This work was initiated to develop a method of sampling quackgrass populations. Shoot and bud distribution of 36 field populations was obtained. The results demonstrated that shoot count was inappropriate in assessing quackgrass bud populations and that bud sampling depth should be at least 20 cm if an accurate estimate is required. When shoot count is the only possibility, quadrat size should be as large as possible to minimize the error. Descriptive statistics of the field populations were used to generate a series of 24 simulated quackgrass bud populations. The field and simulated data were computer sampled with a program designed to compare the effects of varying sample size (number of quadrats) and sample shape (quadrat size and form). The intensity of sampling must be a function of resources and cost, since sampling precision increased linearly with sample size. Precision of sampling was generally higher when a large number of small quadrats were used compared to a small number of large quadrats. Sampling intensity per unit area must be increased when bud density increases to maintain a given degree of precision, but it can be decreased when plot size increases.

An experiment was established at three sites to determine the longevity and distribution of rhizome buds of two quackgrass biotypes in the soil profile under two tillage systems (no-till or fall-plow). The experiments were established in May 1987 at sites initially free of quackgrass. Rhizome segments with three nodes were planted 2 to 5 cm deep to give an initial density of 21 buds m-2. Production of new buds was prevented in subsequent years. Rhizome bud populations were sampled every 6 mo between October 1987 and October 1989. Buds were produced until snow cover, indicating the need to control quackgrass until late fall to prevent a bud population increase. Under no-till conditions, 94% of quackgrass buds occurred in the top 10 cm of soil while 68 and 19% were found below 10 and 20 cm, respectively, in the fall-plow treatments. A control program against quackgrass should aim at keeping the majority of rhizomes in the top 10 cm in order to facilitate control by having most shoots emerging at the same time. There was no statistically significant difference in bud longevity between biotypes, sites, and tillage systems. Viability of the rhizome buds declined rapidly during the first year. In most cases it took 2 yr for the bud populations to reach extinction although 0.6% of buds of one biotype survived as long as 30 mo in one of the three sites. Therefore, a minimum of 2 yr of total control would be required to eradicate quackgrass from most locations.

Photosynthesis decreased 32% in quackgrass infected with rust. Photoassimilate transport in rust-infected quackgrass, assessed by autoradiography, was less than that of control (no rust) leaves 35 min after exposure to 14CO2. Greenhouse-grown quackgrass height, foliar and rhizome dry weights, rhizome length, and bud numbers decreased 11, 25, 28, 19, and 21% in rust-infected plants, respectively, compared to control plants. Foliar and rhizome biomass decreased 31 and 39%, respectively, in field-grown rust-infected plants. Rhizome bud death 48 h after treatment (HAT) in both control and rust-infected plants increased as glyphosate rate increased from 0.13 to 1 kg ae ha−1; however, control plant bud death was significantly greater than that of rust-infected plants.