The Beet armyworm (Spodoptera exigua) is an important pest of many crops, including spinach. The larvae of this pest feed on foliage, often causing severe damage that can reduce crop yield and quality. This pest is found in many parts of the world and can cause significant economic losses to farmers.
Management of Beet Armyworm in Spinach
The Life Cycle of Beet Armyworm
Egg: Eggs are laid in clusters of 50 to 150 eggs per mass, usually on the lower surface of leaves near blossoms and the tip of the branch. They are greenish to white, covered with a layer of whitish scales that give the egg mass a fuzzy or cottony appearance. Eggs hatch in 2-3 days during warm weather.
Larva: The larval stage of this insect typically goes through five instars, although there may be more. During the first two instars, the larvae are usually pale green or yellow, but in the third instar, they develop pale stripes. By the fifth instar, the larvae have a varied appearance, often green on their back with pink or yellow on their underside and a white stripe along their sides. They may have dark spots or dashes along their back and sides. The larvae have smooth bodies and lack hairs and spines.
Pupa: Pupation occurs in the soil. The chamber is constructed from sand and soil particles held together with an oral secretion that hardens when it dries. The pupa is light brown and measures about 15 to 20 mm long. The pupal period lasts 6-7 days during warm weather.
Adult: The moths are moderately sized, with a 25 to 30-mm wingspan. The forewings are mottled gray and brown, normally with an irregular banding pattern and a light-colored bean-shaped spot. The hind wings are a more uniform gray or white, trimmed with a dark line at the margin. Moths usually live for 9-10 days.
Damage Symptoms of Beet Armyworm in Spinach field
- Skeletonization of foliage: Young Beet Armyworm larvae feed gregariously and skeletonize foliage, leaving behind only the veins and stems. This results in a lace-like appearance of the foliage.
- Irregular holes in foliage: As the larvae mature, they become solitary and eat large irregular holes. This can cause significant damage to the spinach leaves and reduce the yield of the crop.
- Burrowing into the crown: Beet Armyworms may burrow into the crown or center of the spinach plant, causing damage to the growing point. This can result in stunted growth and reduced yield.
- Feeding on buds: In addition to feeding on the foliage, Beet Armyworms may also feed on the buds of the spinach plant, causing damage to the developing leaves and reducing the overall quality of the crop.
Management of Beet Armyworm in Spinach by Cultural Method
- Disk fields immediately following harvest: After harvesting spinach, it is recommended to disk the fields immediately. This helps to kill any remaining larvae or pupae in the field. Destroying the habitat of Beet Armyworms reduces their population and limits their ability to infest the next crop.
- Destroy weeds along field borders: Beet Armyworms often migrate into newly planted fields from weed-infested areas. Therefore, it is important to destroy any weeds along the field borders. This helps to reduce the number of Beet Armyworms in the field and prevent them from infesting the spinach crop.