By GEOFF MIERS
Citrus trees are highly productive food bearing trees that certainly deserve special care particularly over the summer months.
Pest and disease, inadequate water and nutrient deficiencies can seriously impact on the health of your trees and more so over the extremely hot weather.
Ants racing up and down the tree are a great indicator that some pest is active on the tree.
At this time of the year scale insects can become a problem. Scale are sap sucking insects that can be coated in a waxy white, brown, black, pink, orange or brown coating and appear as small raised bumps on the foliage or stems of the tree.
Scale deplete plants of important sugars and nutrients that can affect the trees health. Scale excrete a sticky sweet substance called honey dew that ants feed on. This sticky sweet substance can build up on the foliage and on it black sooty mould can grow.
Black sooty mould will spoil the trees appearance and can also affect the trees health as the black substance thickens it can literally block out the sun affecting the trees capacity to utilise the sun’s rays in the process of photosynthesis.
If the scale insects are controlled the sticky substance, sooty mould and ants will gradually disappear. To manage the scale spray with pyrethrum and a light application of white oil. Do not spray when temperatures are over 35 degrees.
If you use white oil in hot weather apply in the evening and wash off first thing in the morning to limit the potential for the white oil to burn the foliage. Spray twice over two weeks as you need to cover the scale insects as the oil stops them breathing and smothers them to death.
I must stress do not spray when temperatures are over 35 degrees and adopt the practice of spraying when the sun has gone down and washing the oil off before the sun has risen and is beaming down on the tree.
Ensure you do not allow mulch or leaf litter to build up around the trunk of the tree as this can create a warm, moist, humid environment ideal for fungal disease to grow.
This disease can literally ring bark the tree so to limit this happening pull the mulch back from around the trunk of the tree.
If this disease has eaten into the tree you will need to trim up any dead, lifting or cracked bark and paint the wound with copper oxychloride. This generally will kill the disease.
If you notice any splitting of bark on the trunk or branches then your tree may have a fungal disease called phytophthora cinnamomic. This pathogen has the capacity to cause the bark to split or crack, die-back and lift off the tree. If left untreated it can kill off main branches or even the whole tree.
Where splitting has occurred cut off the dead and lifting bark back to green wood and paint up the area with copper oxychloride.
Further to this treat the tree with phosphorous acid marketed as Yates Anti-Rot. This is a systemic fungicide and when sprayed over all the foliage of the tree it will travel right throughout the sap system.
You mix the chemical with water, add a small quantity of white oil or any wetting agent and spray the foliage over the entire tree. This will be absorbed by the tree and taken way down into the deepest roots as well as also up into the upper canopy of the tree.
Spray two to three times six weeks apart and this should overcome the problem and the tree will repair itself. Use the product at the rate of 100-150mls per 12 litres of water per mature tree.
With temperatures in the high 30s or low 40s watering becomes critical over the hot spring and summer months. A deep and thorough water every four days is necessary to help reduce water stress and limit fruit drop of next season’s crop.
One, two or three drippers on for a short period is not sufficient. You really need to water the entire root zone. The root zone can be found within the drip line of the tree, that is the area under the entire leaf canopy of the tree.
Watering is even more critical if citrus are being grown in containers as they can dry out quite quickly. Contemplate adding soil wetter or water crystals to help hold the moisture in the potting mix.
With some citrus carrying fruit over summer it maybe necessary to guard against fruit fly. Fruit fly can become a real problem as fruit become fully ripe or are over ripe.
Consider using Spinosad for the control of fruit fly in fruit and vegetables. Spray it onto the trunk of your trees, the foliage of even a timber plant or on a nearby fence.
Repeat this weekly or after rain while you have fruit or vegetables ripening and susceptible to attack from fruit fly.
The fruit fly will feed on the Spinosad and die. It’s best to keep the Spinosad off your fruit and vegetables.
Any fruit fly affected fruit that has fruit fly maggots should be placed into a plastic bag and baked in the sun to kill them off. Alternatively you can cut the fruit in half and placed into a container filled with water.
If the root zone of the tree is exposed to excessive sun it might be best to consider applying a layer of mulch under the tree being careful not to allow it to build up around the trunk of the tree.
Pea straw makes for a great mulch as it will help limit weed growth, will reduce water loss through evaporation and importantly isn’t over woody resulting in the loss of nutrients as the mulch breaks down. Woody mulch can result in “nitrogen draw-down” thus robbing the tree of necessary nutrients and in particular nitrogen.
Citrus trees can quickly become nutrient deficient particularly if the soils pH is high. When the soil is alkaline certain nutrients can be taken up by the tree. Best to take to your local nursery leaf samples and a small soil sample for testing.
The nutrient deficiency can be identified and remedial work undertaken without guessing.
If the soil pH is high then you need to work on lowering the pH. Once the pH is lowered increasingly nutrients will again become available to the tree.
PHOTO courtesy Pip Mcmanus.