By Island County Extension Agent, Donald B. Meehan
THE YEAR OF THE APHID
Each year it seems like I encounter an abundance of one particular plant problem more than others. This year seems to belong to the aphids and fungal diseases. I thought I would address the aphid problem in today's column and wait until this fall or winter to discuss the key fungal diseases that have been most prevalent.
Aphids or plant lice are soft-bodied insects that come in all colors. Usually they are pale green, but can be brown, black, yellow and even pink. They range from 1/16 inch long to 1/8 inch. They feed on plants by inserting a hollow stylet into the plant tissue to draw out the sap. Some inject a toxic substance into the plant. The common result is that plants are weakened by a heavy infestation of aphids.
Aphid damage is fairly easy to recognize. If the leaves of your favorite fruit tree or deciduous shrub are curled up, mis-shaped or twisted, you can almost bet that aphids caused the damage. This type of damage frequently occurs when the new leaves are just starting to break out of the bud.
When wet spring conditions come along, such as we had this year, large populations build up quickly. Once a large population is established and favorable weather conditions continue, serious attention to the problem is required.
Aphids are often host plant specific. In other words, aphids that attack one kind of plant group may not attack a different plant group. For example, aphids found on fruit trees are not likely to ever be found feeding on spruce trees, and vice versa. Some aphids will have several host plants they prefer and others may only have one.
Like most other living things in our environment, aphids have their place. They provide honeydew for ants to feed on and unfortunately to drip on our cars. The honeydew also acts as a food source for fungus as well. Many shrubs that are covered with a black, sooty mold have become covered with honeydew which allows the fungus (mold) to grow. This is generally not harmful to the plant and will go away once the aphid population drops off in the fall.
Aphids are a serious problem in transmitting plant viruses. This problem is most common in strawberry fields and home gardens. Garden peas which are planted too early are often attacked by aphids carrying the pea virus.
It is worth mentioning something about the life cycle of aphids. Understanding this important aspect will help you to better control aphids and to recognize favorable conditions.
Aphids will typically winter over as fertilized eggs on some perennial plants. Some do so on remnants of vegetable plants. When the weather warms enough, small nymphs hatch out. These nymphs grow quickly to full size. They never develop wings. These first season aphids are called stem-mothers. They provide the nucleus for a large population build-up. They are all females and do not need to mate to reproduce. All of their young are born alive, unlike themselves. This second generation can reproduce similarly without mating and bearing live nymphs. Only a week or so is needed from the time they are born to give birth to the next generation. Each can produce 50-100 more nymphs. During this period of population growth, all or some of nymphs can develop wings and fly to other plants. Some will fly to similar host plants and some will fly to their summer host plant, usually an annual.
As cold weather approaches, a new generation is produced of winged males and winged females. The winged females give birth to nymphs that mate with the winged males. These female nymphs will then lay 1-4 eggs which have been fertilized. The eggs may be laid next to a stem or bud awaiting the warm spring weather. This life cycle is considered the standard and one can expect some variations to it.
It is clear from reviewing this life cycle that the most crucial time to control aphids is at the beginning of the life cycle or the stem-mother generation. Once winged forms are created, control becomes more difficult.
Because weather can be a major determinant in the number of generations created, it pays to pay attention to weather conditions so you can predict population build-up.
What alternative does a person have to keep aphid populations low? First and foremost is an early detection program. If you are not out inspecting your trees, shrubs and vegetables for aphids at the very beginning of the season, you've already lost the first battle. Second, once you have detected aphids you can control them by hosing them off, smashing them between thumb and forefinger or spraying an insecticide on. I prefer the hosing or smashing method. You'll find that the adoption of those two methods makes you a lot more aware of your plants, saves you money and eliminates any risk to the environment from chemical sprays. Should you chose to use an insecticide, it is important that you use the correct one for the kind of plant you will be applying it to. Malathion and Diazinon are both acceptable for food plants. They will also work well on most ornamental plants also. Both of these insecticides need to be applied at the proper rate. That rate can best be determined by reading the label on the pesticide container.
Most people fail to read the pesticide label thoroughly. It is a legal document approved by EPA. If the plant you want to spray is not listed on the label, you should look for another source of insecticide.
If you have questions about applying an insecticide contact me or any of the Island County WSU-Master Gardeners for advice. Several publications are available to purchase from our office that cover chemical control of garden pests, fruit and berry pests and ornamental pests. They can be obtained by contacting us by phone (679-7327 or 321-5111, ext 327). We will mail them to you.
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