What pesticides are effective for controlling pomelo pests and diseases?
Every year around National Day, large quantities of pomelo go on the market in our country and are very popular among people. At present, many regions of our country are growing them, but during the growing period, various pests and diseases appear, and pesticides must be sprayed for control. So what pesticide should be used for pomelo control?
1. Gummosis disease
Damage symptoms: It damages the trunk and main branches, affecting tree vigor. In severe cases, the lesions expand and “girdle” the trunk, causing the plant's branches and trunk to wither and die.
Control method: First scrape off the rough bark at the diseased part (until greenish-yellow is exposed), then make several longitudinal cuts deep into the xylem, and then apply Hushu Jiangjun for smearing treatment.
2. Foot rot disease (root crown rot scar)
Damage symptoms: It mainly damages the root crown of the trunk. The bark at the base of the trunk of affected plants rots, causing yellow leaves and withered branches, weakened tree vigor, and reduced yield. In severe cases, the entire plant withers and dies. The incidence rate is high in the hot and rainy season from July to August.
Control method: Scrape off the diseased tissue and burn it in a centralized manner. After scraping, apply Hushu Jiangjun. At the early stage of the disease or before it occurs, spray with 800 times dilution of Xingao Zhimo for control.
3. Red spider mite
Damage symptoms: It damages leaves, fruits, and tender shoots. Affected leaves show grayish-white spots, and in severe cases the whole leaf turns grayish-white, loses its luster, and falls early, weakening tree vigor. Affected fruits drop. Adults are nearly oval and dark red. Red spider mites can cause damage throughout the year.
February to March is the overwintering damage period for red spider mites, April to June is the secondary peak period for red spider mites, and July to August, with high temperatures, has a small occurrence and is the low peak period for red spider mites; September to November, with dry climate, has a large occurrence and is the second peak period for red spider mites; if the second peak period has long periods of rain and a small occurrence, and the secondary peak is controlled in time, the pest population density will be greatly reduced, and as the population density of the second peak decreases, spraying can be reduced or omitted.
Control method: In February during overwintering, spray once with 2000 times dilution of Kemante. During the secondary peak from April to May, spray once with 2000 times dilution of Dazinquone, or 2500 times dilution of Tiansaoli. In June, spray once with 3000 times dilution of Kemante. In September, spray once with 3000 times dilution of Kemante. If the pest source has no peak occurrence or there is fewer than one pest per leaf, use Kemante at a concentration of 3500 times dilution. After harvesting fruit in mid-November, if red spider mite population density is high, spray once with 1500 times dilution of Kemante. If orchard inspection shows few red spider mites, spraying may be omitted, and waiting until mid-to-late December when spraying rosin mixture will also combine with controlling red spider mites for an effect.
4. Rust mite
Damage symptoms: Also called rust mite. It is a common and serious pest of red-fleshed honey pomelo. The decline of many pomelo orchards is mostly caused by rust mites damaging fruits and leaves. Affected fruits have a brown surface, commonly known as “black skin,” and affected leaves easily cause defoliation.
Rust mites prefer shade and fear light, and mostly damage inner-canopy fruits, fruits on drooping branches, and the shaded side of fruits. At first it looks like a layer of yellow powder. Once black-skinned fruit appears, even if pesticide is sprayed to kill the rust mites, the black skin cannot be reversed. Generally, in late April to early May they move to young fruits to damage and multiply in large numbers, and this is the key time for pesticide control.
Control method: In early May, mid-June, and late July, focus on control 1-2 times each, and in late August control once in time. Pesticides: 500 times dilution of 80% zineb, 1000 times dilution of amidothion. Choose either one and mix with other insecticides. Prune moderately to prevent the canopy from becoming too dense and improve orchard ventilation.
5. Swallowtail butterfly
Damage symptoms: Swallowtail butterflies lay eggs at the tips of tender leaves. The larvae (also called big-head worms) bite and feed on the tender leaves of red-fleshed honey pomelo, causing damage. When large, they can eat an entire leaf clean. They overwinter as pupae on fruit trees and emerge in spring when it warms. On severely damaged new shoots, only the petiole and midrib remain. If disturbed, the larvae extend an osmeterium and release a fragrant odor
Control method: Common pesticides include 1000 times dilution of 40% dimethoate, 800 times dilution of 90% trichlorfon aqueous solution, and 1000 times dilution of 80% dichlorvos.
6. Scale insects
Damage symptoms: Common ones in pomelo orchards include: brown soft scale, arrowhead scale, citrus mealybug, and cottony cushion scale. They mainly gather as nymphs and female adults on leaves, fruits, and branches, sucking plant sap and causing great damage to red-fleshed honey pomelo. Affected plants grow poorly, showing yellowing leaves, early leaf and fruit drop, and in severe cases the plant withers and dies, reducing economic value. Scale insects prefer shaded environments, and overly dense branches and leaves favor their survival and reproduction.
① Brown soft scale: purplish-brown, with pale brown margins, raised center, yellow body. It damages pomelo branches and fruits, often piling up in stacks on branches and leaves. Brown soft scale has about 5 generations per year. Mid-to-late April is the first-generation nymph stage, mid-to-late June is the second-generation nymph stage, early-to-mid August is the third-generation nymph stage, late September is the fourth-generation nymph stage, and mid-to-late December is the fifth-generation nymph stage. If control is timely before the third generation, the fifth generation occurs in smaller numbers. For brown soft scale control in May, June, and July during the first and second nymph stages, focus on control for better results. For each generation, apply pesticide during the peak occurrence of first-instar nymphs.
② Arrowhead scale: purplish-brown with grayish-white margins. The male scale cover is entirely white, while the female scale cover is arrowhead-shaped, purplish-brown with grayish-white margins. Arrowhead scale occurs in three generations per year: early-to-mid May is the first-generation nymph stage, mid-to-late July is the second-generation nymph stage, and early September is the third-generation nymph stage. For control in each generation, pesticide should be applied during the peak occurrence of newly hatched nymphs of that generation and the second generation.
③ Citrus mealybug: The female adult is oval and flat, covered with rough white waxy material, and when the body is crushed it exudes a reddish-brown liquid. Nymphs have white waxy powder on their backs. Citrus mealybug has 5 generations per year. A few nymphs begin to hatch in early April, the first-generation nymph stage is after mid-April, the second-generation nymph stage is in mid-June, and the third-generation nymph stage is in early-to-mid July. The first and second generations damage new shoots and leaves, and attention should be paid to control from June to September.
④ Cottony cushion scale: The female is oval with a raised back, reddish-brown body, with white powdery material and slender waxy filaments on the body, and when laying eggs secretes a white egg sac from the abdomen. Cottony cushion scale occurs in three generations per year: early May is the first-generation nymph stage, early-to-mid July is the nymph stage, and late September is the third-generation nymph stage. Control timing should seize the nymph stage for spraying.
Control method: From May to September, choose any one of the following pesticides: 1000 times dilution of Jieshate, 1000 times dilution of amidothion, 700 times dilution of malathion, 1000 times dilution of 20% amitraz, 700 times dilution of Supesha (used in autumn), and from mid-to-late December to mid-to-late January of the following year spray once with 15-17 times dilution of rosin mixture. In winter, rosin mixture is an effective pesticide for controlling scale insects. Rosin mixture has strong alkalinity and can corrode the waxy coating of scale insects, causing their spiracles to close after application. It also has control effects on aphids, red spider mites, rust mites, sooty mold, lichens, and mosses.
7. Leafminer
Damage symptoms: Leafminer is a major pest in nurseries and young trees, and damage is especially serious on summer and autumn shoots. The larvae bore under the epidermis of tender stems and leaves, forming silvery-white winding tunnels. Affected leaves curl or harden and easily fall off, and the wounds formed often invite canker disease. Damage is serious from May to September. Starting when pomelo shoots are 0.5 cm long, spray once every 5-7 days, for a total of 3-4 sprays.
8. Longhorn beetle
Damage symptoms: Longhorn beetle larvae lurk in the trunk to overwinter, then become adults between April and May. They often come out of holes at noon to mate and lay eggs on the trunk about one chi above the ground. The eggs hatch after about ten days. Newly hatched larvae feed on the bark, then gradually bore inward and downward into the xylem and roots, and in September turn toward the upper part of the trunk.
Control method:
① Capture: After early May, adults of various longhorn beetles successively come out of holes to cause damage and mate and lay eggs. Adults should be captured around the trunk at noon on sunny days in time.
② Scrape off eggs: After the start of summer is the adult egg-laying period. Patrol the orchard frequently and inspect the trunk about one chi above the ground. If saliva-like gum secretion is found, that is the egg-laying site. A small knife can be used to dig out and destroy the eggs. Use pesticide to plug and inject insect holes or hook and kill larvae; frequently find insect holes in the trunk, remove the frass inside, then use a cotton ball with 10 times dilution of dichlorvos to plug the hole, and seal the hole with wet mud to kill the larvae. Strengthen garden management. Combined with pruning and branch training, promptly cut off and handle dead branches with insects; weak-growing trees are prone to longhorn beetle damage, so forest management should be strengthened to promote vigorous tree growth and reduce damage. Pine sawyer beetles and similar pests prefer to damage trees that are about to die or have died. Each year before adults fly out, cut them down in time and thoroughly clean up and handle dead trees in the forest
9. Stink bug
Damage symptoms: Adult and nymph stink bugs insert their needle-like mouthparts into fruits to suck sap, and also damage branches and leaves. They cause many yellowish-brown wound spots. They overwinter as adults (can live until August of the following year) and begin activity and egg-laying in April. The damage period is from April to October, with serious fruit damage in July to August when there is sweetness. Early piercing wounds are not obvious, then gradually appear.
Control method: ① Capture adults and remove egg masses. ② When fruits begin to expand rapidly, spray once to protect the fruit, and thereafter spray pesticide at least once a month. You can use 800 times dilution of 90% trichlorfon, 1000 times dilution of 40% omethoate, 2000 times dilution of 5% Baishida, or 1500 times dilution of 52.25% Nongdile, etc.
10. Geometrid caterpillar
Damage symptoms: Geometrid caterpillars occur in three generations per year. The first generation is 1st-2nd instar larvae from late April to early May, the second generation is 1st-2nd instar larvae in early July, and the third generation is 1st-2nd instar larvae in early September. The larvae like to stand upright on leaf tips, and at night spin silk and hang from the outer canopy swaying with the wind or move to other plants to cause damage. Feeding damage is heavy on cloudy days and at night.
Control method: 800-1000 times dilution of trichlorfon aqueous solution, 500 times dilution of fenitrothion emulsifiable concentrate. At the peak hatching period of eggs, use 7216 bacterial agent or 100 times dilution of Bt emulsion, and also 500-1000 times dilution spray of 10 billion viable spores/g Bacillus thuringiensis wettable powder for control.
11. Scarab beetle
Damage symptoms: Scarab beetles are pests, mostly occurring in mountainous orchards, and cause relatively great damage to newly planted red-fleshed honey pomelo trees. Adults feed on the tender leaves of young trees and can also damage flowers and young fruits. One generation per year, with the adult peak period from early-to-mid May to mid-July.
Control method: Spray foliage with 1000 times dilution of trichlorfon aqueous solution, 1000 times dilution of 80% dichlorvos, and 750 times dilution of malathion.
12. Aphid
Damage symptoms: Aphids are one of the main pests damaging tender shoots in spring, summer, and autumn. Damage to tender shoots causes leaves to wrinkle and curl. Their secretions can induce sooty mold, inhibit growth, and also spread viruses, causing huanglongbing.
Control method: 700 times dilution of 50% malathion, 1000 times dilution of 80% dichlorvos, spray 1-2 times each time shoots grow 0.5-5 cm. Combined with pruning, thoroughly remove residual flowers and diseased dead branches and leaves where aphids have inhabited or eggs have lurked, and burn them in a centralized manner.