Erin Lizotte, Michigan State University Extension, MSU Department of Entomology Dave Smitley and Jill O’Donnell, MSU Extension-April 1, 2015
Spruce spider mites are important pests of Michigan Christmas trees. Minimizing the use of pesticides can help growers protect beneficial predatory mites, thereby helping to control this important pest.
In Michigan, spruce spider mite (Oligonuchus umunguis) is an important pest of coniferous trees. This tiny insect infests all commercially produced Christmas trees and often causes significant economic losses in the cultivation of spruce and Fraser fir. In traditionally managed plantations, the population of predatory mites is small due to the use of insecticides, so spider mites are usually pests. Predatory mites are beneficial to growers because they feed on pests and help control populations. Without them, the spruce spider mite population will burst out suddenly, causing damage to the trees.
As spring approaches, growers should be prepared to increase their mite hunting plans. In order to spot spruce spider mites, growers should sample multiple trees in each plantation and make sure to choose trees from different altitudes and rows indoors and outdoors. Larger tree samples will increase the accuracy of growers when assessing populations and potential risks. Reconnaissance should be conducted throughout the season, not only after symptoms appear, because it is usually too late for effective treatment. The easiest way to detect adult and juvenile mites is to shake or beat branches on a scout board or paper (photo 1).
The spruce spider mite egg is a small bright red ball with a hair in the middle. The hatched eggs will appear clear (photo 2). In the exercise phase, the spider mite is very small and has a soft body shape. The adult spruce spider mite is a solid oval shape with hairs on the top of the abdomen. Skin tones vary, but Tetranychus spruce is usually green, dark green or almost black, and never white, pink or light red. Beneficial predatory mites are usually white, milky white, pink or light red, and they can be distinguished from pest mites by observing their activities. When disturbed, the adult predatory mites usually move faster than the pest mites, and it can be observed to move quickly on the scout board. Red spruce spiders tend to crawl slowly.
Photo 2. Adult spruce spider mites and eggs. Image source: USDA FS-Northeast Regional Archives, Bugwood.org
Symptoms of spruce spider mite damage include chlorosis, needle pricks and discoloration and even brown leaf patches, which may eventually spread to the entire tree. When observing the injury through a hand mirror, the symptoms appear as small yellow round spots around the feeding site (photo 3). Through careful monitoring, resistance management and the use of pesticides that are less harmful to natural predatory mites, spruce spider mites can be prevented from being destroyed. The easiest way to determine management needs is to assess whether the investigation indicates that the population is growing or is at a level of destruction. It is important to remember that the spruce spider mite population fluctuates rapidly, so just looking at the damage to the tree does not accurately indicate whether treatment is needed, because the population that has died since then may have caused the damage, so spraying is meaningless.
Photo 3. The spruce spider mite feeding needle is damaged. Image credit: John A. Weidhass of Virginia Tech and State University Bugwood.org
The following table contains current treatment options, their chemical category, target life stage, relative efficacy, control time and relative toxicity to beneficial predatory mites. If insecticides are not used, red spiders rarely become a problem, because predatory mites will keep them under control. Try to avoid spraying pesticides to encourage natural control.
Chlorpyrifos 4E AG, Government 4E, Hatchet, Lorsban Advanced, Lorsban 4E, Lorsban 75WG, Nufos 4E, Quali-Pro Chlorpyrifos 4E, Warhawk, Whirlwind, Yuma 4E insecticide, Vulcan (poisoned rif)
Avid 0.15EC, Ardent 0.15EC, transparent decoration, Nufarm Abamectin, Minx Quali-Pro Abamectin 0.15EC, Timectin 0.15ECT&O (abamectin)
Appreciate Pro, Couraze 2F, Couraze 4F, Mallet 75WSP, Nuprid 1.6F, Pasada 1.6F, Prey, Provado 1.6F, Sherpa, Widow, Wrangler (imidacloprid)
1 Movement forms include mite larvae, nymphs and adult stages. 2S is relatively safe to mite predators, M is moderately toxic, and H is highly toxic. 3Avermectin, thiazole and tetronic acid acaricides are slower, so growers should not be surprised if the mites are still alive after application. It may take 7 to 10 days to see full mortality. 4Gardening oil can cause phytotoxicity, especially when used in summer, and can reduce the blue color in spruce blue. It is usually safe to spray highly refined horticultural oil with a concentration of 1% at any time of the year, but when the concentration is 2% or higher, it may damage the blooms caused by the changes in spruce ice crystals and cause adverse symptoms. . 5 The Apollo label should be read and carefully followed to ensure proper use and slow down the development of resistance.
Pyrethroids, organophosphates and abamectins all have good knockdown activity and residual control of spruce spider mites in the active life stage, but their lethal effects on predatory mites make them poor treatment options. Due to the reduction of natural enemies and predatory mites populations, the spruce spider mites populations erupt, the use of these materials usually needs to continue to be processed this season. Neonicotine, which contains imidacloprid as an effective ingredient, is also a poor choice for controlling spruce spider mites, and in some cases may actually cause an outbreak of spider mites.
Compared with the above-mentioned materials, carbamates, quinolones, pyridazinones, quinazolines and the insect growth regulator ethoxazole all show good effects on Tetranychus spruce and moderate to predatory mites. toxicity. The use of these materials will reduce the risk of mite outbreaks and provide three to four weeks of residual control for all life stages of spruce spider mites, but etozol has limited activity in adults.
Tetronic acid, thiazole, sulfite and horticultural oil also show good effects on the residual length of spider mite. Horticultural oils have risks of phytotoxicity and chlorosis, so growers should be cautious when using new products or on untreated species. Tetronic acid, thiazole, sulfite and horticultural oil also have important additional benefits, that is, it is relatively safe to predatory mites and has a low possibility of causing mite outbreaks.
Growers may find that more than one treatment is needed, especially when population pressure is high, or when using pesticides that are ineffective at all life stages. Please read the label carefully, as some products can only be used in one type per season. In early spring, check the needles and twigs for eggs of Tetranychus spruce. If the eggs are abundant, apply horticultural oil at a concentration of 2% to kill them before hatching. A high-quality gardening oil with a concentration of 2% is safe for most Christmas trees, except for blue spruce, which loses some of its blue luster after being sprayed with the oil.
In order to delay the development of anti-acaricides, the Michigan State University Promotion Department encourages growers to follow label recommendations, limit the number of specific products applied in a certain season, and choose acaricides from more than one insecticide. For example, as the population begins to rebound, growers may fertilize dormant oil in the spring and then apply tetronic acid. The next application should come from a category other than tetrahydroacid.
Pesticide regulations are constantly changing, and the information provided in this article will not replace label instructions. In order to protect yourself, others and the environment, please be sure to read and follow the label.
This material is based on work supported by the National Institute of Food and Agriculture of the United States Department of Agriculture under agreement number 2013-41534-21068. Any views, findings, conclusions, or recommendations expressed in this publication are those of the author and do not necessarily reflect the views of the United States Department of Agriculture.
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