 |
| If bermudagrass flowers like this one are left to release pollen in the air, they will cause “hay fever”. That’s why common bermudagrass is not permitted for planting in Clark County, Nevada. |
Pollen Alert
That’s what we see on our
advisories in the early spring regarding pollen from mulberry, ash and
junipers. The pollen alert continues through the “pollen season” as we go from
mulberry to pine to olive. Pollen season might last until May. Right now we’re
in “mulberry season”. Some pollen like mulberry is light enough and can be pushed
by the wind and carried by pollinators like honeybees. This type of pollen
causes “hay fever” while others are considered “sticky” or “heavy”, too large
to travel long distances in the air and not considered allergenic.
 |
| Male flowers from the ‘Bonita’ ash tree. Because this ash tree is male, it produces only male flowers. Great for producing no seed but not if you dont want pollen. |
Hay Fever
“Hay fever” was a misnomer from the
start. It was an old historic association with the cutting of hay in the spring
and not paired with flowering of plants that cause the release of pollen. Back
then pollination by plants was not studied much. Tree and shrub pollen was not considered
responsible for “hayfever”. Most allergenic pollen comes from uncontrolled,
wild grasses growing where rain was available. These allergies were caused by
pollen floating in the air but the idea of “pollen fever” never caught on. Until
recently people with severe symptoms were told to move to the desert Southwest
where “pollen fever” was never considered much of a problem. Maybe that was the
case back then, but they are wrong now!
 |
| Common bermudagrass flowering and it will seed next spreading pollen and seed everywhere. When bermudagrass escapes mowing, it creates pollen, allergies and seed. |
Desert and Hay Fever
As people moved to the desert
Southwest and started planting more and more “desert trees” like Acacia,
Mesquite and Palo Verde, “pollen fever” (aka, hayfever) developed into more of
a problem. Typically, trees and shrubs with large showy flowers like oleander do
not contribute much to the “hayfever problem”. This pollen is heavy or sticky
and did not travel in the air far from the flower and the plants released
pollen too large to cause “allergy problems”. Most of the “problem pollen” comes
from “non-showy” flowers commonly found on olive, mulberry, pines, ash trees, mesquite
and the like.
 |
| Oleander flowers are quite “showy”. Showy flowers are not typically allergenic because the pollen is large and/or sticky. |
Planting Restrictions
Now we have planting restrictions in
population dense Clark County that prohibit the planting of male mulberry trees
or olive trees that produce lots of fruit. So, is it “illegal” to plant
mulberry trees in Clark County? Yes and no. It is “illegal” to plant male
mulberry trees but not the female trees.
 |
| Mulberry flowers are called “catkins”. Flowers in mulberry are like ash trees; they are either male or female depending on the sex of the tree. |
How about olive trees? Yes and no, but for
a different reason. Olive trees always have both male and female parts in the same
flower so we focus on the so-called “fruitless mulberries” and hope that these
trees reduce “hayfever” in large communities. Mulberries, similar to ash trees,
are bought as either male trees or female trees. As I have always said, plant
sex is much more interesting than animal sex because of its diversity.
 |
| Olive trees are both male and female so their flowers, unlike mulberry and ash, contain both male and female parts. |