How to carry out pest and disease prevention and control for tropical crops after a severe typhoon?

This year's No. 9 super typhoon “Rammasun” made landfall successively in Hainan, Guangdong and Guangxi on July 18-19, with maximum wind force of 17. The areas the typhoon passed through experienced violent winds and rainstorms, causing severe damage to crops such as banana, lychee, mango and sisal. The high temperatures after the disaster can very easily trigger the outbreak and spread of many pests and diseases, such as banana fusarium wilt, leaf spot disease and black spot disease; lychee anthracnose, downy blight and leaf-eating insects; mango branch blight and bacterial black spot; and sisal zebra disease. Relevant departments and monitoring stations should pay close attention to weather changes and the occurrence of tropical crop pests and diseases in their areas, guide fruit growers to promptly carry out production self-rescue, and earnestly do a good job in pest and disease prevention and control.

Monitoring and control of banana pests and diseases

For banana pests and diseases that easily occur after typhoons and rainstorms, the following control measures are recommended.

1. Strengthen banana tree vigour and improve resistance to pests and diseases. After typhoons and rainstorms, banana trees that were not snapped off have many broken leaves and many damaged roots, and the wounds created will rot, leaving the whole banana tree in weak vigour. It is recommended to spray foliar fertiliser and copper preparations such as Kocide (to prevent bacterial and fungal rot), and then apply fertiliser 7-10 days later when new leaves emerge and new roots grow, so as to strengthen banana tree vigour and improve resistance to pests and diseases.

2. Control of banana fusarium wilt. The banana fusarium wilt pathogen spreads with flowing water, and waterlogged rotting roots are susceptible to the disease. Therefore, for banana plantations located in areas where fusarium wilt occurs, first drain the accumulated water as quickly as possible, and avoid irrigating the whole plantation, which would cause fusarium wilt throughout the plantation.

3. Control of banana leaf spot disease and black spot disease. Typhoons and rainstorms can split a single complete leaf of a larger banana tree into many small leaflets, leaving many wounds on the leaves, which makes it very easy for pathogen spores to invade. Violent winds blow the pathogen conidia all over the plantation, and abundant rain makes it easy for the spores to germinate. Therefore, after typhoons and rainstorms, the chance of outbreaks of leaf spot disease and black spot disease in banana plantations greatly increases. It is recommended that tropical crop pest and disease monitoring stations and farmers strengthen monitoring. When the leaf incidence of leaf spot disease and black spot disease reaches 5%, an early warning should be issued, and close attention should be paid to the development of the disease; when the incidence reaches 10%, control action should be taken. For banana leaf spot disease, fungicides such as propiconazole, tebuconazole, triadimefon and mancozeb are sprayed on the leaves for prevention and treatment. For banana black spot disease, fungicides such as trifloxystrobin · tebuconazole, pyraclostrobin, flusilazole, myclobutanil, difenoconazole and tebuconazole are sprayed on the fruit and leaves for prevention and treatment.

4. Control of banana weevil. Large banana trees snapped or knocked down by the typhoon are dealt with, for production recovery, by cutting the banana tree at 1 m and keeping new suckers. The banana pseudostem weevil bores into banana stems. After a typhoon, there is a large amount of banana stem material for the pseudostem weevil to reproduce, and at the same time the banana trees have many damaged roots and weak vigour; under such conditions, the weevil can very easily break out. When banana weevil is found, immediately take control measures, using insecticides such as chlorpyrifos or phoxim for pseudostem spraying or pouring the pesticide solution from the base of the leaf stalk, or injecting the solution at 1.5 m height on the pseudostem of affected plants. Both the residual plants in the banana plantation and the normally growing banana trees should be treated.

Prevention and control of lychee pests and diseases

At present, lychee in Hainan is at the stage where the first autumn flush produced after fruit harvest has matured or the second autumn flush is emerging, while in Guangdong and Guangxi most are emerging their first autumn flush. The super typhoon caused some branches and shoots to break and a large number of leaves to shatter, and even whole trees to be blown down or tilted. In order to restore tree vigour as quickly as possible, cultivate strong autumn flush fruiting mother branches, and do a good job in pest and disease prevention and control, the following recommendations are put forward:

1. Promptly drain accumulated water and clean the orchard. Seize the time to dig open water ditches to drain the accumulated water from the orchard, to prevent the root system from being harmed by prolonged soaking; promptly saw off severely damaged main branches, and prune the severely wind-damaged branches once to promote new shoots.

2. Moderately right the trees and earth up. For lychee trees blown down or tilted by the wind, promptly right them to a moderate degree and earth up and firm the soil, and where conditions permit add supports for protection to prevent shaking in the wind.

3. Strengthen fertiliser and water management, appropriately apply one additional quick-acting fertiliser, and supplement organic nutrition through the leaves to speed up the recovery of tree vigour.

4. Prevent and control the occurrence of pests and diseases. Promptly spray fungicides to prevent the occurrence and spread of fungal diseases such as anthracnose caused by large numbers of wounds. Recommended agents: prochloraz (Sportak), prochloraz manganese salt (Sporgon), azoxystrobin (Amistar), difenoconazole (Score), thiophanate-methyl, carbendazim, mancozeb (Mancozeb) and miebingwei, etc. (refer to the product instructions for use concentrations); at the same time, pay close attention to the occurrence of various leaf-eating pests, especially strengthen the prevention and control of lychee geometrid and tortrix moths. According to the emergence of new shoots in the orchard, selectively spray oil-tea geometrid nuclear polyhedrosis virus (BsSNPV), Bt, diflubenzuron, abamectin, emamectin benzoate and chlorantraniliprole, etc. (refer to the product instructions for use concentrations); to promote the growth of branches and leaves, foliar fertiliser may be mixed in the spray.

Monitoring and prevention and control of mango pests and diseases

Focus on the occurrence and damage of mango branch blight and bacterial black spot, and guide fruit growers to take effective measures for control, ensuring that there is no major outbreak and spread of pests and diseases after the disaster.

1. Strengthen water and fertiliser management, enhance tree vigour, and cultivate strong branches and shoots, thereby reducing the harm of secondary disasters.

2. Recommended agents: bacterial black spot: the selected agents include Bordeaux mixture, copper oxychloride, thiodiazole-copper, quinoline copper, zhongshengmycin and kasugamycin, etc. Branch blight: the selected agents include triadimefon, thiodiazole-copper, tebuconazole, propiconazole and lime sulphur, etc. Anthracnose and scab: the selected agents include difenoconazole, kresoxim-methyl and thiophanate-methyl, etc. Leafhoppers and pests such as the mango shoot borer, leaf gall midge and leaf-cutting weevil: use spray control; the main agents include abamectin, chlorpyrifos, cypermethrin and deltamethrin, etc.

Prevention and control of sisal zebra disease

The specific measures for the prevention and control of sisal zebra disease are as follows:

1. Strengthen patrols of the sisal plantation, and do a good job in flood prevention and drainage.

2. In diseased fields and susceptible fields (young sisal fields), strictly prohibit all field operations that damage plants and avoid livestock damage, so as to prevent wound infection; control nitrogen fertiliser application to prevent excessive growth, so as to avoid a decline in resistance.

3. During the rainy season, send people to frequently inspect the sisal plantation. If diseased plants are found, treatment should be chosen in clear weather: dig out the diseased plants and burn them, and spray the diseased holes with 2% copper sulphate solution or spray the area around the diseased holes with 1:1:1000 Bordeaux mixture.

4. Spray the leaves below the 45 degree angle from the central diseased plant with 50% dimethomorph or 58% metalaxyl · mancozeb (10% metalaxyl · 48% mancozeb) or 72% metalaxyl · mancozeb (8% metalaxyl · 64% mancozeb) wettable powder at 50-100 times dilution, or 90% yishuangling (also known as aluminium triethyl phosphonate, phosethyl-Al) wettable powder at 45-90 times dilution, for 2-3 consecutive applications, sprayed once every 7-10 days. Considering that the occurrence of zebra disease is followed by infection with sisal stem rot, in order to effectively control the “two diseases”, it is necessary to add 40% carbendazim · sulphur suspension concentrate at 70-100 times dilution to the zebra disease control agents used in the area for spray control.