What to do when aphids attack vegetable plants
Q. Help! I have aphids covering my newly planted vegetable plants. What can I do to rid my plants of this aphid hoard? I would like to use something organic.
A. Aphids are a sucking insect that have soft pear-shaped bodies with long legs and antennae. They may be green, yellow, brown, red or black depending on the species and the plants they feed on. Some species appear waxy or woolly due to the secretion of a waxy white or gray substance over their body surface, and they all secrete a sticky substance called honeydew. Most species have a pair of tube-like structures called cornicles projecting backward out of the hind end of their body. The presence of these cornicles distinguish aphids from all other insects.
Because aphids are soft-bodied insects and easily dislodged, first try a strong blast of water from the hose. This will knock the aphids off the plants and most will be unable to make their way back onto the plant. A few may, so you may have to repeat this process a couple of times. Be sure to direct the spray of water to the tips of the stems and the underside of the leaf as this is where aphids usually hide. As long as you reduce the numbers of aphids on each plant and you keep plants from becoming water or nutrient stressed they should be fine even if there are a few lingering aphids.
The University of California’s Integrated Pest Management website states “almost every plant has one or more aphid species that occasionally feed on it, but low to moderate numbers of aphids usually aren’t damaging to gardens or landscape trees. Although aphids can curl leaves and produce sticky honeydew, they rarely kill plants, and can usually be washed off with water. When aphid numbers are high, natural enemies often feed on them, eliminating the need for pesticides.”
However, large populations of aphid can turn leaves yellow and stunt growing plants. They can also produce large quantities of honeydew, which often turns black with the growth of a sooty mold fungus. This mold can block plants from photosynthesizing well, causing further stunting. Additionally there are some species of aphid that inject a toxin into plants, which causes leaves to curl and further distorts growth. A few species can also cause leaf gall formations.
So if hosing them off doesn’t work to control the “hoard” try spraying with an insecticidal soap or Neem oil. This will provide temporary control if you spray all leaf surfaces. Be sure to spray under the leaves as well as the upper leaf surfaces. You may need to reapply a couple of times to get good control as eggs may hatch after you sprayed.
It’s best to spray at night so you have less chance of harming bees and other beneficial insects. If the temperature is over 90 degrees, wait until it drops below 80 degrees before spraying. Using these sprays when temperatures are hot may cause the leaves of the plants to phytoburn, causing damage to the leaves.
To learn more about aphids check out the U.C. Pest Note website at bit.ly/3x2u2Ky.
The Shasta Master Gardeners Program can be reached by phone at 530-242-2219 or email email@example.com. The gardener office is staffed by volunteers trained by the University of California to answer gardeners' questions using information based on scientific research.