Weed Biological Control & Management Program

For the past 15 years the Maryland Department of Agriculture Weed Biological Control Program has not only continued to monitor weed biological control efforts implemented in years past but has conducted new and novel research and demonstration projects and tested and implemented non-conventional weed control methods. These projects have concentrated on the development of sustainable alternative methods for control of a number of weed species problematic in the State of Maryland.

Strategies include: Introduction and tracking of insects that feed on specific weed species; Monitoring naturally occurring plant disease and invertebrate pest populations and their impact on particular hosts; and Manipulation of successional plant habitat through the planting of competitive vegetation. These projects have been implemented and evaluated by the department's Plant Protection and Weed Management Program staff. ​

The program has partnered with Maryland state agencies such as the Maryland State Highway Administration (SHA), the Maryland Department of Natural Resources, and the Maryland Environmental Service; county agencies such as the Howard County Department of Recreation and Parks, and the Maryland National Capital Park and Planning Commission; and federal agencies such as U.S. Department of Agriculture, the U.S. Fish and Wildlife Service, and U.S. Geological Survey. The department has also partnered with the New Jersey Department of Agriculture and the University of Delaware on specific weed biological control projects. ​

Particular research and trials for individual weed species are outlined below. ​

Mile-a-Minute Weed, Persicaria perfoliata has become a major right of way landscape and natural area problem. This annual vine can grow up to 20 feet or more in a single season and its seed are spread by songbirds and waterways. Its rampant growth can smother native plants and other desirable vegetation, especially along riparian buffers and forest edges. ​

In 2007, in cooperation with researchers at the University of Delaware in a region wide program aimed at biological control of this weedy vine, the department began releasing the Mile-a-Minute Weevil, Rhinoncomimus latipes at locations in central Maryland. The Howard County Department of Recreation and Parks partnered with the department and provided sites for weevil releases and assistance in monitoring establishment and impact of the weevils on Mile-a-minute populations. ​

Soon afterward, the department, again with assistance from the New Jersery Department of Agriculture, began mile-a-minute weevil rearing at the Annapolis greenhouse and laboratory facilities. In cooperation with and utilizing funding from the Maryland State Highway Administration and the USDA APHIS, rearing of mile-a-minute weevils is ongoing at the department and release of mile-a-minute weevils and monitoring their establishment and efficacy at reducing populations of mile-a-minute weed in Maryland is a continuing program along state and county road right of ways. ​

Purple Loosestrife, Lythrum salicaria is a European native that was likely introduced to North America by early settlers who valued it for both its ornamental qualities and for the abundant nectar it produces; a benefit for honeybee husbandry. This plant is a prolific seed producer and has outcompeted native plant species in certain areas of North America. ​

The Chrysomelid leaf beetle species, Galerucella pusilla and Galerucella calmariensis, adults and larvae of which feed specifically on purple loosestrife, Lythrum salicaria, were released in Maryland starting in the 1990’s. By 1999, the department was releasing thousands of the adult beetles per year in areas infested by purple loosestrife in central Maryland and on Maryland’s eastern shore. Initially all adult beetles were supplied by the New Jersey Department of Agriculture, Phillip Alampi Beneficial Insect Laboratory. By 2001, the department began releasing adult weevils reared in the greenhouse and laboratory facilities in Annapolis. Programs for the rearing and release of Galerucella beetles have since been curtailed, but monitoring and evaluation of theimpact of these herbivores on populations of purple loosestrife statewide continues. ​

Canada Thistle ​

Several insect herbivores have been introduced to combat the spread of Canada thistle, including: Canada Thistle Bud Weevil, Larinus planus; and Cassidine Leaf Beetle; likely Cassida rubiginosa. Most of these herbivorous insects were released by the department and federal counterparts over the past three decades and their efficacy at suppression of target thistle species in Maryland continues to be monitored and evaluated. ​

Plant Diseases:

Thistle Chlorosis - Likely caused by Pseudomonas syringae pv tagetes. Other thistle species that have also been targeted using herbivorous insects include: Plumeless Thistle, Carduus acanthoides, and Musk Thistle, Carduus nutans. These two thistle species are attacked by two introduced insect herbivores: the Thistle Head Weevil, Rhinocyllus conicus, and the Thistle Rosette Weevil, Trichoseracalus horridus. In many parts of the state, the combination of these two herbivores has nearly eliminated populations of the two problematic biennial thistle species. ​

Competitive Vegetation ​

Additional weed suppression trials have included the use of competitive vegetation, whereby native plants are planted to compete with undesirable thistle species. ​

Some of the most promising results using competitive vegetation have been achieved using native species of grasses such as Switchgrass, Indian Grass, Smooth Paspalum, Beaked Panicum,Big Bluestem and Little Bluestem. The use of grasses as competitive vegetation also does not preclude the use of targeted application of broadleaf herbicides as a weed management tool, a problem where broadleaf vegetation such as crown vetch has been used in right of way revegetation and soil stabilization plantings. ​

Competitive Vegetation Trials at the Cheltenham facility ​

Multiflora Rose and Rose Rosette Disease ​

Multiflora Rose, Rosa multiflora, in an old hedgerow.Multiflora rose,Rosa multiflora, purposely introduced in the 1930’s through 1960’s to help stabilize soils and control erosion, has since proven to be a problem weed in some areas of the country where it readily colonizes old pastures and hedgerows and can prolifically reproduce via seed spread by songbirds. This vigorous woody shrub can be very difficult to control using mechanical or chemical measures. ​

Rose rosette disease, caused by a plant virus thought to be native to North America and transmitted by plant feeding mites, causes shoot proliferation symptoms in multiflora rose, a phenomenon known as “witch’s broom”. Plants infected with the disease exhibit loss of vigor gradual dieback and eventual death. ​

Rose rosette disease symptoms ​

While rose rosette disease has been effective at local elimination of multifora rose populations in Maryland, it is, unfortunately, not specific to multiflora rose. To address concern regarding disease infection of desirable rose species and cultivated roses, the department performed Rose Rosette Disease Susceptibility trials to investigate relative susceptibility of several native roses common to Maryland as well as a number of more popular cultivated rose varieties. Most of the native rose species tested in the trials proved to be either resistant or immune to the disease. Unfortunately, several of the most popular cultivars used in the nursery and landscape trade proved to be susceptible to rose rosette disease. ​

See Historical Biocontrol Programs at the right.