Alternaria is a ubiquitous mold found almost everywhere in the country and is a normal agent of decay and decomposition as well as plant associated disease. Alternaria pores are usually present in outdoor air throughout the year, frequently exceeding the number of pollen by 100- to 1000-fold or more, depending on environmental factors, such as water, nutrients, temperature, and wind. In Arizona, Alternaria spore levels increase during the summer monsoon season and peak during the fall. Airborne levels are affected by fall harvesting of crops and temperature inversion, trapping particulates including mold and pollen close to the ground.
Palo Verde is one of the most common trees of the Sonoran Desert and is found throughout southern Arizona and southeastern California. Starting in April, the Palo Verde produces a brite yellow flower that stands in contrast to it’s characteristic green trunk and branches. In late spring it is common to see the Palo Verde covered in yellow blossoms with a blanket of yellow at it’s base from dropped flowers. It is this fact that makes the Palo Verde a bit of an allergy enigma.
As a general principle, plants that produce conspicuous and fragrant flowers do so to attract insects such as bees to distribute their pollen. In addition, the pollen is typically heavy and sticky so that it sticks to the insects rather than being wasted blowing in the wind. Wind pollenated plans on the other hand produce copious amounts of light pollen that easily catches a ride in a breeze, and often finds it’s way to the nose and eyes of allergy sufferers. Palo Verde, although an insect pollenated tree, can cause allergy problems just because of the huge volume of flowers that fall to ground, dry, and then picked up by the wind
Johnson Grass is found in washes, along road sides and other areas where there is enough water. Although it is an allergenic grass, pollen counts in the Phoenix area tend to be low because of it’s sparse distribution. It pollenates May through October.
The olive tree is native to the Mediterranean, Asia, and Africa and has been cultivated for it’s fruit for thousands of years. It is a hardy, drought and disease resistant tree, well suited for the harsh conditions of the Sonoran desert. It is an evergreen tree which can grow to 30 ft and has an attractive gray, often gnarled and twisted trunk gaining character with age. Some trees are hundreds of years old. The olive tree produces a small, inconspicuous pale, white flower which is wind pollinated and produces volumes of airborne pollen in the spring. Olive tree pollen is one of the most potent and sensitizing of the allergenic plants of Arizona. Because of it’s association with severe springtime allergy symptoms, the city’s of Phoenix and Tucson have banned the planting of fruiting Olive trees since the 1960s. More
Because of it’s resistance to heat and drought, Bermuda grass is well suited for Arizona and the desert southwest. Common Bermuda is propagated by seed and produces significant amounts of pollen. It is used extensively in school sports fields, parks, golf courses, and green belts. Hybrid Bermuda grasses such as Tif and Midiron, are the result of mating common Bermuda grass with African Bermuda grass resulting in a plant with a finer leaf texture and which does not produce pollen or seed. These hybrid varieties are used in many home lawns and smaller fields. In 1994, Phoenix passed the Airborne Pollen Ordinance which requires that Bermuda grass lawns be kept short to prevent pollen-producing seed heads (see picture) from forming. It pollenates May through October
The Mulberry tree (also know as Fruitless Mulberry or White Mulberry) is often cited in stories relating how Arizona went from a favored destination for allergy sufferers to one of the worst places to live if you have allergies or asthma. New Arizona residents moving in from the South and East preferred the stately, large-leaved, shade trees they left behind to the local desert varieties and so thousands of Mulberry, Olive, and Ash trees were planted throughout the valley. Spring tree pollen levels in Phoenix were fairly low 40-50 years ago but over the past 30 years, pollen levels in Phoenix have skyrocketed and along with it, the Phoenix allergy-misery level. To stem the flood, Phoenix passed the Airborne Pollen Ordinance which restricted the planting of male Mulberry and Olive trees. As a result, there are few Mulberry trees in the newer communities of Phoenix such as the Foothills in Ahwatukee, although there are enough established trees in the valley to supply the rest of the area with pollen for many years ago come.
Pollination: February through April
Arizona Ash is a medium to large deciduous ornamental shade tree used in landscaping throughout Phoenix. Because of it’s high water requirements, it is infrequently used in desert landscaping and therefore is less common in the newer communities of Ahwatukee, Chandler, and Maricopa, although it can be found frequently in older parts of Ahwatukee, equestrian properties such as Warner Ranch, as well throughout Tempe, Scottsdale, Mesa, and Central Phoenix. Other varieties of Ash are very popular in Ahwatukee and Chandler and a large number have been planted in schools and parks. The Ash is in the same family as the Olive tree (Oleaceae family) and individuals who are sensitive to Olive tree pollen will also have problems when exposed to Ash tree pollen.
Pollination: February through April
A type of pigweed, this wind pollinated weed is not native to Arizona. It may be found along road sides, in agricultural area, ditches, and vacant fields in the fall. It can be found covering open fields in September through November in the Phoenix area if monsoon rains have been frequent.
Pollinates: May through November
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