05 mg·L⁻¹ or greater; leaf number, leaf area, and stem dry weight were significantly reduced by Cu²⁺ levels 1.55 mg·L⁻¹ or greater. Copper (Cu²⁺ levels 1.05 mg·L⁻¹ or greater) also caused root browning. Some plants under the 2.05 mg·L⁻¹ Cu²⁺ treatment started to wilt after 6 weeks of continuous Cu²⁺ treatment. Copper treatment did not result in any change in leaf greenness until after Week 9 from the start of the treatments. There was no sign of a negative Cu²⁺ effect on cucumber fruit numbers after the first 2 weeks of production, but plants under the highest Cu²⁺ concentration treatment (2.05 mg·L⁻¹) gradually produced fewer cucumber fruit than the control (0.05 mg·L⁻¹) and eventually resulted in lower cucumber yield. Nutrient solution can be treated with 1.05 mg·L⁻¹ of Cu²⁺ in cucumber production greenhouses; however, it is not recommended to use Cu²⁺ concentrations 1.05 mg·L⁻¹ or greater continuously long-term (more than 3 weeks). When applying Cu²⁺, it is suggested that cucumber roots be examined regularly because roots are a better indicator for Cu²⁺ toxicity than leaf injury.

Copper is one of the essential micro-nutrient elements for plants, but when in excess, is toxic to plants and other living organisms. Electrolytically generated copper and cupric sulphate are increasingly used by the greenhouse industry to control diseases and algae in hydroponic systems. However, there is little information regarding appropriate strategies for employing copper in greenhouse crop production. We investigated the physiological responses, growth and production of several ornamental crops (miniature rose, chrysanthemum and geranium) and greenhouse vegetable crops (pepper, cucumber, and tomato) with respect to Cu₂₊ concentration in the root zone. Tests were conducted using plants grown in nutrient solution, Promix and rockwool. Results showed that phytotoxic levels of Cu₂₊ were dependent on the crop species and growing substrate. Plants grown in nutrient solution exhibited symptoms of phytotoxicity at lower Cu₂₊ concentrations than those on the solid substrates. The ability of copper to control Pythium aphanidermatum and green algae was evaluated under both laboratory and greenhouse conditions. Copper was effective in suppressing green algae in nutrient solution, but did not control Pythium effectively. This presentation is a comprehensive summary of the research conducted over the last three years by our group on copper application in greenhouse systems.