Urea

Two stump treatments are available in the UK to prevent infection by the highly damaging wood rotting pathogen Heterobasidion. Urea can be applied to freshly cut stumps of all conifer species when thinning or clear-felling to prevent infection by the pathogen. For pine species, the biocontrol agent, PG Suspension, is a recommended alternative.

Note: Our research suggests Sitka spruce growing on deep peat soil (>20cm), or on shallower peat (>5cm) in areas with annual rainfall exceeding 1600mm, is at low enough risk of disease that stump treatment during thinning and clear fell is not needed. All other species should be treated on all sites to protect forest sustainably.

Urea is a highly soluble nitrogen-containing compound that is widely used as a fertiliser. While commercially available urea is manufactured through industrial processes, it also occurs naturally as a metabolic by-product in many organisms.

When used as a stump treatment, enzymes in the woody tissue break down the urea, producing ammonia and making the surface more alkaline. Heterobasidion species are not adapted to deal with this change in environment, reducing their ability to colonise the stump.

For effective stump treatment urea should be diluted to a 37% w/v solution with water. Urea is available in multiple forms such as premixed liquid, or granules (commonly sold as ‘prills’).

Once diluted, the urea solution can be applied to stumps in a variety of ways:

• For small scale use, urea can be applied to stumps using a brush to effectively coat the surface after felling.
• For medium scale, a backpack sprayer can be used to treat multiple stumps quickly and effectively.
• In commercial forestry situations, urea is pumped through the head of the harvesting machine and sprayed directly onto the stump during cutting.

The urea solution must cover the entire stump surface to be effective.

Urea is a chemical that is mainly sold and used as a fertilizer, but it can also be used in forestry as a fungicide to prevent conifer stumps being colonised by Heterobasidion. For this reason, it has approval as a ‘commodity substance’. This means that you store and transport it as you would any other fertilizer, and only when you apply it to stumps do you treat it as a pesticide.

When you use it as a fungicide you should treat it as you would any other pesticide (albeit a low risk one) according to the approved pesticides codes of practice,

Urea should be stored in a bunded, cool, dry, and well-ventilated area in tightly sealed containers to prevent moisture uptake. In powdered form exposure to humidity can result in caking and reduced product quality. Urea should be kept away from incompatible materials, excessive heat, and sources of ignition, and stored in accordance with the manufacturer’s recommendations and relevant safety data sheet (SDS) requirements.