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 26 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 currently 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, a mycoplasma-like pathogen which causes distortion and discoloration of leaves as well as stunted, hairy and bitter roots in both carrot and parsnip. Lettuce, celery, celeriac, parsley, corn and potato are also susceptible. Aster leafhoppers also feed in 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, transmission of the aster yellows mycoplasma is ‘persistent’. This means that to become infected with aster yellows, adults or nymphs must feed for at least 2 hours on an infected host, which could be a crop in a southern state prior to 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 to 3 weeks inside the leafhopper; thereafter it is able to transmit the pathogen for the duration of its life.  Transmission from the leafhopper to a non-infected plant also requires at least 2 hours of feeding. It takes 10 to 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 37/100 in tolerant varieties. In the absence of actual 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.

carbaryl (Sevin XLR Plus): 1 to 2 qt/A; PHI 7d, REI 12h, Bee: H, Group 1A.

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 10.5 oz/A; PHI 7d, REI 4h, Bee: L, Group 4D.

imidacloprid (Admire Pro): 0.3 to 0.7 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. Carrots only.

methomyl (Lannate* LV): 1.5 to 3 pt/A; PHI 1d, REI 48h, Bee: H, Group 1A. Carrot only.

pyrethrin (PyGanic EC5.0OG): 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.

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 h of seeding as an in-furrow or narrow surface band with sufficient water for incorporation, or in drip irrigation.

zeta-cypermethrin (Mustang*): 1.9 to 4.3 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 to 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 on a daily basis. Clusters of 1 to 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 to 9 mm when full 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 surface of the root, 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 carrot, the larval mines are mostly in the lower portion of the root, but in parsnip, 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 flyers and are limited to one crop family, crop rotation to a separate field is effective. If possible, plant carrots in open fields where wind protects them from adult flights. 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 fly. Some varieties show partial resistance to rust fly. 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 to 0.2 flies per trap per day, although there are currently no available registered products in New England. Where active periods coincide, sprays for carrot weevil may help control carrot rust fly.

Carrot Weevil (Listronotus oregonensis)

Carrot weevil attacks crops and weeds in the Umbelliferacae 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 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 takes place in the soil and new adults emerge from the soil after 1 to 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 be used to 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 a useful tool. 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.

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% WDGOG): 1 to 2 lb/A soil drench; PHI 0d, REI 4h, Bee: M, Group M.

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 EC5.0OG): 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 (XenTariOG): 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 DFOG): 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.

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 14d, REI 4h, Bee:L, Group 18. Suppression only.

spinosad (SeduceOG): 20 to 44 lb/A or 0.5 to1 lb/1000 sq ft.; PHI 1d, REI 4h, Bee: M, Group 5. Spread bait on soil around plants.

zeta-cypermethrin (Mustang*): 1.4 to 4.3 oz/A; PHI 1d, REI 12h, Bee: H, Group 3A.