Mediterranean Plant Pests and Diseases

Summer is the time when a Global Plant Doctor will start to see an accumulation of pest and diseases hidden in our gardens, either they have been dormant over the winter months, or we simply find that new pests appear this year because of several factors. The major reason why we have an abundance of pests and diseases, more so in Mediterranean countries rather than the colder countries is because of the much higher temperatures – beginning mid April and carrying on through the summer into late December.

Plant pests and diseases love to find shelter in dense perennial plants, shrubs, conifers, hedging and climbers, the denser the plant and the less aeration the more the adequate an environment is established for the pests to breed. And they will breed much more quickly if there is no rain or wind to be able to blow the pests away. Once they are able to get inside the foliage and reproduce they will breed ten times quicker if they are left without disturbance such as wind, rain, or aeration. And as you will discover there will nothing that you can do to get rid of them, except of spraying with toxic chemicals and sometimes this is worse than the pest itself, causing non-evasive, non-predators to suffer. This is why it is vital that at this time of year to really start to take notice of your plants. Try to spend at least ten minutes in your garden throughout the summer months to identify any changes in the colour, health and condition of your plants. It’s easy to do, here’s a few tips – try to get down close enough to the shrub, tree or flowering plants so that you can study the leaves underneath, as well as above of course. If your shrub, bush, tree or conifer is dense, separate the foliage and look deep inside the centre of the plant to discover if there are any signs of unhealthy change. There are particular signs that can be recognised with each plant pest and disease to look out for – try to identify and diagnose the problem yourself. For instance, at this time (mid to end of April) a particular pest, commonly known as cuckoo spit is found. (We can see this pest in the UK quite often). It is a small pest known as froghopper, it’s scientific name is Philaenus spumarius. It encircles itself with something that can only be described as something that looks like spit. The symptoms that you will see with these pests are severe distortion of the leaves causing them to curl up and become deformed, sometimes even, before they have had chance to develop into a full leaf. The spit is made from a small greenish adult hopping-type insect which creates a cocoon of spit around it’s small cuckoo spit larva, created by the sap of the plant leaf. There are no safe chemical controls for this pest. The safest, more organic method to get rid of the spit is to spray the completely infected plant with a hosepipe – very lightly on top of the leaf and under the leaf. However, you must hose the plant in the evening when the weather is cooler. If the plants get wet in high season, the sun will scorch the leaf so avoid spraying in the daytime and only spray early evening. The other major problem that occurs in Mediterranean countries is a pest called Leafminer. This is usually seen on Citrus trees – a bit later in the year but if it is left unnoticed it will damage the blossom of Citrus trees so it must be controlled before it can take hold. The symptoms are a seen by a small mining line that mines through the leaf of the citrus plant and if severe enough eventually causes the leaf to become distorted. You can tell this is Leafminer (scientific name Phyllognistis) because it creates this distinct mining effect, just like someone has drawn a thin uneven line through the leaf. For an organic prevention and to prevent this insect from damaging the new blossom and leaf growth for the new spring season try to place sticky traps on the trees early on in the season or prune the tree from the previous seasons growth and keep an eye on the tree in case you see new signs of damage in the next year’s leaf growth. Try to avoid using a systemic insecticide – although in some cases, if the symptoms are severe enough this is the only solution.

Another very important pest that occurs on orange trees, deforming the fruit, is the Mediterranean Fruit Fly, (Ceratitis Capitata). The fly lays their eggs in the fruit and then the eggs hatch into larvae. The symptoms can be seen on the face of the oranges showing small black dots. The fruit drops into the soil, the larvae then create a new generation of fly. It can reproduce up to 6-8 generations per year therefore your fruit is always under threat. The best biological control for this is, again, sticky traps placed early on in the season before the fly begins its adult stage. These sticky traps are safe and can be found in most agricultural stores.

The longer you leave pest problems, the more severe the damage to the plants – sometimes you will find you will need to replace the plants if the damage is too severe. Going back to the reason why we accumulate more pests in Mediterranean countries – it is simply this. We have abundance of much higher heat levels allowing for the ability for insects to breed more easily, and coupled with this, less rainfall and less aeration circulating through plants and we have the perfect environment for pests to breed. Any dense-foliaged plants will be a pleasure for any new pests arriving to find a nice home, and allow them to settle down and breed ten times quicker than they would, say in any other cold climate.

One of the most consistent problems in Mediterranean countries, especially in protected and sheltered gardens, is the pest, the red spider mite (scientific name tetranychus urticae). This is a very tiny red spider, so small it cannot be seen with a naked eye. You need a microscope to diagnose the problem. The obvious signs, is the mottling effect that can be seen on the upper side of the leaves. The leaves will turn from a lovely green colour to a milky, faded grey colour. This is because the damage from the spiders sucking the sap is so small it’s like thousands of tiny pin-pricks all over the leaf and when the leaf is full of these pin-pricks it looks like the colour of the leaf has faded. If the damage is too severe, it can eventually kill the plant.

The other, very obvious sign shown under the microscopic is mass webbing on the plant. If you have a plant with dense foliage i.e. mostly conifers and flowering shrubs etc. then look closely into the foliage and you will see a matt of dense webbing, similar to the webbing found on larger spiders webs. If the webbing is quite dense then you need to act quickly. There are two methods to prevent the pest spreading, one is a biological approach which is much more safe for the environment, the other is a chemical control.

If you use the chemical control you need a contact insecticide which will kill the pest, but to prevent its reoccurrence you need a systemic insecticide. If you are going to use chemical methods as a long term cure, you must be aware that red spider mite is becoming resistant to some chemicals, therefore using this on a long term basis is not recommended. Please always contact your Plant Advisor, Plant Doctor or Garden Doctor if you are using chemical controls.

The other biological methods are much more safe, both for the animals and for the environment. The first technique uses another, predator spider mite called phytoseiulus persimilis. If this spider mite is placed with the pest spider mite it will devour the pest spider mite and also breed at the same time, so therefore reducing the possibility of the pest reoccurring in the garden. You will not find this spider mite in gardens in more cooler climates. The spider mites need hot, dry conditions to breed out of doors. However, if you are growing plants or vegetables under glass or polythene tunnels you will most likely find this pest breeding if the conditions are adequate, in other words if the glasshouse or poly-tunnel is warm and free from aeration.

Finally, if you would like to find a much safer and organic approach with instant relief from this pest problem, try hosing your plants with a fine rose spray to remove the pest in the evening – after sunset. Evenings are much more suitable and prevent the leaves from scorching once wet. Spray late at night, when it is cooler. However, my own method to prevent this pest from breeding, and should be used as a method to remove all pest and disease issues in the summer months is to prune all of your flowering plants and shrubs back on a regular basis. Prune all flowering shrubs hard back to the last green tips every 3 months. And because plants grow ten times quicker in Mediterranean countries it is also a means of keeping your plants healthy and happy and flowering for many more years to come.

Need some plant advice? For more details, pest and disease advice or plant ideas for your own individual garden conditions – please contact me on the home page or write to me at the plant diagnostic service contact home page

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