In this edition of tips and techniques I will work through the different methods for controlling Holly (Ilex aquifolium) and Ivy (Hedera helix) on your property. Harvesting for festive season decorations is not an effective control technique!
Little reliable information is known about the most effective control techniques for these two introduced evergreen species; often the environmental conditions of the site and extent of invasion determine the best method for control.
Ivy is a climber with shoots up to 30 metres long. It tolerates low light levels and can therefore invade remnants and replace native ground cover plants. It competes strongly with native plants for light, nutrients, and soil, and can smother or strangle even mature trees that it grows over.
A dominance of ivy results in an 'ivy desert', with a loss of native biodiversity and reduced animal feeding habitats.Presently, there is little published information on treatment methods for ivy, although it is increasingly recognised as a threat to restoration efforts and native plant communities. Its ability to spread adventitiously and be easily dispersed by birds causes concern when the plant is used as an amenity planting close to natural forest or riparian areas.
The technique that is most cost effective for smaller infestations is to pull or dig out and then mulch or compost the green waste.
For larger infestations, cut the main stems of the plant and immediately (within 15 minutes) liberally paint both cut surfaces with Escort at a rate of 5g per 1 litre water.
The waxy surface layer on ivy's leaves and stems gives it a high resistance to herbicide uptake. Spraying herbicide on ivy is therefore only suggested with reservations. The sprays suggested by the Department of Conservation include: Tordon BK (for spraying at a rate of 60ml per 10 litre with 10 ml of penetrant); Escort (at 5g per 10L water plus 10ml Pulse when using a knapsack, or at 35g per 100L water plus 100ml Pulse when using a handgun); or glyphosate (Roundup or similar at 1% plus surfactant).
Please, be aware that some chemicals are particularly nasty if used without caution, and spraying at higher concentrations than those suggested tends to burn off the leaves rather than translocating throughout the plant. The best time to spray ivy is at flowering. Spraying will need to be repeated.
Holly is a prickly tree which may grow up to 10 metres tall. It can invade forest margins and prevent natural regeneration. It tolerates both sun and shade: although semi-shade is preferable in midsummer, the more light it has the denser its foliage will be.
The most cost-effective control method is herbicide injection. Drill holes at regular intervals around the tree using a cordless drill, brace and bit or chainsaw driven auger. The holes should slope down into the sapwood. As each hole is drilled, squirt 1.5ml of undiluted Tordon Brushkiller or 20% glyphosate (2 parts glyphosate to 8 parts water) into the hole using a sheep drench pack with gun. If necessary, wait until the liquid subsides then apply the remainder. The best results are achieved during spring/summer, when the plants are growing most rapidly.
Another technique for controlling holly is to cut across the base of the plant with a straight flat cut and painting the stump with herbicide. The cut must be horizontal so that the herbicide rests on the cut area while being absorbed. Immediately apply a mixture of either 20% glyphosate or 20% Tordon Brushkiller to the cut stump using a paintbrush, eyedropper or small squeeze bottle.
Alternatively, the plant can be controlled by 'frilling'. With a sharp chisel or axe, make deep cuts into the sapwood at regular intervals around the base of the tree, taking care not to ring-bark the plant. Immediately apply 1.5ml of undiluted Tordon Brushkiller or Roundup to each cut using a paintbrush or a squeeze bottle.
I must highlight the need to be very careful when applying herbicides within covenanted areas as some herbicides, such as Tordon, are 'broad spectrum' and will wipe out most natives, especially podocarps, that they touch.
Some information provided is Crown Copyright; Department of Conservation. Other sources include:
Porteous, T; 1993; Native Forest Restoration; QEII National Trust (Out of print)
Morisawa, T. 1999. Weed Notes: Hedera helix L.
Open SpaceTM Magazine No. 53, December 2001 © QEII NationalTrust