The poplar family of trees, which goes by the name of cottonwood, has representatives in nearly every state in the country. Poplars such as the eastern cottonwood, Fremont cottonwood, balsam poplar and Lombardy poplar grow over a wide geographical range. The cottonwood name comes from the seeds, which emerge from the fruit attached to fluffy hairy cotton-like fibers that carry them everywhere. Poplars are the victims of some diseases that can do damage to the leaves, shoots and wood of the tree.
Septoria Leaf Spot
Septoria leaf spot is the result of an infection from a fungus called Septoria musiva. It can affect those poplars growing in the wild or the many types that landscapers use to highlight a certain piece of property. Symptoms range from small white or silver spots developing on the leaves to much more noticeable and bigger brown ones. Septoria leaf spot can make all or most of the leaves fall from a poplar before they should, with the possibility of weakening the tree for more serious problems later on in its life.
The growing shoots on a poplar can feel the adverse effects of a disease called shoot blight, precipitated by the Venturia populina fungus. When wet conditions promote the growth and spread of this fungus, the shoots on a poplar tree will shrivel up. As they do, they will turn almost black and then perish. Luckily for the poplar infected with shoot blight, the disease, although it can make the tree unsightly, normally will not hurt the tree unless it happens every year over a period of time.
Marssonina Leaf Spot
Another poplar ailment that can make the leaves drop from a tree before autumn is Marssonina leaf spot, a different fungal disease. Brown spots on the leaves that have yellow on their borders are the first sign of this malady. This normally occurs just a few weeks after the leaves develop in the springtime and it results in smaller leaves than usual, which will fall off in premature fashion. The disease typically infects the lower part of a poplar and moves upwards as the growing season progresses. Over time, the infected foliage changes to a brown-yellow color before falling from the branches. This type of leaf spot, if it repeatedly occurs year after year, will kill branches and leave the tree at risk from other diseases.
Poplar trees have another fungus with which they must contend, one that brings with it a disease known as rust. Melampsora medusae first show up in the middle of summer, bringing with it symptoms such as tiny yellow blisters on the leaves that have inside them the reproductive spores of the fungus. They spread from one tree to another, covering the leaves with an orange coating that resembles rust. The leaves fall off the poplar early, making it a potential victim of other sicknesses.
The most serious disease many poplars face is canker, which describes a condition where fungi infect a part of the tree and the tissue in the wood dies off. If a large enough area of the poplar has these cankers then that part of the tree can die, with the whole tree in danger of succumbing as well. Many times these canker fungi enter the tree through open wounds caused by broken branches or in any scars in the bark of the trunk. Canker on the bark looks discolored and has a sunken appearance, with some poplars producing a terrible smelling sap from an infected area.