What to do this week –By Mark Govan, Host “Florida Gardening”
In my last article I covered several of the diseases affecting citrus trees and the proper care you must perform to prevent these diseases from limiting your citrus crop. Because many of the diseases I mentioned last week can be easily confused with insect problems, I would like to continue with the citrus theme in this article and give you some easy identification clues which will help you to identify insect problems. Some of these insect problems will require specific control times, so get your calendar out and make notes of treatment times to ensure you get the most out of your citrus trees. Once you are able to distinguish these different problems you will be able to make an educated decision on how and when to control these pests. Again, because there is so much information to go over, I will save another section on citrus called Citrus Disorders until my next article.
Citrus Rust Mites or Phyllocoptruta oleivra are extremely small insects that can not be seen with the naked eye. This makes control difficult because you can not see the symptoms until after the damage has been done. Symptoms of this pest include a dull brown color of the fruit instead of the bright orange color you expect. Citrus rust mites feed on oranges as they develop on the tree. Most damage occurs as the fruit becomes pea sized. Late March and April is when the mites are most active and control is recommended.
Mites feed on the developing fruit by puncturing the epidermal cells of the newly emerged oranges causing the fruit to take on a brown or dull brown appearance. This discoloration is usually more prevalent on the sunny side of the fruit. Mites like the heat of the sun so this is the primary side of the fruit that is initially infested. Once the injury has occurred, your oranges will not change color back to their normal appearance. Even if you take control measures at this point, the fruit has already been damaged and you will unfortunately have brown colored fruit. Even the leaves on heavily infested trees can be affected taking on a speckled appearance and eventually falling from the tree. You can distinguish citrus rust mite damage on the leaves from Melanose damage because the leaf will be smooth not rough as when damaged by the Melanose fungus I went over in my last article. This is why control of this insect must start as the fruit achieve pea to marble size.
Control of rust mites and the following insects below is achieved through regular routine bi-monthly spraying of your citrus trees with Malathion and Oil spray mixed together. This product is available in concentrated form with both products mixed together or each can be sold separately. If you purchase these products separately, you will need to read the label on each product and mix your spray canister accordingly. Make sure you use all the spray you mix in one application as the product, once mixed with water will begin to break down and lose its effectiveness.
Spray your trees in the early morning hours after you have heavily watered your trees the night before. First spray the trunk of the tree, then the branches, next spray the underside of the leaves. Once you finish spraying the underside of the leaves you will need to spray the upper side of the leaves and fruit. Make sure to work in a circular motion around the tree to cover the entire tree. Do not use high pressure spray like the dial-a-matic sprayers as you may knock off some of the developing fruit and you may have a tendency to over-apply. Trees with ripe fruit may be eaten in seven days after application as these products will not penetrate the fruit.
Aphids or Homoptera aphididae are another problem we must deal with. Aphids damage new foliage by piercing the tender new growth with their mouthparts and sucking out the plant juices causing a deformity of the leaf. Leaves infested with aphids tend to curl up on themselves giving the feeding pests shelter to continue their damage. Many of these new leaves will be stunted. As the aphid feeds, they excrete honeydew. Honeydew is a sticky substance which ants prefer to feed on. Many ant species will actually protect these aphids from predators and will carry them to other areas of the tree to continue feeding and produce more honeydew for the ants. This is the main reason you may see ants running up and down your citrus tree as they take food back to the colony.
Another problem related to the feeding of aphids is called sooty mold. Sooty Mold or Capnodium citri looks like someone has painted the leaves of the citrus black. As the aphids feed on the upper leaves, their excrement falls on the leaf surfaces below. Sooty mold grows on this honeydew producing a black film over the leaf and fruit surfaces. If you run your finger over the top of the leaf surface, the sooty mold will peel off the leaf leaving behind a shinny leaf. If left on the tree, sooty mold can reduce the amount of light the tree receives thus interfering with the natural fruit production of the tree. Both scales and aphids produce the honeydew which sooty mold grows on. Control is best achieved during April, June, and August.
Malathion will help kill the aphids and scales however; some scales have a waxy coating shielding their bodies. This waxy coating must be broken down in order to kill the scale and the horticultural spray oil will accomplish that task. Horticultural spray oils break down the scales waxy coating allowing the Malathion to kill the adult scale and its eggs. Horticultural oils also work on the sooty mold problem. One the oil is applied to the tree, the oil works its way under the sooty mold eventually dislodging it from the leaves surface. This process is not immediate. Usually the sooty mold will break down slowly over a period of several weeks gradually flaking off the tree.
There is another pest of citrus which can strip large sections of leaves from the tree in a short period of time. This pest is called the Orange Dog Caterpillar. This large caterpillar is camouflaged to look like a fresh bird dropping, black and white. During the day this caterpillar rests on the branches somewhat concealed from view making them hard to spot. In the early mornings or late afternoon they can be seen munching on the new growth.
The adult stage of this pest is the Giant Swallowtail butterfly. This large black butterfly with yellow stripes on its wings can be seen fluttering around the citrus trees eventually depositing translucent eggs on the new growth. Within several days the eggs hatch and the larval stage of the butterfly emerges and promptly goes to work eating the tender new growth. Damage at this stage is minimal but these larvae have only one desire, to feed. As the caterpillar grows, their appetite increases eventually devouring not only the new tender growth but also the older leaves. Look for leaves partially devoured or complete stems stripped of their leaves. Small trees can be killed so check them often.
One of the interesting things about this particular caterpillar is the defensive characteristics they possess. When disturbed, or when pressure is applied to the head area, this caterpillar shoots out two long red glands which emit a fowl smell. Although harmless to you or me, this odor can kill or turn away certain predators of the orange dog caterpillar. Even though some pests may look interesting, they are still pests and need to be removed from the tree. Control these pests in May, late June, and August.
There are many other pests I could not fit into this article but I try to give you the information on the most challenging pests we normally see. This article should help you identify these pests and treat them accordingly. Remember to mark your calendar and get your trees on a routine spray schedule before one of these pests gives your yard a visit. Enjoy your trees and remember, without plants we would not be here!