Aphids
NOW is the time when winged forms of aphids are migrating from woody plant hosts to alternative hosts, including vegetable crops, and establishing new colonies. Many aphid species are host-specific, feeding only on particular plant species or families.
Aphids are small, soft-bodied insects belonging to the order Hemiptera, commonly known as “true bugs.” Like all true bugs, aphids have piercing-sucking mouthparts. They are typically pear-shaped and are easily recognized by the pair of cornicles (tube-like structures) protruding from the rear of the abdomen.
Aphids have complex life cycles that vary among species. Most species in Utah overwinter as eggs. In spring, eggs hatch into first-instar nymphs—usually all females—which feed on host plants and progress through four nymphal stages before becoming adults. Development is rapid, with a generation completed in as little as one week.
In spring (70–81°F), wingless females emerge and reproduce parthenogenetically. When populations become overcrowded, winged females develop and disperse to new host plants, where they continue reproducing. Toward the end of summer, shorter days and cooler temperatures trigger the production of both males and females. These mate, and females lay overwintering eggs on winter hosts. A single female can produce up to 12 nymphs per day, totaling 50–100 offspring.
Aphid feeding can cause leaf curling, yellowing, distortion, and stunting. Their sugary excretions (honeydew) make leaves sticky, promote sooty mold growth, and attract ants. Aphids are also important vectors of plant viruses.
For more information on species-specific aphids, their hosts, and monitoring tips, refer to our fact sheet Aphid Pests on Vegetables.
Management
- Visually inspect plants for colonies and feeding symptoms, especially at growing tips and curled leaves. Since most aphids prefer the undersides of leaves, turn foliage over while scouting. Use a 10–20x hand lens to identify aphids and look for molted white skins.
- Use yellow sticky traps near host plants to monitor winged aphids.
- Dislodge colonies by spraying with a strong stream of water.
- Remove weeds and volunteer plants that can act as alternate hosts.
- Attract natural enemies by planting yarrow, alyssum, herbs, or other plants with small flowers that provide nectar and pollen. These help support beneficial insects such as lady beetles, lacewings, and parasitic wasps. Predator populations may lag behind aphid outbreaks.
- Apply insecticidal soaps or plant-based oils (e.g., neem). These work by suffocating aphids or disrupting their protective wax coating. Full coverage is essential.
- Manage nitrogen levels in vegetable crops. Excessive nitrogen can promote aphid reproduction. Use lower, staggered fertilizer applications or delayed-release products rather than a single high dose.
Caterpillars
Caterpillars are the larval stage of various moths and butterflies. Several species are currently active and can cause significant damage to Utah’s vegetable crops. Their aggressive feeding habits lead to reduced yields and compromised plant health, making early monitoring and management essential.
Species Description and Damage
- Diamondback Moth: Females lay round, yellow eggs (~0.4 mm). Larvae go through four instars, reaching 1.25 cm in length, and are plain green or gray. Adults are grayish-brown with white diamond-shaped markings and a 1.5 cm wingspan. Hosts include Brassicaceae crops (e.g., broccoli, cabbage, kale) and related weeds. Larvae chew holes in leaves and tunnel into developing heads, leaving frass (fecal matter) that contaminates produce.
Watch this video for more information. - Cabbage Looper: Eggs are dome-shaped and light yellow. Larvae pass through five instars, are pale to dark green, and have white or yellow stripes with tapered heads. Pupation occurs in a fuzzy cocoon (~3 cm). Adults are gray-brown with silver markings and a 4 cm wingspan. Hosts include most Brassicas. Larvae chew irregular holes in leaves and tunnel into heads, contaminating them with frass.
Watch this video for more information. - Imported Cabbageworm: Butterflies lay bullet-shaped eggs (~1 mm). Larvae grow up to 4 cm, are green with thick yellow stripes and short hairs. Chrysalides are yellow, gray, or green and 2 cm long with a distinct keel-like ridge. Adults are white with 1–2 black wing spots and have a 5 cm wingspan. Hosts are similar to those of other Brassica pests. Feeding causes defoliation and frass contamination.
Watch this video for more information. - Cutworms: Larvae are gray to brown and curl into a “C” when disturbed. Adults vary in color and pattern, with a wingspan up to 1.5 inches. Common species include army cutworm, black cutworm, pale western cutworm, and variegated cutworm. These pests feed on nearly all vegetables and many weeds, clipping seedlings at the base or feeding on foliage and fruit.
- Armyworms: Moths are mottled gray or brown with wingspans of 25–40 mm. Larvae range from tan to nearly black. Common species include beet armyworm, fall armyworm, and western yellow-striped armyworm. These pests feed on a wide range of vegetables and weeds, chewing irregular holes and boring into stems, buds, and heads.
Monitoring
- Inspect plants regularly, focusing on new growth.
- Shake plants over a white tray to dislodge larvae.
- Check undersides of inner leaves for eggs and larvae. Look for feeding damage and frass.
- Monitor at least 10% of a crop or representative plants throughout the garden or field.
- Look for adult butterflies or moths. For example, white butterflies (imported cabbageworm adults) are often seen flying during the day.
- Use sticky traps to detect the presence and abundance of adult moths.
- For suspected cutworm damage, dig 1 inch around the base of affected plants to locate larvae.
Management
- In small gardens, handpick and destroy larvae during inspections.
- Use row covers to exclude egg-laying adults.
- Plant early or select early-maturing crop varieties. Older plants tolerate damage better than seedlings.
- Remove crop debris after the season to eliminate overwintering sites.
- Choose tolerant varieties. For instance, glossy-leaved Brassicas are less attractive to diamondback moth larvae.
- Tilling soil in spring or fall can reduce overwintering populations.
- Remove weeds near the garden or field. Cool-season weeds like lambsquarters and wild mustards are especially attractive to egg-laying adults.
- Promote beneficial insects. Lady beetles and lacewings feed on eggs; wasps and birds target larvae.
- Apply Bacillus thuringiensis (Bt), a microbial insecticide effective against young caterpillars. Bt is safe for humans and beneficial insects and is commonly used in organic production.
- Use registered insecticides as needed. Choose products labeled for your target pest and crop, and follow label directions for safe and effective use.