&middotDrought damage - needles gradually turn yellowish-green and then light brown. This starts at the top of the tree and progresses downward and from the outside in. &middotAnimal injury - dog urine can cause some browning and dropping of lower branches on arborvitae and junipers.
There are many different brands of cat flea collars. Generally, flea collars work by either emitting a toxic gas to the local area (head/neck of the pet) or by exuding chemicals that are absorbed into the animal's skin. Some flea collars have an Insect Growth Regulator (IGR), to prevent development of cat fleas, eggs and larvae.
Being too sensitive to essential oils, and the fact they lick themselves so much, makes natural flea repellents for cats trickier than it is for dogs. Many natural methods deal with prevention (vacuuming, regularly washing bedding, and so on) but there are a few that you can take immediate action with.