In this issue:
- Seedcorn maggot and Asparagus beetle descriptions and management
- Round up of pest, disease, and agronomic tools to support decision-making
- Deep frost this winter limits potato volunteers and late blight risk in 2025
Vegetable Insect Update – Russell L. Groves, Professor and Department Chairperson, UW-Madison, Department of Entomology, 608-262-3229 (office), (608) 698-2434 (cell), e-mail: rgroves@wisc.edu.
Vegetable Entomology Webpage: https://vegento.russell.wisc.edu/
Seedcorn maggot – (https://vegento.russell.wisc.edu/pests/seedcorn-maggot/). Populations of adult seedcorn maggot (SCM) have emerged across southern Wisconsin and will rapidly progress across the state over the next 7-10 days. Seed corn maggots overwinter as pupae in the soil. Adult flies have begun emerging and the peak emergence for the first generation occurs across southern Wisconsin. You can find adult SCM near recently tilled soil and adults often swarm over brightly colored objects. Adults will mate and lay eggs in these risk areas and preferred egg deposition sites are locations with germinating or decaying seeds, plant residue, incorporated green manures or where organic fertilizers have been recently applied. Adults often mate and lay eggs within 2-3 days of emergence. Eggs hatch 2-4 days later depending on soil temperature. The larval portion of the SCM life cycle occurs below ground over the course of a few weeks. Once hatched larvae burrow into the soil 6-8 cm to locate food resources. A complete life cycle for is typically 16-21 days and these are 3-5 generations per year in most portions of the state.
Once eggs are laid, the larvae hatch and begin to damage germinating seeds and young seedlings of a wide range of vegetable and agronomic crops. In addition to sweet corn, seedcorn maggots have a large host range including common vegetable crops. SCM can cause economic damage to the seed of artichoke, beet, Brussels sprouts, cabbage, cantaloupe, carrot, cauliflower, cucumber, kale, lettuce, bean (lima, snap, red), onion, pea, pumpkin, tomato, and turnip. Management for SCM is only effective when used in a preventative manner. Once direct larval damage is detected there is no control option for the pest. Therefore, there are no economic thresholds for this insect pest. SCM forecasting models predict peak flight windows and are very useful for growers. Documenting peak flights can help to forecast subsequent generations of SCM. (Source: https://agweather.cals.wisc.edu/vdifn). Two common chemical delivery techniques are available for SCM management: seed treatment or an at-plant soil application. Numerous combinations of insecticidal compound and fungicide are available as pre-plant seed treatments directly from seed vendors. Many active ingredients are reduced risk insecticides which have lower non-target impacts and these include spinosad (Entrust, Regard, Lumiverd), cyantraniliprole (Fortenza and Lumiposa) and chlorantraniliprole (Lumivia). Refer to the UW-Extension publication Commercial Vegetable Production in Wisconsin (A3422) for a list of registered insecticides and management recommendations.
Asparagus beetle – (https://vegento.russell.wisc.edu/pests/asparagus-beetle/). The common and spotted asparagus beetles are annual pests of asparagus in Wisconsin. The common asparagus beetle is the most prevalent and the only one that causes economic damage to asparagus. The overwintering emergence of adult asparagus beetles can occur quite early, and emergence of damaging of populations will be happening over the next 2-3 weeks in southern Wisconsin.
Both species of adult beetles have a slim, long shape with hard wing covers. The common beetle is bluish-brown with cream spots, while the spotted beetle is orange with black spots. Both are about ¼-inch in size. Eggs of both species are shiny dark rods 1/8” long. Those of the common asparagus beetle are found in groups and oriented in rows. Eggs of the spotted asparagus beetle are oviposited singly. Larvae are plump, resembling slugs, wrinkled and have visible legs. Those of common asparagus beetles are cream to gray-colored with a dark head and legs, while those of the spotted asparagus beetle are orange.
Adults of the common asparagus beetle feed on the plant’s spears and ferns. Disfigured and unmarketable spears can result when the beetles feed or lay eggs on the spears. Spotted asparagus beetle larvae feed more on the berries rather than the ferns of asparagus. Larvae secrete a black fluid onto the plants. Spring spear feeding reduces crop quality (browning, scarring, staining, and bent growth). Summer fern feeding can cause defoliation and reduces yield of subsequent years. Eggs laid on spears are unattractive to consumers, though harmless. Large populations of asparagus beetles, if left unchecked, can defoliate the plants.
Asparagus beetle overwinters in plant debris and brush as an adult. Adults become active in spring when new spears emerge. The spotted asparagus beetle becomes active later in spring than the common asparagus beetle. Common asparagus beetles lay eggs on spears while spotted asparagus beetles lay eggs on ferns. About a week later eggs hatch. The larvae feed for about two weeks on asparagus and then pupate in the soil. About one week later the next generation of adults hatch. Two to three generations occur in a growing season. Most larvae and adults are more active in the afternoon when the temperature and sunlight are at their peak.
Begin sampling for these insects now in early spring and continue throughout the growing season. In spring, sample twenty plants each at five different locations, and in summer, sample ten plants each in five different locations. See scouting thresholds for when to begin treatment. Spring sampling thresholds are designed to reduce spear damage while later-season thresholds are designed to reduce long-term damage caused by defoliation. Scouting should occur in the afternoon when the beetles are most active.