Judul: First Report on powdery mildew on chili (Capsicum annuum L.) in Tegal Regency
Abstrak: Tanaman cabai merah di Kabupaten Tegal terjangkit penyakit langka dengan tingkat keparahan yang cukup tinggi. Akhir-akhir ini, sering dilaporkan adanya penyakit embun tepung di Kabupaten Tegal, Provinsi Jawa Tengah. Tujuan penelitian adalah untuk mendeskripsikan dan menganalisis keberadaan, gejala, dan keparahan penyakit embun tepung pada tanaman cabai di Kabupaten Tegal. Metode penelitian yang digunakan pada penelitian ini adalah pengamatan langsung di lahan, wawancara dengan petani terkait budidaya tanaman cabai, dan pengamatan laboratorium. Tanaman cabai merah dengan gejala klorotik pada permukaan daun bagian atas berwarna coklat kekuningan yang ditandai dengan adanya serbuk putih pada bagian bawah daun ditemukan di Kecamatan Bumijawa dan Kecamatan Margasari, Kabupaten Tegal pada bulan November 2020. Berdasarkan hasil pengamatan secara mikroskopis penyakit pada tanaman cabai merah dengan gejala tersebut berasosiasi dengan cendawan genus Leveillula taurica yang umum diketahui sebagai penyebab penyakit embun tepung.. Keparahan embun tepung pada cabai di Kecamatan Bumijawa lebih tinggi dibandingkan dengan Kecamatan Margasari., Red chili plants in Tegal Regency are infected with a rare disease with a fairly high severity. Recently, powdery mildew has been reported in Tegal Regency, Central Java Province. The purpose of this study was to describe and analyze the presence, symptoms, and severity of powdery mildew on chili peppers in Tegal Regency. The research method used in this study was direct observation in the field, interviews with farmers related to chili cultivation, and laboratory observations. Red chili plants with chlorotic symptoms on the upper leaf surface are yellowish brown which is characterized by the presence of white powder on the underside of the leaves found in Bumijawa Districts and Margasari Districts, Tegal Regency in November 2020. Based on microscopic observations of diseases in red chili plants with these symptoms associated with a fungus of the genus Leveillula taurica which is commonly known as the cause of powdery mildew. The severity of powdery mildew on chili peppers in Bumijawa District is higher than that of Margasari District.
Keyword: defoliasi, embun tepung, Leveillula taurica, defoliation, powdery mildew, Leveillula taurica

Judul: Disease Intensity and Their Control Efforts of Bacterial Wilt and Anthracnose of Chili in Tanah Datar Regency, West Sumatra
Abstrak: Cabai merah (Capsicum annuum L.) merupakan salah satu komoditas hortikultura penting di Indonesia. Permintaan cabai yang tinggi sepanjang tahun baik dari masyarakat maupun industri pangan menuntut produksi dan produktivitas cabai yang stabil. Penanaman cabai masih menghadapi berbagai kendala yang dapat menyebabkan kehilangan hasil, antara lain masalah penyakit layu bakteri oleh Ralstonia solanacearum dan antraknosa Colletotrichum acutatum. Tanah Datar merupakan salah satu daerah yang potensial sebagai penghasil cabai di Sumatera Barat. Penelitian ini bertujuan untuk mengukur intensitas penyakit layu bakteri dan antraknosa pada pertanaman cabai merah (C. annuum L.) di Kabupaten Tanah Datar, Sumatera Barat dan menganalisis pengendalian secara kimiawi yang dilakukan petani setempat. Metode penelitian meliputi pengamatan intensitas penyakit di lapangan dan wawancara dengan 40 responden petani menggunakan kuesioner terstruktur. Hasil penelitian menunjukkan bahwa insidensi penyakit antraknosa mencapai 100% dan layu bakteri mencapai 60%. Severitas penyakit antraknosa mencapai 86,40%. Intensitas penyakit tersebut dapat menyebabkan kehilangan hasil yang tinggi. Upaya pengendalian penyakit yang dilakukan petani masih mengandalkan metode kimiawi. Sebagian besar 75% petani menggunakan pestisida sintetik secara intensif dan aplikasinya secara terjadwal. Bahan aktif yang paling banyak digunakan petani berturut-turut adalah: propineb 70%, mancozeb 82%, klorotalonil 77%, fluopikolid 62,5 g/l + promakokarb hidroklorida, dan azoksistrobin 200 g/l + difenokonazol 125 g/l., Red chili pepper (Capsicum annuumL.) is one of the important horticultural commodities in Indonesia. The high demand for chili throughout the year from both the public and the food industry demands stable chili production and productivity. Chili cultivation still faces various obstacles that can cause yield loss, including the problem of bacterial wilt disease by Ralstonia solanacearum and fungal anthracnose by Colletotrichum acutatum. Tanah Datar is one of the potential areas as a chili producer in West Sumatra. This study aims to measure the intensity of bacterial wilt and anthracnose on red chili (C. annualL.) in Tanah Datar District, West Sumatra and analysis of the chemical control carried out by local farmers. The research method included observing disease intensity in the field and interviewing 40 farmer respondents using a structured questionnaire. The results showed that the incidence of anthracnose disease reached 100% and bacterial wilt reached 60%. The severity of anthracnose disease reached 86.40%. The intensity of those diseases can cause high yield losses. Disease control efforts by farmers still rely on chemical methods. Most 75% farmers were using synthetic pesticides intensively and the scheduled application. The active ingredients mostly used by farmers were: propineb 70%, mancozeb 82%, chlorothalonil 77%, fluopicollid 62.5 g/l + promacokacarb hydrochloride, and azoxystrobin 200 g/l + diphenoconazole 125 g/l.
Keyword: Colletotrichum acutatum, fungisida sintetik, insidensi penyakit, Ralstonia solanacearum, severitas penyakit, disease incidence, disease severity, synthetic fungicides

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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