Insect Control

NOTES:  For the insecticides listed below, one product trade name and formulation is provided for each active ingredient (AI) as an example of rates, preharvest interval (PHI), restricted entry interval (REI), and special instructions. In many cases, there are other products available with the same AI. Please see Table 27 and Insecticides Alphabetical Listing by Trade Name for more information on these insecticides.

• The designation (Bee: L, M, or H) indicates a bee toxicity rating of low, moderate, or high. See the Protecting Honeybees and Native Pollinators section for more details.
• The symbol * indicates a product is a restricted use pesticide. See Pesticide Safety and Use for more details.
• The symbol ^OG   indicates a product is listed by the Organic Materials Review Institute (OMRI) as approved for use in organic production. See Organic Certification section for more details.

Aster Leafhopper (Macrosteles quadralineatis)

Aster leafhopper is a minor pest in New England but a major pest in the Midwest.  Although it inflicts very little direct feeding injury to carrots or parsnips, it is important because it vectors aster yellows. This mycoplasma-like pathogen causes distortion and discoloration of leaves and stunted, hairy, and bitter roots in both carrots and parsnips. Lettuce, celery, celeriac, parsley, corn, and potato are also susceptible. Aster leafhoppers also feed on cereal grains, especially oats, wheat and barley, clover, and various weeds. The adults are small, less than 4 mm, light green with grey wings, and have 6 pairs of black spots on the top and front of the head. Among vegetables, lettuce is the primary crop that is suitable for leafhopper reproduction.  Eggs are laid in plant tissues, and the yellowish nymphs feed and develop into adults in 3 to 4 weeks. There are 3 generations per year in northern states. Aster leafhoppers migrate north annually from the southern US, and can arrive as early as May, sometimes already infected with the aster yellows pathogen.  In northern states, they can also overwinter in the egg stage, on weeds or winter grains.

Unlike many insect-vectored viruses, adults or nymphs must feed for at least 2 hours to become an infected host to transmit the aster yellows mycoplasma. This could occur on infected crops in a southern state before migration or a local crop or weed. Weeds that may be infected include thistle, fleabane, wild lettuce, sow thistle, chicory, wild carrot, galinsoga, dandelion, plantain, and cinquefoil.  There is an incubation period of 2-3 weeks inside the leafhopper; thereafter, it can transmit the pathogen for its lifetime.  Transmission from the leafhopper to a non-infected plant also requires at least 2 hours of feeding. It takes 10-15 days for infected plants to show symptoms.

If aster yellows disease becomes a problem on your farm, plant tolerant or resistant varieties, which are available for carrot and lettuce. Control weed hosts and avoid growing susceptible crops in fields close to winter grains. Reflective or light-colored straw mulch effectively reduces aster yellows infection, and row cover prevents infection by keeping out leafhoppers. Cool, wet weather limits leafhopper activity and disease transmission. Monitor nearby grain fields or carrot crops in July and August using sweep nets. Thresholds widely used in the Midwest are based on the aster yellows index, which is the product of the percent infection of the leafhopper population (determined by testing) and the number of leafhoppers per 100 sweeps. At 2% infection, the threshold in carrots is 25 leafhoppers per 100 sweeps in susceptible varieties and 37 leafhoppers per 100 sweeps in tolerant varieties. In the absence of test results for % infection, assume 2%. It is important to control leafhoppers before infection takes place. Because several hours of feeding are required for the aster leafhopper to transmit aster yellows to a plant, disease suppression can be achieved by killing the vector before inoculation occurs.

• alpha-cypermethrin (Fastac* EC): 1.8 to 3.8 oz/A; PHI 1d, REI 12h, Bee: H, Group 3A.
• beta-cyfluthrin (Baythroid*XL): 1.6 to 2.8 oz/A; PHI 0d, REI 12h, Bee: H, Group 3A. Carrot only. 
• carbaryl (Sevin XLR Plus): 1 to 2 qt/A; PHI 7d, REI 12h, Bee: H, Group 1A. Do not apply to crops in bloom. 
• deltamethrin (Delta Gold*): 1.5 to 2.4 oz/A; PHI 3d, REI 12h, Bee: H, Group 3A.
• esfenvalerate (Asana* XL): 5.8 to 9.6 oz/A; PHI 7d, REI 12h, Bee: H, Group 3A. Carrot only.
• flupyradifurone (Sivanto): 7 to 14 oz/A; PHI 7d, REI 4h, Bee: L, Group 4D.
• imidacloprid (Admire Pro): 0.31 to 0.74 oz/1,000 row ft or 4.4 to 10.5 oz/A; PHI 21d, REI 12h, Bee: H, Group 4A. Soil applications only.
• kaolin (Surround WPOG): 25 to 50 lb/A or 0.25 to 0.5 lb/gal; PHI 0d, REI 4h, Bee: L. Suppression and repellence only.
• malathion (Malathion 57 EC): 2 pt/A; PHI 7d, REI 24h, Bee: H, Group 1B. Carrot only.
• methomyl (Lannate* LV): 1.5 to 3 pt/A; PHI 1d, REI 48h, Bee: H, Group 1A. Carrot only.
• pyrethrin (PyGanic EC5.0^OG): 4.5 to 17 oz/A; 0.25 to 0.50 oz/gal, 3 gal/1000 sq ft in greenhouse for backpack sprayers; PHI 0d, REI 12h, Bee: M, Group 3A.
• sodium tetraborohydrate decahydrate (Prev-AM): 100 oz/100 gal; REI 12h, Bee: L, Group 25. Do not apply in midday sun or mix with copper, sulfur or oils.
• sulfoxaflor (Transform WG): 1.5 to 2.75 oz/A; PHI 7d, REI 24h, Bees: H, Group 4C. Do not apply between 3 days prior to bloom and until after petal fall.
• thiamethoxam (Actara): 1.5 to 3 oz/A; PHI 7d, REI 12h, Bee: H, Group 4A.
• thiamethoxam (Platinum): 5 to 12 oz/A; REI 12h, Bee: H, Group 4A. Systemic insecticide used at seeding or within 24 hours of seeding as an in-furrow or narrow surface band with sufficient water for incorporation, or in drip irrigation application to the seed/seedling root zone during or after planting/transplanting operations.
• zeta-cypermethrin (Mustang*): 1.76 to 4 oz/A; PHI 1d, REI 12h, Bee: H, Group 3A.

Carrot Rust Fly (Psila rosae)

Carrot rust fly feeds on many umbelliferous crops and weeds. Though it is considered principally a pest of carrots, it can also damage parsnips, celery, celeriac, parsley, and dill. Adults are slender flies, 4-5 mm long, with slightly iridescent wings, yellowish-brown head and legs, dark red eyes, and shiny black thorax and abdomen. Adult flies enter fields to oviposit and return to field edges daily. Clusters of 1-3 eggs are laid in the soil near the base of food plants. Larvae are milky-white to yellowish, without legs, tapered at the head with dark mouth hooks, and 6-9 mm when fully grown. Root feeding of hatching larvae may kill young plants or cause forked, stunted, or fibrous roots. Larvae burrow into the main root as they grow larger, then leave the root to form an oval brown pupa up to 10 cm deep in the soil. Sometimes larvae overwinter in fall carrot roots, but mainly pupa overwinter in the soil, and adults emerge in May and June. Cool, moist conditions favor adult emergence. Early-season carrots are susceptible to attack by this first flight, especially the earliest successions, as flies tend to select larger carrots to lay eggs. The summer generation of adult flies emerges in August and is active through September, causing damage to late or long-season carrots. Fall damage may increase in later harvests. The larva mines the root's surface, leaving trails and blotchy areas that develop a rusty color and render the root unmarketable.  Wounds provide entry to plant pathogens. The foliage may become red or yellow.  In carrots, the larval mines are mostly in the lower portion of the root, but in parsnips, they are in the upper portion.  In celery, the larva may tunnel upward into the crown and stalks. Damage is often worst near sheltered field edges, with damage decreasing toward the center of the field.

Avoid leaving crops in the field over the winter, where they support overwintering larvae or attract spring egg-laying. Because adults are weak fliers and are limited to one crop family, crop rotation to a separate field is effective—plant carrots in open fields where wind protects them from adult flights if possible. The crop is most vulnerable around the edge of sheltered fields surrounded by woods. Row covers protect the crop from egg-laying. Intercropping with onion has been shown to reduce damage by carrot rust flies. Some varieties show partial resistance to rust flies. Stagger plantings to distribute risk, or if possible, time plantings to avoid the first and second flight periods. In the fall, harvest edges first, as these may have the most damage. Monitor flight with yellow sticky traps placed upright on a stake just above the canopy and several feet into the field; count flies twice weekly. Use multiple traps per field, especially along field edges that are sheltered from wind. Traps reflect population levels and indicate the beginning, peak and end of flight periods, and are used to time insecticides or determine when it is safe to remove row cover. In Quebec and Ontario, insecticides are recommended at thresholds of 0.1-0.2 flies per trap per day, although no registered products are available in New England. Where active periods coincide, sprays for carrot weevil may help control carrot rust flies.

Carrot Weevil (Listronotus oregonensis)

Carrot weevil attacks crops and weeds in the Umbelliferae family and can cause severe damage to parsley, dill, carrot, celery, and parsnip. Adult beetles are brown, less than 6 mm long, with the typical weevil ‘snout-like’ mouthparts. They overwinter in soil or plant debris near previous host crops. Although able to fly, they travel and invade fields mostly by walking. In spring, females lay eggs into holes that they gouge in petioles or tops of roots but only oviposit in plants that are older than the 4-leaf stage.  Egg-laying starts at 234 growing degree days (GDD), using a base temperature of 44.6°F. Young larvae tunnel in stalks or roots and may kill young plants. Larvae tunnel downward as they grow.  Tunnels are very pronounced and may be invaded by fungi. Unlike carrot rust fly, feeding damage by weevil larvae is limited to the upper third of the root. Pupation occurs in the soil, and new adults emerge after 1-2 weeks. There is generally 1 generation per year in New England. Weevils tend to be worse in organic soils. To prevent damage, rotate carrot and parsnip crops to new fields to escape overwintering adults.  Delay planting until after eggs have been deposited (90% of oviposition is expected to be completed by 820 GDD). Carrot-baited traps (Mason jar, Boivin, or modified Boivin traps) deployed at field edges can detect incoming adults.  Sampling roots is an effective way to estimate the population of larvae. Insecticide must be applied before egg-laying begins, so timing is important; GDD can be useful. Sprays targeting the adult beetles should be applied once or twice, 10 to 14 days apart, from the 1- to 3-leaf stage.

• alpha-cypermethrin (Fastac* EC): 1.8 to 3.8 oz/A; PHI 1d, REI 12h, Bee: H, Group 3A.
• beta-cyfluthrin (Baythroid*XL): 2.8 oz/A; PHI 0d, REI 12h, Bee: H, Group 3A. Carrot only. 
• esfenvalerate (Asana*XL): 9.6 oz/A; PHI 7d, REI 12h, Bee: H, Group 3A. Begin treatment when weevils become active, and provide thorough spray coverage of crowns. For carrot only.
• Isaria fumosorosea Apopka Strain 97 (PFR-97 20% WDG^OG): 1 to 2 lb/A soil drench; PHI 0d, REI 4h, Bee: M, Group UN.
• malathion (Malathion 57 EC): 1 to 2 pt/A; PHI 7d, REI 24h, Bee: H, Group 1B. For parsnips only.
• oxamyl (Vydate* L): 2 to 4 pt/A; PHI 14d, REI 48h, Bee: H, Group 1A. Use as a soil directed spray in 20 gal water/A. Must be incorporated into soil by water or mechanical means to a depth of at least 2 ". Carrot only.
• pyrethrin (PyGanic EC5.0^OG): 4.5 to 17 oz/A; 0.25 to 0.50 oz/gal, 3 gal/1000 sq ft in greenhouse for backpack sprayers; PHI 0d, REI 12h, Bee: M, Group 3A.

Cutworms

In carrots, cutworms feed on petioles, cutting them near the ground. One cutworm can destroy several plants in a single night. See cutworms in the Pepper and Tomato (Outdoor) sections for more information on the black and variegated cutworms. Use spot treatments in affected areas.

• alpha-cypermethrin (Fastac* EC): 1.3 to 3.8 oz/A; PHI 1d, REI 12h, Bee: H, Group 3A.
• Bacillus thuringiensis aizawai (XenTari^OG): 0.5 to 1.5 lb/A; PHI 0d, REI 4h, Bee: L, Group 11. Must be ingested; apply in evening or early morning, before larvae are actively feeding. Adherence and weather-fastness will improve with use of an approved spreader-sticker. Use high rate at cool temperatures. For resistance management, may be rotated with Bt kurstaki products (Dipel).
• Bacillus thuringiensis kurstaki (Dipel DF^OG): 0.5 to 2 lb/A; PHI 0d, REI 4h, Bee: L, Group 11. Must be ingested; apply in evening or early morning, before larvae are actively feeding. Adherence and weather-fastness will improve with use of an approved spreader-sticker. Use high rate at cool temperatures. For resistance management, may be rotated with Bt aizawai products (XenTari).
• beta-cyfluthrin (Baythroid* XL): 1.6 to 2.8 oz/A; PHI 0d, REI 12h, Bee: H, Group 3A. Carrot only. 
• bifenthrin (Brigade* 2EC): 5.1 to 6.4 oz/A; PHI 21d, REI 12h, Bee: H, Group 3A.
• carbaryl (Sevin XLR Plus): 1 to 2 qt/A; PHI 7d, REI 12h, Bee: H, Group 1A. Most effective on species that feed on upper portions of the plant.
• esfenvalerate (Asana* XL): 5.8 to 9.6 oz/A; PHI 7d, REI 12h, Bee: H, Group 3A. For carrot only.
• methomyl (Lannate* LV): 0.75 to 1.5 pt/A; PHI 1d, REI 48h, Bee: H, Group 1A. For variegated cutworm on carrot only.
• methoxyfenozide (Intrepid 2F): 8 to 16 oz/A; PHI 1d, REI 4h, Bee:L, Group 18. Suppression only.
• spinosad (Seduce^OG): 20 to 44 lb/A or 0.5 to1 lb/1000 sq ft.; PHI 3d, REI 4h, Bee: M, Group 5. Spread bait on soil around plants.
• zeta-cypermethrin (Mustang*): 1.28 to 4 oz/A; PHI 1d, REI 12h, Bee: H, Group 3A.