Stay on Top of Weed & Algae This Spring

Weed and algae cause a number of problems in water. They reduce water oxygen levels, impede flow in drainage systems and interfere with fishing and other forms of recreation.

In this blog we are looking at using straw as a pre-emptive measure and removal of algae in its early stages. If you already have an established weed or algae problem then our Weed Nets are a very effective strategy for removal.

Weed and Algae Management

There are hundreds of different types of algae that can cause a problem in ponds, from those that are suspended in water to others that spread across the surface in long fibres. Apart from looking unsightly, algae can lead to the deoxygenation of water with a detrimental effect on pond life.

They impede flow in drainage systems, block pumps and sluices, fishing and other forms of recreation, cause taint and odour problems and, in some instances, create a health hazard to humans, livestock and wildlife.

How straw works

In order to use straw effectively it is necessary to understand how the process works.

When barley straw is put into water it starts to decompose. During this process chemicals are released which inhibit the growth of algae. Rotting is a microbial process that is temperature dependent. It is therefore faster in summer than in winter.

It may take 6-8 weeks for straw to become active when water temperatures are below 10 degree. But only 1-2 weeks when the water is above 20 degrees.

Once the straw has started to release the chemical it will remain active until it has almost completely decomposed. The duration of this period varies with the temperature and the form in which the straw is applied.

Types of straw

Barley straw works more effectively and for longer periods than wheat or other straws and should always be used in preference to other straws. If barley is unavailable, other straws, including wheat, linseed, oil seed rape, lavender stalks and maize can be used as a substitute.

Hay and green plant materials should not be used because they can release nutrients which may increase algal growth. Also they rot very rapidly and may cause deoxygenation of the water.

Speed of effect

Once the straw has become active, the time taken for control to become effective varies with the type of algae. Small, unicellular species which make the water appear green and turbid, usually disappear within 6-8 weeks of straw application.

The larger filamentous algae, often known as blanket weeds, can survive for longer periods and may not be controlled adequately in the first season if the straw is added too late in the growing season.

It is, therefore, preferable to add the straw very early in the spring before algal growth starts.

How to apply straw

Where large quantities of straw are needed bales should be broken up on the bank and the loose straw wrapped in Barley straw netting.

A tree wrapping machine can be used to construct straw sausages. They can be made up to about 20m long and contain some 50kg of straw. It is advisable to incorporate some floats within the netting to keep the straw near the surface when it becomes waterlogged.

When first constructed, these sausages float well and can be anchored by rope. It is preferable to anchor these straw sausages at one end so that they can swing round to offer minimum resistance to wind or currents.

Straw sausages can interfere with angling so their positioning needs to be carefully considered as to have the minimum adverse effect on water users. Floats or buoys can be attached as markers to warn anglers of the position of the straw.

When to apply straw

Straw can be applied at any time of year but it is much more effective if applied before algal growth begins. Anti-algal agents released by the straw are more effective in preventing algal growth than in killing algae already present. Therefore, straw is best applied in the spring and autumn, when water temperatures are low.

The straw will become active within a month and will continue to inhibit algal growth for about 6 months. However rapid algal growth can take place once the straw has rotted away and so further applications should be made every 4 to 6 months.

Regular observations should be kept so that fresh straw can be added before the end of the 6 month period if necessary.

Effects on fish

A number of observations of improved growth, vigour and health of fish in waters treated by straw. Benefits of clean clear water include:

• Increased food supply in the form of invertebrate animals.
• Fish find it easier to find food in the water.
• Better light penetration = a great amount of photosynthesis

To conclude

When algal problems occur in water bodies ranging from garden ponds to large reservoirs, lakes and rivers, barley straw offers an environmentally acceptable and cost-effective form of control.

• Straw should be applied twice each year, preferably in early spring before algal growth starts and in autumn
• In static water the straw should be loose, so water can pass easily and should be held in Barley Straw Nets.
• Straw should be supported by floats so that it does not sink
• If the straw starts to smell then it is not working and should be removed

Be patient, this is a natural process which takes time to work!

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