Azolla, or water fern, is a very common pond weed in the Bandon area.  It spreads quickly and will completely cover an irrigation pond.  The plants will take on a reddish hue, especially during the winter months when they are stressed.  During the summer, they tend to be green.  

It reproduces both vegetatively and by producing spores that are released into the water column.  These spores will overwinter and produce new material in the spring.  They are also a source or reinfestation, meaning that multiple treatments of an infested area are necessary until all the spores have germinated and can be eliminated. 

Azollais a free-floating plant that builds up thick mats of material.  This material can be problematic, as you can imagine.  The free-floating weeds can be drawn into water intakes and block pumps and filters.  

How do you control it???

You can physically remove the weed from smaller bodies of water.  It is most easily done when the floating mats are collected on one side of the pond.  The wind can help with this … or  you can use baffle boards.  Physical removal of azolla is labor-intensive and will require repeat treatments – those free-floating spores will germinate and produce new plants - but may be necessary if water use restrictions on the label conflict with irrigation needs.

Chemical options.  According to a Azolla document out of the UK, herbicide treatments are the most effective form of control (http://www.ceh.ac.uk/sci_programmes/documents/waterfern.pdf).  Our PNW Weed Management Handbook lists three aquatic herbicides labeled for use on floating aquatic weeds:  Diquat, glyphosate, and penoxsulam.  Diquat and glyphosate are believed to be most effective, so I’ll list the PNW Handbook information for those chemicals below.  (For more information on aquatic weed control, see https://pnwhandbooks.org/weed/aquatic).  Herbicides must be approved for irrigation if you are going to use that water for frost control or heat control (see PNW Handbook and label restrictions).  Also, please note any hold times for use of water.

Diquat (Diquat Herbicide and Reward)

                Rate       1 to 4 lb ai/A (0.5 to 2.0 gal per surface area).

                Time       Apply when weeds are actively growing and water temperatures are above 50°F.

                Remarks              Add a registered nonionic surfactant when spot spraying at <0.5 gal per acre.  Apply only to ponds and lakes with little or no outflow.  Use diquat in waters that are totally under your control.  In public waters, only federal or state public agencies, or contractors under their direct control, may use this product.  Treat floating weeds by spot or broadcast treatments.  Safe for fish at the rates given.  There are no swimming or fishing restrictions for treated water.

CautionA moderately toxic herbicide that requires protective gear for handling and application.  Do not allow spray to drift or come in contact with adjacent crops.  Do not use treated water for domestic purposes, animal consumption, spraying or irrigation for 1 to 5 days, depending on water use and rate applied.  Safe for fish at rates given.  Do not let spray come in contact with skin, eyes, or clothing. Do not breathe spray mist.

                Site of action       Group 22: photosystem I electron diversion

                Chemical family  Bipyridilium

Glyphosate (Rodeo, AquaNeat, AquaPro, AquaMaster, Cinco, Accord Concentrate and others)

Rate       0.75 to 3.75 lb ae/A (1.5 to 7.5 quart/A) applied as a broadcast spray or 0.75 to 2.0% solution in water applied through hand-held or high-volume equipment

                Time       Apply when weeds and brush are actively growing and most foliage is above the water surface.

                Remarks              See label for application rate and growth stage of weed and brush species.  Floating mats of vegetation may require re-treatment.  Add a surfactant labeled for use in water at the manufacturers’ surfactant label recommendations; surfactant must be at least 80% ai. 

CautionRain within 6 hours after application may reduce effectiveness.  Do not apply within 0.5 miles upstream of potable water intakes.  Apply to moving bodies of water only while traveling upstream.  Do not overlap bank side applications more than 1 foot into open water.  Do not exceed 3.75 lb ae/A in a single application being made over water.  Take care to avoid drift to desirable plants.  Do not spray where weeds do not exist.

                Site of action       Group 9: inhibits EPSP synthase

                Chemical family  None generally accepted.