http://www.mnn.com/your-home/organic-farming-gardening/blogs/why-are-my-plants-turning-yellow
(will help you identify the problems, nutrient deficiency, pest, etc.)
PART 1. INFECTIOUS DISEASES
Fungal Diseases---Acremonium Leaf Spot and Stem Rot of Syngonium and Dieffenbachia; Alternaria Leaf Spots of Calathea, Brassaia, and Their Relatives; Aspergillus Stem and Rhizome Rot of Sansevieria and Dracaena; Botrytis Blight (Gray Mold); Calonectria Collar Rot and leaf Spot of Leea; Ceratocystis Blight (Black Cane Rot) of Syngonium; Cercospora Leaf Spots; Colletotrichum Leaf Spot (Anthracnose); Coniothyrium Leaf Spot (Brown Leaf Spot) of Yucca; Corynespora Leaf Spot; Curvularia Leaf Spot (Tan Leaf Spot) of Rhoeo; Cylindrocladium Root and Petiole Rot of Spathiphylllum; Cytosporina leaf Spot (Gray leaf Spot) of Yucca;
Dactylaria Leaf Spot of Philodendron; Fusarium Basal Stem Rot of Cacti; Fussarium Leaf Spot of Dracaena and Sansevieria; Fusarium Stem Rot of Dieffenbachia; Fusarium Wilt of Fatshedera; Gliocladium Blight of Palms.
Diseases Caused by Helminthosporium-like Organisms---Leaf Spots of Palms, Exserohilum Leaf Spot of Aechmea, Drechslera Leaf Spot of Maranta and Calathea, Drechslera Stem Rot of Cacti and Succulents, Kutilakesa Stem Gall and Canker of Codiaeum and Aphelandra, Leptosphaeria Leaf Spot (Brown Leaf Spot) of Dieffenbachia, Myrothecium Leaf Spot, Powdery Mildew of Saintpaulia and Cissus, Pestalotiopsis Dieback of Cissus, Phomopsis of Dieback of Ficus, Phyllosticta Leaf Spots of Dracaena and Peperomia.
Diseases Caused by Phytophthora---Diseases Caused by Phytophthora palmivora, Diseases Caused by Phytophthora parasitica, Plectosphaerella Leaf Spot of Dieffenbachia.
Diseases Caused by Pythiuim---Diseases Caused by Pythium aphanidermatum; Diseases Caused by Pythium irregulare; Diseases Caused by Pythium myriotylum; Diseases Caused by Pythium ultimum; Pythium splendens Root Rot, Rhizoctonia Root Rot, Aerial Blight, and Leaf Spot; Rhizopus Blight; Rust Diseases; Sclerotinia Blight; Southern Blight; Stemphylium Leaf Spot of Succulents; Verticillium Wilt of Ficus and Peperomia.
Bacterial Diseases---Crown Gall of Ficus and Codiaeum; Erwinia Leaf Spot, Blight, and Stem Rot. Diseases Caused by Pseudomonas---Pseudomonas Leaf Spot and Blight of Asplenium; Pseudomonas Blight of Caryota; Pseudomonas Leaf Spot and Blight Caused by Pseudomonas cichorii; Pseudomonas Leaf Spot of Dracaena; Orange Soft Rot of Cacti.
Diseases Caused by Xanthomonas---Xanthomonas Leaf Spot and Blight of Begonia; Xanthomonas Leaf Spot of Dieffenbachia and Blight of Anthurium (Araceae); Xanthomonas Leaf Spot of Hedera (Araliaceae); Xanthomonas Leaf Spot of Codiaeum (Euphorbiaceae); Xanthomonas Leaf Spot of Pilea and Pellionia (Urticaceae); Xanthomonas Blight of Syngonium.
Viral Diseases---Bidens Mottle Virus of Fittonia; Cactus Virus X of Schlumbergera; Commelina Mosaic Virus; Dasheen Mosaic Virus of Aroids; Fig Mosaic Disease; Maranta Ringspot (Cucumber Mosaic Virus); Peperomia Ringspot Disease; Schefflera Ringspot Disease; Tobacco Mosaic Virus of Rhoeo; Tradescanita-Zebrina Virus.
Nematode Diseases---Burrowing Nematode; Cactus Cyst Nematode; Foliar Nematodes; Lesion Nematodes; Root-Knot Nematodes.
PART II. NONINFECTIOUS DISEASES
Air Pollution
Light
Nutrients---Nutrient Deficiencies, Nutrient Toxicities.
Pesticide Phytotoxicity
Temperature
Water
Disorders of Unknown Cause---Aphelandra Lef Crinkle; Flecking of Dracaena marginata; Leaf Burn of Massangeana Cane; Bent Tip of Aglaonema.
Houseplant Pests
Aphids
Aphids are tiny, sucking insects about 1/8-inch long. They can be black, red, orange, green, yellow or tan in color. The foliage of damaged plants loses its green color and can appear stunted, distorted or curied. Aphids secrete a sticky substance called honeydew which gives the plant a shiny appearance and leads to the growth of black, sooty mold.
Mealy Bugs
Mealy bugs are slender, flat insects covered by a waxy substance. They form a white, cottony-mass. Adult mealybugs inhabit cracks and crevices of buds, stems and branches, weakening the growth of the plant. Mealybugs secrete honeydew.
Scale
Scale insects are about 1/4-inch long. The scale is actually a covering that serves to protect the scale insects. Females lay eggs under the protective covering. When the young hatch, they are transparent, oval and flat. The first growth stage is the crawler, susceptible to insecticides. Check for scale along leaf veins and on stems. Infested plants exhibit poor, stunted growth and often you will see the small, raised, brown shells of the scale insects.
Whiteflies
White flies are tiny, snow-white insects. Adult females can lay up to 100 crescent-shaped eggs per month on the undersides of leaves. Whiteflies breed continuously in interior environments, rapidly creating large populations. Infested plants become weak, deformed and pale, and eventually die. Whiteflies secrete honeydew.
Fungus/Gnats
Fungus/gnats are small, slender, black flies. They are commonly found in highly organic soils or unsterilized soil and rarely cause damage to plants. Any damage that does occur will be in the form of chewing injury to feeder roots.Larger roots, seedling and succulent stems.
Two-Spotted Spider Mite
Spider mites produce fine, spiker-like webs on the undersides of plant leaves. The web protects both the mites and their eggs. Mites are wingless and usually pale yellow to red in color. Mite damage first appears as whitish or yellowish speckled areas. Leaves may take on a bronze appearance and may die and fall from the plants. Warm, dry conditions favor mite infestations. Mites can be very hard to control because they reproduce rapidly in high temperatures, building up large populations quickly, and they can develop a tolerance to miticides.
Thrips
Female thrips insert their eggs into host tissue. One week later, the eggs hatch and within two to four weeks their life cycle is completed. Thrips suck plant juices and in doing so, rasp and shred the leaf. The injured plant turns white and shows signs of black secretions. Thrips are usually found in blossoms and in the axils of leaves.
http://emp.byui.edu/ROMNEYB/325Analects.html