Aphids are one of the most common garden pests. They suck the life out of plants, by feeding on the plant’s sap. These pests attack almost all plants, including most food crops (except chives and garlic), flowering plants and fruit trees. It is possible to find them worldwide, but they prefer temperate areas. Do not use chemical pesticides to kill these pests since they may be resistant and you could end up killing beneficial insects instead.
What are Aphids?
These insects are part of the Aphididae family. There are over 4,400 species of aphids, but only 250 are destructive. These pests come in a variety of colors including black, green, yellow, white, red, pink and brown. They are quite small, about 1/8 of an inch long. Most of these insects are pear shaped, with long antennae and legs. They have a proboscis, which is a long beak used as a straw to suck liquid from plants. Some, like wooly aphids, appear to have a wooly or waxy coating like mealybugs. This is caused by a secretion they produce.
Adults are usually wingless, although most species have wings at some point and can develop them if necessary to maintain the population. They may move to other plants to find food if the population is too high, especially during spring or fall. These insects can be found in the bottom of leaves and stems. They won’t move, even if disturbed. Do not confuse them with whiteflies that jump, these insects can crawl and even fly but it is quite rare.
What do Aphids Eat?
These insects tend to live where they eat. Different species will eat different plants, but they are mostly found in fruit and vegetable crops, as well as flowers, trees and bushes. Some, like the potato aphid, only eat potato plants. While others, such as the green peach aphids eat peaches and plums, as well as roses, peppers, tomatoes, spinach, lettuce, carrots, corn and cucurbits. Lettuce root aphid is harder to spot since it will suck the root of the plant, causing the same damage as other species.
Aphids bite the underside of a leaf and eat the plant’s sap which is stored in the leaf. Small populations will not cause problems, but they can reproduce quickly. Larger populations will cause your plants to turn yellow, leaves to curl and wither. Black sooty mold will start appearing on plants, which is an aphid secretion known as honeydew. This black fungus will prevent the plant from absorbing the light it needs for photosynthesis and eventually die. Honeydew is a major problem since ants will come and feed from it. Ants will farm and protect aphids.
Aphids are carriers of disease that they suck from one plant and spread to the next. They suck toxins out from a plant, which can infect another when they feed. These insects live in colonies moving from one plant to another once the host plant is overpopulated or is dying.
How do Aphids Reproduce?
These insects don’t actually have to mate to have offspring. Most varieties produce live young, not eggs, except for the sexual forms. Female adults give birth to female nymphs, in a process called pathogenesis, in moderate temperatures where they can live all year. Those living in moderate climates need to be on top of controlling population numbers, since they reproduce quite rapidly.
Nymphs go through four stages of development, shedding their skin as they get bigger in size. In warm climates, they can grow to full maturity in 7 to 10 days. An adult nymph can produce as many as 80-90 babies per week. There are many overlapping generations each year.
Some species that live in colder climates produce sexual, winged forms during the late summer and early fall. After they mate, eggs are laid on the bottom of leaves of perennial plants. These eggs will not hatch until the weather is suitable, usually in the spring, when your garden gets an increment of aphid population.
How to Get Rid of Aphids?
Pruning and Spraying
Those that notice the presence of these insects fast can start pruning infected portions of the plant. Spray your plants with a water hose to knock these insects from the plant. This will also remove some honeydew. Do it daily until there are no more pests.
Insecticidal soaps are great at killing aphids, as well as other pests including mealybugs, soft scales, whiteflies, mites, earwigs, grasshoppers and others. You can buy insecticidal soap or make your own with organic liquid soap, which won’t harm your plants. Use a tablespoon of dish soap, a pinch of cayenne pepper and a quart of water. This soap will cover the bodies of the creatures so they can’t breath and suffocate.
Potassium salts of the fatty acids are the active ingredient of this alternative. For severe problems, try adding pyrethrins to the mix. This will also work for cockroaches, ants, and mosquitos. Apply weekly as needed. Do not use insecticidal soap at the peak of the day to prevent harming your plants. It is best to use it early or late during the day.
Isopropyl alcohol (also called isopropanol or rubbing alcohol) works fine to control aphids. However, ethanol (grain alcohol) seems to be better. Buy 70 percent alcohol and mix it in equal proportions with water. You can also add alcohol to the soapy mix to make it more effective. Test a small area of your plant before covering the whole plant since it can be sensitive.
Neem oil is quite effective in killing most insect pests. This oil will also coat eggs and smother them, having a similar effect in the adult population. Neem oil has antifungal properties which will clear up the black sooty mold caused by these insects, as well as powdery mildew. It also slows down the reproduction speed by acting as a repellent on the leaves and stems. Do not use sulfur based fungicides within a week of using neem, as these two products could increase plant burn.
This repellent is made of finely powdered shells from diatoms. Buy food grade diatomaceous earth that is completely harmless to humans and pets, but it is deadly to soft body insects that crawl over it. Sprinkle or dust it over the surfaces of plants to create a repellent barrier. Reapply after rain. Do not apply diatomaceous earth when plants are in bloom since it is harmful for pollinators.
This entomopathogenic fungus attacks many problematic crop pests, even resistant strains! Apply weekly to prevent reproduction of populations. This fungus can provide protection similar to chemical pesticides without the risks.
Sprinkle plants with flour (just like diatomaceous earth) to constipate these insects and keep them from staying. It also needs to be reapplied after the rain.
Sticky traps are a good alternative if you have ants, as well as aphids. They are very practical for use on fruit trees or woody plants. This can also work on roses, but it won’t work on softer plants or kill aphids. These traps will catch ants as they climb up stems and keep them from farming aphids or getting to the fruits. Cut the lower parts of the plant so they don’t reach the ground, providing easy access to ants. Be careful when using this method since it is extremely sticky and could cause problems for children or pets.
Silver colored reflective mulch can repel infestations, especially during the summer months of the year. This is quite beneficial for curcurbits, summer squash and other similar plants.
Frogs and Beneficial Insects
Frogs like to eat aphids and other garden pests such as cabbage loopers, cabbage worms and squash bugs. Encourage them to live in your garden. Beneficial insects can also eliminate and control this and other pests. Release ladybugs, since they love eating these insects. Make sure to release them at dusk or dawn since they will fly away during the day. Spray a fine mist of water on the plants before releasing them, because they will appreciate the moisture. There is still a possibility they will fly away eventually, but at least they will eat your pests before doing so.
Lacewing larva can eat up to 600 aphids before it becomes an adult. Parasitic wasps do not eat these insects, but they do consume other pests that may eat aphids and populate your garden. These wasps will keep the aphids for the lacewing and ladybugs instead of other pests. They can also put eggs inside an aphid’s body and kill the host.
Grow flowering plants such as marigolds, cosmos, sweet alyssum, yarrow, mint, dill, fennel, caraway and chives to keep beneficial insects in your garden. They also eat the nectar of these plants and would be more likely to stay if they can find food. Create insect houses to provide shelter for these good bugs.
Some plants will prevent aphids from living next to another plant. Garlic, chives and catnip are great repellent. Plant these species close to roses or other flowering plants that tend to attract these pests, as well as edible plants such as lettuce. Mustard and nasturtium attract aphids away from other plants.
These insects are attracted to plants with soft new growth. Avoid over fertilizing (these pests love high nitrogen levels) or over watering plants which will attract more pests. Maintain older plants properly to protect them. Younger plants can be grown under row covers, which can be removed when they start flowering for pollinating purposes.