Includes spinach leafminer (Pegomya hyoscyami)
Pest description and crop damage Adults are small black to gray flies with yellow markings. The body is covered with long stiff bristles. Larvae are a nearly translucent white or yellow color and about 0.25 inch long when mature. Eggs are white, cylindrical, and laid singly or in small groups. Both larvae and adults damage plants. Larval feeding results in slender, winding trails on the leaves, which form large white blotches if mining becomes severe. Adults can make as many as 100 feeding punctures on a single leaf. Around 5% of these punctures may contain actively feeding larvae. Excessive mining renders leaves unmarketable, reduces photosynthetic capacity, and provides easy access for disease organisms.
Biology and life history Leafminers overwinter as pupae in the soil. Adults emerge in late May, mate, and females lay eggs on the undersides of beet and chard leaves or on lambsquarters. The eggs hatch in about 4 days, and the small maggots eat into the leaf. There may be several maggots in a leaf. When mature, larvae fall to the ground and pupate just under the soil surface. Adults emerge in 10 to 25 days and begin laying eggs for another generation. There are at least three generations each year.
Pest monitoring Regularly check young seedlings for leaf mines. Most mines occur on cotyledons and the first true leaves. Some mines are more visible when seen from the underside of the leaf. If leafminer populations build to high levels when seedlings have four to five leaves, a chemical treatment may be necessary. Treat if you find more than an average of one mine per leaf in your overall field sample. To be effective, sprays must be applied to the larval stage.
Natural enemies, especially parasitic wasps, commonly reduce populations of leafminers, unless they are killed by insecticides applied to control other pests. To avoid killing beneficials, choose selective pesticides for treating other pests, whenever possible. Other parasites attack leafminers, but because leafminers feed within the leaf, they generally are protected from most predators.
Liriomyza leafminers attack a wide variety of vegetable crops. Where possible, avoid planting next to infested fields, especially those near harvest. Postharvest disking of fields destroys pupae and reduces migration of adult flies into susceptible fields. Row covers work well in excluding egg-laying female flies.
Home gardeners: Remove and destroy affected leaves.
Management-chemical control: HOME USE
- azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
- kaolin-Applied as a spray to foliage, it acts as a repellent to some insect pests. Some formulations are OMRI-listed for organic use.
- plant essential oils (rosemary, etc.)- Some formulations are OMRI-listed for organic use.
- pyrethrins-Some formulations are OMRI-listed for organic use.
- spinosad-Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
- abamectin (Agri-Mek) at 0.009 to 0.019 lb ai/a. PHI 7 days. REI 12 hr. Retreatment interval 7 days. Do not exceed 0.056 lb ai/a per season. Addition of a silicone surfactant will increase translaminar movement of abamectin.
- azadirachtin (Neemix)-See label for rates. Acts slowly; apply early. PHI 0 days. REI 4 hr. Thorough coverage and repeat applications are necessary. Some formulations are OMRI-listed for organic use.
- bifenthrin (Brigade WSB) at 0.033 to 0.1 lb ai/a. PHI 40 days. REI 12 hr. Retreatment interval 7 days. Limit 4 treatments per year. Do not exceed 0.4 lb ai/a per season.
- bifenthrin + avermectin (Athena) at 0.092 to 0.116 lb ai/a. PHI 40 days. REI 12 hr. Retreatment interval 7 days. Do not exceed 0.056 lb ai/a avermectin or 0.4 lb ai/a bifenthrin per year.
- bifenthrin/imidacloprid (Brigadier) at 0.08 to 0.096 lb ai/a. PHI 40 days. REI 12 hr. Do not exceed 0.24 lb ai/a imidacloprid and 0.24 lb ai/a bifenthrin per season. Retreatment interval 7 days.
- chlorantraniliprole (Coragen) at 0.065 to 0.098 lb ai/a as soil, chemigation or foliar treatment. PHI 1 day. REI 4 hr. Do not exceed 0.2 lb ai/a per season.
- cyantraniliprole (Exirel) at 0.088 to 0.133 lb ai/a. PHI 1 day. REI 12 hr. Retreatment interval 5 days. Do not exceed 0.4 lb ai/a per year.
- cyromazine (Trigard) at 0.125 lb ai/a. PHI 7 days. REI 12 hr. Do not make more than six applications per crop.
- dinotefuran (Scorpion 35SL) at 0.05 to 0.13 lb ai/a foliar, 0.23 to 0.27 lb ai/a soil. PHI 7 days for foliar, 21 days for soil. REI 12 hr. Retreatment interval 7 days. Do not exceed 0.266 lb ai/a foliar or 0.532 lb ai/a soil per season.
- emamectin benzoate (Proclaim) at 0.01 to 0.015 lb ai/a. PHI 7 days. REI 12 hr. Retreatment interval-7 days. Do not exceed 0.09 lb ai/a per season.
- Isaria fumosorosea (PFR-97 20%WDG) at 1 to 2 lb product per acre. PHI 0 days. REI 4 hr. Repeat every 3 to 10 days as needed. OMRI-listed for organic use.
- permethrin (Loveland Permethrin) at 0.1 to 0.2 lb ai/a. PHI 1 day. REI 12 hr. Retreatment interval 3 days. Do not graze or feed treated crop refuse to livestock. Do not exceed 0.6 lb ai/a per season.
- spinetoram (Radiant SC) at 0.047 to 0.078 lb ai/a. PHI 1 day. REI 4 hr. Retreatment interval 4 days. Do not exceed 0.266 lb ai/a per season. Do not apply to seedling leafy vegetables grown for transplant within a greenhouse, shade house, or field plot. Limit 6 treatments per season.
- spinosad (Success, Entrust SC) at 0.094 to 0.156 lb ai/a. PHI 1 day. REI 4 hr. Treat eggs, at hatch, and small larvae. Do not exceed 0.45 lb ai/a per crop. An adjuvant improves control. Spinosad takes several days to achieve full effect. Monitor fields and pest populations carefully. Multiple applications may be necessary. Entrust SC is OMRI-listed for organic use.
- thiamethoxam (Platinum) at 0.078 to 0.172 lb ai/a, soil. PHI 30 days. REI 12 hr. Do not exceed 0.172 lb ai/a per season. See label for recommended in-row application instructions. Suppression only.