Pests
Plants and pests go hand in hand and you will have to accept that you will get pests at some point. Leaves may become mottled, yellow and wilted. Growth can be stunted and in the worst case even death.
Prevention is always better than the cure. Always check the plants you are buying. Check the leaves and stems before bringing a new plant home. If you purchase online, again double check every inch of the plant before placing it with your others.
Ladybird plant care specialise in pest control and have some fantastic products which are all organic. They offer Nematodes for Fungus Gnats to Amblyseius cucumeris for Thrips and lots more. We sell their horticortural soap instore and online. To see their other products click through to their website.