Efficacy of application of foliar fungicides for control of Cercospora leaf spot in sugar beet, 2008.

摘要

Sugar beet cv. 5534N was PAT-treated and planted at the Michigan State University Bean and Beet Farm, Saginaw, MI on 21 Apr. Seed was planted at 1 in. depth into four-row by 50-ft plots (ca. 4.375 in. between plants to give a target population of 275plants/100ft. row) with 30 in. between rows replicated four times in a randomized complete block design. Fertilizer was drilled into plots immediately before planting, formulated according to results of soil tests (125 lb 46-0-0/A). No additional nitrogen was applied to the growing crop. Cercospora beticola infected leaves collected the previous season were used on 16 Jun to inoculate plots. Fungicides were applied a) on the day of inoculation (16 Jun) and 1, 2, and 3 days after inoculation (DAI), Proline 480SC 5 fl oz + Induce 480XL 0.125 % v/v only or b) on a twenty-one-day interval (three applications), starting after the 55 Beetcast disease severity values were recorded in the area (Ontario Weather Network, Ridgetown, ON, Canada), starting on 16 Jul. Although four treatments were scheduled, disease pressure was low throughout the year and only three applications were made. Fungicides were applied with a hand-held R&D spray boom delivering 25 gal/A (80 p.s.i.) and using three XR11003VS nozzles perrow. Weeds were controlled by cultivation and with a mixture of Pyramin DF at 5 lb/A plus Nortron at 4 pt/A applied at planting. Insects were controlled as necessary. Foliar leaf spot severity (%) was measured on 27 Aug and 17 Sep using a 1 – 10 scale 1= 1 - 5, 0.1%; 2 = 6 -12, 0.35%; 3 = 13 - 25, 0.75%; 4 = 26 - 50, 1.5%; 5 = 51 - 75, 2.5%; spots/leaf or severity; respectively; 6 = 3% (proven economic damage); 7 = 6%; 8 = 12%; 9 = 25%; and 10 > 50% severity. Beet roots were machine-harvested on 3 Octand individual treatments were weighed. Sugar content was measured at the Michigan Sugar Company analytical service laboratory. Meteorological variables were measured with a Campbell weather station located at the farm, latitude 43.3787 and longitude -84.1128 deg. Maximum, minimum and average daily air temperature (oF) from planting on 21 Apr were 80.8, 20.1 and 53.5 (Apr), 83.9, 27.3 and 53.6 (May), 92.5, 45.0 and 67.8 and 1-d with maximum temperature >90oF (Jun), 91.4, 43.3 and 70.3 and 1-d with maximum temperature >90oF (Jul), 90.3, 42.7 and 67.6 and 1-d with maximum temperature >90oF (Aug) and 89.5, 33.3 and 60.4 (to 3 Oct). Maximum, minimum and average daily soil temperatures (oF) over the same period were 60.9, 42.8 and 52.3 (Apr), 66.0, 47.3 and 52.6 (May), 76.2, 56.9 and 67.1 (Jun), 81.2, 60.8 and 71.5 (Jul), 80.0, 61.7 and 70.8 (Aug) and 77.1, 50.1 and 63.7 (to 3 Oct). Maximum, minimum and average daily relative humidity (%) over the same period was 96.1, 10.9 and 55.8 (Apr), 96.6, 10.5 and61.4 (May), 96.1, 20.7 and 67.0 (Jun), 95.8, 27.1 and 67.1 (Jul), 96.0, 26.0 and 67.6 (Aug) and 96.0, 27.2 and 71.6 (Sep to 3 Oct). Maximum, minimum and average daily soil moisture (% of field capacity at 4” depth) was 83.8, 78.7 and 81.9 (Apr); 83.9, 61.0 and 80.2 (May); 93.2, 61.5 and 70.6 (Jun); 100.2, 73.4 and 80.5 (Jul), 99.9, 81.1 and 83.0 (Aug) and 103.5, 78.7 and 82.9 (Sep to 3 Oct). Precipitation was 0.10-in. (Apr), 1.13-in. (May), 3.88-in. (Jun), 3.94-in. (Jul), 2.1-in. (Aug) and 5.74-in. (Sep to 3 Oct). There were 175 Beetcast DSV values accumulated in the Saginaw area from 1 Apr to 23 Sep.