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  • Author or Editor: David N. Sasseville x
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Tomato plants were grown in a greenhouse in a sand:soil mixture with six pesticide treatments applied weekly at 1 mg a.i./kg soil mixture as a soil drench. Plants were grown for six weeks with nitrogen applied weekly at 80 mg per plant as calcium nitrate. Glyphosate (Roundup) was toxic to plants with reduced dry weight of all tissues, but greater nitrate concentration in the leaf and root tissues. Captan produced the greatest dry weight, with mot tissues dry weights significantly greater than the control treatment. Captan resulted in significantly higher nitrate content in the tissues, but there was no difference between captan and the control on total N content. Both nitrapyrin (N-Serve) and sethoxydim (Poast) had significantly less growth and total N content than the control, as well as higher nitrate content in the growing medium. It appears that these two chemicals may inhibit nitrate uptake or cause other phytotoxic effects The other chemicals metalaxyl (Subdue) and etridiazole (Terrazole) had intermediate responses. While they both had reduced growth and total N content, these were not significantly different from the control treatment. Etridiazole had reduced nitrate content, but metalaxyl nitrate content was significantly greater than the control and comparable to captan, primarily because of high nitrate content in the leaves.

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Tomato cv. 'Show Me' were grown in the greenhouse for six weeks in a 50%;50% (v:v) soil:sand mixture and provided weekly with a quarter-strength Hoagland solution with nitrogen provided as 100%:0% 50%;50% 0%:100% nitrate:ammonium ratios at rates of 0, 10, 20, 40, 80 mg N/kg medium with and without 5 mg/kg nitrapyrin. Nitrapyrin induced plant phytotoxic symptoms of stunted growth, curled leaves and deformed terminal buds. These effects were reduced with increasing amount of applied nitrogen and greater percent of nitrate. A second similar experiment using 0, 80, 160, 240, 320 mg N/kg medium and 1 mg/kg nitrapyrin showed no phytotoxic effects and also induced no significant changes in dry weight, tissue nitrogen content or residual medium nitrogen content regardless of nitrogen treatment. N concentration and N form effects were similar to previously reported research with an accumulation of nitrates in tissues with higher nitrate nutrition.

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According to the Missouri Mastery Achievement Tests, elementary students in Missouri have a need for strengthening basic sciences and mathematics in their curriculum. Areas in the plant sciences such as seed germination and plant growth are among subjects needing particular emphasis. A pilot enrichment program was developed to address this need. Lesson plans were developed which paralleled topics in the Core Competencies and Key Skills for Missouri Schools and targeted for third grade students. The lesson plans were field tested in public and private schools for three years to evaluate lesson plans, equipment, handouts, and other instructional materials. The materials currently include three units: soil, water and plants. The materials are adaptable to all types of organized youth activities and are the primary materials used in Missouri for 4-H plant and soil science programs. Instructional materials have also been developed on how to implement the use of these tools by youth leaders and Extension personnel.

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Nitrate and NH 4 + absorption by southernpeas (Vigna unguiculata (L.) Walp.) during the growth cycle was determined in solution culture at 7-day intervals. Dry weight and total mg of N for each plant part were determined at bloom initiation, pod initiation, and seed maturity. When the N concentration was deficient virtually all of the N 3 was absorbed by southernpea plants from the 3rd week until harvest. At sufficient N concentrations a single peak N 3 uptake period occurred in the growth cycle prior to bloom initiation. Nitrate absorption predominated when NH 4 + constituted 50% or more of the N form at both N concentrations. Ammonium had either 1, 2 or 3 absorption peaks depending upon its relative concentration with NO 3 . The first NH 4 + absorption peak was the largest and coincided with the growth cycle just prior to bloom initiation. Dry weight and N accumulation were greatest prior to bloom initiation. Subsequent accumulation occurred primarily in the seed. A reduction in N content and dry weight in the vegetative portions, particularly the leaves, coincided with the accumulation of N and dry weight in the seeds. Use of total mg of N in the vegetative tissue as a means of indicating the N status of the plant and subsequent yield was not accurate.

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Benlate 50 DF has been implicated in causing long term damage to leatherleaf ferns. Damage to leatherleaf fern including frond distortion, discoloration and growth suppression continues to occur even after two or more years following last Benlate application. Electron micrographs of affected plants roots indicate a loss of root hairs and a proliferation of associated soil bacteria on the root surface compared to healthy plants. Plants with history of continued Benlate application have extensive bacterial colonies embedded on the root surface, but these colonies were not parasitic. Lcatherleaf fern plants which only had their rhizomes dipped in Benlate at planting lacked the embedded colonies, but were extensively covered with bacteria. Bioassays of bacteria taken from the rhizoplane and rhizosphere of the these leatherleaf ferns showed that these bacteria have the ability to produce growth regulators and/or toxins which may be detrimental to plant growth when absorbed through the root. Consequently, Benlate may be influencing fern growth indirectly by modifying bacteria composition of the growing media to favor proliferation of deleterious, non-parasitic bacteria.

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