i. Fruit tree canker
The disease happens in the apple planting areas throughout the country. The disease is severe in old orchards, orchards with extensive management, and orchards with weak tree vigor. If the fruit tree is frozen in winter, the tree tends to catch disease. If the disease if not treated in time, the tree vigor will be weak and the disease will aggregate. If the condition lasts for a few years, the bough or lateral branch will die, or even the whole tree will die.
There are two types of symptom of the apple tree canker: canker and branch withering.
Way of prevention and control: The main method of preventing and curing apple tree canker is to shave off the sick speckles. Apply medicaments after that to sterilize. The common medicaments are: Fubiqing emulsion 2 times diluent, 5% hydrochloride AC 30—50 times diluent, 2% Agricultural Antibiotic 120 AC 10—20 times diluent, 10% Yinguo oil concentrate 150 times diluent, etc. Apply the medicaments once more 15 days after the first application. In order to prevent the disease from relapse, the medicaments should be applied on the scar in the next spring.
The disease causes damage to the branches as well as fruits. The pathogen lives through winter in the sick knurl on the tree trunk and has the trait of latent infection. The pathogen infects the fruit at young fruit stage and the disease will come on at the late stage of fruit growth and development. Generally 10 days after the flower falls, if it rains, the pathogen will infect the young fruit. The infection period of pathogen is from late May to early September. The fastigium of infection is from early June to mid August. If it rains during this period, the fruits are surely infected by pathogen. The incidence degree is greatly affected by the quantity and frequency of rainfall. When the frequency and quantity are high, the disease will be severe. When the weather is dry, the disease is not severe. The disease resistance of different breeds of apple differs much. The breeds like Jinguan and Fuji is more susceptible to disease.
Way of prevention and control:
a. Shave the sick knurls. It’s an effective way to remove pathogen to shave the sick knurls on the trunk and apply medicaments on it. When the sick knurl is shaved, apply 50% carbendazim WP 50 times diluent. This can remove pathogen and reduce primary source of infection.
b. Chemical prevention and control. The medicaments should be sprayed for the first time 15 days after the flowers wither, and once every 15 days after that until mid August. The times of spraying should be decided upon the rainfall after the flowers wither. Common pesticides are: 50% carbendazim WP 600—800 times diluent, 70% mancozeb WP 600—700 times diluent, 80% Dasheng WP 800 times diluent, 70% thiophanate methyl WP 800 times diluent, bordeaux liquid, etc. Practice showed that, the effect of prevention and control can be improved by alternately applying bordeaux liquid and organic synthetic antiseptics, especially in the rainy season.
iii. Early leaf cast
Early leaf cast is mainly caused by Alteranria mali Roberts and M.mali. The former one is more important. The disease is more severe on fruiting trees than on young trees. And the disease tends to be severe on the breed of Yuanshuai. When the disease is severe, the fruit trees usually defoliate in advance, badly affecting the flower bud of the next year and the fruit quality of the same year. Rainfall is the main environmental condition for the disease arising. In the year when it rains much, the disease often prevails. The trait of Alteranria mali Roberts is that once it infects the tree, the disease may come on immediately, and cause defoliation soon.
Way of prevention and control: Chemical prevention and control is mainly applied to early leaf cast of apple. Pesticides are mainly sprayed from mid May to early August. When the sick leaf rate reaches 10%, pesticides should be sprayed. After that, pesticides should be applied once again when the sick leaf rate reaches 20%--30%. Three times is enough for pesticides application. The following pesticides are effective: 50% iprodione WP 1000—1500 times diluent, 10% polyoxin WP 1000—1500 times diluent. These pesticides can be applied alternatively with bordeaux liquid and mancozeb.
2) Insect pests
i. Hawthorn spider mite
Hawthorn spider mite is a main pest to apple trees that happens every year. If it is not prevented and control in time, the fruit tree will defoliate in advance. The female adult mite lives through winter on the tree trunk. The female adult mite stops hibernation when the fruit tree pullulate, and begins to lay eggs when the fruit tree expanses leaves. It’s favorable for the Hawthorn spider mite when the temperature is high and it is drought. Therefore, the population density increases rapidly in June and July. If prevention and control measures are not taken in time, great number of colonies will come into being, and the mites will spin and form webs to prevail among the fruit trees. The infected leaves are pale without green, and begin to fall from late July. The reproducing speed of Hawthorn spider mite is high (6—10 generations per year). It has had pesticide resistance to various acaricides, hindering the prevention and control.
Way of prevention and control: Two key periods should be grasped to prevent and control Hawthorn spider mite. The first is when the adult mite come out of hibernation (when the flower buds are sprouting); effective acaricides are: 50% sulphur deflocculant 200 times diluent, 20% clofentezine deflocculant 2000 times diluent. The second is before the wheat is harvested when the number of mite increases. The following pesticides can be applied: 15% pyridaben emulsion 2000—3000 times diluent, 1.8% Abamectin oil concentrate 5000 times diluent, 10% liuyangmycin emulsion 1000 times diluent.
ii. Apple leaf minor
Apple leaf minor is a main tortrix that causes damage to fruit trees. Its larvae damage the leaves and fruits. There are three generations within one year. The second- instar larvae live through winter under the sticking barks and in the bark gaps on the tree trunk. When the fruit tree pullulates in the next year, the larvae come out of hibernation, eating the flower buds at first, then rolling the leaves. The first generation larvae damage the leaves, the second generation larvae damages leaves and fruits as well, the third generation larvae get to the hibernaculum to live through winter after a certain period of time.
Way of prevention and control:
a. Apply pesticides on the cut. After or at the pruning of fruit tree, apply the following pesticides on the cut to eliminate the hibernating larvae: 80% ddvp oil concentrate, 50% phoxim oil concentrate or 48% Lorsban oil concentrate 50 times diluent.
b. Chemical prevention and control. The key period of applying pesticide is when the hibernated larvae come out of hibernation and the first generation larvae are hatched. Common pesticides are: 20% Fenvalerate oil concentrate 2000 times diluent, 2.5% Deltamethrin oil concentrate 2000 times diluent, 20% fenpropathrin oil concentrate 2000 times diluent (Hawthorn spider mite can also be controlled), 25% diflubenzuron deflocculant 2000 times diluent, 30% Taoxiaoling oil concentrate 2000 times diluent.
c. Manual prevention and control. Around the shatter of the fruit tree, it’s an effective way to kill the larvae in the leaf roll with hand when applying flower and fruit thinning. It’s especially effective in the sapling orchard.
iii. Golden yellow gracilarlid
Golden yellow gracilarlid is a main insect pest that damages the leaves of apple tree. Since 1980s, it arises in all apple planting areas, causing the apple tree to defoliate early, affecting the output and quality of fruits, and the formation of flower buds in the next year. There are 5 generations of golden yellow gracilarlid every year. The nymphae live through winter in the infected leaves, and imagoes emerge in the next year when the fruit tree pullulates. The imagoes lay eggs on the tender leaves, mainly in the tree trunk and on the root shoot. The population of the first generation is less, and increases with each generation. The second (early June) and third (early July) cause the heaviest damage. The two periods are the key periods to apply pesticide prevention and control.
Way of prevention and control:
a. Manual prevention and control. Remove the deadwood and fallen leaves to eliminate the nymphae living through the winter, so as to reduce the population of the insect pest in the next year.
b. Chemical prevention and control. The key period of chemical prevention and control is when various generations of larvae are being hatched. The second and third generation larvae should be mainly controlled. Common pesticides are: 25% diflubenzuron deflocculant 1000—2000 times diluent, 50% Emanling oil concentrate 1500—2000 times diluent, 50% Xinniao oil concentrate 1500—2000 times diluent.