The cartoon character, Popeye, was known for his craving for spinach. As you recall, when he immediately ate it while in trouble, his strength increased significantly just in time to punch his famous rival.
In the gardener’s garden or the commercial grower’s field, spinach is not so defensive. Its strength lacks the ability to ward off most pests such as aphids.
Numerous species of aphids like vegetables, fruit trees and other crops. One of the more common is the green peach aphid, a pale yellow to green-colored pest. Another is the potato aphid, which is a pink to green color. According to the former University of California Integrated Pest Management (IPM) team of Steven Koike, a plant pathologist farm advisor in Monterey county; William Chaney, a former emeritus entomology farm advisor in Monterey county; and Michelle LeStrange, a former emeritus farm advisor in Tulare county, the larger potato aphid is not nearly as important among crops as the green peach aphid.
The typical aphid is about 1/10-inch in length, according to Eric Day, an Extension entomologist with Virginia Tech, and these soft-feeling aphids can vary in color. Common among most aphids is two tubes, which he indicates are cornicles that rest on their rear ends. Aphids use cornicles to secrete defensive substances.
Their tubercles, or base of their antennae, point toward each other, the University of California IPM team noted.
Because of their complex lifecycles, aphids can build up in numbers quickly, Day says. Aphid species can overwinter as fertilized eggs stuck to a host stem or some other plant section. Nymphs hatch from eggs and are wingless females. These females reproduce without mating. They hold eggs within their bodies before hatching, thus the young are born alive.
Day indicates that female offspring then mature and start to reproduce. This cycle or pattern continues as long as possible. In Virginia, he noted that growers may see 12 or more generations a year.
Growers may notice that young aphids may develop wings, and when they do they can go to other plants as alternate hosts, according to Day. When the climate gets cooler and days become shorter, aphid generations can be male and female. Once they mate, females lay fertilized eggs.
Something most growers may not hear is that ants can protect colonies of aphids, Day noted. They gather aphids or eggs and tote them to their nests. Once spring arrives, the ants will carry the aphids to host plants and protect them from dangerous pests. In return, the aphids release honeydew as a waste product, and the ants collect the sticky honeydew.
When hungry, aphids feed in clusters, he noted, and they like new or young shoots and leaves. Their feeding consists of sucking the plant’s juices using a food channel. While they are doing this, aphids inject saliva into the host.
The University of California IPM team noted that aphid populations may start small and land on the lower leaves first where they start feeding. Then they move up the plant and can branch out onto other parts of the spinach plant.
This feeding is not as harmful if aphid numbers are low; however, if those numbers increase, they can cause significant damage, curling and wilting of leaves, Day noted. Some damage may even stunt shoot growth and delay flower and fruit production. The plant’s vigor also may suffer. Another cause of concern for growers is that aphids can act as vectors of plant diseases when they transmit pathogens while feeding.
Their honeydew can land on lower leaves, he noted, and those leaves may become full of this waste, which can produce fungi as sooty molds. These molds can interfere with photosynthesis in leaves.
Growers are advised by the University of California IPM team to inspect fields twice a week, checking closely the edges of spinach plants, which they noted is the first place growers will see aphid infestation. They also advised inspection of several plants in a field for aphid clusters.
Day noted that aphids have natural enemies such as lady beetles, lacewings, damsel bugs, flower fly maggots, certain parasitic wasps, birds and fungal disease. For garden aphids, he advised growers to be cautious using insecticides so these natural, beneficial enemies are not harmed. He added that aphids like to attack unhealthy and struggling plants, so he advised keeping plants as vigorous as possible.
To control aphid numbers, commercial growers can apply insecticides. The University of California IPM team advised treating as soon as plants are stressed with high aphid populations. If they do, growers may be able to keep contamination under control. They warn to monitor further in case another application is necessary.
Before using any insecticides, Day advised to following label directions and contacting their local Extension agent or specialist with questions.
According to the University of California IPM team, the fungus Entomophthora aphidis may cause disease that can sometimes kill aphids. However, they note that natural enemies may not provide the control that most growers want to keep aphids off their spinach.
Additionally, row covers such as plastic tunnels or Remay-type enclosures may assist in reducing aphid populations below the desired threshold. Unfortunately, the University of California IPM team noted that these row covers can be costly for some growers. Also, if growers apply a large amount of nitrogen fertilizer, they may see more aphids.
Remember, don’t let the softness of aphids fool you. Their numbers can increase rapidly, and unlike Popeye, spinach may not be able to ward off these pests before they suck all the juices out of the plant.