Algae: Friend or foe?
Algae Control and Prevention
Algae can be difficult to control. Prevention via
light exclusion from the nutrient solution, reservoirs, growing channels and surfaces of
growing media is the main form of defense
for most growers and is the most effective.
For larger-scale growing beds or containers, a plastic film cover over the substrate
and around the base of the plant might
be required. Some growing mediums are
designed to stay dry on top, which prevents
excessive algae growth on the surface. Algae
might still be a problem directly under
drippers or emitters where light naturally
hits the nutrient solution before it flows
into the substrate. Complete control over
all algae growth in most hydroponic systems
can be difficult. Most growers tolerate small
amounts of algae in their system, provided it
does not become excessive, and this usually
causes no problems. When algae growth
becomes thick and widespread, the best
option is to clean up the whole system after
plant removal, and often this requires a good
scrub of all surfaces to dislodge stubborn
algae, as well as running hydrogen peroxide, chlorine and other sterilization agents
through the system, then rinsing well with
water before replanting.
There is a range of chemical algaecide
products that can be added to the nutrient
to kill algae; however, since algae is a form
of plant life, there is the potential with many
of these to damage young or sensitive root
systems, so care must be taken with the dose.
Algae will regrow quickly after applications
of algaecide products, requiring more chemical to get good control. In a European study
on algae control in hydroponic systems, a
number of products tested for control of
algae in nutrient solutions were either totally
ineffective in killing algae, or they killed off
much of the algae but were also phytotoxic
to the plants and caused root damage. It was
also found that dosages of 50 ppm of hydrogen peroxide was required to control algae,
but this dose was too phytotoxic for young
plants, although older plants survived this
dose rate. Therefore, careful and selective
use of hydrogen peroxide could be used on
“Most growers tolerate
small amounts of algae
in their system, provided
it does not become
excessive, and this usually
causes no problems.”
Top: Algae on the surface of a rockwool propagation medium.
Left: Algae on the surface of perlite substrate creates an
unsightly stain.
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Maximum Yield USA | February 2014