VELVET TREE PEAR (Opuntia tomentosa) is a native of Central Mexico. The story behind its introduction into Australia in the late 1800s is not known, but it would be safe to assume it was brought out here as a garden plant and/or emergency stock fodder.Velvet tree pear is now locally established over thousands of hectares of northern inland New South Wales and southern/central inland Queensland.
There has been a continued and very significant increase in velvet tree pear numbers over the past couple of decades. Although officially a declared noxious weed it has been generally ignored by many landholders because (a) there are other, more serious cactus species in these same areas, (b) the high cost of chemical treatment and (c) velvet tree pear has some limited value as supplementary fodder during dry times.
Plants eventually grow into large trees, often up to 5m high. Velvet tree pear produces massive numbers of fruit. Great food for the birds who continue to spread the seeds over greater distances. And, what seed is not removed, falls to the ground to germinate when ready.
There is more of an urgency now to deal with this plant. Groups of plants become so thick they shade out useful grasses and native flora. And, this noxious weed is very “high-profile”: not a good look for property management or land values.
Most dominant feature is the actual size/height of the plant. It grows way beyond the height of normal, common prickly pear. Young leaves are shiny but take on a “velvety” appearance as they mature. Flowers are a beautiful orange/deep red colour (image #5).
CONTROL METHODS – biological and/or chemical?There are effective herbicides available. This mode of treatment is certainly recommended for small and/or isolated infestations, or in areas where cochineal has proven to be a failure (eg climate too cold, timber too thick to allow sunlight through, local types of ant species that prey on cochineal insects). On the debit side, chemical treatment can be expensive, hard on the environment, and certainly never-ending. A long-term biological control program is certainly worth considering!
(1) BIOLOGICAL CONTROL A very useful biological control agent is available for velvet tree pear – the cochineal insect Dactylopious opuntiae. It attacks both velvet tree pear and common pest pear (Opuntia stricta spp). This cochineal insect is already established – in varying degrees – in most tree pear areas.
But – they need a hand! Cochineal insects don’t get enough credit for their ongoing control work. People notice the healthy, large pear plants and dismiss the cochineal as being useless. What they don’t notice is the work happening on the ground – the leaf fall and the way the tiny cochineal insects continue to find and destroy thousands of new seedlings… With our help, the cochineal insects can also be effective on large plants!
GETTING A BIOLOGICAL CONTROL PROGRAM STARTED
Cochineal insects can do a lot of good work. BUT, the young, tiny insects (<1mm – see image #6) have limited mobility and sometimes need to be manually transferred into new areas and/or isolated plants. This process is as easy as collecting some infected plant material from one spot and dropping it off in a new patch. The tiny, newly-hatched “crawlers” can only travel 3-4 metres on their own. Thick ground cover hinders them, and cracked ground (eg black soil country) is fatal because they can drop into the cracks! The tiny insects travel best on hard, reasonably bare ground. Sometimes the tiny, newly-hatched “crawlers” are picked up and scattered by
strong winds, and (if their luck holds) they’ll land on or close to plants in totally new areas.
The key to increasing insect populations is in providing them with some protection from the elements. Simply cutting down or pushing over the infected plant creates a better environment for the insects. The new cochineal colonies will have a “roof over their heads” and will be less disadvantaged by heavy rain or extremes of heat.
FELLING COCHINEAL-INFESTED TREE PEAR DOES TWO (2) VERY IMPORTANT THINGS:
(1) it severs the plant’s own food supply, thereby reducing the plant’s resistance to the effects of the tiny cochineal insects, and
(2) most importantly, it provides a sheltered environment (the underside of the leaves) for the cochineal insects to flourish in. After the insects are established on the plant itself, the biocontrol program will be further enhanced by cutting some of the main plants down (about 300mm above ground level). Bow saws, chains saws, brush-cutters or better still, pole chainsaws, are the “weapons of choice”. (Gwydir Shire weeds officers also take this process one step further by immediately spraying the butt with a “Grazon-type” mixture – works great: no regrowth from the butt). Even pushing infected plants over with a tractor or 4WD can be effective – and the plants are easily injured in this process.
Biocontrol is a long term plan – try knocking over small areas of infected plants at a time rather than going “all out”. Creating and monitoring these “nurseries” will be a guide to how (and when) the insect numbers are on the increase – they will also be a reliable source of insects for distribution to other areas where there are needed. (NB – cochineal doesn’t work as well in heavily shaded areas – try and pick nursery sites where the plants get plenty of sun.)
It’s important to note that plants really need to be showing reasonable insect presence before they are cut down. Too few insects will not be enough to impact on the plant before it starts re-growing – and it surely will! (Two growing cycles each year: October and February.) In these situations infected material from other plants should be added to boost the numbers.
When cutting plants branch by branch, try and drop individual branches on top of each other around the base of the plant. The less plant material actually touching the soil means less material to take root and start growing again. Similarly, pushing plants over on top of each other and onto rocks/logs also minimises their contact with the soil and their ability to quickly take root.
When cutting plants off near the butt, try and throw or push some of outer pieces back onto the main part of the plant. This helps to reduce the incidence of plant parts liable to take root in good soil. Not so important on the hard, red, ridge country where a lot of our velvet tree pear tends to grow. Velvet tree pear is nowhere near as hardy as common pest pear – most of these broken-off pads will not survive anyway on hard ground.
MAINTAINING SUPPLIES OF BIOCONTROL AGENTS FOR THE FUTURE?
Velvet tree pear will always survive and this does have its positive side. Tree pear serves as a “bank” for the ongoing presence of cochineal, the same cochineal that also helps to control the more aggressive common pest pear. And, also of great importance, the velvet tree pear will always be an option for desperate cactoblastis moths unable to locate their favoured common pest pear on which to lay their eggs – the young leaves and seedlings of velvet tree pear are soft enough for the young cactoblastis to enter and eventually complete their life cycle, thus paving the way for their next generation (photo, left, shows hollowing-out of tree pear leaves indicating current or recent cactoblastis activity).
While cactoblastis larvae can demolish thousands of young tree pear seedlings in some seasons , they have zero impact on large plants because tree pear contains tough, fibrous material and the grubs, literally, can’t “chew their way through” the plant.
Also on this website: two new pages on velvet tree pear one covering results of trials on (1) Peates Road near North Star and (2) herbicide treatment results – velvet tree pear on the property “Baree”, North Star.
Chemical treatment of velvet tree pear is effective. The plants are easy to find, but the work can be very costly because of the volume of herbicide needed to cover the plants. According to NSW DPI’s excellent booklet “Noxious and Environmental Weed Control Handbook 5th Edition“, and other sources, herbicide treatments include:
|Triclopyr 600 g/L eg Garlon 600®||High volume 3.0 L + 500 mL Uptake spray oil in 100 L water or knapsack application 300mL in 10L of water plus 50mL Uptake spray oil OR 1.0 L in 75 L diesel
(800 mL/60 L)
|Apply to actively growing plants – see APVMA permit PER 14442 for more details (in force 23 October 2013 to 30 June 2018 – NSW only).
[Editor’s note: Water-based sprays are very slow acting (>12 mths) but this can be an advantage if cochineal insects are present; the adults will persist and continue to produce offspring; the new insects will help to control re-growth and the inevitable new plant seedlings… Les Tanner – 2/10/2011]
|Triclopyr 300 g/L+ picloram 100 g/L eg Grazon DS®, Ken-Zon® etc
Triclopyr 300 g/L+ picloram 100 g/L + aminopyralid
|High volume: 500 ml Grazon® (or equivalent)+ 500 mL Uptake® spray oil in 100 L water
Knapsack application 50mL in 10L of water plus 50mL Uptake® spray oil
(Important to use spray oil or similar to help the spray “stick” to the leaves)
|Triclopyr + Picloram eg Access®||1.0 L in 60 L diesel||Apply thoroughly as a foliar spray|
|Amitrole + Ammonium thiocyanate Nufarm Amitrole T®||1mL injected into cuts at 3cm spacings around lower trunks of mature plants||Tree pears may take up to 12 months to die. Re-spraying may be necessary in some cases.
Registered for use in Qld only…
|Apply a mix of 1 part Amitrole T in 25 parts water liberally to small plants and regrowth||Tall plants may be lopped before spraying. Apply the spray liberally over the entire plant and on adjacent soil.
Registered for use in Qld only…
|You might also like to check the latest results and comments on BRG-CMA tree pear trials commenced in April 2013? Info supplied by North West Weeds: “Baree” North Star herbicide trials also Peates Rd herbicide and biocontrol trials near North Star which have been comparing chemical and non-chemical treatments – LRT 23 Mar 2016|
IMPORTANT: USE OF PESTICIDES – ALWAYS READ THE LABEL
Pesticides must only be used for the purpose for which they are registered and must not be used in any other situation or in any manner contrary to the directions on the label. Never use a herbicide in any way contrary to the label recommendations.
DISCLAIMER: The information contained in this web site is based on knowledge and understanding at the time of writing. However, because of advances in knowledge, users are reminded of the need to ensure that information upon which they rely is up to date and to check currency of the information with the appropriate officer of North West Weeds or the user’s independent adviser. Les Tanner 15/07/2015