What makes plants vulnerable to aphid attacks?
Written by
Liu Xiaohui
Reviewed by
Prof. Charles Hartman, Ph.D.Aphids are attracted to certain weaknesses in plants. These potential weaknesses include new, nitrogen-rich growth, which provides a nice, soft feeding area. Secondly, low air movement leads to a humid condition, which is also comfortable. In my garden, I have observed that stressed plants tend to attract more pests than healthy ones.
Growth Conditions
- Excess nitrogen fertilizer promotes succulent growth
- Rapid new shoots lack protective compounds
- Dense foliage creates humidity pockets
Environmental Stress
- Drought weakens plant defenses
- Overwatering causes root stress
- Temperature fluctuations increase susceptibility
Garden Design
- Monoculture planting simplifies pest spread
- Lack of companion plants for natural protection
- Insufficient space between plants
A significant increase in risk is caused by nitrogen imbalance. Plants that are growing well send off stronger chemical signals. In turn, aphids will detect these signals at some distance. To mitigate what I believe to be a risk during high summer seasons, I reduce the use of fertilizer. Instead, I use a slow-release fertilizer that prevents sudden growth surges in the plant.
Inadequate air circulation can create ideal conditions for aphids to breed. Plants should be spaced 18 to 24 inches from one another. Additionally, prune the inner branches regularly. I've seen my roses improve considerably after thinning canes that were crowded together. Good circulation will dry up honeydew deposits that attract more pests.
Monoculture planting makes aphid infestations easier. They move around from one plant to the next if they are all the same type of plant. I interplant garlic with roses and basil with tomatoes. Various species can complicate a pest's work and can provide shelter for beneficial insects. These small nuances minimize a pest's ability to spread from plant to plant, as a natural barrier is introduced to the area.
Drought stress weakens the plant's defenses. A deficiency of water or an abundance of water will cause problems. To water, I continue to water deeply three times a week, early in the morning. I used mulch to help hold the moisture consistently. Healthy plants produce naturally occurring repellent-like properties that deter aphids quite well.
Strategic companion planting helps to protect delicate plants. For example, mint planted in proximity to cabbage helps repel aphids. Marigolds defend tomatoes. I also use garlic borders around my roses. Such companions can mask appealing scents while also providing shelter for beneficial predators, helping to combat pest problems.
Read the full article: How to Control Aphids: Proven Methods Guide
