Lettuce pests can be controlled in large commercial plantings. Due to the high planting densities and large fields, scouting is often neglected. Most pests are found near a specific location or concentrated in an area close to either other crops or forests. If these areas are sprayed first and regularly the spread of pests deeper into commercial plantings can be avoided to some extent. Remember all pests have predators that eet them so it is important not to kill the predators as well. They help lowering spraying costs naturally.
American bollworm (Helicoverpa armigera)
The first in star larvae are almost black and the colour of the older larvae can vary from nearly black to brown, green or even pink. The underside is a dirty white. It is mostly recognised by the dirty white line along each side of the larvae with distinct spiracles. The adult larvae are 3 cm long. It penetrates the lettuce head from the bottom of the leaves and eat their way up into the heads. Eggs can also be laid on top of the plant and when they are hatched, they penetrate the head from the top. American bollworm renders the lettuce head unmarketable by destroying the tender leaves first.
Control: deltamethrin EC
Controlling aphids (Hyperomyzus lactucae) in lettuce
Aphids are small delicate pear-shaped soft-bodied insects with long legs and antennae. They are found in small colonies sucking the sap of the tender growth of young leaves. They are very small but they have characteristic cornicles on the ends of their abdomens. Aphids are 2-3 mm long, green with pale legs and the winged from has a broken, dark, dorsal patch on the abdomen. These aphids are vectors of various lettuce viruses.
Control: mevinphos EC or SL
Cutworm (Agrotis segetum)
Cutworms are lettuce pests found all over the world. Dirty grey hairless waxy larvae. Usually found 2-5 cm below the soil surface near the cut off plant. They are active during the night, cutting the stems of young plants just above or below the soil surface. They also penetrate the heads at the bottom of the leaves. Cutworm are a serious pest of transplanted seedlings as well as younger field sown crops. They cut through the stems near the ground, causing a total loss of plants. They eat very little of the plant and move on to the next plant.
Control: deltamethrin EC or chlorpyrifos EC