Detailed Explanation of the Occurrence Patterns and Control Methods of the Jujube Inchworm

The jujube inchworm, also known as the jujube spanworm, dingmenchi, or gongyao worm, belongs to the order Lepidoptera, family Geometridae, and is one of the major pests of jujube leaves.

I. Occurrence Patterns

The larvae damage the tender buds, leaves, and flower buds of jujube. It has 1 generation per year, overwintering as pupae in the soil 10-15 cm deep around the tree canopy. In early March of the following year, they emerge as adults. After mating, they lay eggs. The female adults are wingless and must crawl up the tree trunk to lay eggs. After an egg stage of about 22 days, from late March to early April, the larvae hatch and climb up the tree to cause damage. Larvae in the 1st to 3rd instars have a small appetite and mainly feed on tender leaves, while larvae in the 4th to 5th instars greatly increase their food intake and often strip the leaves completely. After the larvae develop through 5 instars, from late April to mid-May, they enter the soil to pupate, oversummering and overwintering. Their larvae are highly voracious and damage all green tissues of the jujube tree, including tender buds, leaves, flower buds, fruit-bearing shoots, and new twigs. When outbreaks are severe, they can completely consume all jujube leaves or buds, causing serious yield reduction or total crop failure. The length of the egg stage is closely related to temperature; the higher the average temperature, the shorter the egg stage. The damage caused by larvae increases as they grow older, and the larvae exhibit death-feigning behavior and chemotaxis.

II. Control Measures

1. Capturing Larvae

In spring, within a 1 m diameter area around the tree trunk, turn and dig the soil to a depth of 15 cm to dig out and destroy the overwintering pupae. When digging around the tree base in early winter or early spring, pick out the pupae as they are found. You can also take advantage of the larvae's habit of feigning death and falling to the ground when disturbed; during the larval damage period, shake the tree to dislodge the larvae and kill them on the spot.

2. Collecting Eggs

From late February to early March, wrap plastic film or a paper skirt around the tree trunk to prevent female moths from climbing up to mate and lay eggs, and handpick the moths tree by tree every morning or evening. Because the trunk is wrapped with a skirt, the female moths cannot climb up and tend to concentrate in the bark crevices beneath the skirt to lay eggs. Therefore, regularly inspect the coarse bark and scrape off the eggs, or tie two loops of straw rope beneath the skirt to attract female moths to lay eggs, replacing the straw rope about every 10 days and burning it.

3. Chemical Control

Based on the characteristics and damage patterns of the jujube inchworm, chemical control can be applied twice. For the first application, when the jujube buds have grown to about 3 cm, spray 50% dichlorvos or 75% phoxim at 800-1000 times dilution, or spray 50% parathion at 1000-1500 times dilution. For the second application, when the jujube buds have grown to 5-8 cm, spray 20% fenpropathrin-malathion emulsifiable concentrate at 4000 times dilution, or 35% chlorethoxyfos emulsifiable concentrate at 1000 times dilution, etc.

4. Biological Control

Protect natural enemies and reduce pest population density.