Judul: Hama dan penyakit tanaman buah naga (Hylocereus sp.) serta budidayanya di Yogyakarta
Abstrak: Dragon fruit (Hylocereus sp.) has been introduced to Indonesia recently and became a commercial crop cultivated in this country. The plant, which belongs to family of Cactaceae (cactus), is native to Mexico, Central, and South America. There are no many reports about significant losses due to pests and diseases of the plant in Indonesia, or even in other countries. However, it is potential that pests and diseases can become problem in the future as the plant become widely grown in Indonesia. The objective of this research is to gather information about pest and disease occurrences found in dragon fruit and its cultivation in Yogyakarta. The research methods including interview with farmers, observation, and sampling of the pests and diseases at six dragon fruit orchards, field, and laboratory identification of the causal agents, and data processing. The pests found in dragon fruit were mealy bugs (Hemiptera:Pseudococcidae) species Pseudococcus jackbeardsleyi, Ferrisia virgata, and Planococcus sp.; aphids (Hemiptera:Aphididae) species Aphis gossypii., Branchycaudus helichrysi, and Toxoptera odinae; ants (Hymenoptera:Formicidae) species Oecophylla sp., Camponotus sp., Euprenolepis sp., and Polycharis sp.; grasshoppers (Orthoptera:Acrididae) species Valanga sp., Oxya sp., and Atractomorpha sp.; mite (Acarina:Tetranycidae); snail (Acathina fulica); and birds. Chickens are not considered as a pest, however, they can cause severe damage on fruit if they are allowed to present in the orchard. Diseases found in dragon fruit were algae red rust (Cephaleuros sp.), vine orange spot (Fusarium sp.), white vine (Botryosphaeria sp. and Phomopsis sp.), stem blight (Helminthosporium sp.) and anthracnose (Colletotrichum sp.), Dothiorella spot, brownish stem rot, stem yellowing, fruit rot (Colletotrichum sp. and Helminthosporium sp.) fruit orange spot (Alternaria sp.). A black spot disease on stem has not been identified yet. Pests and diseases have not been controlled in particular system, probably because their occurrences have not resulted in a significant loss.
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Judul: Insidensi Penyakit yang Disebabkan Cendawan pada Tanaman Buah Naga Merah (Hylocereus polyrhizus) di Kecamatan Cijeruk dan Leuwiliang Kabupaten Bogor
Abstrak: Tanaman buah naga (Hylocereus sp.) merupakan komoditas hortikultura yang banyak ditanam di Indonesia seiring dengan permintaan pasar yang meningkat. Penyakit tanaman cukup penting dalam usaha tani tanaman buah naga dan sebagian besar disebabkan oleh cendawan. Suatu bentuk usaha pengendalian dapat dilakukan dengan mempelajari insidensi penyakit serta cendawan patogen yang menginfeksi tanaman buah naga merah. Penelitian ini bertujuan mengamati insidensi penyakit dan identifikasi cendawan penyebab penyakit pada tanaman buah naga merah (H. polyrhizus) di sentra pertanaman buah naga Desa Tanjungsari, Kecamatan Cijeruk dan Desa Purasari, Kecamatan Leuwiliang, Kabupaten Bogor. Cendawan patogen pada tanaman buah naga merah di Kecamatan Cijeruk dan Kecamatan Leuwiliang adalah Fusarium sp. (1), Fusarium sp. (2), Gliocladium sp. (1), Gliocladium sp. (2), Colletotrichum sp., Neoscytalidium sp., Alternaria sp. dan empat isolat cendawan patogen belum teridentifikasi. Penyakit pada tanaman buah naga di Kecamatan Cijeruk dan Leuwiliang adalah kanker sulur (Alternaria sp., Neoscytalidium sp.), antraknosa (Colletotrichum sp.), busuk coklat (Fusarium sp.), nekrosis sulur, dan bercak buah. Kanker sulur, nekrosis sulur, dan antraknosa merupakan penyakit utama tanaman buah naga di Kecamatan Cijeruk dan Leuwiliang. Tingkat insidensi dan keparahan penyakit di kedua lahan dipengaruhi oleh pola tanam, pengendalian penyakit, keberadaan gulma, dan iklim mikro
Keyword: kanker sulur, keparahan penyakit, Neoscytalidium sp., patogen

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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