The size of a pinhead, aphids are tiny insects that feed on plant sap. They belong to the family Aphididae, order Homoptera, and are known as plant lice, greenflies, or ant cows. Most species have cornicles on their abdomen. Aphids can cause significant damage to plants by stunting growth, producing plant galls, transmitting plant viruses, and deforming leaves, buds, and flowers.
Management of Aphids in Radish
The Life Cycle of Aphids
- Eggs: In some species of aphids, reproduction occurs in the fall or winter, and females lay eggs that will overwinter on perennial plants. In other species, an adult females give birth to live young without mating. These young aphids are called nymphs and do not hatch from eggs.
- Nymphs are immature aphids that emerge from their mother’s body and go through several molts, shedding their skin as they grow. The number of molts varies by species, but most aphids molt four times before becoming adults.
- Winged forms: Some species of aphids produce winged forms in response to environmental cues such as crowding or food scarcity. Winged aphids can fly to new plants or habitats, spreading the population and potentially avoiding predators or adverse conditions.
- Adults: Adult aphids are in the reproductive stage of the life cycle. They are typically wingless and feed on plant sap with specialized mouthparts, piercing the plant’s tissue and sucking out the fluid. Adult females can give birth to live young without mating, producing up to 12 offspring per day. They can continue to reproduce throughout the year, leading to rapid population growth in favorable conditions.
Identification of Aphids in Radish Field
- Look for small, soft-bodied insects in the radish plant.
- Aphids are typically green, yellow, or brown.
- Aphids have pear-shaped bodies and are about 1/8 inch long.
- Look for two cornicles, or tail pipes, at the end of their abdomen, which can be seen with a magnifying glass.
- Look for white cast skins left behind as aphids molt and grow, which can be found on the leaves of the radish plant or stuck in honeydew secretions.
- Take action to control the population of aphids using insecticidal soaps, introducing natural predators like ladybugs, or washing the plants with a strong stream of water.
Factors Favoring Population Growth in Aphids in the Field
- Optimal temperatures for aphid development in radishes are between 20 and 25 °C.
- Upper limits for temperature range from 25 to 30 °C.
- Temperature directly affects the rate of aphid development.
- Extreme temperatures can negatively impact aphid populations.
- Temperature fluctuations outside the optimal range can significantly impact aphid populations in radishes.
- Monitoring and controlling temperature is important for managing aphids and ensuring healthy plant growth.
Damage Symptoms of Aphids in Radish
- Aphids remove sap from the host plant, which can cause the plant to wilt and weaken over time.
- Salivary enzymes injected by aphids during feeding can clog the vascular system of the radish plant or cause injury to the surrounding tissue.
- These injuries can lead to yellowing spots on the radish leaves, distorted growth, and even tissue death or necrosis.
- Severely damaged foliage may fall from the radish plant, reducing its aesthetic value and making it unsaleable.
- Infestations of aphids can also stunt the growth of radish plants, reducing their yield and overall quality.
- Aphid damage can create opportunities for secondary infections by fungi or bacteria that can further harm the radish plant.