Effects of Planting Date on Development of Net Blotch Epidemics in Winter Barley in Pennsylvania

Delserone, L. M., and Cole, H., Jr. 1987. Effects of planting date on development of net blotch epidemics in winter barley in Pennsylvania. Plant Disease 71: 438-441. The influence of planting date on fall and spring net blotch epidemics (caused by Pyrenophora teres) was evaluated with the winter barley cultivar Pennrad. Experiments were conducted in Centre County, Pennsylvania, in 1982 and 1983 and in Lancaster County, Pennsylvania, in 1983. The three planting dates evaluated corresponded to the recommended date as well as dates I wk earlier and later than recommended for each specific location. Planting date had a significant influence on fall net blotch epidemics, with the greatest and least disease severities observed in the earliest and latest plantings, respectively. When spring environmental conditions were warm and humid, previous differences in disease severities attributable to date were eliminated. With less favorable spring weather, planting date had a significant influence on spring net blotch severities. Planting date also affected yield components, specifically the number of seeds per head and the thousand-kernel weight and the calculated yield. The greatest values for these factors generally were observed for the latest planting. Applications of fungicides during the spring epidemics generally resulted in a significant decrease in disease severity and an increase in one or more yield components. Planting in midto late September at either location resulted in the lowest net blotch severities and greatest yields. Net blotch of barley caused by Pyrenophora teres Drechs. (anamorph: Drechslera teres (Sacc.) Shoem., syn. Helminthosporium teres Sacc.) has increased in incidence and severity in the United States and Canada in recent years (10). This disease (among other factors) has caused barley production in Pennsylvania to decline from 60,750 ha in 1975 to 30,352 ha in 1982 (I). Yield loss attributed to net blotch is not documented. However, sprays of maneb applied at regular intervals from the three-leaf stage through flowering increased yields by 65% (9), and one spray of propiconazole applied at flag leaf emergence increased yields 17-23% (3). Planting date may affect the development of a net blotch epidemic. Some Portion of a thesis submitted by the first author to The Pennsylvania State University for the M.S. degree. Present address of first author: Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Pennsylvania growers plant barley before the recommended dates to ensure winter survival. Preliminary studies indicated greater disease levels in earlier plantings (J. A. Frank, unpublished). The objective of this study was to determine the effect of planting date on the development of fall and spring net blotch epidemics and on yield. These data then could be used for developing planting date recommendations to minimize the severity of net blotch in Pennsylvania. MATERIALS AND METHODS Treatments and design. Field experiments were conducted on The Pennsylvania State University Research Farms in Centre and Lancaster counties. Planting dates, tillage, and rotation conditions are listed in Table I. In the Centre County study of 1982-1983 (CC 1982/83), the earliest planting date was that recommended for barley planting in central Pennsylvania, and in 1983-1984 (CC 1983/84), the earliest planting date was I wk earlier than recommended (2). In southeastern Pennsylvania, winter weather is milder than in the central part of the state, so that the normal planting date is about 2 wk later than that for central Pennsylvania. In the Lancaster County 1983-1984 study (LC 1983/84), the first planting date was about I wk earlier than that recommended for the region. A planned third planting could not be made in the LC study because of unfavorable weather conditions. The winter barley (Hordeum vulgare L. emend. Bowden) cultivar Pennrad was planted in all experiments. Pennrad is resistant to the major foliar diseases of barley in Pennsylvania (leaf rust and powdery mildew) but is susceptible to net blotch (2). The cultivar also has good winterhardiness and is recommended for planting throughout Pennsylvania (2). A planting date test block consisted of two drill strips, each 2.1 m wide and 86 m long, with seven rows per strip. Each drill strip was divided into eight plots, providing 16 plots per planting date block, each 2.1 X 10.7 m. These plots served as replicates nested within the planting date block. In CC 1982/83, both drill strips were sown with untreated seed at the rate of 161.3 kg/ha. Because results from CC 1982/83 indicated that spring fungicide spray alone had no effect on spring epidemics, we used a fungicidal seed treatment in 1983/ 1984 to evaluate the effect of seed-transmitted P. teres on the development of fall epidemics. In CC 1983/84 and LC 1983/84, one drill strip per block was planted with untreated seed and the other with treated seed. The seed treatment consisted of a mixture of imazalil (5.8% a.i.) applied at the rate of I ml/ kg of seed and triadimenol (0.15 kg a.i./L) applied at the rate of 0.9 ml/kg of seed. The seeding rate in the 1983/ 1984 studies was reduced to 134.4 kg/ ha, because winter-kill was not extensive enough to warrant the seeding rate used in 1982/1983. In all studies, the drill Contribution 1536, Department of Plant Pathology, Pennsylvania State Agricultural Experiment Station. Authorized for publication as Journal Series Paper 7299. Table 1. Planting dates and cultural factors of the date-of-planting studies Accepted for publication 22 October 1986. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement"' in accordance with 18 U.S.C. § 1734 solely to indicate this fact. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. 438 Plant Disease/Vol. 71 No.5 Site" and year Planting dates Tillage CC 1982/83 14 Sept. Chisel-plow, disc