How Do I Get Rid of Aphids on Petunias

Petunias a very prone to aphids infestation. They have a sticky foliage surface that aphids attach on and multiply. It is a very challenging situation for lovers of petunias. However, the good news is that you can successfully get rid of aphids on petunias.

There are three approaches very effective in getting rid of aphids on petunias. The methods include chemical control using insecticides, biological control using beneficial insects, and mechanical control. Also, prevention measures such as the use of a silver-like mulch and companion plantings aids in getting rid of aphids.

The effectiveness of the methods depends on the aphid’s population and how spread the infestation is. Do not use mechanical or biological control on a heavy infestation and expect good results.

Why do my petunias get aphids?

Are you wondering why your petunias attract aphids? Below are some of the primary reasons why your petunias get aphids:

  • Over-fertilization: High levels of nitrogen triggers vigorous, nutritious new growth that attracts aphids.
  • Over-watering: In the early stages, overwatering promote lush and healthy new growth, which entices aphid’s infestation.
  • Inadequate sunlight: Aphids evade sunlight. That is why they thrive well under the leaves. So, if your petunias have insufficient access to sunlight, they will be prone to aphid’s infestation.

Signs of aphids on petunias

  1. Yellowing of leaves

Aphids feed on the plants by sucking stem sap, which leads to the yellowing of leaves. Damaging of stems interferes with the transportation of nutrients and water to the leaves. Lack of enough nutrients, especially nitrogen and water, causes the yellowing of leaves. Also, aphids multiply at a fast rate, completely covering the leaf’s surface. This limits adequate light penetration for photosynthesis. Even plants that receive less light, their leaves start yellowing.

  • Stunted growth

Aphids feed by sucking plants sap directly from the phloem. This leads to the curling and yellowing of leaves, which distorts the plant’s growth rate. Also, aphids release a sticky substance, honeydew, which attracts the growth of sooty mold fungus. The fungus reduces the photosynthetic ability of your petunias. With the lack of enough food, water, and energy, your petunias will grow at a slow rate.  

  • Mold fungus

Aphids consume a lot of sugars and liquids from the plants than they need. After digesting what they need, they excrete excess sugars and liquids as a sticky substance known as honeydew. Honeydew covers the plant’s surface where aphids are feeding on and hardens fast, forming a protective sheath-like layer. A black mold fungus develops on the plant’s surface, reducing it is photosynthetic ability.

  • Curling of leaves

Curling of leaves results from lack of enough fluids to maintain their rigidity or leaf tips sticking on the sticky excretion – honeydew. Curling of leaves reduces the photosynthetic ability of the host plant leading to stunted growth.

  • Gall formation

Aphids are notorious insects for forming galls in petunias in late spring and summer. Gall formation occurs in late spring during the stimulated growth period of new growth – leaves, stems, and leaves. Aphids damage petunias by feeding on their sap, and their secretions increase the production of normal plant growth hormones. High production of growth hormones leads to increased cell sizes and numbers. The abnormal cell growth is galling.

How to Get Rid of Aphids on Petunias

  1.  Chemical control

There are three ways you can use a chemical control method to get rid of aphids:

  1. Insecticidal soap

The approach of using insecticidal soap is beneficial when it comes to managing aphids on petunias. Insecticidal soap controls aphids and also washes away fungus without adverse effects to your petunias, beneficial insects, and the environment. Insecticidal soap contains fatty acids that destroy the structure of the insect’s cell membranes. The cell contents leak from the damaged cells, killing the aphids quickly. Here is the procedure of using insecticidal soap:

  1. Mix ivory liquid soap with warm freshwater in a ratio of 1:1
  2. Add one cup of oil such as vegetable, soybean or peanut oil et cetera.
  3. Put the mixture in a sprayer and sprinkle on your petunias early in the morning or evening to maximize effectiveness.
  4. Spray the affected petunias thoroughly but not to the point of runoff.
  5. Repeat the application weekly to kills all the aphids.
  • Oil insecticides

Oil insecticides, either using neem or horticultural oil, are very useful when it comes to getting rid of aphids. Here is the procedure of using the oil insecticide approach:

  1. Mix 2 to 5 tablespoons of either neem or horticultural oil with 1 gallon of water (regular watering can).
  2. Spray the topside and underside of the petunias leaves.  
  3. Repeat the spraying weekly until your petunias are free of aphids.
  • Systemic insecticides

This is not the best treatment approach for your petunias as it kills even the beneficial insects which aid in controlling aphids. But, in case of a heavy aphid’s infestation use of systemic insecticides is the most appropriate method. Here is the procedure of using systemic insecticides:

  1. Add systemic insecticides that contain either azadirachtin or pyrethrin in spraying can.
  2. Spray your petunias thoroughly.
  3. Spraying petunias with insecticides kill even the beneficial insects. So, after spraying, purchase a batch of beneficial insects for your garden.
  • Biological control

The use of beneficial insects (natural enemies) is the effective biological method of getting rid of aphids. Beneficial insects such as parasitic wasps, ladybeetle, syrphid fly, and lacewings are very effective in controlling aphids. The predators feed on the aphids suppressing their numbers from the start. Parasitic wasps parasitize aphids by laying their eggs inside them. The parasitized aphid’s skins turn crusty and golden brown, a form known as a mummy. After the formation of mummies, the aphids are likely to reduce significantly within 7-14 days.

  • Mechanical Control

Mechanical control is an effective way of controlling aphids. There are two ways you mechanically eliminate aphids:

  1. Rinse them off the leaves of the host plants: Use a water hose and nozzle with enough pressure to knock them off the plant’s foliage but not damage the plant.  After washing them off the plant, aphids cannot climb back to the plant, and as a result, they will starve to death. This is effective for a large population of aphids.
  2. Rubbing aphids off the plant using your fingers or a wet cloth: This approach is practical for a small population of aphids and at the early stages of infestation.

Prevention

  • Using eggshells: The edges of crushed eggshells make several cuts on the aphid’s body, dehydrating them, and eventually death.
  • Avoid over-fertilization: High levels of nitrogen promote succulent, nutritious new growth, which attracts aphids. Use small amounts of fertilizers throughout the growing season to reduce the chances of an aphid outbreak.
  • Use a reflective silver mulch:  Aphids hide beneath petunias foliage to evade predators and sunlight. Using a silver mulch increases the amount of solar energy reflected onto the leaves. This scares off aphids.
  • Companion planting: Some plants repel aphids such as catnip and nasturtiums. So, interplant them with your petunias to keep away aphids.  
  • Avoid overwatering: Overwatering promotes healthy and soft new growth, which attracts aphids. So, give your petunias just enough water to thrive well.
  • Plant your petunias in full sun: Aphids thrive well in the absence of enough sunlight. So, to prevent your petunias from aphid’s infestation, plant them in full sun.

References

  1. University of California, Agriculture and Natural Resources: Aphids Management Guidelines
  2. University of Connecticut, Home and Garden Education Centre: Insecticidal-soaps