What Pesticides Are Best for Controlling Pests and Diseases on Peach Trees?
The peach tree is a common fruit tree in our country, grown over a fairly wide area. Every June it begins to come onto the market in large quantities and is very popular. During the growing period, appropriate amounts of pesticide must be sprayed to control pests and diseases, so what pesticide should be used on peach trees?
1. Peach leaf curl
Symptoms of damage: Peach leaf curl mainly damages the young, tender parts of the peach tree, chiefly the leaves, though in severe cases it can also damage flowers, young shoots and young fruit. Leaves: in spring, when the young shoots have just emerged from the bud scales, they appear curled and red in color. As the leaves gradually unfurl, the curling and wrinkling become more pronounced, the leaves thicken and become brittle, and turn reddish brown. In late spring and early summer, a layer of grayish white powdery material, the fungus's ascus layer, forms on the leaf surface. Finally the diseased leaves turn brown, wither and drop off. After the leaves fall, the axillary buds often sprout and send out new shoots, and the new leaves are no longer affected. Shoots: affected shoots turn grayish green or yellow, have shorter internodes than normal branches and are slightly thickened and swollen, with leaves often clustered on them. In severe cases the whole branch dies.
Control methods
(1) Chemical control: when the flower petals show red but have not yet opened, spray once with 2-3 degrees Baumé lime sulfur mixture or 1:1:100 Bordeaux mixture; this is very effective at killing the overwintering pathogens on the tree.
(2) Strengthen management: as soon as diseased leaves appear but before the white powdery material forms, pick them off promptly and burn them in a central pile, which can reduce that year's overwintering inoculum. For peach trees with severe infection, since large numbers of leaves wither and drop, fertilizer should be applied promptly and cultivation management strengthened to help the tree regain its vigor.
2. Iron deficiency yellow-leaf disease of peach trees
Symptoms of damage: the leaf surface shows green net-veined chlorosis. As the disease progresses, the chlorosis worsens, the entire leaf turns white, the leaf margins wither and burn, and defoliation follows. With severe iron deficiency, the tips of new shoots die.
Control methods
Improving the soil and releasing the fixed iron element is the fundamental measure for controlling iron deficiency; supplementing with soluble iron as appropriate can treat affected trees.
3. Peach gummosis
Symptoms of damage: semi-transparent yellow gum oozes from the diseased part, and the gumming is especially severe after rain. After the exuded gum contacts the air it turns reddish brown and becomes jelly-like, and after drying it becomes a hard reddish brown to tea-brown gum mass. The diseased part is easily infected by saprophytic fungi, causing the cortex and xylem to turn brown and rot, weakening the tree; the leaves turn yellow and become smaller, and in severe cases the branches or the whole plant die.
Control methods
(1) Strengthen management and improve tree vigor. Apply more organic fertilizer; in low-lying, waterlogged land pay attention to drainage; for acid or alkaline soil, apply lime or superphosphate as appropriate to improve the soil; in saline-alkali land pay attention to removing salt; prune reasonably to reduce wounds on branches and trunk, and avoid continuous cropping in the peach orchard. Control pests and diseases of the branches and trunk, prevent pest and disease wounds, and control peach tree pests such as scale insects, aphids and longhorn beetles early. In winter and spring, whitewash the trunk to prevent freeze damage and sunscald. For branches and trunks with severe gummosis, scrape and treat them in autumn and winter, and disinfect the wounds with 5-6 degrees Baumé lime sulfur mixture or 100-fold copper sulfate solution; or brush them with 1:4 alkaline water, which also has a certain curative effect.
(2) What is the pathogen of infectious peach gummosis? How many fungi cause it? What are their mycelial characteristics? Which medium suits this fungus, and what is its formula?
(3) Peach gummosis occurs mostly on the main branches, trunk and branch crotches of the peach tree. In the early stage, the diseased part swells slightly and exudes transparent gum; the gumming worsens after rain, and afterwards the gum gradually becomes jelly-like, loses water and appears yellow-brown, finally turning into a hard amber-colored gum mass. When fruit is affected, yellow gum oozes out from the stone, spills onto the fruit surface, and the diseased part becomes hard and sometimes splits, making the fruit inedible.
(4) Any wound caused by insect damage, disease damage, freeze damage, hail damage or sunscald can trigger non-infectious peach gummosis (no pathogenic fungus); in addition, gummosis caused by physiological disorders of the tree resulting from heavy, sticky soil, poor drainage, or excessive or insufficient irrigation is infectious peach gummosis caused by fungi, whose asexual-stage spores spread by wind and rain, entering through wounds and lateral buds. There are two disease peaks a year, namely late May to early June and early August to early September.
To control peach gummosis, spray promptly to control pests and diseases and whitewash the trunk to avoid freeze damage, sunscald and mechanical wounds. At the same time, strengthen fertilizer and water management, improve tree vigor and raise the tree's disease resistance.
4. Peach scab (black spot)
Symptoms of damage: fruit infection mostly occurs on the shoulder of the fruit, first producing small dark brown round dots, then black mole-like spots 2-3 mm in diameter; in severe cases the spots merge into patches. Affected fruit often cracks. When the fruit stalk is affected, the fruit often drops early; when new shoots are affected, they show oblong, light brown spots 3×6 mm in size, which then turn dark brown and expand further, with the diseased part raised and gummosis often occurring. The boundary between diseased and healthy tissue is clear, and the fungus damages only the surface layer without penetrating deeper. The following spring, dark, downy dot-like bodies may appear on the spots; on leaves, irregular or polygonal grayish green spots appear on the underside. Later the diseased part turns dark or purplish red, and finally withers and drops off, forming a shot hole. The spots are relatively small, rarely exceeding 6 mm. On the midrib, long strip-like dark brown spots may form. In severe cases it can cause defoliation.
Control methods
(1) Eliminate the primary inoculum source: together with winter pruning, remove diseased stones, mummified fruit and stub remains, and burn or bury them deeply. During the growing season, diseased and dead branches can also be pruned out and diseased fruit picked off.
(2) Chemical control: before flowering, spray 5 degrees Baumé lime sulfur mixture, 0.3% sodium pentachlorophenate or 45% crystalline lime sulfur mixture at 30-fold dilution. Half a month after petal fall, spray 70% mancozeb wettable powder at 500-fold dilution, or 80% carbendazim-thiram wettable powder at 800-fold dilution, or 70% thiophanate-methyl wettable powder at 1000-fold dilution; use the above pesticides alternately with 0.5:1:100 zinc sulfate-lime solution or 0.3 degrees Baumé lime sulfur mixture, once every half month, for a total of 3-4 sprays.
(3) Strengthen management: pay attention to drainage after rain, prune reasonably and prevent the branches and leaves from becoming too dense.
(4) Choose disease-resistant (disease-escaping) varieties: in places where the disease often occurs severely, early-maturing varieties can be planted.
(5) Fruit bagging: bag the fruit 3-4 weeks after petal fall.
5. Peach shot hole disease
Symptoms of damage
(1) Bacterial shot hole: the most widely distributed, mainly damaging leaves but also able to damage shoots and fruit. Affected leaves first show oily spots, which after enlarging become round or irregular spots, brown to purplish brown, with a ring of yellow-green halo around the spot; in humid weather, sticky bacterial ooze seeps from the diseased part, and soon the diseased part dries up and drops off, forming a shot hole. Shoot infection causes cankers: one is spring canker, in which dark brown small scabs appear on the branches when leaves unfurl in spring, mostly on branches put out the previous summer that became infected; the spots can spread lengthwise and sideways along the branch, and in severe cases can kill the branch. The other is summer canker, which mostly occurs on new shoots put out in the current year, centered on the host's lenticels, appearing as oily brown to purplish brown round or oval, slightly sunken spots, but the spots spread only to a limited extent and are not very infectious.
(2) Mold spot shot hole: affected leaves show brown, round or irregular spots, and in humid conditions a grayish black mold layer grows on the underside of the spots, and finally the diseased part drops off, forming a shot hole. Affected shoots show long oval dark brown spots with purplish brown margins, cracking and gummosis. Affected fruit show brown spots with red margins and slightly sunken centers. 3. Brown spot shot hole: the leaf spots are round or nearly round, brown, with reddish brown margins bearing faint ring patterns; in humid conditions a grayish brown mold layer grows on both sides, and finally the diseased part withers and drops off, forming a shot hole with neat edges. The spots on new shoots and fruit are similar to the leaf spots, and a mold layer also grows in humid conditions.
Control methods
(1) Do a good job of winter orchard cleanup. Together with winter cleanup, thoroughly remove dead branches, fallen leaves and fallen fruit, and spray once with 1-2 degrees Baumé lime sulfur mixture before sprouting in spring, which can greatly reduce the overwintering inoculum.
(2) Strengthen fertilizer and water management. Apply more organic fertilizer and phosphorus-potassium fertilizer, and maintain a moderate fruit load, so as to keep the tree vigorous and enhance disease resistance.
6. Peach anthracnose
Symptoms of damage: after small young fruit are infected they quickly wither into mummified fruit hanging on the branches; when larger fruit are infected, the spots are sunken and brown, and in humid conditions a pink sticky substance (fungal spores) is produced; the diseased fruit soon drops, or the whole fruit rots, loses water and becomes mummified fruit hanging on the branches. Branch infection occurs mainly on the fruiting branches of early spring; the spots are brown, oblong, slightly sunken, accompanied by gummosis, and in humid weather pink spores also densely cover the spots. When the spots encircle the branch completely, the upper part of the branch dies; on the part of the diseased branch that has not died, the leaves shrink and droop, curling into a tube shape toward the upper side.
Control methods
(1) During winter pruning, carefully remove dead branches, mummified fruit and stub remains from the tree to eliminate the overwintering source of disease. Perennial aged branch groups and thin, weak branches easily accumulate and harbor pathogens, so they should also be pruned out. At the same time, main and secondary branches that are too tall or too large should be cut back, to facilitate the renewal and rejuvenation of the canopy and branch groups and to make orchard cleanup and spraying work easier.
(2) From bud swelling to around flowering, promptly prune out the first diseased branches to prevent re-infection; fruiting branches showing leaf-curling symptoms should also be pruned out and buried deeply in a central pile.
(3) Choose disease-resistant varieties for planting.
(4) Strengthen drainage, apply more phosphorus and potassium fertilizer, improve tree vigor, and avoid leaving branches too dense or too long.
7. Peach dieback
Symptoms of damage: in the early stage the cortex of the diseased part swells slightly, tinged with purplish red, and gummosis appears; finally the cortex turns brown and dies, with a distillers' grains smell, and small black raised grains form on the surface. When the tree is vigorous, the spots sometimes heal on their own; when the tree is weak, the spots quickly spread to both ends and both sides, eventually killing the branch. On affected branches, new shoots grow poorly at first, the leaves turn yellow, and old leaves curl and wither; later the branch dies as the disease develops.
Control methods
(1) Strengthen fertilizer and water management in the orchard, prune reasonably, keep a reasonable fruit load, and prevent the tree from declining.
(2) After the disease appears, scrape off the spots with a sharp knife, then brush the wound with 20% antibacterial agent 402 at 100-fold dilution or copper sulfate at 100-fold dilution.
(3) During the growing period of the peach tree, when spraying carbendazim, zineb and zinc-copper-lime solution to control other diseases, also pay attention to spraying the branches and trunk for protection.
8. Peach crown gall
Symptoms of damage: it occurs mainly at the root crown, but also on lateral roots or branch roots. The gall is milky white or slightly red when first formed, smooth and soft, then gradually turns brown, becomes lignified and hard, with a rough, uneven surface. Galls on branch roots are smaller, those at the root crown are larger, and galls at the root crown have the greatest impact. Affected peach trees grow very poorly, are stunted, bear little and poor-quality fruit, and in severe cases the whole plant dies.
Control methods
(1) In nursery land and peach orchards, avoid continuous cropping as far as possible.
(2) Strictly reject diseased seedlings when they leave the nursery; when establishing a new peach orchard, strengthen quarantine to prevent bringing in diseased seedlings.
(3) Strengthen orchard inspection; for suspicious diseased plants, dig away the topsoil, and once the disease is found, scrape it off with a knife or thoroughly scrape it off and disinfect with 1% sodium pentachlorophenate or 0.1% mercuric chloride solution; 20-fold root gall spirit can also be used to soak the roots (for diseased seedlings) or pour on the root area (for large trees).
(4) In the nursery, use disease-free soil for raising seedlings, and cultivate healthy, disease-free nursery stock.
(5) Strengthen soil management, fertilize reasonably, improve the soil and enhance tree vigor.