Research was conducted on a sandy clay loam in Georgia during 1987–88 and 1988–89 to determine winter wheat, oats, barley, and Italian ryegrass tolerance to flurtamone. Flurtamone was applied PPI, PRE, and early POST at 0.28, 0.56, and 1.1 kg ai ha-1. Order of tolerance of the four species was barley > wheat > oat > Italian ryegrass. Flurtamone potentially can be used to control Italian ryegrass in winter wheat and barley, but not in oats. In general, wheat and oat injury with flurtamone was PPI > PRE ≥ early POST, particularly at 1.1 kg ha-1.

Three approaches to data analysis were compared to describe competitive interactions between wheat and Italian ryegrass. Replacement series were performed using the two species at total densities of 100, 200, and 400 plants/ m2, and separate monoculture experiments for each species at densities from 33 to 800 plants/m2. Approaches to data analysis included: 1) conventional analysis of replacement series experiments, 2) development of synthetic no-interaction responses from monoculture experiments for comparison with results from mixtures, and 3) responses of the reciprocal yield of individual plants to variation in densities of the two species. Wheat was the superior competitor to ryegrass; however, the three approaches varied in ability to quantify this competitive relationship. The conventional replacement series analysis was least sensitive in describing the influences of either density or proportion on the plant association. The synthetic no-interaction approach provided the most detailed analysis of the influence of proportion on the species interaction. The reciprocal yield approach provided the simplest and most sensitive analysis of the joint influences of density and proportion. The latter approach also provided the most quantitative analysis of the influence of density on the species interaction. Plant density and species proportion are important variables for interpreting the process of plant competition.

Cotton and pitted morningglory emergence and dry weight decreased approximately 60 to 80% when these plants were grown under greenhouse conditions in the presence of increasing amounts (0.8 to 6.7 mg debris/g soil) of field-grown crimson clover or hairy vetch debris incorporated into the soil medium. Conversely, corn dry weight increased 20 to 75% when legume debris was placed on the soil surface; incorporated debris had very little effect on corn emergence or dry weight. Germination and seedling growth of corn, Italian ryegrass, cotton, pitted morningglory, and wild mustard decreased progressively, with species-dependent variation, when exposed to increasing concentrations (8.3 to 33.3 g debris/L) of aqueous crimson clover and hairy vetch extract. Mustard and ryegrass germination and growth were almost completely inhibited by full-strength extracts of both legumes. Bioassay species exhibited greater phytotoxic responses to hairy vetch than to crimson clover in the debris and extract studies. Emergence and growth of corn and cotton were not affected when planted into soil samples, containing root biomass and possible leaf and root exudates, collected from beneath field-grown hairy vetch and crimson clover plants. However, morningglory dry weight increased 35% in the presence of either legume root debris and accompanying soil.

In 1987, two applications of the methyl ester of diclofop failed to effectively control Italian ryegrass in some growers' fields. As a result of these observations, studies were initiated to determine if the surviving ryegrass is more tolerant to diclofop than previously untreated ryegrass. Growth chamber studies on five accessions of ryegrass demonstrated that collections from two growers' fields were highly tolerant of diclofop. Diclofop GR50 (rate required to reduce shoot weight by 50%) values of accessions A and B and commercial ryegrass, when diclofop was applied to seedlings at the two-leaf stage, were 2.9, 3.4, and 0.0056 kg ai/ha, respectively. Diclofop-tolerant biotypes were not more tolerant to postemergence barban or preemergence-incorporated triallate plus postemergence diuron or metribuzin. These herbicides are possible alternative treatments in fields where diclofop is no longer effective.