Question
I purchased my Meyer Lemon tree last May and kept it outside until Fall where it is now in a sunny South location.

The leaves were becoming a bit yellow, but I thought it just needed more fertilizer since it had just finished bearing fruit.  Last Friday I noticed little cobwebs forming at the juncture of the stems.  

Please tell me how to treat this disease.

Answer
Hi Brenda, Would need more information as there are good webs and bad webs.  This article I found may help.
Citrus trees are the prey of numerous insects. Some types of citrus are more vulnerable than others due to natural characteristics and the type of root stock onto which they were grafted. The most damaging are the sucking and chewing insects; these include insects that are in larval form, such as caterpillars. Identification of a webbed insect requires a visual inspection of the bug, but clues such as location, time of year and the damage they cause also can help you figure out what is harming the tree.

Spider Mites
True spider mites make webbing. There is a false spider mite and several citrus mites that plague citrus fruit trees, but none of these makes a web. The two-spotted spider mite overwinters in the trees and continues to feed if the weather isn't too cold. Spring brings an increase in their population and activity and the insects begin laying their eggs on the undersides of tree's leaves. Two-spotted mites cover leaves and fruit with their webbing. Their conspicuous damage includes yellow or brown spots between leaf veins and clusters of dead dry leaves covered by webbing. In severe infestations the pests can cause leaves and fruit to drop.

Eastern Tent Caterpillars
Silk tents that are noticeable in April or May could be Eastern tent caterpillars. The tents contain white or yellowish cocoons that they retire to after feeding. The cocoons get larger as the caterpillars grow. By late June adult moths emerge from the cocoons. The caterpillars are black with a white stripe down their backs. There are blue spots along the sides of their 2- to 2-1/2 inch long bodies and they have fine hair all over. Eastern tent caterpillars feed on the leaves of fruit and other trees. Leaves are left with distinct serrations from their feeding.

Fall Webworms
Fall webworms appear around July and August. The colony of worms enlarges the web and eventually the caterpillars spin cocoons in fall. The entire colony feeds within the web and expands it as they eat all the foliage. The caterpillars are pale yellow with dark red or black spots along their backs. They are small insects, a little over 1 inch long. Heavy infestations can completely defoliate a tree.

Beneficial Insects
Webbing doesn't have to mean a problem. Spiders are good predators that take care of bad insect infestations and spin beautiful webs. Praying mantises spin webbing to protect their egg sacs. These unusual-looking insects also prey on problem pests. Numerous other beneficial insects also make cocoons or webs.

Check under the leaves for bugs, if you can not see a bug it could be the good bug that cleans the tree and I just can not remember its name at this moment.  Yellow leaves can be not enough water or the tree is getting rid of some leaves for flowers, it can not do both.  kathy  and Happy New Year