SPECIES AND SPACING
There are several approaches about which species to plant and also the plant spacing and row widths to use.
A commonly used practice is to use a planting pattern of one Q. robur, two hazels, one Q. ilex. This is repeated down the row and the next row is off-set (i.e. one Q. ilex, two hazels, one Q. robur).
The most commonly used spacing is 3 metres between plants and 8 meters between rows. This works out to be about 400 trees per Hectare.
The theory of this set up is that the hazels will come into truffle production earlier than the oaks and eventually the larger oaks will fill the canopy over the Hazels. The hazels can later be removed as they fall out of production and this will reopen the canopy to allow entry of light.
A recent trend has seen many growers moving towards wider spacing between the trees (4 metres) to maximize winter light on the soil.
Some growers prefer to only use Oaks and not Hazels because hazels do require a little more pruning maintenance in winter. Alternatively it is possible to plant an all Hazel truffiére, with commercial nut varieties being pollinated by truffle colonised trees. Thus a return from a proper, uniform characteristic nut crop can be realised prior to truffle season. Contact us for further advice on this possibility.
In our own truffière at Gembrook we have included Quercus suber (Cork Oak) and are trialing a number of different planting patterns and spacings. We have also inoculated an extensive range of other oak species and are evaluating the degree of colonisation achievable and how the different growth characteristics can benefit future trial plantings.
Currently under trial are Q. pallustris, Q. cerris, Q. lobata, Q.faginea, and Q.coccifera.
There are a number of methods suitable for planting a small copse or hedge of truffle trees, even in a backyard, and a variety of trees available to create interesting landscape features or windbreaks. One such option would be a single oak, surrounded by hazels, selected to successfully produce hazelnuts.
Lime requirements can be easily met with bags and hand cultivation. Contact us for some suggestions.
In our dry Australian climate it will be necessary to provide irrigation to the trees. Oaks especially are hardy and once established can survive our long dry summers without irrigation. However we need to remember that we are actually growing a shallow root system with an attached fungus. The top 100 to 150mm top soil zone needs to have adequate soil moisture to prevent desiccation and deterioration of the mycorrhiza.
Generally while the trees are young, sprinklers with a small diameter are preferred to avoid water waste and excessive weed growth. As the trees grow the sprinkler size and throw capacity needs to be increased to water out to the “drip zone” of the tree. Sprinklers are available to accommodate this requirement.
Be aware that in summer exposed poly pipe can build water temperatures to a point that can be damaging to roots and of also any foliage that comes into contact, especially when the plants are still young. At Gembrook, all our poly-pipe main lines (40mm) and laterals (25mm) are buried underground to avoid heating of the water and protect the lines from mowing. When the plants are small the sprinklers (on stakes) are kept inside the tree guard to avoid wetting unneeded areas. Ideally, the distribution system should anticipate upgrade to higher capacity sprinklers in future (7-15 years), although this does need to be considered versus initial cost.
Some method of soil moisture monitoring needs to be employed to either trigger the automatic system or advise the irrigator of the right time to commence irrigation. Experienced irrigators can tell the moisture content of their soil by feeling it however more accurate measurements can be obtained using a range of soil moisture sensors. Significant water savings of up to 50% can result.
Some of the soil moisture sensors available include:
• Moisture blocks
• Neutron probe meters
• EnviroScan capitance probe
Some systems can be connected to computers which automatically switch on watering systems when soil moisture levels fall below an established level.
We can offer customers help in designing a suitable irrigation system, if required.
Any unchecked excessive weed growth around the truffle trees will rob the plants of moisture, nutrients and light and will affect tree growth. In the past Round-Up (Glyphosate) was seen as the best remedy for weeds. Round-Up is translocated within the plant and kills the roots of weeds and was thought to be de-activated in soil so not affecting roots. However, recently growers have been alleging that Round-Up may indeed have an effect on root growth and truffle mycorrhiza. Some growers are using Basta (glufosinate-ammonium) and are suggesting it may be a better alternative. It is a fast acting knockdown controlling a broad range of grasses and broadleaf weeds with less soil activity. Other growers are taking the organic approach, accepting the increased labour this entails.
The safest way to control weeds is either mechanical (pulling or slashing) or cultivation. If mowing is used to control weeds then a side throw mower should be used to direct the grass clippings away from the trees. Grass clippings and mulch will increase acidity in the decomposition process. Shallow cultivation (with spring tynes) can be used in early spring to increase soil air porosity (aeration) and check weed growth.
A brûlé is a marked area of ground around a truffle colonised tree that appears burnt. It is thought that the mycorrhiza produces phytotoxic chemicals that burn the weed’s roots. The brûlé is an indication that the truffle fungus is active and quite often signals the beginning of truffle production in the next few years.
Pruning is required in the formative years to develop a central leader and remove all side branches near the ground. Oaks are apically dominant and generally require very little pruning. The aim when growing the French black truffle is to produce a tree with a single trunk to about 1 metre high and then the foliage in an ice-cream cone shape. This allows easy access under the tree canopy for weed control, entry of light to the root zone, an even irrigation watering pattern and eventually access for harvesting of truffles.
Hazels produce many suckering basal shoots that need to be removed with either pruning or spraying with Basta in winter or early spring before bud burst.
PEST AND DISEASE CONTROL
There are several diseases that can infect the tree species we use for truffles, including powdery mildew, stem cankers, wood rots, spots and rusts. However care must be taken before using chemical control methods because of the possible affects on the mycorrhiza.
Many diseases can be less troublesome if preventative measures are used. Firstly watering only in the early morning so that foliage is dry at night and also not irrigating in the heat of the day can limit the spread of unwanted fungi.
Powdery mildew is one disease easily spread in a high humidity greenhouse and in the field when climatic conditions are favourable. Good preventative and hygiene measures can be successful in limiting the spread of this disease. Care must be taken with the use of chemicals however small outbreaks can be controlled with a spray of Milk (1:5 rate). Don’t allow any run-off onto the soil. The milk kills the powdery and is then broken down in sunlight.
Occasionally insect pests like aphid appear on new soft growth. These can be controlled using a garlic or pyrethrum spray. Various caterpillars can be controlled using pyrethrum or a biological agent “Dipel” which is a bacterium that kills grubs and caterpillars.