Beet Armyworm Infestation in a Garden

Beet armyworm (via Wikimedia Commons, CC BY 2.5)

Beet armyworm infestations in a garden can cause serious damage to crops and plants. These pests belong to the Lepidoptera order and are known for their voracious appetite, feeding on the foliage of a wide range of plants, including vegetables, fruit trees, and ornamental plants. Infestations often occur during the warm months of the year and can quickly spread if left uncontrolled. Beet armyworms can cause significant damage to plants in a short period of time, leading to reduced yields and plant death. Gardeners should be aware of the signs of an infestation and take steps to prevent or control beet armyworm populations in their gardens.


It is important to monitor plants regularly and address infestations promptly to prevent significant damage to the garden. Early detection and control measures can minimize the impact of beet armyworm infestations and protect the health of the garden.

  • Large holes in the leaves, which can quickly cause the leaves to become skeletonized
  • Chewed or missing leaves, which can result in defoliation of the plant
  • Silken webs and frass (insect excrement) on the foliage and stems of plants, which can indicate the presence of caterpillars
  • Reduced plant growth and vigor, as the pests feed on the plant’s sap and nutrients
  • Withered or dead plants, in severe infestations
  • Increased populations of natural enemies, such as parasitic wasps or birds, feeding on the pests, which can indicate a heavy infestation
  • Sticky or gummy substances on leaves and stems, which can be a sign of honeydew excreted by the pests

What is a Beet Armyworm

Accurate identification of pests is important for effective control and management. If you are unsure about the identity of a pest in your garden, it is recommended to consult with a specialist or reference materials for assistance.

  • The adult moth is brown or gray with a wingspan of approximately 1 inch. The wings are mottled with darker and lighter shades, and the front wings have a scalloped edge.
  • The caterpillar stage is the damaging stage for plants. Caterpillars are green with a black head and are about 1.5 inches long when fully grown.
  • The caterpillars have a distinctive white stripe down the center of their backs and two white stripes along their sides. They also have a series of black dots along their sides.
  • The larvae have six true legs and two pairs of prolegs (false legs) near the hind end. The prolegs are used for gripping and crawling.
  • The caterpillars can change color as they grow and mature, becoming brown or gray before pupating into adult moths.

Treating a Beet Armyworm Infestation

It is important to address beet armyworm infestations promptly to prevent significant damage to the garden. By being vigilant and taking preventative measures, gardeners can protect the health of their plants and maintain a thriving garden.

It may be necessary to use multiple methods to effectively control beet armyworm infestations in a garden. For example, combining physical removal with the use of physical barriers and biological control can be an effective way to reduce the population of caterpillars.

Physical Removal

  • Handpick caterpillars from plants and place them in a container filled with soapy water to kill them.
  • Check the undersides of leaves and stems, as caterpillars often feed there.
  • Remove and dispose of infested plant parts, such as leaves or stems, to reduce the population of caterpillars.
  • Use a strong jet of water to knock caterpillars off plants, which can also help reduce the population. This method is particularly effective for small-scale infestations.

Physical Barriers

  • Use row covers made of lightweight, breathable material to physically exclude caterpillars from plants. The covers should be secured to the ground to prevent caterpillars from crawling underneath.
  • Install fine mesh screens or netting around plants to prevent moths from laying eggs on foliage. The screens or netting should be securely attached to the ground to prevent caterpillars from crawling underneath.

Cultural Practices

  • Rotate crops and avoid planting the same crop in the same location year after year to reduce the risk of large-scale infestations.
  • Plant a diverse range of crops to reduce the risk of large-scale infestations. Beet armyworms are less likely to cause significant damage if they have multiple food sources.
  • Practice good garden hygiene, such as removing crop debris and weeding regularly, to reduce the habitats and food sources for beet armyworms.

Biological Control:

  • Encourage natural enemies, such as parasitic wasps, ladybugs, and birds, to control caterpillar populations.
  • Plant flowering plants that provide nectar and pollen for beneficial insects, such as wasps, ladybugs, and lacewings.
  • Avoid using broad-spectrum insecticides that can harm beneficial insects.


  • Apply an appropriate insecticide to control caterpillar populations. Insecticides that are safe for use in the garden and compatible with the plants being treated should be chosen.
  • Follow the manufacturer’s instructions for application rates and timing.
  • Apply the insecticide in the evening, when caterpillars are less active and less likely to fly away.
  • Repeat applications as needed, following the manufacturer’s instructions.