The Bindweed Mite Distribution Program in Colorado

Bob Hammon & Melissa Foley, Tri River Cooperative Extension, Grand Junction CO
Terri Locke, Colorado Department of Agriculture, Palisade CO

The Bindweed Mite, Aceria mahlerbae

Field bindweed (Convovulus arvensis) is one of the most widespread and difficult to manage weeds in the United States. It is a major weed in agricultural, wildland, rangeland, urban, landscape and many other settings. Its vining growth habit allows it to climb over and out compete adjacent vegetation for sunlight. The extensive root system provides drought tolerance and stores nutrients to fuel growth. The plant thrives in the arid western states and will grow on many sites where other plants cannot exist.

Bindweed control is difficult, requiring a multi year commitment and diligence. Chemical controls rely on broad spectrum herbicides such as glyphosate or broadleaf herbicides such as picloram. These compounds can give acceptable control under some circumstances, but options are limited in the vast majority of cases. Control in localities with desirable vegetation, inaccessible areas, and in many agricultural systems is nearly impossible with herbicides. Management of bindweed for home and small acreage owners and gardeners is one of the more difficult issues they face.

The USDA began searching for biological control agents for field bindweed in the early 1980's in southern Europe. The bindweed mite, Aceria mahlerbae, was selected as a potential biocontrol agent from Greece and introduced into the US after extensive research in a quarantine facility. (Coombs et al. 2004.) Host plant research showed that it fed only on field bindweed and some closely related Calystegia species (Rosenthal & Platts, 1990). Initial releases were made in Texas in 1989 (Boldt & Sobhian. 1993). Bindweed mites have been released and established in Montana and Alberta, Canada (McClay et al., 1999), New Mexico (Laurialt, 2004) and in South Africa (Craemer, 1995). The first Colorado releases were made in 1997 by the Colorado Department of Agriculture Insectary at Palisade (CDA).

Bindweed mites are microscopic and cannot be seen with the unaided eye. They resemble a grain of rice, and measure about 0.1mm in length. Mites spend the winter feeding on underground buds on bindweed rhizomes. When growth begins in the springtime, the mites move the new growth of the plant. Mite feeding causes the plant to form a gall, with swollen or distorted growth. Infested vines do not elongate, flowering is inhibited, and growth is reduced. Infested leaves thicken and develop a “fuzzy” or rough texture, are folded, or can be so distorted they no longer resemble leaves.

Bindweed mite presence is usually determined by the damage symptoms. The damage can be categorized in three types. Type 1 is the first response to mite feeding. The leaf blade is folded, and the midrib is thicker and has a fuzzy or wooly appearance. It sometimes turns a light reddish color. Only one or two mites can cause this type of damage after a short period of feeding. As the mites continue feeding, the leaf begins to gall or growth is distorted so there is no flat leaf surface. Type 2 damage is characterized by the presence of these highly distorted leaf gall on typical bindweed vines. This damage occurs when mites attack bindweed above ground while it is actively growing. With type 3 damage, the plant no longer appears as normal bindweed. All leaves and stems are a tight knotted up mass. Leaves do not expand, plants do not flower and vining does not occur. Type 3 damage occurs when mites are present on the underground buds and affect growth before it ever reaches the soil surface. Type 3 damage is responsible for most of the long-term damage to bindweed plants.

The impact of bindweed mite infestations has varied considerably, from complete failure to unquestioned success. In general, the greatest success has been on drier sites with some sort of management of the bindweed, either by mechanical mowing or grazing by domestic or wild animals. Bindweed mites have had dramatic success in several prairie dog towns, in part due to the grazing and movement of the rodents. The time from release to impact has also varied, with some sites showing results within a year or two. Mites have been established at other sites for several years with minimal impact. The reasons for this variation are not clear. What is clear however is that bindweed mites can have a significant impact on the weed in many instances. They are a long-term, sustainable, inexpensive, environmentally friendly addition to our existing arsenal of management tools for this tenacious weed.

The Bindweed Mite Distribution Program in Colorado, 2004-06

The Environmental Protection Agency Region 8 awarded Colorado State University Cooperative Extension, Tri River Area (CSUCE) two grants (IPM and FQPA Transition & Sustainable Agriculture) to develop a bindweed mite distribution program throughout Colorado during the 2004-2006 time period. This program was developed in cooperation with the Colorado Department of Agriculture Insectary in Palisade. The CDA had been doing initial releases in the state since 1997 with the intention of developing collection sites for further distribution. The infrastructure of CSUCE allowed extension agents in each county to coordinate distribution and educational efforts within their region.

An abandoned field near Grand Junction was identified during the spring of 2004 as ideal collection site for bindweed mites. This site had large stands (several acres) of field bindweed that was not contaminated with other weed species. The bindweed was almost 100% infested with mites in many areas. It was easily accessible, and the landowner gave permission for us to harvest. Collecting began in early May. Infested bindweed was hand harvested into cardboard boxes or coolers, with each box contained enough bindweed for about 30 distributions. The mites were refrigerated in walk in coolers immediately after collection. They were typically distributed to landowners within 48 hours of collection.

Infested bindweed was distributed to anyone wanting to establish their own colony of bindweed mites. Mites were distributed via Cooperative Extension offices and the Colorado Department of Agriculture Insectary at Palisade. A distribution consisted of a small paper sack about 1/3 to 1/2 full of infested bindweed. Distributions were done without charge during 2004. CSUCE initiated a $15.00 charge per distribution in 2005 to help cover costs. The charge also helped to limit demand, which was overwhelming in many counties. CDA charged $10.00 for distributions which were picked up, and $15.00 for those that were delivered by mail in 2005. They determined that TABOR restrictions did not allow charging for services, so all charges were dropped in 2006.

In 2004 over 1,200 distributions were done in Mesa, Delta and Montrose counties. When residents came to collect the bindweed mites they were asked to fill out a simple form regarding where they were going to release the mites and their best guess about the size of the bindweed infestation in which they were releasing the mites. The CSUCE release program was conducted state-wide in 2005. The program was publicized to county extension agents during their annual meeting in November 2004. Interested agents organized release programs and educational workshops in their counties. Landowners signed up in advance so the number of distributions was known.

Mites were gathered at the Grand Junction collection site each week, and then delivered to an area of the state. Trips were made to SE, NE, NW, and SW Colorado. Boulder , Weld and Larimer counties had great demand, so special trips were made to supply their needs. CSUCE handled distributions arranged by county agents, while CDA handled request that arrived to them via either phone or their web site. More than 4000 distributions were made to almost 50 counties between 2004 and 2006. Mite distributions began in early May in 2004 and mid May in 2005. Good collecting, typified by extensive stands of heavily infested bindweed plants occurred a full three weeks later in 2005 than 2004. The bindweed mite population collapsed in February 2006. Spring and early summer collecting was difficult, but the CDA did 400 distributions. Mite populations rebounded in mid-summer 2006, and extensive infestations were present by early August.

It is obvious after three years of intensive collection and distribution that there is significant variation in early season mite populations from year to year. This variation is a result of differences in overwintering success. The factors influencing overwintering success remain unknown.

In September and October 2005 a survey was conducted to determine where the mites were established in Colorado. Thirty-eight counties were surveyed. In eastern Colorado the sites were chosen by drawing a 40 miles grid in a map and locating a bindweed patch within 5 miles of where the lines intersect. On the west slope, we chose random spots within areas that were known to be infested with bindweed, and a search was done within 5miles of that spot. Some isolated roads were traveled, and bindweed patches were inspected as they were seen. G.P.S. coordinates were recorded at each location that was surveyed for mites. A 0-5 rating system, based on the amount of bindweed and the degree of bindweed mite infestation, was used to rate each site.

The survey showed that bindweed mites are established to some extent throughout areas of the state where bindweed grows. The best establishment of mites is in the lower valleys of the west slope, where the number of releases has been most intense. Mites can be found on bindweed in many areas of the eastern plains. Few or no mites were found the extreme NE and SE part of the state, and these areas need to be targeted for more releases. Many infestations were found in areas where no known releases had been made. It appears that the mite is spreading to new areas on its own.

The mites are having significant impact on bindweed infestations at many sites throughout the state. Bindweed cover is being reduced, they are producing less seed at many sites, and plant vigor is being affected in heavily infested areas. This success story is bound to get better over time!

• More than 4000 Colorado residents received bindweed mites from CSUCE and CDA during the three year project. All of these individuals learned first hand the reality of biological control - success and/or failure. Bindweed mites are an excellent tool for teaching the public about the realities of weed management.• Bindweed mites are now established throughout Colorado where bindweed grows. Their impact on field bindweed will increase over time. The process is now irreversible. Bindweed mites are now a permanent resident of the state.

• The highway US 50 corridor from Whitewater to Fruita is an example of the impact bindweed mites can have on field bindweed infestations. Initial releases were made in 1997 on Orchard Mesa, and by 2005 mites were distributed for miles in either direction from the release site. Roadside mowing is a major factor for the distribution of the mite. Areas that were once solid bindweed have been reduced to scattered patches

.• Cooperative Extension and Colorado Department of Agriculture personnel have addressed more than 20 workshops, symposiums, and other public gatherings to educate people about bindweed mites. More than 2000 individuals attended these workshops

.• More than $25,000 was brought in to the CSUCE county offices as a result of this project. This money went to covering project costs and was used for county educational programming. The CSUCE distribution program will be financially self-sustaining in the future.

• AJ Urbina, a 12 year old from Grand Junction created a 4H weed science project investigating overwintering bindweed mites. He has the only data regarding overwintering mortality of the mites during the winter of 2005/06. He won the Grand Champion prize for 4H weed science displays at the 2006 Colorado State Fair!

• Kaitlyn Lingus contacted us in 2004 about obtaining bindweed mites for a high school science project in Branson, CO. She was in the 10th grade at the time, and asked for advice regarding her project. She released the mites and documented the spread over time. She entered her project in the Society of Range Management Youth Forum, at the 2006 annual meeting in Vancouver BC Canada. She was awarded 3rd place and her report was published in Rangelands magazine (Lingus, 2006).

Boldt, P.E. & R. Sobhian. 1993. Release and establishment of Aceria malherbae (Acari: Eriophyidae) for control of field bindweed in Texas. Environmental Entomology 22(1): 234-237.

Coombs, E.M, J.K. Clark, G.L Piper & A.F Cofrancesco (eds). 2004. Biological Control of Invasive Plants in the United States. Oregon State University Press, Corvallis OR. 467 p.

Degennare, F.P., & S.C. Weller. 1984. Growth and reproductive characteristics of field bindweed (Convolvulus arvensis) biotypes. Weed Science 32:525-528.

Lauriault, L.M., D.C. Thompson, J.B. Pierce, G.J. Michels, and W.V. Hamilton. 2004.Managing Aceria malherbae gall mites for control of field bindweed. New Mexico State University Cooperative Extension Circular 600. 8p.

Lingus, K. 2006. One “mite-y” mission: Compensation suppression of Convolvulus arvensis after implementing host-specific Aceria malherbae. Rangelands 28(4):12-14

McClay, A.S., J.L Littlefield & K. Kashefi. 1999. Establishment of Aceria malherbae (Acari: Eriophyidae) as a biological control agent for field bindweed (Convolvulaceae) in the nothern Great Plains. Canadian Entomologist 131:541-547

Rosenthal, S.S, & B.E. Platts. 1990. Host specificity of Aceria malherbe (Acari: Eriophyidae), a biological control agent for the weed Convolvulus arvensis (Convovulaceae). Entomophaga 35(3), 459-463

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