My tulip poplar trees had tiny leaves on them then it got 28 degrese 2 nights and the leaves turned brown will they come back.i dont think my trees are dead

Contact Citori directly to inqure.

Feeding. Lime trees, like all citrus trees, are heavy feeders and need fertilizing every couple of months. Use citrus plant food or slow-release fertilizer with extra nitrogen. The nitrogen content should be nearly double when compared to the phosphorous and potassium content; for example, 20-10-10
I have learned through out the years also that if your leaves are turning like a yellowish brown they are lacking magnesium. in that case add a tablespoon or 2 of epsom salt.

not sure if this link will help you out.
mandarin tree leaves are turning yellow and brown spots on leaves Google...

Scab is the most common and damaging pecan disease. It is caused by a fungus that affects rapidly growing leaves, shoots, and nuts. Symptoms on all plant parts are similar. Velvety olive-brown to black spots occur on the husks. Several spots may develop to form black blotches or may blacken the entire surface of the husks. Severely affected nuts of susceptible varieties may drop prematurely or they may stop growing, die and remain attached to the shoot. Leaf symptoms first appear on the underside as tiny olive-brown lesions on the veins. Later, leaf symptoms appear on the upper surface as small olive-brown to black spots. Severely infected leaves may be shed prematurely and weaken the tree, thus reducing the crop next year. The most practical method of scab control is to plant varieties having some degree of resistance to scab such as: Desirable, Cape Fear, Elliott, Chickasaw, Gloria Grande, and to a lesser extent, Stuart. Varieties severely affected by scab are Schley, Mahan, Success, Van Deman, and Mohawk. Use of "resistant" varieties does not necessarily assure complete absence of the disease as no variety is totally resistant. If possible, removing and destroying all leaves and husks may help reduce the amount of scab the following year.
A spray schedule is available for growers who have spray equipment adequate to cover the trees, or for growers who hire custom spray applicators. The following fungicides are registered on pecans: benomyl (Benlate 50WP), propiconazole (Orbit 3.6EC), fenbuconazole (Enable 2F), and thiophanate methyl (Topsin-M 70WSB). Spray applications should be made every 2-3 weeks beginning when leaves first emerge until shell hardening (early August). Spray at 2-week intervals when the tree is growing rapidly or during wet periods. Check fungicide labels for restrictions on grazing in sprayed orchards and the need to use tractors with enclosed cabs while spraying.

Older leaves will do this. Keep a proper nutrient balance for the tree, color will respond to nutrients required by tree type. Research your tree. Google it.

Cottonwood trees are a common name given to several trees in the poplar family. In the Eastern U.S. cottonwood describes populous deltiodes, (the one I am familiar with), a large, fast growing weak wooded tree with roughly serated triangular leaves. There are however other trees throughout the u.s.and Europe that are commonly referred to as cottonwood, the all however are in the poplar (populous) family. It is generally best to determine the Latin name because that will always only refer to one specie of tree, whereas a common name can refer to several species and often differ in different regions. Likewise a tree can have several common names Such as red Maple, soft maple, swamp maple these all refer to Acer Rubrum

You don't say where you are, but from the description the fungal disease Cypress Canker is possible. It is difficult to treat.

http://forestry.about.com/od/forestdiseases/p/dis_com_con.htm

A Yellow Poplar, also known as a Tulip Tree (Liriodendron Tulipifera) can easily get to 120+ feet in height. I have one in my back yard that is about 40 years old and roughly 100 feet tall. One I started from a seedling around 1992 is now about 60 feet tall. Not really sure why that was posted under "Problem with Saddlemen Track Seat Kawasaki Ninja 250R 2008-2012 Standard Height".