Occurrence Regularity and Integrated Control Technique of Grubs in Peanut Producing Areas of Linyi City

Hongjie TANG, Jiejie ZHANG, Qingfu DU

Linyi Academy of Agricultural Sciences, Linyi 276012, China

Abstract In order to effectively control the harm of grubs in peanut field, Linyi Comprehensive Experimental Station of Shandong Peanut Industry Research System conducted an investigation and study on the occurrence regularity and control techniques of peanut grubs, and summarized the occurrence regularity and causes of the outbreak of grubs in peanut field. Moreover, effective and sustainable control measures are proposed.

Key words Linyi; Peanut; Grubs; Occurrence regularity; Control technique

1 Introduction

Peanut is a main cash crop. Linyi City is one of the main peanut producing areas in Shandong Province, and the annual peanut planting area is about 100 000 hm2. In recent years, underground pests in peanut field are becoming more and more serious, and grubs are important pests that harm peanut. The investigation during peanut harvesting period shows that, there are 3.9 grubs per square meter on average, 67 grubs per square meter to the maximum, and 11 grubs found in a hole of peanuts at most. The yield of peanut is generally reduced by 30%-40% after being damaged, and some plots have patches of dead seedlings, or even no harvest. In order to effectively control the harm of grubs, Linyi Comprehensive Experimental Station of Shandong Peanut Industry Research System conducted an investigation on the occurrence regularity and control techniques of grubs in peanut fields and carried out experimental demonstration, and remarkable results have been achieved. Based on the analysis of tests and investigations in recent years, the author summarized the occurrence regularity of grubs in peanut field and proposed effective and sustainable control measures.

2 Morphological characteristics

Grubs are the general term for cockchafer larvae, with milky white body, soft and wrinkled body wall, sparsely fine hairs on body surface, large and round head, and three pairs of pereiopoda. They will play dead in case of disturbance and shrink into "C" shape. There are 14 species of grubs that harm peanut in Linyi City, among whichHolotrichiaparallelaandAnomalacorpulentaare the major grubs. Except forHloltrichiadiomphaliain Sichuan which usually has one generation every two years, other grubs have one generation each year.

3 Occurrence regularity

The larvae survive the winter at a depth of 20-40 cm in the soil, then begin to pupate in middle April of the next year and reach the peak pupation period in late April. The larvae will emerge into adults (cockchafer) in early May and reach the peak of adult emergence in early and middle June. After emergence, the adults are unearthed in the evening every day, and feed on mulberry branches and leaves, ears of corn orVitexnegundoto supplement nutrition and mate. At about 5 o’clock in the morning of the second day, they fly back to the peanut nest at a depth of 5-10 cm to lurk and lay eggs. A female adult lays a large amount of eggs, generally 15-195 eggs, with an average of more than 80 eggs. They reach the spawning peak around late June (the early stage of peanut pod setting), and the eggs begin to hatch into the first instar larvae after about 7 d, namely the end of June. At this time, the larvae only eat peanut young roots and organic matter near the roots. When they grow to the second instar larvae in middle and late July, they greatly harm peanut pods. From the end of July to early August, the third instar larvae cause the largest harms on peanuts, leaving empty kernels and mud pots, or even broken taproots and patches of dead seedlings. According to the investigation, peanuts that are covered by mulching film suffer heavy damage; peanut plants with good growth suffer heavy damage; soil with sand and land with good permeability also suffer heavy damage; bunch type peanuts suffer more than trailing type peanuts.

4 Damage symptoms

When the seedlings are damaged, the rhizomes are often bitten off by a flat cut, resulting in the phenomenon of missing seedlings and broken ridges. When peanuts are damaged at pod stage, the fruit stem is bitten off and young fruits are bitten or eaten to feed on the kernel. In severe cases, all tender fruits are eaten up, leaving only the fruit stem. Some bite off fruit stems, making the pods germinate and decay. Some eat the entire kernel to form a "mud pot", and some peel the taproot, leading to the death of the plant.

5 Integrated control technique of grubs in peanut field

The plant protection policy of "prevention first, comprehensive control" should be implemented, and the concept of "public plant protection, green prevention and control" must be established. Multiple methods, such as combination of agricultural control, physical control and chemical control, simultaneous prevention and control of adults and larvae, simultaneous control at seedling stage and acicula forming stage, and combination of field control and off-field control, must be adopted simultaneously to carry out comprehensive control.

5.1 Agricultural controlApplication of fully decomposed farmyard manure, intensive cultivation, scientific watering and fertilization, reasonable proportion of nitrogen, phosphorus and potassium fertilizer, appropriate control of nitrogen fertilizer, increased application phosphorus, potassium and micro-fertilizer will promote the healthy growth of peanuts, and improve the ability of peanuts to resist diseases and insect pests.

Castor-oil plants can be planted in scattered open spaces near fields, field edges, villages and ditches. Castor-oil plants contain ricin, which can poison feeding cockchafer and reduce the initial quantity of adults.

When harvesting peanuts, the grubs turned out should be picked up and destroyed concentratedly, which can effectively reduce the population density in the next year.

5.2 Physical controlAdult insects can be induced and killed by solar frequency trembler grid lamp. Fields can be equipped with moth-killing lamps at a density of 1 lamp/3.33 hm2, and lamps are turned on at night during the adult exhumation period from June to August to trap and kill cockchafers and reduce the spawning of adults.

5.3 Chemical control

5.3.1Seed dressing. Before sowing, seeds can be dressed with seed coating agents, or mixed with 50% phoxiphos EC (500 mL agent diluted with 10-50 kg water and mixed with 400-500 kg seeds). The duration of the agent is up to 4 months, which can reach the effect that single seed dressing controls the pests in the whole growing period. This method can also effectively control rodent damage.

5.3.2Soil treatment. Before peanut sowing, 5% phoxim GR can be broadcasted at a density of 5-6 kg/667 m2in sowing ditches or sowing holes along peanut ridges, which has good control effect. Broadcasting before rain or watering after broadcasting will receive better effect. The pod enlargement stage of peanut is the most important and effective period for prevention and control. 2.5-3.0 kg of 5% phoxim GR can be mixed with 15-20 kg of fine soil, and broadcasted in the rhizosphere of peanuts per 667 m2. The areas with better source of water can be irrigated with above drug liquids.

5.3.3Use of new long-acting agents. Green Eagle (35% phoxim), a new environmental microcapsule insecticide, has the characteristics of environmental protection, low toxicity, low residue, high efficiency, long duration, easy application and labor saving. The duration of the agent is up to 120 d when used to control grubs, and single application could effectively control grubs in the whole growth period of peanut. In 2021, the author conducted a comparison test of multiple points and multiple methods, and the control effect reached more than 90%, while the peanut yield increased by more than 10%.

In conclusion, on the basis of conscientiously implementing the policy of "prevention first, comprehensive control", we should also adhere to the control strategy of "controlling adults to lower initial population, mainly controlling larvae to protect pods", so as to give full play to the advantages of comprehensive control to control grubs in peanut fields effectively and sustainably, and to obtain the best economic, ecological and social benefits.