Wild oat reduced light penetration and growth of dwarf hard red spring wheat in field experiments performed under nonlimiting nitrogen and moisture conditions. Wild oat grew taller than wheat and had a greater portion of its canopy above 60 cm at maturity. Light penetration in a mixed canopy was similar to that in a monoculture wheat canopy when wild oat was clipped to the height of the wheat. A mathematical model was developed which accurately predicted the reduction in the growth rate of wheat from wild oat interference. The model also predicted that interference from wild oat was due to reduced leaf area of wheat at early growth stages and low wild oat densities, and reduced light penetration to wheat leaves at later growth stages and higher densities of wild oat.

Largeseed dodder is the most troublesome weed in alfalfa fields in the high desert of Southern California. Preemergence treatment with trifluralin controls dodder early in the season, but, as the season progresses, control declines. A method was needed to control attached dodder plants that escaped preemergence treatment. Flail mowing was compared to burning with a handheld propane-fueled weed burner. These methods were equally effective for controlling attached dodder, but flail mowing was more economical, and less injurious to alfalfa yield and stand density. Burning dodder patches at the end of the season reduced dodder seed viability by an average of 99%. Thus, we propose the use of a three tiered integrated approach consisting of PRE herbicide treatment followed by flail mowing in mid-season to control escaped dodder and burning at the end of the season to reduce dodder seed.

In the irrigated desert area of Imperial Valley, Calif., Cocorit 71 durum (Triticum durum Desf.) was developing sufficient yellow berry to be penalized in price received by growers. The objectives of the study were to define the relationship between nitrate fertilizer timing, protein, and yellow berry in grain and to recommend the N fertilization program leading to the highest yield of low yellow berry grain yield. The study was conducted on a well drained vertic torriorthent of the entisol order. Plots were fertilized with 0, 135, 202, 270, or 404 kg/ha of N as ammonium nitrate in three treatments: all preplant (P), half preplant, and half at tillering (PT); and one‐third each at the preplant, tillering, and boot stages (PTB). Grain protein content differed significantly between treatments. Yellow berry decreased by 16.4 to 18.5% for each percentage increase in crude protein in the grain. PTB gave significantly higher protein in the grain than the other treatments. Protein content had significant linear correlation with shatter, lodging, average grain size, and grain density. PTB at 270 kg N/ha was the lowest N application that gave a consistently high yield, with less than 25% yellow berry. The wetter of two irrigation treatments had significantly less lodging in 1976, and longer straw, higher yield, and lower grain density in 1977. Effects were similar to the above in comparison treatments of ‘Mexicali 75’ durum and ‘Yecora Rojo’ (Triticum aestivum L.), a hard red spring wheat. It was recommended that N fertilization be 90 kg/ha at preplant, again at tillering, and again at the boot stage.

Common bermudagrass is an invasive, perennial weed of cool-season turfgrass in California. Complete renovation of the infested area has been the only practical method of restoring desirable cool-season turfgrasses. In studies in southern and northern California, common bermudagrass was suppressed with sequential herbicide applications, allowing seedling establishment and regrowth of established cool-season turfgrass species. One application of fenoxaprop, triclopyr, or their combinations did not control common bermudagrass. Sequential applications of these herbicide treatments resulted in 99, 94, and 100% control of common bermudagrass, respectively, and resulted in establishment of seeded perennial ryegrass in Riverside, CA, over a 2-yr period. Similar results were obtained in the recovery of established tall fescue from a common bermudagrass/tall fescue turfgrass mixture in Willows, CA. Both fenoxaprop and triclopyr can reduce emergence and stunt seedling growth of perennial ryegrass and tall fescue. Greenhouse studies showed that stunting and stand loss of tall fescue and perennial ryegrass seedlings could be reduced by delaying applications from PRE to the two-leaf stage.

Competitive interactions of wheat and wild oats in relation to variations in plant density of both species were investigated in field studies under irrigation and added fertilizer. Competition studies included comparisons by both additive and replacement series. The additive series was used to study plant responses to competition under fixed density of wheat and increasing density of wild oats. The replacement series was used to study plant responses to competition under constant total plant density with differing proportions of wheat and wild oats. On a per plant basis, shoot dry weight and leaf area index of wild oats were less than those of wheat at anthesis. However, the replacement series experiment indicated that wheat and wild oats were equivalent in competitiveness. Relative density of wild oats gave a better regression fit for wheat yield than did absolute wild oats density (r2values of 0.83 and 0.61, respectively). Yield of wheat grain was linearly proportional to relative density of wild oats.