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Marshall K. Elson, Ronald D. Morse, Dale D. Wolf, and David H. Vaughan

High summer temperatures may reduce plant stands of direct-seeded fall broccoli (Brassica oleracea var. italica Plenck). The influence of constant and diurnally alternating temperatures in the range of 5 to 42C on germination and emergence of `Packman' broccoli was evaluated. Germination was defined as protrusion of the radicle from the seedcoat, and emergence as 10 mm elongation of the radicle. The range of constant temperatures from 10 to 30C for 14 days was satisfactory for 90% germination and 75% emergence. However, alternating temperatures extended the acceptable emergence range to 5/17 through 20/32C. Since soil temperatures in warm climates often exceed 20/32C during the summer, high-temperature inhibition of seed germination and seedling emergence is a potentially important factor limiting direct-seeded broccoli stands.

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Robert F. Polomski, John A. Barden, Ross E. Byers, and Dale D. Wolf

Abstract

Terbacil, a photosynthetic inhibitor, and shade applied to apple (Malus domestica Borkh) limbs and whole trees altered the contents of fruit nonstructural carbohydrates and induced fruit abscission. Shade (92%) from 5 to 15, 10 to 20, 15 to 25, 20 to 30, and 25 to 35 days after full bloom (DAFB) induced fruit abscission. At 15 and 20 DAFB, fruit from limbs shaded for 10 days contained less total nonstructural carbohydrates (TNC) than fruit from limbs shaded for 0 or 5 days. Terbacil at 50 and 100 ppm applied to whole ‘Redchief Delicious’ trees at 15 DAFB markedly inhibited net photosynthesis. Fruit dry weight, TNC, total sugars, and reducing sugars declined with increasing rates of terbacil and 100 ppm resulted in abscission of all fruit. Trees treated with 0 and 50 ppm retained 4.6 and 1.4 fruit per cm2 of limb cross sectional area (LCSA), respectively. Terbacil at 75 ppm and 92% shade were applied to whole ‘Redchief Delicious’ trees at 18, 23, and 28 DAFB. Fruit dry weight and contents of total sugars and reducing sugars were lowered by shading and terbacil. Shade for 5 or 10 days induced total fruit drop. Terbacil at 75 ppm resulted in 0.8 vs. 2.9 fruit per cm2 of LCSA on the controls. Chemical name used: 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedion (terbacil).