Hot, Dry Conditions Beginning to Trigger Spider Mite Reports in Soybean

Robert Koch (Extension Entomologist), Angie Peltier (Extension Crops Educator), Anthony Hanson (Extension IPM Educator) and Arthur Ribeiro (Researcher, Entomology)

As we move through July 2026, high temperatures and dry conditions across parts of Minnesota are creating prime conditions for two-spotted spider mite outbreaks. Daily highs are expected to frequently be near or above 90 °F the last week of July with little chance of rain in the forecast. We are beginning to receive reports of spider mite activity and field infestations in several areas of the state. Here, we provide an overview of how to identify this pest and its injury to soybean, and how to scout for and manage the pest.

IDENTIFICATION & PLANT INJURY

• Appearance: Spider mites are extremely small (nearly invisible without magnification), appearing as tiny yellow, green, or brownish moving specks on leaf undersides (Fig. 1). Spider mites are significantly smaller than soybean aphid and other common insects found in soybean.
• Field ID (the paper test): Hold a sheet of white paper beneath a soybean leaf and firmly tap the leaf. Watch for tiny specks crawling across the paper.
• Webbing: Look for fine, silky webbing on the undersides of leaves. This webbing may provide some protection of colonies from both predators and crop protection chemicals.
• Stippling: Spider mites feed by puncturing individual leaf cells to extract fluids. Early feeding creates stippling, which are small, white-to-yellow specks visible on the leaf surface (Fig. 2).
• Progression: As the quality of plant material bordering soybean fields declines due to drought, field infestations generally begin on field edges and progress into the interior of fields. Within individual plants, infestations generally begin on lower leaves and progress upward through the canopy. Unchecked feeding causes foliage to turn yellow, bronze, and brown. Severely damaged leaves dry out and drop from plants (lower canopy leaf loss). Protecting the middle and upper canopy foliage is crucial to preserving crop yield potential.  

Figure 1. Two-spotted spider mites (red arrows), their eggs (blue arrows) and stippling injury on the underside of a soybean leaf. Photo: Angie Peltier

Figure 2. Stippling on soybean plants on upper leaves from spider mite feeding.

HOW TO SCOUT FOR SPIDER MITES

• Check Edges First: Walk field borders adjacent to permanent grass or alfalfa. Look for stippling or yellowing of leaves in the lower soybean canopy.
• Sample Field Interior: If stippling or live spider mites are detected on field edges, walk a pattern through the field interior, inspecting plants at multiple locations.
• Confirm Live Spider Mites: Damage remains long after spider mites disperse or die. Always confirm the presence of live, moving spider mites with the white paper test before making a spray decision.
• Rescout Schedule: Recheck fields every 4 to 5 days during hot, dry weather, as populations can explode rapidly.

ACTION THRESHOLDS: THE 0-TO-5 INFESTATION RATING
Use this standardized rating scale to decide when a treatment is justified. The goal is to protect the upper two-thirds of the canopy, which requires action when a rating of 3 is reached. Treatment past the R6.5 (yellow pod) stage is generally not economical.

Rating	Infestation Level	Visual Symptoms & Mite Distribution	Action Threshold
0	None	No spider mites or leaf injury observed.	Do not treat.
1	Very Light	Minor stippling on lower leaves; no premature yellowing.	Monitor field.
2	Alert Level	Stippling common on lower leaves; small scattered areas of plant yellowing.	Prepare to treat if hot/dry weather continues.
3	Spray Threshold	Heavy stippling on lower leaves; stippling progressing into the middle canopy. Spider mites present in the middle canopy with scattered colonies in the upper canopy. Yellowing of lower leaves is common; minor leaf drop.	Apply miticide/insecticide to protect the middle and upper canopy.
4	Economic Loss	Lower leaf yellowing apparent; leaf drop common. Stippling, webbing, and spider mites are common in the middle canopy.	Treat immediately; yield loss is occurring.
5	Severe	Lower leaf loss is common; yellowing/browning leaf discoloration moving into the middle canopy. Heavy stippling and leaf distortion in the upper canopy.	Severe yield loss.

TACTICAL MANAGEMENT & APPLICATION GUIDELINES

• Treat the whole field: By the time edge damage is visible, wind-blown spider mites are typically spread throughout the interior of the field. Border sprays are rarely effective; treat the entire field when thresholds are reached.
• Insecticides & miticides: Several chemical control options exist for managing spider mite infestations, but not all products control all life stages.
• Organophosphates (group 1B): Multiple products containing chlorpyrifos (alone or in mixtures) or dimethoate are labeled for spider mites in soybean. They control adults and immatures (but not eggs).
• Pyrethroids (group 3A): Multiple products containing bifenthrin (alone or in mixtures) are labeled for spider mites in soybean. They control adults and immatures (but not eggs). Use of other pyrethroid insecticide active ingredients (e.g., lambda-cyhalothrin) for spider mites is likely to flare (make worse) infestations, so pay close attention to the label to ensure the product contains bifenthrin and not other pyrethroids.
• Avermectins (group 6): Some products containing abamectin (e.g., Agri-Mek) are labeled for spider mites in soybean. It controls adult and immature stages of spider mites.
• Etoxazole (group 10B): Zeal which contains etoxazole is labeled for spider mites in soybean. It controls eggs and immature stages of spider mites.
• Isoxazolines (group 30): Some products containing isocycloseram (Plinazolin technology), such as Vertento, are labeled for spider mites in soybean.
• Resistance management: Rotate mode-of-action groups if an additional application becomes necessary.
• High carrier volumes required: Spider mites live on the undersides of leaves and often lower in the canopy. Consequently, high water volume is needed for canopy penetration: at least 20 gpa for ground applications and 5 gpa for aerial applications.
• Re-evaluate in 5 to 7 days: Most insecticides do not kill spider mite eggs. In warm, July temperatures, surviving eggs hatch rapidly. Always re-scout fields 5 to 7 days post-treatment to check for population growth.
• Managing co-infestations (mites + aphids): Soybean aphid infestations remain low in Minnesota, which may be due (a least partially) to the high temperatures working against aphid population growth. However, if soybean aphids begin to increase and co-occur with spider mites, select a product targeting the main economic pest while ensuring it does not flare the secondary pest. Many soybean aphid populations are resistant to pyrethroids such as bifenthrin. Keep in mind broad spectrum insecticides like pyrethroids can reduce natural enemy populations and cause both spider mite and soybean aphid populations to increase.
• A warning on rain: Do not rely on a single summer thunderstorm to clear an infestation. Once spider mite populations build, it takes extended periods of cooler temperatures, high humidity, and heavy overnight dews to foster the natural fungal diseases needed to collapse populations.

*Any mention of pesticide trade names is for educational purposes only and is not an endorsement of any particular brand or product.