Deleterious activity of cultivated grasses (Poaceae) and residues on soilborne fungal, nematode and weed pests

Experiments were conducted in laboratory bioreactors and in field plots to test effects of certain cultivated members of the grass family (Poaceae = Gramineae), including wheat (Triticum aestivum cv. Yolo), barley (Hordeum vulgare cv. UC337), oats (Avena sativa cv. Montezuma), triticale (X Triticosecale), and a sorghum-sudangrass hybrid (Sorghum bicolor x S. sudanense = “sudex”, cv. Green Grazer V) for soil disinfestation potential. Soilborne pest organisms tested for effects on survival and activity included the phytopathogens Sclerotium rolfsii, Pythium ultimum and Meloidogyne incognita, and a variety of weed taxa. Following soil amendment, bioreactors were incubated for 7 days at ambient (23°C) or elevated, but sublethal (38°C day/27°C night), soil heating regimens. Addition of each of the poaceous amendments to soil at 23°C resulted in inconsistently reduced tomato root galling (49–97%) by M. incognita, or reduced recovery of S. rolfsii and P. ultimum (0–100%) fungi in soil, after 7 days’ incubation (P ≤ 0.05). When the organisms were exposed to the poaceous soil amendments at the 38o/27o temperature regimen, nematode galling and recovery of active fungi were consistently and significantly reduced by 98–100%. These results demonstrated feasibility of soil disinfestation (“biofumigation”) by activity of poaceous amendments, further aided by combining plant residues with soil heating (e.g. solarization). Results from three field experiments with sudex cover crops, conducted throughout the growing season, demonstrated biocidal activity on a range of weedy plants, including Amaranthus retroflexus, Calandrinia ciliata, Cerastium arvense, Digitaria sanguinalis, Echinochloa crus-galli and Poa annua. Both shoots and roots of sudex provided allelopathic weed biomass reductions of 35–100%, and for at least 106 days after shredding. Deleterious activity of shredded residues incorporated in soil was less persistent. These properties in poaceous crops can be useful for soil disinfestation; however, harmful phytotoxicity to subsequent crops may also result. In order to take full advantage of these low-input measures for controlling soilborne diseases and pests, further understanding of their properties must be gained, and user guidelines developed.