Sporisorium cruentum teliospores and sporidia (cultured from teliospores with about 30-fold spore increase) caused about equal, although variable, levels of smut infection of individual Sorghum halepense plants when applied to the foliage. Teliospores were applied in a water–surfactant suspension (106 spores ml−1) at 935 L ha−1 and sporidia in a water-in-oil invert emulsion (about 107 spores ml−1) at 468 L ha−1. In crop interference studies, a single foliar application of teliospores to space-planted S. halepense plants in a first-year crop of Saccharum sp. hybrids caused about 55% infection (at least one smutted panicle per plant) but did not reduce the level of S. halepense infestation or substantially improve Saccharum yield compared to noninoculated plants. Smutted panicles usually appeared 30 to 60 d after the foliar treatment, but many culms on a plant produced only healthy panicles. Two applications of teliospores, either 7 d apart in one experiment or 1 yr apart in another, significantly increased (P = 0.05) smut infection over one application but generally did not improve Saccharum yield substantially over plots infested with noninoculated S. halepense. In contrast to foliar spray inoculation, S. halepense plants injected with teliospores in the seedling stage prior to transplanting to the field were 98% infected with smut and were much less competitive with the crop than noninoculated transplants. In host range studies using several S. bicolor genotypes injected with teliospores in the greenhouse, the ratios of resistant to susceptible were 17 to 2 for grain types and 16 to 5, with 2 intermediate, for forage types, showing that genotypes have a relatively high level of resistance to the disease. The result of these experiments indicate that loose kernel smut has potential as a biocontrol agent for S. halepense, but only if infection by foliar treatment can be improved to levels at least comparable to injection.

To identify the most commonly regulated weedy plants in the United States and southern Canada, we compiled a database of noxious weed lists obtained from the 48 continental states and six bordering provinces. The 10 most frequently listed weeds are Cirsium arvense, Carduus nutans, Lythrum spp. (includes purple loosestrife), Convolvulus arvensis, Euphorbia esula, Acroptilon repens, Sorghum spp. (includes johnsongrass and shattercane), Cardaria spp. (includes hoary cress, also called whitetop), Centaurea maculosa, and Sonchus arvensis. When genera are ranked, the top genus is Centaurea, which includes C. maculosa, C. diffusa, and C. solstitalis. Biological control programs have targeted many of the top dicotyledonous weeds of national concern, but none of the weedy grasses and sedges. We recommend that exploratory studies be initiated to determine the feasibility of developing biological control agents for the latter species. The complete database of noxious weed lists is available on the Internet at http://invader.dbs.umt.edu. This information may be useful to resource managers and regulatory officials in assessing which weeds are problematic in adjacent geographic areas and by researchers to help select which weeds to target with new management strategies.