Mint Spider mites

From Bugwoodwiki

Author: Sue Blodgett & Bill Grey

T. urticae
Scientific Name
Tetranychus urticae
Common Names
twospotted spider mite

Spider mites

Spider mites are the most important insect pest of mint in Montana.

Identification (life cycle and seasonal history)

The two spotted spider mites are tiny pale yellow to green spiders with eight legs and two large spots on either side of the body, seen with the aid of a hand lens. Female mites overwinter in the soil and in plant debris becoming active in the spring as temperatures warm. The entire life cycle takes 1 to 3 weeks depending on temperature. Hot, dry summer weather is favorable for mite populations allowing them to increase very rapidly.

Plant response and damage

All mobile stages of spider mites feed on the undersides of leaves, sucking plant juices. Their presence is typically accompanied by silken webbing. Feeding damage causes stippling, and silvering of the foliage with injury occurring when populations of spider mites reach five per leaf.

Management approaches

Hollingsworth at Oregon State University has developed a sampling method. The under-side of 15 leaves from each position (bottom, middle and top of plants) are examined at 14 field sites per 30 acre field. Leaves are considered infested when 5 or more mites are present. Fields should be inspected at weekly or biweekly increased sampling frequency during hot periods) to detect the buildup of damaging populations.

Biological Control

Predator mites occur in mint fields and can be a significant factor in limiting spider mite populations and problems. Learn to distinguish between spider mites and predator mites.

Chemical Control

Treatment of spider mites is justified if there are no predator mites and if 18 or more of the leaves in the 45-leaf sample (40%) taken at each site are infested with five or more spider mites. It is also important to estimate the number of spider mite eggs on the leaves, because their number will help predict an emerging infestation. Sulfur can be used in the early season for mites but avoid applications close to harvest when sulfur residues can negatively impact oil quality.

Development of acaricide resistance in mite populations has occurred when populations that have been repeatedly treated with miticides such as Kelthane (dicofol). Although Kelthane is registered on mint it is highly toxic to predator mites, and its use is not recommended when predator mites are contributing to natural control. Fewer miticide applications will help delay the development of mite resistance, protect beneficial predators, and reduce production costs.

Product list for Spider Mites

Pesticide Product/Acre Preharvest Interval, Remarks
Acramite 50WS ¾ - 1 ½ lbs 7 PHI, 12 hr REI. Apply in 50 GPA. One treatment/A/season.
Agri-Mek 0.15EC R 8 – 12 oz 28 days, Do not apply in less than 20GPA. Do not apply more than 12 oz/A/application. Do not apply more than 3 applications/A/yr. Do not graze treated foliage.
Dicofol 4E 1 ¾ - 2 ½ pts 30 days. Do not make more than 1 application/A/season. Do not feed treated crop to livestock.
Malathion 1.5 pts (5EC)

1 pt (8E)

7 days. 12hrs REI.
Metasystox-R SC R, 2 3 pts 14 days. Apply with ground equipment in at least 20 gal/A. For established infestations, make 2 applications 10-14 days apart.
Omite 6E 2-3 pt 14 days, 7 day REI. Apply in 20-50 GPA by ground, minimum of 10GPA by air. Only 2 applications/A/yr. Do not feed treated foliage to livestock. Rotation restrictions.
1 Label allows chemigation, 2 Generic active ingredient, several formulations available, see labels for rates, R Restricted use pesticide

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.