Pest Advisories: Aphids and Grasshoppers

Aphids and Grasshoppers

pestadvisories.usu.edu/2024/05/16/aphids-and-grasshoppers

In this Issue

Grasshopper Nymph Monitoring and Management

Aphids Finding Host Crops

GRASSHOPPER NYMPHSAND OUTLOOK

After the severity of plant damage caused by grasshoppers last season, many vegetable growers are rightfully cautious going into the 2024 season. Last year, we primarily saw residential and urban areas (especially those adjacent to undisturbed open lands) most affected by the high grasshopper numbers. The outbreak was attributed to the ideal climatic conditions, population sizes of the prior year, and unmanaged breeding areas from which grasshoppers migrated into our gardens.

Grasshoppers overwinter in the egg stage in the soil and are unaffected by cold air temperatures. High snowpack in the winter months can provide insulation, keeping soils consistently moist and cool, and creating ideal conditions for grasshopper eggs to survive. Spring conditions are favorable when temperatures are warm and there is minimal precipitation.This allows for successful egg hatching and nymph growth. However, if temperatures are cool and there is a lot of moisture in spring, this can promote infections of newly hatched nymphs by fungi and other pathogens.

Utah is home to three major groups of grasshoppers: the slant-faced grasshoppers, the band-winged grasshoppers, and the spur-throated grasshoppers.All three use their large back legs to launch themselves when disturbed. The slant-faced variant’s face is more angular faces and long, thin bodies which help them blend into grassy vegetation. The bandwinged variety uses hindwings to fly short distances. They make a snap and crackle noise as they fly The spur-throat name is derived from the tubercle projecting between their front legs.They tend to cause the most damage.

Most of these species in Utah produce one generation per year.After hatching, grasshopper nymphs go through five stages before reaching adulthood. Because various species have different development timelines, a mix of nymphs and adults may be present throughout the

season.

Grasshoppers are known to feed on agronomic crops, rangeland plants, weeds, fruits, vegetables, and ornamental plants. Their chewing mandibles cause damage as they consume foliage, flowers, fruits, seed heads, and stems—essentially all above-ground plant parts. If populations are high enough, this feeding can lead to economic setbacks, and farmers in some areas are reporting economic losses due to grasshopper damage.

MANAGEMENT

Many gardeners around the state have reported seeing small nymphs already emerging from the soil. NOW is the time to monitor your farms and garden spaces and begin planning management strategies.

Monitor for nymphs in weedy areas along fences and roadsides. This nonflying life stage is less mobile and easier to treat.

Grasshopper eggs in the soil at the base of a plant.

Newly hatched grasshopper nymphs on a potted plant in Salt Lake City

In small gardens, grasshoppers can be excluded using row covers with insect netting or lightweight spun-bond material. They can also be hand-removed (during early, cool mornings) and placed into soapy water

Natural predators such as kestrels, reptiles, mammals, and other arthropods feed on grasshoppers, but unfortunately not usually enough to mitigate damaging numbers. Some small-scale farmers have had success with guinea hens or other poultry in managing grasshoppers. However, success with this method is situational and may not be appropriate for all farms.

If high populations are noted, an insecticide might be needed and should be used on nymphs. Unfortunately, organic bait products containing the microsporidium Nosema locustae(such as NoLo Bait and Semaspore) are unavailable or in short supply. Other bait products using active ingredients such as zeta+cypermethrin + bifenthrin, malathion, permethrin, and carbaryl are labeled for grasshopper use in home gardens. Consult your local garden center about what products are currently in stock and verify that the target crop and grasshoppers are listed on the label.

APHIDS

NOW is the time winged formed of aphids are moving from woody plant hosts to alternative hosts (including vegetable crops). Various species of aphids will only specifically feed on certain host plant species or families.

Aphids are small, plant-feeding insects belonging to the order Hemiptera, also known as the “true bugs”. Like all true bugs, aphids have piercing-sucking mouthparts. They are generally pear-shaped, soft-bodied insects, and are easily identifiable by the presence of a characteristic pair of cornicles on the posterior end of their abdomen.

The life cycle of aphids is complex and can vary among species. Generally, aphids overwinter as eggs. In the spring, these eggs hatch into first-instar nymphs, which are typically all females.These nymphs begin to feed on host plants and progress through subsequent nymphal stages.There are typically four nymphal stages before molting into the adult stage.The complete development of aphids can be very rapid, sometimes taking only a few days to hatch and grow into the adult stage.

Aphid feeding can result in leaf curling, yellowing, distortion, and stunting of plants. The honeydew excreted by aphids is messy, sticky, and serves as a substrate for sooty mold fungi.Additionally, aphids can vector viral diseases.

MANAGEMENT

Visually inspect plants for aphid colonies, feeding symptoms on growing tips, and curled leaves. Since most aphid species prefer the undersides of leaves, be sure to turn foliage over when scouting. Use a 10-20x hand lens for identification. Look for small white flakes, which are the molted skins of aphids. Place yellow sticky traps adjacent to host plants to monitor the presence of winged aphids. Spray a strong stream of water at colonies to knock back populations. Look for a sticky substance called honeydew on leaves and stems, as this can also attract ants.

Prevent aphids by removing weeds and volunteer plants that can serve as alternate hosts.

Encourage natural enemies by planting strips of yarrow, alyssum, herbs, and other plants with small, attractive flowers that provide nectar and pollen for beneficial insects. Several natural predators feed on aphids. Scout for these predatory and parasitic insects and eggs in and around your high tunnels. These natural predator populations can maintain aphids at low levels. However, predators will only show up if a food source exists, so there can be a lag time between the appearance of the aphids and the appearance of predators.

Spray aphids with insecticidal soap or plant-based oils. These products kill aphids on contact by physical means (suffocation and disruption of waxes in the exterior cuticle), so thorough coverage is essential for good efficacy.

Manage nitrogen levels with your vegetable plants. High levels of nitrogen fertilizers tend to encourage aphid reproduction. Use several staggered applications of lower concentrations of nitrogen rather than a single high dose. Consider using delayedrelease fertilizers to manage nitrogen levels effectively.