Apple sawdust - Damage and control


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apple tree

The apple sawfly belongs to the family of the real sawfly wasps and is a worldwide parasite that attacks only apple trees and can cause significant damage to them. The larvae of the pest hatch inside the apples, leaving spiraling miners on the fruits. Infested apples are usually no longer enjoyable and are repelled by the tree. Ideally, an infestation is detected preventively, so that the larvae can not do too much damage, otherwise there are some practical tools to combat them.
appearance
The apple sawfly can grow as a mature insect several millimeters long and forms a compact physique. The upper side of the body has a black tint, in contrast to the chest area and the legs in an orange hue. The larva of the apple sawfly grows up in the young apple and has at first a black head, which turns brownish with age. Due to the small size of the parasite is initially paid little attention, but this factor changes drastically when an infestation with the larvae of apple sawdust decimates the apple harvest. The following aspects should be considered in the appearance:
  • Length of the apple sawfly is up to 7 mm, with 4 transparent wings
  • The body shines dazzling in the sunlight
  • Between chest and abdomen the typical wasp waist is missing
  • Larvae measure between 9-11 mm, form at the 7 abdominal legs
distribution
The larvae of the pest are often found in the local gardens and can cause considerable damage to the fruit of the apple trees. The apple sawfly spends the winter as a fully grown larva in a cocoon in the ground and then pupates in the spring, matching the time of the apple blossom. In summer, the larvae leave the last infested apples and go for hibernation in the ground. In the years with a strong BlĂŒtenbesatz the appearance of the apple sawfly has quite useful effects, because the larvae of the insects allow a natural thinning directly on the apple tree. However, the pest can cause extremely high crop losses at very low flowering and heavy infestation, sometimes even destroying whole crops. The following criteria are crucial for the dissemination:
  • Pupation lasts about 17-20 days, takes place in March
  • Has a saw-shaped laying drill for oviposition, thus drills a slot
  • Place about 20 eggs one at a time, directly into the fruit plant of the apple blossom
  • Larvae hatch after about 2 weeks
  • Development of the larvae takes about 3-4 weeks
  • If the apples inside are hollowed out, they are then transferred to neighboring fruits
  • Larva can destroy up to five apples during its stages of development
  • In July-August the caterpillars leave the apples
  • Over winter in about 5-10 cm depth in the soil
Harming
The oviposition can be detected early on the exiting cell juice, so the apple trees should be permanently under observation from the beginning of flowering. The newly hatched larvae minieren in the early days directly under the epidermis of the fruit and then hollow out gradually. On already longer infested apples can be seen holes and drill holes, which have a diameter of 2-3 millimeters, from these dripping the feces of the larvae out. As a rule, the affected fruits fall prematurely from the tree, but it can also happen that they remain on the tree. When damage picture is to pay attention to the following notes:
  • Danger for infestation depends on the weather conditions, the location, the flower bud, the infestation pressure and the apple variety
  • Slit for oviposition turns brown and is clearly visible
  • Leave spiral-like and corked miner's course on young fruits
  • First feeding is created directly under the shell and turns purple
  • Exudation of smoldering and dark feces
  • Larvae usually eat their way to the core
  • Ripe apples have brown corking due to the feeding
fight

apple harvest

In order to combat the apple sawdust, there are various chemical products on offer that are often used to destroy other and very useful insects. However, these should better not be used in view of the subsequent consumption of the fruits, so as not to endanger one's own health. A powerful antidote are the so-called Quassiextrakte, an extract of quassia wood, which has been proven in organic fruit growing for the regulation of apple sawdust. In this preparation, the quality of the extract and the right time of use is extremely important, otherwise the effect is greatly reduced:
  • Check young apples for oviposition by laying eggs
  • Remove stamens and remove the egg deposited on the flower floor and destroy it
  • Apply Quassiextrakt shortly before the Eischlupf with outgoing bloom
  • Wet the entire apple tree thoroughly with the extract
Tip: Under certain circumstances, a treatment with the Quassiextrakt is not enough and it must be another 2-3 follow-up treatments to completely prevent the infestation with the apple sawdust.
prevention
In order to prevent an infestation with the apple sawdust, certain procedures have proven successful. Especially if an infestation already occurred in the previous year, now should be acted preventively. Particularly suitable are white traps, which are glued before installation and capture flying pests. The white boards simulate the blossoms of the apple trees and entice the apple saw buds to approach. About a week after the end of the flowering the white traps have to be removed, so that no other insects that are useful for the garden are caught unnecessarily. If this method can not catch apple sawdust during flowering, then this year is usually free of infestation by the pest. The following measures have been proven in prevention:
  • Regularly check the trees
  • Approximately Set up traps one week before the apples bloom
  • Hang white traps in the tree in the outer crown area and turn to the sun
  • Ideal is an installation height of about 1.5-2 m
  • Shake off infected apples between Mail and June and destroy them out of reach
Tip: The danger of the damage threshold can be calculated by the number of saw-saws caught on the white board. If less than 20 to 30 specimens are caught until flowering, then the risk is relatively low.
Conclusion
In general, an infestation with the apple sawfly leads to a strong reduction of the harvest, since its larvae can eat through several fruits in their developmental stage. These are then no longer enjoyable and should be disposed of directly in an infestation, ideally away from the tree, to prevent further spread. For a first overview of the possible risk of infestation are especially sized white traps, which are set up before and during flowering. If an infestation has already occurred in the previous year, rapid countermeasures are indispensable. Quassiextrakte have proven to be effective for immediate and sustainable control. These eco-friendly agents are derived from the quassia wood and are a useful alternative to chemical control agents that can harm human health. A regular inspection of the apple trees is of great importance, so that enough time is available for the fight.

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