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Evaluation of Topaz (propiconazole) for transplant size control and earlier maturity of processing tomato

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Title: Evaluation of Topaz (propiconazole) for transplant size control and earlier maturity of processing tomato
Author: Zandstra, J.W.; Dick, J.; Lang, J.
Abstract: Results and discussion: While propiconazole treated transplants demonstrated a growth response similar to paclobutrazol, the effect was not as great. By the end of the 42 day greenhouse production period, propiconazole treated transplants had greater top fresh weights, root fresh weights, and stem diameters than untreated, but generally not as great as paclobutrazol treated transplants (Table 1). Fertilizer levels in the greenhouse required to produce a paclobutrazol treated transplants were approximately 2.5x the amount required by untreated transplants, while propiconazole treated transplants required about 30% more fertilizer (data not shown). No difference in plant fresh weight or number of flowers per plant were found between untreated transplants, while propiconazole treated transplants when evaluated up to 37 and 42 days after transplanting respectively (Table 2, 3) while paclobutrazol treated transplants demonstrated increased plant weights and flower numbers. Total yields did not differ statistically among treatments, but tended to be greater when transplants were treated with paclobutrazol Table 4). However, all treatments (propiconazole and paclobutrazol) increased the percent red fruit and decreased the precent green fruit when compared to untreated, with paclobutrazol generally giving a greater effect (Table 5). The apparent advanced maturity of propiconazole treated tomato transplants was not expected due to a lack of early flowering and early plant growth.
Description: Given the limited growing season in southwestern Ontario, processing tomato transplants which establish and begin to grow quickly soon after transplanting are desired. Ideal transplants are typically 5-6" in height, and have a thick stem and a vigorous root system. Managing transplant height can at times be challenging, and techniques to help manage plant height would be useful. Triazoles are a group of agricultural chemicals which were initially developed as fungicides but were also found to retard plant growth. The most typical plant growth responses to triazoles is a reduction in stem length, but they also have been found to increase leaf thickness, thicken stems, and increase root development. Triazoles have also been reported to protect plants from environmental stresses, including drought and temperature extremes. Previous work using the triazole paclobutrazol (Bonzi) on processing tomato transplants involved treating the plants with a 5 ppm soil drench at the 2 leaf stage, and subsequently fertilizing heavily (up to 5 times the normal rate) to achieve the desired plant height. This treatment resulted in increased vigor in the field (measures as plant dry and fresh weight), advanced plant development (earlier bloom), advanced fruit maturity and increased yields. However, it is not presently registered on any food crops in North America, so a registration for use on tomato transplants is unlikely. Initial greenhouse screening using another triazole compound, propiconazole (Tilt, Topaz) suggest that this product produces the same growth regulatory effects as paclobutrazol (height control, thicker stems, increase plant weight, increased root development). Propiconazole is of particular interest because it is less active than paclobutrazol and needs to be used at higher rates, which provides a greater margin of safety. It is also presently registered on a number of food crops (Tilt - sweet corn; Topaz - rutabaga, asparagus, apricot, cherry, peach, nectarine).
Date: 2004
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