Home > Knowledge Center> Spider mite control in greenhouse | Damage and treatment

Early detection of spider mites is very important because of their rapid reproduction. In practice, this is often difficult because the spider mites are mainly under the leaves and do not move much. They are often only noticed when you see spider webs in the crop or when the plants are significantly affected - indicating that the spider mites are already present in large numbers in the crop. You can recognize spider mite by:

• Size: Adult mites are about 0,5 millimeters in size. 
• Shape: Adult mites are oval-shaped with eight legs. 
• Colour: Adults are yellow-brown with a brown patch on each side of itsbody. They are often yellow-brown in cucumber crops and red-brown in tomatoes. Larvae are orange-red.
• Movement/Speed: Spider mites generally move little and are primarily on the underside of leaves to avoid sunlight.

The spider mite’s life cycle has several stages and is strongly influenced by the temperature in the greenhouse. Spider mites thrive in warm, dry conditions. Below is an overview of the greenhouse spider mite (Tetranychus urticae) life cycle:

• Egg: The mites lay their eggs around the veins or the underside of the leaf at the base of the leaf stem. 
• Larva: The eggs hatch into larvae, approximately 0.14 millimeters in size and orange in color. In this stage, they have six legs.
• Nymf: After the larval stage comes the nymph stage, during which the mites develop eight legs and molt several times. 
• Volwassen mijt: After the final molt, the nymphs become adult mites. They are about 0.5 millimeters long, with an oval shape and yellow-brown color with brown spots on each side. They can now reproduce and restart the cycle.

The duration of the life cycle heavily depends on temperature. At temperatures above 30°C, the entire cycle takes just one week, while at temperatures below 12°C, spider mite development comes to a halt. Watch the video below to see the life cycle of a spider mite.

Spider mites cause significant economic damage for many growers. Additionally, cosmetic damage and decreased product quality lead to product rejection in the market.

Spider mites damage plants by sucking sap from the underside of leaves, especially in young parts of the plant. This has a negative effect on growth and production as the plant has less chlorophyll available. In the worst case, the plant may even die. Spider mites also cause cosmetic damage, which poses challenges, especially in floriculture. When spider mites are abundant in a crop, the insects can completely cover the plants with webs. These webs provide a breeding ground for further infestation. The symptoms appear as follows:

• Leaves: The initial symptoms are small yellow spots on the leaves (see photo). With severe infestation, the leaves turn entirely yellow, impairing photosynthesis. In extreme cases, leaves may be covered with spider mite webs.
• Colour: Spider mites cause yellow spots, which can eventually spread across the entire leaf. In severe cases, the leaves may also show brown spots due to necrosis.
• Harvest: Damaged leaves produce less energy, resulting in a lower yield. Webbing and discolored leaves reduce the quality of the harvest, thereby decreasing its market value.
• Roots: Although spider mites primarily target leaves, they weaken the plant overall, which also affects root development. As a result, the plant absorbs fewer nutrients.

Due to damage to the leaves, the plant produces less energy, leading to lower yields. Webs and discolored leaves reduce the quality of the harvest, which decreases market value.

Various types of spider mites occur in horticulture, including:

• Greenhouse spider mite (Tetranychus urticae)
• False spider mite (Tenuipalpidae)

The greenhouse spider mite is often confused with the false spider mite. The false spider mite comes from a different family, the Tenuipalpidae. The main difference between the greenhouse spider mite and the false spider mite is the spotting pattern on its body. The false spider mite has a dark spot pattern, while the greenhouse spider mite only has two spots on its body. In terms of color, both mites resemble each other and vary from yellow to orange-red. Although this may cause confusion, you can distinguish the types by paying close attention to the spotting pattern.

If you find spider mites in your crop, it's important to begin control measures immediately. For early infestations, start by removing the affected leaves. to ensure the mites don't spread to healthy leaves. Additionally, start immediately with the use of natural enemies.

Biological spider mite control can be done using natural enemies like predatory mites, gall midges and sometimes predatory bugs. The following natural enemies are used for biological spider mite control:

• PHYTOcontrol (Phytoseiulus persimilis): is a very effective spider mite predator. Can be used in almost all crops. In tomatoes, the predatory mite has difficulty due to the glandular hairs.
• ANDERcontrol (Amblyseius andersoni): targets various spider mites. Andercontrol can be used preventively, because the predatory mite survives relatively long without prey.
• AMBLYCAcontrol (Neoseiulus californicus): also targets different spider mites. AMBLYCAcontrol, like ANDERcontrol, can be used prefentively, because the predatory mite survives relatively long without prey.
• Feltiline (Feltiella acarisuga): contains the gall midge Feltiella acarisuga. You can easily release the gall midge and combine them with Phytoseiulus persimilis. The winged gall midge is very mobile and has a good searching ability. The gall midge controls spider mite larvae and cleans up spider mite webs.

Tip: It is important that you deploy the natural enemies in the wide area around infested plants, even if you do not yet see any infestation on these plants. The spider mite can spread quickly in the crop and this way you prevent this as much as possible. 

Chemical control can be effectively carried out using acaricides. Sulfur is an appropriate control agent against spider mites, but sulfur disrupts the foraging behavior of gall midges. Therefore, never use sulfur at the same time as releasing gall midges. Apply the room treatment in the evening, as spider mites are most active then. In non-illuminated crops, you should adjust spraying techniques during the darker months, as spider mites are then overwintering and are moderately or not at all sensitive to pesticides.

Can't find your answer? Fill out the contact form and our specialist Jan-Paul de Wit will get back to you. On weekdays, even within 24 hours.