Judul: Production and Problems. Plant Diseases of  Siam / Keprok Citrus in Pemalang Regency, Central Java
Abstrak: Jeruk khususnya jeruk keprok dan Siam merupakan buah yang sangat populer dikonsumsi di Indonesia. Produksi jeruk nasional diharapkan dapat ditingkatkan untuk memenuhi permintaan domestik atau bahkan ekspor komoditas ini. Produksi jeruk di Indonesia selama dekade 2010-2019 mengalami peningkatan yang didukung oleh kontribusi produksi jeruk di Jawa dan Bali khususnya Provinsi Jawa Timur dan Bali. Provinsi Jawa Tengah bukanlah penghasil utama jeruk, namun beberapa kabupaten di wilayah ini memiliki potensi untuk dikembangkan. Kabupaten Pemalang memiliki beberapa wilayah kecamatan yang cocok untuk ditanami jeruk. Produksi jeruk keprok/siam di wilayah penanaman kabupaten ini tergolong masih relatif rendah yaitu berturut- turut 86.7 dan 88.9 ton pada tahun 2018 dan 2019. Di samping itu, kapbupaten ini juga menghasilkan jeruk besar dengan produksi yang lebih rendah lagi. Penyakit Kanker dapat menjadi faktor pembatas produksi jeruk. Penyebab Penyakit ini yang sampelnya diperoleh dari tanaman jeruk di Bogor-Jawa Barat diidentifikasi sebagai Xanthomonas citri subsp. citri berdasarkan ciri morfologi koloni dan sifat fisiologi biokimia isolat biakan murni. Pengamatan lapangan pada tanaman jeruk di Kabupaten Pemalang menunjukkan bahwa penyakit ini dominan ditemukan, baik pada tanaman fase bibit/vegetatif maupun fase reproduktif dengan insidensi dan keparahan yang tinggi. Penyakit penting lainnya yang ditemukan adalah huanglongbing (Candidatus Liberibacter asiaticus), kudis (Elsinoe fawcettii) dan cendawan jelaga (Capnodium sp.) dengan intensitas yang lebih rendah. Hama jeruk yang ditemukan baik di fase vegetatif maupun fase generatif adalah kutu putih, pengorok daun dan wereng pucuk, sedangkan kutu kebul hanya di fase vegetatif., Oranges, especially keprok and siam tangerines, are very popular fruits consumed in Indonesia. National citrus production is expected to be increased to meet domestic demand or even export of this commodity. Citrus production in Indonesia during the 2010-2019 decade has increased, which is supported by the contribution of citrus production in Java and Bali, especially the provinces of East Java and Bali. Central Java province is not a major producer of citrus, but several districts in this region have the potential to be developed. Pemalang Regency has several sub-districts that are suitable for planting oranges. The production of tangerines/siamese in the planting area of this district is still relatively low, namely 86.7 and 88.9 tons in 2018 and 2019. In addition, this regency also produces pomello with even lower production. Citrus canker disease can be a limiting factor for its production. The cause of this disease whose samples were obtained from citrus plants in Bogor-West Java was identified as Xanthomonas citri subsp. citri based on colony morphology and biochemical and physiology characteristics of pure culture isolates. Field observations on citrus plants in Pemalang Regency showed that this disease was dominantly found, both in the seedling/vegetative phase and reproductive phase with high incidence and severity. Other important diseases found were huanglongbing (Candidatus Liberibacter asiaticus), scab (Elsinoe fawcettii) and sooty mold (Capnodium sp.) with lower intensity. Citrus pests found in both the vegetative and generative phases were mealybugs, leafminers and leafhoppers, while whitefly were only in the vegetative phase.
Keyword: Canker, disease intensity, huanglongbing, insect pest, scab, sooty  mold

Judul: Application of Pesticides in Pest and Disease Control and Harvest Product Management of Keprok Orange (Citrus reticulata L.) in Dau District, Malang Regency
Abstrak: Jeruk merupakan komoditas yang banyak digemari dan dikonsumsi oleh masyarakat di Indonesia. Jeruk keprok merupakan salah satu kultivar jeruk yang mudah dalam penanamannya, dapat tumbuh pada berbagai kondisi iklim dan dapat ditanam dimana saja, baik di dataran rendah maupun tinggi. Permasalahan yang sering dijumpai dalam setiap pertanaman yaitu adanya serangan hama dan penyakit. Penerapan sistem pengendalian OPT yang belum optimum menyebabkan penggunaan pestisida seringkali tidak tepat sasaran dan melebihi dosis anjuran sehingga berpengaruh pada keamanan konsumen buah jeruk. Penelitian ini bertujuan mengetahui pengetahuan, sikap, dan tindakan petani jeruk keprok dalam penggunaan pestisida, mengetahui hama dan penyakit utama, dan mengetahui tindakan yang dilakukan terhadap produk hasil panen. Penelitian dilakukan di Kecamatan Dau, Kabupaten Malang dengan metode survei langsung menggunakan kuisioner terstruktur. Responden ditentukan dengan menggunakan perpaduan metode purposive sampling dan snowball sampling. Sebanyak 50 petani responden (100%) menyatakan menggunakan pestisida sintetik untuk pertanaman jeruknya. Hama utama pada pertanaman jeruk keprok adalah lalat buah (Bactrocera spp.) (100%), kutu-kutuan (T. citricida, T. aurantii, A. gossypii) (92%), dan penyakit utama yaitu busuk pangkal batang yang disebabkan oleh P. nicotianae (86%). Pengetahuan, sikap, dan tindakan petani dalam penggunaan pestisida dipengaruhi oleh pengalaman bertani yang turun-temurun dan tingkat pendidikan. Jenis pestisida yang digunakan meliputi insektisida sistemik dan kontak, serta fungisida yang bersifat protektif. Organofosfat dan karbamat merupakan golongan pestisida yang paling banyak digunakan. Mayoritas responden (100%) langsung menjual hasil panennya yang menyebabkan kemungkinan adanya residu pada buah jeruk., Citrus is a perennial fruit plant that is consumed by many people of Indonesia. Keprok orange is one of the citrus cultivars that is easy to be cultivated, well grow in various climatic conditions and altitudes, either in the lowlands or in the highlands. Pests and diseases often cause the decrease of keprok orange quantitatively as well as qualitatively. The improper and exceed use of pesticides lead to negative effect citrus fruit consumers. This study aimed to determine the knowledge, attitudes, and practices in the application of pesticides, to determine the main pests and main diseases, and to determine the practice that taken on harvested products. The research was conducted in Dau District, Malang Regency through direct survey methods using structured questionnaires. Sampling of respondents used a combination of purposive sampling and snowball sampling methods. Based on the results of interviews, 50 respondent farmers (100%) used synthetic pesticides for their citrus plantations. The main pests of keprok orange plantations were fruit flies (Bactrocera spp.) (100%), aphids (Toxoptera citricida, T. aurantii, Aphis gossypii) (92%), and the main disease was stem rot caused by Phyrophthora nicotianae (86%). Farmer’s knowledge, attitudes, and practices in the use of pesticides are influenced by their experience and education level. The types of pesticides used include systemic and contact insecticides and protective fungicides. Organophosphates and carbamates are the most widely used pesticides. The majority of respondents (100%) directly sell their harvested products which led to the possibility of residue on citrus fruits.
Keyword: Keprok orange, Residues, Survey, Synthetic pesticide

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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