Since man started to live on agriculture, he has to involve in a constant struggle to protect crops from other animal and adverse environmental conditions. In order to get a maximum crop production and profit from the cultivation farmer has to pay a special attention and bare an additional cost for crop protection even today. Crop protection has become even more important due to the introduction of high yielding crop species. Pest and diseases play a major role in these aspects.
What are pest and diseases?
Disease and causal agents
Disease can be defined as a restriction to the normal functioning of a plant caused by micro organisms due to a specific cause which shows symptoms from the outside. Disease causing agents can be categorized to few main categories such fungi, bacteria and virus and the following diagram shows the disease types which are caused by these categories.
Definition of pests
Any animal or plant which restricts the human activities in an agricultural system can be defined as a pest. This definition can differ according to the place and person. A pest for one person could not be an economically important crop or an animal for another.
There are three main categories of weed within agricultural systems. They ate grasses, sedges and broad leaf weeds. Most of the time these act as secondary hosts for pests.
Identification and categorization of disease causing agents
Most of the disease causing fungi belongs to classes Ascomycetes and Basidiomycetes. Fungal types such as Fusarium and Verticellium comes under Ascomycetes and Rhizoktonia and Puccinia comes under Basidiomycetes. In addition there are fungal types which belongs to Oomycetes. Phytopthora and Phythium fall under this category which cause severe infection to the plants.
Disease causing bacteria belong to "Bacilli" type. They are the major disease causing organisms for plant divisions such as Xanthomonas and Pseudomonas. Phytoplasma which has no cell wall are also bacterial causal organism.
Disease causing viruses make infections through vectors. Generally vectors are fungi, nematodes and protozoa.
Let's identify the major pest and diseases in Sri Lankan field crops
Let's identify the major pest and diseases in Sri Lankan field crops.
Rice sheath blight
Grain spotting and pecky rice
many fungal species and bacteria
Narrow Brown Leaf spot
Xanthomonan campestris pv. Orysae
Bacterial leaf streak
Xanthomonas campestris pv. Oryzicola
Rice thrips (RTH)
Stenchaetothrips biformis (Bagnall) (Thysanoptera : Thripidae)
Brown Plant Hopper (BPH)
Nilapavata lugens (Stal) (Homoptera : Delphacidae)
Yellow Stem Borer (YSB)
Scirpophaga incertulas (Lepidoptera : Pyralidae)
Rice Leaf folders (RLF)
Cnaphalocris medinalis; Marasmia spp. (Lepidoptera : Pyralidae)
Rice Gall Midge (RGM)
Orselia oryzae (Diptera : Cecidomylidae)
Paddy bug (PB)
Leptocorisa oratorius (Hemiptera : Alydida