Read the given passage and answer the following question.
(1) One of the greatest concerns of landscapers is tree disease. Ash trees are among the most common trees in North America, and they are also very susceptible to disease and decline.
(2) One cause of decline in ash trees is ash yellows. This disease infects mainly white and green ash in the Northern United States. Ash yellows is caused by a phytoplasma: virus-like pathogens that are spread by insects. Ash yellows leads to a gradual decline 10 in tree health for about two to ten years before the tree dies. Some common symptoms include short inter-nodes and tufting of foliage at branch ends, pale green or pale yellow leaves, defoliation, and a sparse canopy. Cankers may also form on the branches and trunk. Unsightly “witches’ broom” sprouts might appear on the branches, but it is more common for them to appear on the trunk. The trunk may also develop cracks if the tree is infected with ash yellows. Rarely does an ash tree recover from ash yellows. Experts guess that this disease is more common than most home owners realize because witches’ brooms and yellowing are not always visible on the infected trees. Sometimes cankers and cracks are the only signs of the disease.
(3) The term ash decline is used to refer to a tree with more than one condition. Ash decline may involve the ash yellows disease or another problem called verticillium wilt. Ash decline is often used to describe any decline in health that is unexplainable. Ash decline involves branch tip death, defoliation, and a slow decline over a number of years. Trees with ash decline may appear to recover in the spring and decline again in July and August.
(4) Verticillium wilt on ash can also result in cankers and dieback similar to ash yellows. Trying to diagnose a tree is difficult because symptoms could be caused by a variety of problems. Sick ash trees may suffer from verticillium wilt, ash yellows, environmental stress, or a combination of these ailments.
(5) Ash yellows has been a known disease in the United States since the 1930s. However, the disease was not distinguished from general ash decline involving environmental factors until the 1980s. In the last eighty years, North America has seen a significant decline in some of its ash trees.
(6) No single factor has been proven to cause ash decline. Ash yellows and environmental factors may work together to create ash decline. Studies show that ash yellows is often detected where environmental factors like water shortage or insect damage are present. A survey of several Midwestern states found that some ash decline was found to be independent of ash yellows. The droughts in the 1980s may have caused the decline of ash trees in the Midwest. Cold winter temperatures may also play a role in decline.
(7) Ash trees are important in the ecology of NorthAmerican forests. The decline of these trees may have a severe impact on the health of other plant and animal communities. Green ash provides nesting sites for several species of birds and other wild creatures. Insects and fish flourish in the cool waters made possible by the shade of ash trees. Green and white ash are also very popular in landscaping. Their decline could result in reduced property values.
(8) Ash trees also represent a valuable hardwood resource. An estimated 275 million feet of ash lumber is harvested annually. In the Northeastern UnitedStates, about 33 percent of the commercial forest area includes ash trees.
(9) There are no known cures for the diseases mentioned. Experts recommend removing very sick trees while keeping healthy trees well watered and fertilized. Dead limbs should also be removed to maintain the health of ash trees.
According to the passage, many scientists feel that most ash decline is likely caused:
The passage likens verticillium wilt to ash yellows in that:
The difficulty in diagnosing disease in an ash tree is due to all of the following EXCEPT:
The passage states that ash yellows is caused by:
According to the passage, the author believes that:
According to the passage, which of the following is an argument for NOT blaming ash decline solely on ash yellows?
As it is used in paragraph 7, the word flourish most nearly means:
The author would most likely agree with which of the following statements?
According to the passage, what is NOT a characteristic of the disease ash yellows?
As it is used in paragraph 4, the word diagnose most nearly means: