Aphids are small insects who feed on plant sap from leaf undersides. They are about oneeighth inch long, pear-shaped, soft bodied, and green, yellow, orange or gray. Although a common insect, there has been an increase in aphid calls this year, especially on cucumbers.
High insect populations usually occur when environmental conditions are ideal for their development. It can also be a sign of natural enemy populations being low, possibly due to incorrect insecticide use.
Plants commonly infested by aphids range from vegetables like cucumbers, cabbage and peppers to honeysuckle, viburnum, roses, and oaks.
While aphids act and look similar, different species infest different plants. Honeysuckle aphid is different than aphids found on viburnum or oak; and those infesting vegetables are different than aphids on flowers or woody plants.
I share this as there is concern if nothing is done, aphids will spread to all plants in the landscape or garden. This will not happen. If you have aphids on cucumbers and an oak tree, they are not connected. You were just unlucky or lucky enough to have both.
Aphids rarely kill plants, even annual plants like cucumbers and peppers. As they feed on plant sap from leaf undersides, leaf curling and distortion occurs and plants are stunted. Some leaves may yellow and turn brown. As long as many leaves remain green, plants continue to live and even produce.
A side effect of aphid feeding is plants become sticky and shiny. This is due to aphids exuding a honeydew as they feed on sugary sap. Another sign of aphids is the presence of ants on plants. Ants farm aphids for their honeydew.
A black sooty mold may grow on the honeydew. This mold is unsightly but not harmful to plants and it can be washed off. If it is dense enough on foliage, some leaves may yellow from a lack of sunlight. Honeydew dripping onto cars or patios can be a shortterm nuisance.
Aphid populations build rapidly because females reproduce without mating. This is known as parthenogenesis. They bear live young 3 to 5 times a day over the course of their one-month life span, which is typically shortened by natural enemies.
The majority of aphids are female. If males occur, it is near the end of the season when they mate with females for egg production; the overwintering stage. Eggs are laid on plant stems and buds. In vegetable and annual flower gardens, removing garden debris in fall reduces aphid numbers the next season.
Aphids, like many insects, are interesting to learn about and even observe. If nothing is done about them, most plants will survive and not be harmed in the long run, especially woody plants and perennial flowers. And natural enemies will be conserved to aid in keeping aphid populations low.
To manage aphids, inspect leaf undersides. Pinch off and discard heavily infested leaves. A strong spray of water directed at aphids dislodges them to keep populations lower. Fall sanitation and rotating crops help some.
If populations are high on small plants, organic sprays to apply directly on aphids include insecticidal soap, neem oil and horticultural oils. Avoid using these when temperatures are above 85 degrees F. Treating large, established trees is rarely recommended. It is unnecessary, not very effective, and natural enemies are killed.