Rush skeletonweed (Chondrilla juncea L. CHOJU) infestations occur along the eastern seaboard and in several western states of the United States. This Eurasian species was inadvertently introduced prior to 1870, with established stands first reported in Maryland and West Virginia (16). These infestations (16) were assessed as lacking aggressive characteristics and posed little threat as a problem weed. Although rush skeletonweed was discovered in the Pacific Northwest as early as 1938, the species was not recognized as a potential weed problem until nearly three decades later (27). Subsequent surveys revealed that infestations occupied over 2.3 million ha in California, Idaho, Oregon, and Washington (6). Attempts to generate support for an organized control program in Idaho were met with little enthusiasm during the 1960's.

Four Centaurea species, diffuse knapweed (C. diffusa Lam. # CENDI, spotted knapweed (C. maculosa Lam. # CENMA), yellow starthistle (C. solstitatilis L. # CENSO), and the closely related Russian knapweed [Acroptilon repens (L.) DC. syn. Centaurea repens L. # CENRE] are serious introduced weeds which infest extensive areas of pasture and rangeland in Canada and the United States (1, 10, 14, 17, 18, 26, 30). Russian knapweed and yellow starthistle are also troublesome in cultivated land (1, 14, 26). These four species are members of the Cardueae tribe of the Asteraceae family and have been accidentally introduced from Eurasia as contaminants in crop seed.

Evaluation and introduction of exotic plant pathogens for biological control of weeds in the United States takes place at the Plant Disease Research Laboratory (PDRL) in Frederick, MD. Pathogens of target weed species collected overseas are sent to PDRL and evaluated in a containment greenhouse for aggressiveness and specificity toward the target weed. Currently, rust fungi (Uredinales) are evaluated at PDRL for control of leafy spurge (Euphorbia esual L. #4 EPHES), musk thistle [Carduus nutans L. ssp. leiophyllus (Petrovic) Stoj. & Stef. # CRUNU (= C. thoermeri Weinm.)], and yellow starthistle (Centaurea solstitialis L. # CENSO). Determination of host range is central to the evaluation of potential pathogens, but some difficulty has been experienced in obtaining propagative material of important plant species, especially if the plant is threatened or endangered. A proposal is made to organize a seed bank to meet this need.

The use of biological control agents for the control of noxious pests is not new conceptual research. There are examples that predate by centuries the modern use of both herbicides and insecticides. For example, the successful control of insects by biological control was shown in 1762 by the introduction of the Mynah bird (Gracula religiosa Linnaeus) from India to Mauritius (4). In 1888, the Vedalia beetle (Rodolia cardinalis Muslant) was introduced to control the cottony-cushion scale (Icerya purchasi Maskell) of citrus (3). An example of biological control of weeds was reported in 1863 when it was observed that an infestation of prickly pear cactus (Opuntia humifusa Raf. # OPUHU) was decimated by the imported cochineal insect (Dactylopius tomentosus Lam.) (5).

Weed control strategies for rice (Oryza sativa L.) and soybean [Glycine max (L.) Merr.] emphasize integration of cultural and chemical practices (16, 30, 31). Numerous herbicides are registered and used as preplant, preemergence, or post-emergence applications for control of weeds in rice and soybean (3, 16, 25). Although these herbicide treatments control most of the problem weeds in rice and soybean, most fail to control northern jointvetch [Aeschynomene virginica (L.) B.S.P. # AESVI] in either crop. The two most effective herbicides, 2,4,5-T [2-(2,4,5-trichlorophenoxy) acetic acid] and silvex [2-(2,4,5-trichlorophenoxy) propanoic acid], for control of northern jointvetch in rice have been under the U.S. Environmental Protection Agency's (EPA) Rebuttal Presumption Against Registration (RPAR) process which may ultimately cancel the use of both herbicides in rice (50). New, effective control strategies are needed for control of northern jointvetch in rice and soybean.

Collego™ is a selective postemergent mycoherbicide for the control of northern jointvetch [Aeschynomene virginica (L.) B.S.P. # 2 AESVI] in rice (Oryza sativa L.) and soybean [Glycine max (L.) Merr.]. Collego is a two-component product. Component A is a water-soluble spore rehydrating agent while Component B is a water-suspendible dried spore preparation of the fungus Colletotrichum gloesporioides (Penz) Sacc. f. sp. aeschynomene ATCC 20358. Both components are packaged in an 18.9-L plastic mixing container. A mixture containing 0.95 L of Component A and one package of Component B will treat 4 ha. The dried spore component is packaged by number of viable spores rather than by weight. Consequently, the weight of each package will vary from lot to lot, but each package contains a minimum of 75.7 × 1010 viable spores.

Although the problems with waterhyacinth (Eichhornia crassipes [Mart.] Solms; # EICCR) have diminished in the United States over the last decade, the weed continues to be troublesome and requires constant management on a maintenance basis (29, 30). Chemical herbicides are currently the principal means of control when an immediate solution to a waterhyacinth problem is needed. Preventive maintenance programs also rely on chemicals to keep the weed populations at acceptable levels and to prevent weed migration into unwanted areas. However, when control is not urgently required or is economically unfeasible due to the location of the weed, a combination of biological control agents is used. The latter may have been the important factor that contributed to the lessening of the weed problem in this country over the past decade (43).

Stranglervine (Morrenia odorata Lindl. # MONOD) was identified in 1957 at a commerical citrus grove in Florida. It is believed that this plant pest was introduced into Florida as an ornamental plant from South America. In the early 1960's, it became recognized as a serious weed pest that competed with the citrus trees for sunlight, water, and nutrients; girdled tree limbs; and interfered with spraying, harvesting, and irrigation practices. By the 1970's the vine was distributed throughout most of the citrus-growing areas in Florida. Control measures were limited to herbicides and mechanical cultivation. It was estimated that the cost of controlling this pest was $124/ha/yr. In many instances, control measures were inadequate to keep the vines from becoming established in the trees (11, 12, 13). Studies reported by El-Gholl (4) further demonstrated the inherent ability of this weed to persist.

The use of nematodes as biological control agents has been met with skepticism, partly due to the newness of the approach and also to the potential difficulties of using a parasitic worm as a control organism. Most of the attention directed towards nematodes as biological control agents has been focused on several species that act as insect parasites. Considerable headway has been achieved with several of these parasites, especially with those parasitic on wood-boring insect larvae. The insect gallery of wood-boring larvae provides an optimum microclimate for the nematode to survive and seek out its larval insect host. A system where this strategy has proved successful involves the use of the insect parasitic nematode Neoaplectana carpocapsae Weiser as a biological control agent for carpenterworms (Prionoxystus robinae Peck) in fig (Ficus caria L.) orchards in California (6). Similar systems are being developed both here and abroad with the same nematode or a closely related genus or species. Many of these systems show promise (5).

Biological weed control research at Arkansas has been with indigenous fungal pathogens applied as inundative inoculum to weed populations (9, 19, 22, 32, 34, 39). We term this concept the mycoherbicide approach to biological weed control (35). Our experience with this concept began in 1969 with the discovery by R. J. Smith, Jr., of a previously undescribed fungal pathogen on northern jointvetch, [Aeschynomene virginica (L.) B.S.P. # AESVI] (20, 22, 29). It was ultimately commercialized as COLLEGO™ in 1982 by the Upjohn Co. for use by Arkansas rice (Oryza sativa L.) and soybean [Glycine max (L.) Merr.] farmers. Nothing has been found nor can be foreseen from the experience during discovery, development, and deployment of COLLEGO™ that would preclude extension of the mycoherbicide concept to controlling other weeds in annual crops or noncrop areas (29). Nevertheless, the concept does have limitations. An overview of the COLLEGO™ effort plus a statement of some research interests engendered by it will be useful for assessment of the practical potential of this new approach to biological weed control.

The impact of chemical or biological herbicides in weed control may or may not be absolute. The traditional goal in chemical herbicide evaluation has been the identification of materials and application rates resulting in absolute (100%) kill of susceptible weeds. However, many insects or plant pathogens affecting weeds do not kill their weed hosts but decrease their growth and or reproduction in the field. Obligate plant pathogens dependent upon their weed hosts for their own survival derive no evolutionary advantage from killing their weed hosts and seldom do so under natural conditions. Under field conditions where weeds are subjected to stresses imposed by competition with crop and/or other wild plants, these biological agents can decrease the impact of a weed on crop or wildland productivity to tolerable economic levels. The recognition that the impact of chemical and/or biological herbicides on weeds need not be absolute to be effective has been accompanied by a search for an accurate, efficient, and economical method to measure quantitative changes in weed growth or health. While much of this report will concentrate on measuring impact of plant pathogens on weeds or other plants, all comments and techniques will apply also to other stresses such as herbicide injury.

Legal protection of intellectual property is a requisite to the commercialization of the intellectual property and to the conferring of proper reward to the true owner of the property. Simplistically stated, this situation with regard to intellectual property is no different from the legal protection of a variety of properties, for example, home, land, or automobile. Laws have been established in the various countries of the world that are structured specifically to attain the desired goal of legally protecting property interests. In the intellectual property field, wherein we talk about property such as new inventions, we enter an area of not only protecting the legal rights of the property owner but also insuring the position of the public with respect to the eventual unlimited use of new inventions.

Although herbicides are designed to have no effects on the crops in which they are used, crop damage can occur, especially when overdoses are used or if chemicals are applied at an inappropriate time. Usually the resulting damage is recognized as foliar symptoms but roots may be severely affected as well.