Are Aphids Harmful to Tomato Plants?

Aphids are a common garden pest that can swarm and damage many vegetables, including tomato plants. But how bad are they really? Will a few aphids reduce your tomato yield or are they manageable? Let’s take a closer look at the impact of aphids on tomato plants.

What Are Aphids?

Aphids are tiny, soft-bodied insects that feed by sucking sap from plants. They come in many colors like green, yellow, brown, red or black. Aphids have pear-shaped bodies and long legs. They can be winged or wingless.

There are around 250 different aphid species. Some specialize on certain plants while others are generalists that feed on multiple crops. The most common aphid affecting tomatoes is the green peach aphid.

How Do Aphids Harm Tomatoes?

Aphids can damage tomato plants and fruit in a few ways

• Sucking sap – Their piercing mouthparts tap into plant tissues to withdraw sap. This can stunt and weaken plants.

• Spreading diseases – Aphids transmit viral diseases like tomato yellow leaf curl virus as they feed.

• Secreting honeydew – Aphids excrete a sticky, sugary substance called honeydew. This encourages mold and fungi.

• Deforming plants – High aphid populations can cause twisted, yellowing, or dropping leaves. Fruit may be stunted.

So aphids can certainly harm tomato plants. But an important question is – how many aphids cause meaningful damage?

How Many Aphids Hurt Tomato Yields?

Research by Washington State University found that tomato plants can tolerate fairly high numbers of aphids without suffering major yield reductions.

In their trials, scientists introduced 10, 100, or 1000 aphids per leaf. Here were the results:

• 10 aphids per leaf caused no significant damage. Fruit weights were normal.

• 100 aphids per leaf slightly reduced yields but not greatly.

• 1000 aphids per leaf caused up to a 36% drop in fruit weights. Plants were stunted.

So tomato plants can handle low to moderate aphid populations without large impacts on harvests. But very high infestations of hundreds of aphids per leaf can meaningfully reduce yields.

Severe aphid attacks can also lead to curled, twisted leaves. This decreases the plant’s ability to photosynthesize and exposes fruit to sun scald. Aphids spreads viruses too which seriously harm plants.

Signs of Aphid-Transmitted Virus Diseases

Aphids are carriers of several dangerous tomato viruses including:

• Tomato yellow leaf curl virus – Causes stunted plants, yellowing leaves, leaf curling. A very destructive virus.

• Potato virus Y – Leads to dark green veins, mottled leaves, yellow spots on margins. Stunts growth.

• Cucumber mosaic virus – Yellow mottling and twisting of younger leaves. Fruits may be bumpy or malformed.

Inspect plants regularly for signs of viral infection like leaf yellowing, distortion, or mosaic patterns. These require immediate action as viruses can quickly spread via aphids.

Monitoring Aphids on Tomato Plants

Preventative monitoring can help catch infestations before they escalate out of control. Scout plants twice weekly for colonies of aphids on:

• Undersides of leaves
• Stems
• Shoot tips
• Flower clusters

Look for honeydew, sooty mold, and ants which indicate aphids are present. Check when plants are young and most vulnerable.

Act quickly at first sight of aphids before populations explode.

Organic Ways to Control Aphids in Tomatoes

If you detect aphids, taking prompt action is key to protect your crop:

• Insecticidal soaps – Soap solutions kill soft-bodied insects through membrane disruption and dehydration. Must contact aphids to be effective.

• Neem oil – This botanical insecticide coats aphids in oil and blocks their breathing and feeding. Spray young nymphs before populations spike.

• Strong water sprays – Frequent blasts of water can help dislodge colonies and knock aphids off plants. Don’t damage foliage.

• Row covers – Fine mesh fabric row covers create a physical barrier to exclude winged aphids. Bury edges in soil.

• Attract beneficials – Ladybugs, lacewings, hoverflies and other predators feed on aphids. Plant flowers to attract them.

• Companion planting – Onions, garlic, and nasturtiums nearby help repel aphids through chemical excretions.

Monitor and use multiple tactics together for most effective control. Rotate chemical modes of action to prevent resistance.

When to Take Emergency Action for Aphids

Take aggressive action if you notice:

• Dense clusters of 50+ aphids per leaf

• Rapid spread to new leaves

• Honeydew coating much of the foliage

• Leaves severely curling, yellowing, or dropping

• Flowers and fruits stunted or falling off

• Obvious signs of virus infection

Use stronger pesticide sprays at this stage to save the crop. Always follow label safety directions. Consider the risks to bees and beneficials.

Aphids Can Damage Tomato Plants But Aren’t Always Devastating

Tomato plants can tolerate low to medium aphid populations fairly well. But very heavy infestations of hundreds per leaf pose a real risk through sap feeding damage, virus transmission, honeydew, and leaf loss.

Careful monitoring and timely organic control of aphid colonies is the best way to prevent major crop losses. When in doubt, take action quickly at first signs rather than allowing exponential population growth.

With smart integrated pest management, aphids don’t have to spell disaster for your tomato harvest. A proactive, vigilant stance offers the best protection against these troublesome sap-sucking garden pests.