Aphids In The Garden: Identification, Biological, Cultural & Chemical Control

Because some of you who produce cabbage family plants have noticed aphids in the garden, this seems like a good time to discuss them.

They are pretty simple to manage and should not cause alarm. They’ll be knocked down by water jets or insecticidal soap (such as “Savers”), and predatory insects will also rush to your help.

Even though we will not be utilizing pesticides, I have included the section on insecticides since it provides an excellent overview of the risks associated with chemicals in the environment.

What are Aphids?

Aphids are little, soft-bodied insects with long, slender mouth parts that puncture stems, leaves, and other vulnerable plant parts to suck out plant juices.

Almost every plant has at least one aphid species that feed on it on a regular basis. Many aphid species are difficult to recognize; nevertheless, in most cases, species identification is not required to manage them.

Identification

Aphids come in a variety of colors, including green, yellow, brown, red, and black, depending on the species and plants they feed on. A waxy white or gray material is secreted across the body surface of a few species, giving them a waxy or fuzzy appearance.

All of the insects are tiny, pear-shaped, and have long legs and antennae. Cornicles are a pair of tube-like structures that protrude rearward from the hind end of most animals’ bodies. Aphids are distinguished from other insects by the presence of cornicles.

Adult aphids in the gardens are usually wingless; however, most species can be seen with wings, especially when populations are high or in the spring and fall.

When the quality of the food supply deteriorates, the pest’s capacity to create winged individuals allows it to spread to other plants.

Aphids are generally seen in thick clusters on leaves or stems, even though they can be found single.

Most aphids do not move quickly when disturbed, unlike leafhoppers, plant bugs, and other insects that may be mistaken with them.

Aphid Life Cycle

Aphids produce a large number of generations every year. Most aphids in the garden reproduce asexually throughout most or all of the year in California’s warm environment, with mature females giving birth to live young (sometimes as many as 12 per day) without mating.

Nymphs

Nymphs are young aphids. Before becoming adults, they molt four times, losing their skins each time. There is no such thing as a pupal stage.

Some species mate and lay eggs in the fall or winter, giving them a more resilient stage to weather extremes.

For winter survival, these eggs are sometimes placed on an alternate host, generally a perennial plant.

Many kinds of aphids may develop from newborn nymph to reproducing adult in 7 to 8 days when the temperature is warm.

Aphid populations may grow quickly since each adult aphid can generate up to 80 progeny in just one week.

Aphid Damage

Leaf-feeding aphids in small to moderate numbers usually are unobtrusive in gardens and on trees.

On the other hand, enormous populations induce curling, yellowing, and deformation of leaves, as well as stunting of shoots; they can also generate large amounts of honeydew, a sticky fluid that typically becomes black with the establishment of a sooty mold fungus.

Some aphid species inject poison into plants, causing growth to be distorted even further. A few species cause gall development.

On particular vegetable and ornamental plants, aphids in the garden can spread viruses from plant to plant.

• Squashes,
• cucumbers,
• pumpkins,
• melons,
• beans,
• potatoes,
• lettuces,
• beets,
• chards, and
• bok choy,

are among the crops that are frequently infected by aphid-transmitted viruses.

The viruses induce leaf mottling, yellowing, or curling, as well as plant growth stunting.

Although losses can be significant, they are difficult to prevent with aphid control because infection occurs even when aphid populations are low: the aphid only needs a few minutes to spread the virus, whereas killing the aphid with a pesticide takes considerably longer.

Aphids affect sections of plants other than leaves and shoots in a few species. The lettuce root aphid is a soil-dwelling insect that attacks lettuce roots during the majority of its life cycle, causing lettuce plants to wilt and, in some cases, perish.

In the spring and summer, the lettuce root aphid overwinters as eggs on poplar trees, where it creates leaf galls.

The woolly apple aphid infests woody sections of apple roots and limbs, particularly around pruning wounds, and if roots are affected for multiple years, it can cause overall tree deterioration.

Aphid management

Monitoring the aphids in the garden

Check your plants for aphids in the garden frequently–at least twice weekly if they’re developing quickly. When temperatures are warm but not hot (65° to 80°F), several kinds of aphids do the most harm.

Early detection is vital!

Early detection of infestations is critical. It’s difficult to manage aphids if their numbers are large and they’ve started to distort and curl leaves because the curled leaves protect aphids from pesticides and natural enemies.

Aphids are particularly numerous towards the upwind border of the garden and near other aphid sources, so pay careful attention to these regions.

Turn the leaves over to look for aphids since many species prefer the undersides. To check for aphids on trees, snip off leaves from numerous areas of the tree.

Natural enemies such as lady beetles, lacewings, syrphid fly larvae, and the mummified skins of parasitized aphids should also be looked for.

Look for disease-killed aphids in the garden, which may be discolored, swollen, or flattened. If there are large numbers of these natural control elements, the aphid population can be decreased quickly without treatment. So yet, there hasn’t been any evidence of this.

Ants are frequently connected with aphid populations, particularly on trees and shrubs, and are typically a sign of an aphid infestation. Check for aphids (or other honeydew-producing insects) on limbs and leaves above if you notice a high number of ants crawling up your tree trunks.

Ants defend their food supply by fending off aphid predators and parasites. Ant control is an essential part of aphid control and is described under cultural controls.

Aphids may be tracked in the landscape by measuring honeydew dropping off the tree with water-sensitive paper. This sort of monitoring is beneficial in areas where dripping honeydew tolerance is low, such as in groups of trees along city streets or in parks and tall trees where aphid colonies may be too high to detect.

For further information on honeydew monitoring, see Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide

Biological Management

Natural enemies can help reduce aphids in gardens that aren’t treated with broad-spectrum insecticides (organophosphates, carbamates, and pyrethroids), which kill both natural enemies and pests.

Natural enemy populations usually do not arrive in substantial numbers until aphid populations become large.

Various parasitoid wasps that deposit their eggs within aphids are among the most important natural enemies. The skin of the parasitized aphid becomes crusty and golden brown, forming a mummy-like appearance.

When the temperature is warm, most parasites have a short generation cycle, so if you notice mummies on your plants, the aphid population is likely to be decreased significantly within a week or two.

A variety of predators eat aphids in the garden. Lady beetle, lacewing, and syrphid fly are the most well-known. Natural predators are the most effective, especially in a small garden setting.

When handled appropriately, commercially available lady beetles may provide some temporary control, but most of them will scatter away from your yard within a few days.

When it’s humid, aphids are more susceptible to fungal illnesses. When the conditions are correct, these diseases may destroy whole colonies of aphids.

Look for reddish or brown dead aphids with a fuzzy, faded appearance instead of the glossy, bloated, tan-colored mummies that form when aphids are parasitized.

Aphids are also affected by the weather. Summer heat in the Central Valley and desert locations reduces the populations of many species, and aphid activity is also curtailed during the coldest months of the year. However, certain aphids may be active all year, especially in California’s warmer central coastal zones.

Cultural control

Before planting vegetables, look for aphid sources in the region and eliminate them. Aphids in the garden congregate on weeds like sowthistle and mustards, then migrate to crop seedlings after they sprout. Before planting, inspect transplants for aphids and remove them.

If aphid populations are concentrated on a few curled leaves or young shoots, the best management may be to cut and dispose of these regions. Some aphids grow in the dense inner canopy of giant trees; removing these sections can make the ecosystem less suited.

In some instances, ants tend to aphids and eat on the honeydew excreted by the aphids. At the same time, they guard the aphids against natural predators.

If you detect ants creeping up aphid-infested trees or woody plants, wrap a ring of sticky substance around the trunk (Tanglefoot, etc.) to keep them from climbing.

Teflon compounds have also been employed, which are too slick for ants to crawl over. (Note: Do not apply sticky substance directly to the bark of young or thin-barked trees or trees that have been extensively trimmed; it may cause phytotoxicity.)

Apply adhesive material to the wrap and wrap the trunk with fabric tree wrap or duct tape. Because no one addressed it, I lost numerous orange trees!) Alternatively, ground-based ant stakes or baits can be used to manage ants without harming aphids in the garden, or their natural enemies. Other ant paths, such as branches contacting buildings, the ground, or other trees, should be pruned off.

Pay attention to nitrogen fertilizers

Aphid proliferation is aided by high nitrogen fertilizer levels. Use no more nitrogen than is necessary. Use less soluble nitrogen and apply it in tiny amounts throughout the season rather than all at once. Use a urea-based, time-release formulation instead (most organic fertilizers can be classified as time-release products as compared to synthetically manufactured fertilizers).

Because many vegetables are most vulnerable to aphid damage while they are seedlings, losses can be minimized by growing seedlings beneath protective coverings in the garden, greenhouse, or indoors and then transplanting them when they are bigger and more tolerant of aphid eating. Aphid-borne viruses are also prevented by using protective coverings.

Aphid-borne virus transmission has been successfully reduced in summer squashes, melons, and other vulnerable plants using aluminum foil mulches. Invading aphid populations are repelled, lowering aphid populations on seedlings and tiny plants.

Another advantage is that the increased quantity of solar radiation reflected on leaves generally increases the yields of plants yields on aluminum foil mulches.

To create an aluminum mulch in your garden, eradicate all weeds and cover beds with Reynolds Aluminum Company’s aluminum-coated construction paper in rolls. To keep the paper in place, bury the edges with soil. Cut or burn 3- to 4-inch diameter holes when the mulch is in place, then plant numerous seeds or single transplants in each one.

You can sprinkle or furrow irrigate your beds; the mulch is robust enough to withstand sprinkling. The mulch will improve crop development and suppress weeds in addition to repelling aphids, leafhoppers, and other insects.

However, when the temperatures rise in the summer, mulches should be removed to protect plants from overheating. Spray transparent plastic mulch with silver paint as an alternative to aluminum-coated construction paper. Many garden retailers sell reflective plastic mulches as well.

Another method for reducing aphid numbers on robust plants is to swat them away with a powerful water spray. The majority of aphids in the garden that have been dislodged will be unable to return to the plant, and their honeydew will be rinsed away as well. Plants sprayed with water early in the day dry quickly in the sun and are less vulnerable to fungal infections.

Chemical control – Killing aphids in the garden

Soaps, neem oil, and narrow-range oils (e.g., supreme or superior parafinic-type oil) only kill aphids present on the day they are sprayed, which is a temporary solution, so they may need to be applied again.

Because predators and parasites are more common when aphid populations have become large, nonpersistent pesticides like soap or oil may provide more effective long-term control.

Although these materials kill natural enemies that are present on the plant and are struck by the spray, they do not kill natural enemies that move in after the spray since they leave no poisonous behind.

These and other contact pesticides are often useless in preventing damage from aphids that are protected by galls or twisted foliage, such as the woolly apple aphid or the woolly ash aphid.

When the temperature surpasses 90°F, do not apply soaps or oils to water-stressed plants. These products may be phytotoxic to some plants, so read the labels and test them on a small area of the leaves for a few days before using them on the entire plant.

If administered as a delayed dormant treatment just as eggs are about to hatch in early spring, supreme- or superior-type oils will kill overwintering aphid eggs on fruit trees. These treatments will not completely eliminate aphids and are unlikely to be justified just for aphid control.

Earlier applications will not control aphids in the garden. Woolly apple aphid, green apple aphid, pink apple aphid, mealy plum aphid, and black cherry aphid are all common aphid species that are managed.

Many additional pesticides, including foliar-applied formulations of malathion, permethrin, and acephate, are available to control aphids in the home garden and landscape (nonfood crops only).

While these products may kill more aphids in the garden than soaps and oils, their use should be limited since they also destroy the natural enemies that help keep aphids and other pests under control in the long run.

Repeated applications of these materials may result in the aphid developing resistance to the substance.

When children and dogs are around, insecticides such as oils and soaps are also safer to use. Because pyrethrins break down fast, formulations combining insecticidal soaps and pyrethrins may produce somewhat more knockdown than soaps alone but have less detrimental effects on natural enemies than malathion permethrin, and acephate.

Avoid using diazinon and chlorpyrifos in your urban garden; these chemicals have been linked to contamination in California’s streams and rivers. Carbaryl should not be used since it is ineffective against aphids.

Because acephate has systemic action, meaning it spreads through leaves, it can be useful in areas where aphids are hiding behind curled foliage.

Because it can break down into a far more harmful substance, acephate is not approved for use on food crops in the garden. The soil-applied systemic insecticide disulfoton is occasionally used to control aphids in roses, although it is extremely poisonous to humans.

Conclusion

Remember that modest populations of numerous aphids attacking the leaves of fruit trees or ornamental plants and shrubs do not cause long-term damage when applying insecticides for aphid management.

In most cases, low numbers may be tolerated, and aphids in the garden will often go when natural enemies or high weather come. A strong spray of water or water-soap solution, administered with suitable equipment, may often give sufficient control even on huge street trees.

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