Occurrence rules and control methods of rhododendron red spiders
1 Harmful symptoms
The red spiders that harm rhododendrons are mainly short-whiskered ants (also known as camellia spiders). Adult mites, nymphs and juvenile mites can all be harmed. The mouthpart pierces the leaves and green branches, and absorbs the sap. The leaves are the most heavily damaged, and the leaf surface of the affected leaves shows many small gray-white spots, losing luster, and when severe, the whole leaves are gray and white, a large number of leaves are fallen, and the petioles are purple-brown, affecting the growth and tree posture of rhododendrons.
2 Morphological characteristics
Female adult mites, body length 0.3 to 0.4 mm, dark red, oval, dorsal wart-like protrusions, superstructured white bristles, 4 pairs of feet. The male mites are slightly smaller, bright red, ovate oblate spherical, red, with a stalk on the egg and radial filaments on the stalk. The juvenile mites are 0.2 mm long, have a lighter body color, and have 3 pairs of feet. If the mites resemble mites, they are slightly smaller, in 4 pairs.
3 Occurrence
There are 6 to 8 generations in Nancheng County in one year, and the generations overlap. Eggs and adult mites overwinter in the reverses of the infested leaves, curly leaves and cracks in the branches. Around March of the following year, the eggs hatched in large numbers, and the overwintering adults began to lay eggs. Usually at 12 °C, the insect population begins to increase, at 20 °C, it blooms, and at 20 to 30 °C and the relative humidity of the air is 60% to 70%, it is the peak period of development and reproduction of red spiders, that is, the peak of harm. High temperatures and droughts are very favorable for their reproduction, so they are in full bloom from July to September every year. The amount of occurrence is related to factors such as climate, tree nutrition, overwintering base and natural enemies.
4 Prevention and control methods
(1) Strengthening soil, fertilizer and water management and improving tree resistance can effectively inhibit the occurrence of red spiders. (2) Strengthen the winter clearance of the garden and reduce the source base of overwintering insects.
(3) When the ratio of the mouth of the predator to the red spider is about 1..25, it has a significant inhibitory effect on the rhododendron red spider. The natural enemies of the red spider are 20 species of predatory mites, 10 species of mite ladybirds, and 4 species of grasshoppers. (4) Spray control: In the average number of insects per leaf is more than 3 to 7, spray control should be carried out immediately. The agents are: Lu Ying or Xingnong Fruit has 200 to 300 times liquid, 16% mite natural killing or 73% gram mite 2000 to 3000 times liquid, 53% mite 1500 times liquid, 5% pyridine 2000 times liquid, Tolk 1500 to 2000 times liquid or 5% mite king 2000 times liquid. To prevent resistance, pesticides should be rotated or mixed.
