HPIPM:Banks Grass Mite FC

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Author: Frank B. Peairs[1]

Identification (and life cycle/seasonal history)

Banks grass mites (BGM), Oligonychus pratensis (Banks), are minute, 0.45 millimeter (0.017 inch), greenish colored arthropods with eight legs and a rounded body. BGM has dark pigmentation along both edges of the body near the rear and along the sides. Fertilized female BGM move into winter wheat in the fall as their summer hosts, especially field corn but also other grasses, begin to dry down. These over-wintering forms are bright orange in color. They return to corn by walking short distances or by being windborne on silk threads over longer distances. In the spring small pearly white eggs are laid which eventually give rise to pale to bright green male and female adults.

Plant Response and Damage

Webbing on leaves and discoloration are often the first signs of an infestation. Initially, BGM are most abundant on the lower third of the plant and density declines as the infestation moves up in the plant. Mites damage corn and small grains by piercing plant cells with their mouthparts and sucking the plant juices.

Management Approaches

Chemical Control

Banks grass mite builds up on the plant from the bottom up. Treat when there is visible damage in the lower third of the plant and small colonies are present in the middle third of the plant before hard dough stage. An alternative method for determining the need for control of Banks Grass Mite in grain corn, developed by T. Archer and E. Bynum at Texas A&M University at Lubbock, is based on total infested leaves and total percentage of leaf area damaged (Table XI-1).

After calculating the percentage of infested leaves look at the position in the table corresponding to your expected control cost and crop market value per acre. If the percent infested leaves is greater than the value given in the table, then determine the percent leaf surface showing chlorotic and stippled mite feeding damage. If this value exceeds the second value in the table, then a miticide treatment should be cost-effective. If the mites build up early and hot, dry weather persists, a second application may prove necessary. Areas of stressed plants are often the main source of infestation for the rest of the field. All registered materials have failed to control mite outbreaks at one time or another. Control with Comite may not last for the full season.

In the areas where both Banks grass mite and two-spotted mite species occur, the only effective chemical treatment seems to be an application of bifenthrin 2E^R, Onager, Comite II, or Oberon 2SC, as described for Banks grass mite control. Other materials registered, but not recommended, for this situation include dimethoate.

Table XI-1. Economic threshold for Banks grass mites in grain corn (based on % infested leaves/% leaf area damaged).

Control Cost($ per Acre)	Market Value $ per Acre
	350	400	450	500	550
10	17/9	15/8	13/7	12/6	11/6
15	25/13	22/12	20/10	18/9	16/9
20	34/18	29/16	26/14	24/13	21/11
25	42/22	37/20	33/17	29/16	27/14

Product list for Banks grass mite

Efficacy data for some products against Banks grass mite can be found in the Colorado Agricultural Experiment Station Technical Report series "20xx Colorado Field Crop Insect Management Research and Demonstration Trials" located at [2].

Pesticide	Product/Acre (Fl oz. or oz. product)	Preharvest Interval, remarks
bifenthrin^R,1,2	See labels	30 days. 12 hour REI. Research indicates that this product is more effective if applied in combination with dimethoate and crop oil. Highly toxic to Bees! Do not apply to blooming crops, weeds.
bifenthrin + chlorpyrifos^R,1,2	See labels	30 days to grain or silage. 24 hour REI. Highly toxic to Bees! Do not apply to blooming crops, weeds. See labels for additional restrictions for individual active ingredients.
Swagger^R,1	10.3	30 days to grain or silage. 12 hour REI. Maximum 76.8 fl oz product/season. Highly toxic to Bees! Do not apply to blooming crops, weeds. See labels for additional restrictions for individual active ingredients.
Hero^R,1	10.3	30 days to grain or fodder. 60 days to forage. 12 hour REI. Highly toxic to Bees! Do not apply to blooming crops, weeds. See labels for additional restrictions for individual active ingredients.
dimethoate^1,2	See labels	28 days grain, 14 days forage. 48 hour REI. Not more than 3 applications/yr. Extremely Hazardous to Bees! Do not use during pollen shed. Buffer to pH 5.0.
Zeal SC	2-6	21 days. 12 hour REI. No more than 6 fl oz/A/season.
Portal XLO	32	14 days. 12 hour REI. No more than 64 fl oz/A/season. Maximum two applications per season, with a minimum of 14 days between applications.
Onager¹	10-24	30 days. 12 hour REI. No more than 24 oz per season. Do no apply after the V15 growth stage.
propargite^R,1,2	36 - 54	30 days. 13 day REI. This material will prevent buildup, but will not control already high populations. Apply at flagleaf or pretassel stage when populations are still low. A second application may be applied, but no more than 54 oz total for the season.
Oberon 4SC¹	2.85 - 8	30 days grain or stover, 5 days silage. 12 hour REI. No more than 8.5 fl oz/A/season. Maximum two applications per season, with a minimum of 14 days between applications. See label for crop rotation restrictions.
^RRestricted use pesticide. ¹Labeled for chemigation. ²Generic active ingredient, several formulations.

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.