Control Methods for Green Leaf Bug in Jujube Tree Cultivation
The green leaf bug, also known as the alfalfa plant bug, can damage a variety of economic crops such as fruit trees, vegetables, cotton, and alfalfa. In 2001, the green leaf bug occurred on a large scale in the Cangzhou jujube region and severely damaged the fruit, which was rare in history. According to a survey from June 16 to 18 (the peak period of the second generation of the green leaf bug) of 26 jujube orchards in Yangsi, Liuzhuangzi and other places in Huangdipu Township, Cang County, there were an average of 2688 bugs per jujube tree, with the highest reaching 4032 on a single tree. It occurred commonly in jujube regions such as Cang County and Xian County, with an affected area of nearly 667,000 hectares.
1 Occurrence and damage characteristics
The green leaf bug uses nymphs and adults to pierce and suck the sap of jujube tree buds, tender leaves, flower buds, and young fruit. Damaged leaf buds first show chlorotic spots, and as the leaves expand, the small spots gradually become irregular holes, commonly known as “broken leaf disease” and “broken skylight.” After flower buds are damaged, they stop developing, wither, and fall off; in severe cases, almost all flowers fall off. After young fruit is damaged, some develop black necrotic spots, and some develop raised small blisters, with the fruit flesh tissue becoming necrotic; most damaged fruit falls off, seriously affecting yield.
In this region, this insect has 5 generations per year. It overwinters as eggs in weeds, diseased residues, and shallow soil. In March to April of the following year, when the average temperature is above 10°C and the relative humidity reaches about 70%, the overwintering eggs begin to hatch. The peak period of the first generation is in early May, damaging jujube buds. The peak period of the second generation is in mid-June, damaging jujube flowers and young fruit, and is the generation that damages jujube trees most severely. The occurrence periods of the third, fourth, and fifth generations are respectively mid-July, mid-August, and mid-September. Generation overlap is serious. It mainly damages crops such as beans and corn under the trees.
2 Reasons for outbreak and disaster
1) Wide host range. The green leaf bug was originally a pest on alfalfa and cotton in this region, but with agricultural structural adjustment, it shifted to damaging economic crops such as fruit trees and vegetables. In this region, jujube trees, snap beans, eggplant, and melons were severely damaged in 2001, and some plots even had total crop failure.
2) Suitable climatic conditions. The occurrence of the green leaf bug is closely related to climatic conditions. A temperature of 20-30°C and relative humidity of 80%-90% are most suitable for its occurrence. In April 2001, the average temperature was 21°C, and on April 29 there was 25.6 mm of rainfall; the temperature and humidity were very favorable for the hatching of overwintering eggs, leading to the first generation of the green leaf bug reaching a peak of damage in early and mid-May. On the one hand, this directly affected jujube tree flower bud differentiation and flower bud development; on the other hand, it directly damaged young buds, causing flower buds to fall off and affecting later flower bud formation. This was also one of the reasons for the relatively few jujube flower buds in 2001. On June 13, 14, and 16, this region had continuous rainfall, with rainfall reaching 35 mm. In addition, the control effect on the first generation of the green leaf bug was not ideal, and the insect population base was large, which further led to an outbreak and disaster of the second generation of the green leaf bug. According to statistics, the fruit drop rate reached 40%, and in severe cases reached as high as 70%, reducing small jujube yield by 30%-60%.
3) Untimely control. The green leaf bug had been found in this region since 1986, but effective control was not achieved. On the one hand, adult green leaf bugs mostly crawl onto leaves and buds at night or early morning to feed and damage, crawl quickly when disturbed, and because of their small size and body color similar to leaf color, are not easy to find. On the other hand, in past years, its occurrence was uneven and small in scale, did not constitute a disaster, and thus did not attract attention in production. In 2001, it was likewise not listed as a key control target, and by the time severe damage to jujube fruit was discovered, the green leaf bug had already grown into adults with very strong flying ability, and the spraying timing had been missed, making control difficult.
3 Control methods
1) Agricultural control. The green leaf bug overwinters as eggs in dead branches, weeds, and cracks in rough bark. Combined with winter orchard cleanup and scraping bark in early spring, overwintering eggs can be reduced. Alternatively, in mid-to-late March, combined with bark scraping, spray 3-5° Be' sulfur lime mixture, which can kill some overwintering eggs.
2) Chemical control. Hatching of green leaf bug eggs requires relative humidity above 65%, so according to weather conditions, spray promptly during the nymph stage of each generation in early May, mid-June, and mid-to-late July for control. The best effect is achieved by mixing and spraying pesticides with good contact action and strong systemic action. For example, mix and spray 4.5% beta-cypermethrin emulsifiable concentrate at 2500-3000 times dilution and 5% acetamiprid (Lüyuan No. 2 emulsifiable concentrate) at 3000-3500 times dilution. Because the green leaf bug generally hides during the day on weeds under the trees and on inter-row crops, and climbs onto the trees at night to damage them, spraying should focus on the trunk, weeds on the ground, and inter-row crops. Spray thoroughly and completely both on the trees and under them. Once adults break out in large numbers, jujube farmers in the entire village, and even the entire township, should be required to spray uniformly in the evening or morning to prevent adults from flying between areas and achieve eradication.