Question
I have a marginate tree in my morning room.  I have notice some white stuff all over the plant.  I was told to spray it with an insecticide but it did not seem to help, the leaves started to die and break off.  Now it just seems like it is dying.  Is there anything that I can do to get rid of all the white spots.  It looks like spider webs by the roots and on the leaves.

Answer
Hi Valeria,
  You probably have spider mites. Unfortunately you now likely have a very high population of spider mites and they have already done a great deal of damage to the plant. There is a chance that the plant may not recover. Check the plant carefully to positively identify that the plant does indeed have spider mites. Spider Mites are tiny, spider like mites that can barely been seen with the naked eye. The most visible sign of a Spider Mite presence is webbing on the undersides of leaves and between stems, however, webbing indicates a high population of Spider Mites. Although Spider Mites are very hard to see with the naked eye, their eggs can usually been seen easily, grouped together on the undersides of leaves. The most common Spider Mite is the Two-spotted Spider Mite, they have greenish colored, soft pear shaped bodies with 2 dark spots on their backs.
It is important to get rid of the spider mites as soon as possible. Spider Mites are very difficult to get rid of or control. Often they are resistant to chemical pesticides and many insecticides do not work for Spider Mites. If you are going to use a commercial pesticide be sure that it is listed on the label that the product is effective for Spider Mites.
The first step in getting rid of spider mites (and most crawling insects) is to spray the leaves, especially the undersides, with a strong spray of water. This will wash off as many of the insects as possible. Since Spider Mites are often resistant to most chemical pesticides it is best to use an insecticidal soap spray. Another good thing to use is pesticides made with neem oil. Be sure to cover all leaf surfaces completely. Repeat treatment every 5-7 days until there is no sign of Spider Mite presence.

You can use a commercial insecticidal soap spray or you can make your own insecticidal soap spray. It is best to make homemade insecticidal soap using soap that contains no perfumes, dyes, moisturizers or deodorants. Never use liquid hand soap, such as Soft Soap, to make insecticidal soap spray.  A lot of people commonly use dishwashing liquid to make insecticidal soap spray, but dishwashing liquid contains a lot of perfumes, dyes and degreasers that can be harmful to plants. What I recommend doing is getting a small bar (or cutting a sizable chunk off of a larger bar) of a 'pure' soap, such as Ivory. Cut the bar (or chunk) into several small pieces, put them in a small amount of water and allow them to 'melt'. You now have a concentrate that can easily be mixed with an additional amount of water to make an insecticidal soap spray. Here is a good recipe for homemade insecticidal soap that I have had good results with;

Mix 4 TBSP of the soap concentrate (or 1 TBSP of dishwashing liquid) and 1 TBSP of vegetable oil into 2 quarts ( 8 cups) of lukewarm water. You can also use this recipe without the vegetable oil for most insects. I usually only add the vegetable oil for heavy populations of spider mites. Remember, you will need to repeat treatment every 5-7 days until there is no longer any signs of spider mites. You may have to repeat treatment several times before the spider mites are completely gone.

The most important part of insect control is early detection. A few insects on a plant is much easier to get rid of than an infestation of hundreds on several plants. Check plants often for any sign of insect presence and if found, act quickly. Keep affected plants away from other plants to prevent the insects from spreading to other plants. Keeping plants clean by spraying plants with water about once a month will not only wash away dust and dirt but also any insects that may have found their way into your home, preventing them from evolving into an out of control infestation.

Plants that are healthy are much less susceptible to infestations of insects. Always follow good cultural practices. Warm and dry conditions commonly found in most homes are ideal conditions for some insects such as Spider Mites. Misting plants regularly may help.

If you have any questions or need additional information please don't hesitate to ask.
Thanks
Tracy

PS ~  I have written a guide on insect control on houseplants. It contains a lot of information on the most common insects that are found on houseplants and the different types of insecticides used to control them. Here is a link to the guide if you would like to read it;

http://reviews.ebay.com/Insect-Control-On-Houseplants_W0QQugidZ10000000004625662