Dwarf Mistletoe

Dwarf mistletoes are small, leafless, parasitic flowering plants. The seeds, explosively discharged from the fruit by a stream of pressurized water at almost 60
mph, are sticky and adhere to any surface they strike. Seeds that adhere to young branches of susceptible trees germinate, and the mistletoe rootlet penetrates
the bark. Birds occasionally may spread the seeds to uninfected trees. Dwarf mistletoe seeds generally are dispersed in August and early September.

Mistletoes spread slowly from tree to tree. Six years pass from the time seeds are discharged until they produce mature berries. In closely spaced trees of about
the same height, this spread is 1 to 2 feet per year. Because the seeds are spread by expulsion, seed distribution is primarily found in the lower 2/3rds of
adjacent trees. The spread from large to small trees can extend 60 feet, but the average usually is less than 30 feet. Most dwarf mistletoes are specific to a
particular type of tree (i.e., lodgepole pines, ponderosa pine, and white fir, amongst others) and do not infect hardwood tree species.

Dwarf mistletoes grow into the bark and phloem of the tree. The parasite produces root-like structures called "sinkers" that form each year. Sinkers become
embedded deep in the wood as twigs grow. These sinkers provide the parasite with water and nutrients obtained from the host.

Dwarf mistletoes kill by slowly robbing the tree of food and water. Diseased trees decline and die from the top down as lower infected branches take more food
and water. Death occurs slowly in most cases and depends on the severity of infection and on the vigor and size of the tree.

Male and female flowers are produced on separate plants. Small, inconspicuous flowers arise from axils of
shoot segments in May or June. Female flowers are pollinated by insects and fruits develop during the next 14
to 15 months, ripening in late summer. Mature fruits are ovoid berries about three-sixteenths inch long. Their
color is similar to that of the shoot, but the upper and lower parts of the fruit are of different shades of green.

Management & Removal
Because the seed berries are "shot" by high pressure water onto
nearby trees, dwarf mistletoe spread can be slowed by having a
dense stand. The close proximity of other trees will act as a shield
for trees 30 - 60 feet away.

However, the necessity of far more resources required by a dense
stand of conifers (water, available mineral nutrients in the soil, air
circulation, and light penetration) is a major deterrent to this
strategy except in historically wet environments such as the Pacific
Northwest.

In drier climates, such as that found in Southern California, this
strategy is not realistic. Indeed, a high density strategy will lead to
far worse consequences than the spread of dwarf mistletoe!

Unfortunately, growth inhibitors have not been effective in slowing
the rate of spread, and cannot kill the mistletoe.

Where does this leave the owner of infected trees in drier
climates? Branch pruning is very effective in controlling the spread
of dwarf mistletoe. Complete removal is best, but not always
desirable for aesthetic reasons.