Invertebrate seed predators (ISPs) are an important component of agroecosystems that help regulate weed populations. Previous research has shown that ISPs' seed preference depends on the plant and ISP species. Although numerous studies have quantified weed seed losses from ISPs, limited research has been conducted on the potential for ISPs to consume cover crop seeds. Cover crops are sometimes broadcast seeded, and because seeds are left on the soil surface, they are susceptible to ISPs. We hypothesized that (1) ISPs will consume cover crop seeds to the same extent as weed seeds, (2) seed preference will vary by plant and ISP species, and (3) seed consumption will be influenced by seed morphology and nutritional characteristics. We conducted seed preference trials with four common ISPs [Pennsylvania dingy ground beetle (Harpalus pensylvanicus), common black ground beetle (Pterostichus melanarius), Allard's ground cricket (Allonemobius allardi) and fall field cricket (Gryllus pennsylvanicus)] in laboratory no choice and choice feeding assays. We compared seed predation of ten commonly used cover crop species [barley (Hordeum vulgare), annual ryegrass (Lolium multiflorum), pearl millet (Pennisetum glaucum), forage radish (Raphanus sativus), cereal rye (Secale cereale), white mustard (Sinapis alba), crimson clover (Trifolium incarnatum), red clover (Trifolium pratense), triticale (×Triticosecale) and hairy vetch (Vicia villosa)] and three weed species [velvetleaf (Abutilon theophrasti), common ragweed (Ambrosia artemisiifolia) and giant foxtail (Setaria faberi)]. All four ISPs readily consumed cover crop seeds (P < 0.05), but cover crops with hard seed coats and seed hulls such as hairy vetch and barley were less preferred. Our results suggest that farmers should select cover crop species that are avoided by ISPs if they plan on broadcasting the seed, such as with aerial interseeding.

The influence of soil moisture stress, temperature, and bulk density on the germination and seedling emergence of downy brome (Bromus tectorum L.) was investigated in the laboratory. Reductions in soil matric potential from -2 to -16 bars markedly reduced the percentage and rate of emergence. Seedling emergence was better at constant than at alternating temperatures. At high matric potentials, the rate of emergence was accelerated by warmer soil temperature (20 C), while at very low matric potentials, the percentage and rate of seedling emergence were least restricted at cooler temperatures (10 and 15 C). Soil matric potential did not influence the percentage or rate of emergence of seedlings grown from seed lots harvested during climatologically diverse years. Seedling emergence but not germination was inhibited by increased levels of soil compaction. Soil compaction times moisture interaction were not observed, as measured by final seedling emergence.

The interaction of reduced rates of bentazon, chlorimuron, imazaquin, and imazethapyr with cultivation for broadleaf weed control in soybeans was investigated in field experiments conducted at three sites in Missouri in 1987 and 1988. Single reduced-rate herbicide applications provided soybean yields equal to full rates although visual weed control was slightly lower. Sequential applications of all four herbicides at reduced rates provided weed control and soybean yields equal to full-rate applications. The number of velvetleaf plants m−2 and seeds plant−1 were not influenced by herbicide, herbicide rate, or application timing. Cultivation improved weed control and soybean yield and decreased late-season weed populations and seed production.

A field experiment involving seven cultural practices was begun in 1974 in an area heavily infested with velvetleaf (Abutilon theophrasti Medic.) seed. Our objective was to determine the time required to eradicate velvetleaf seed from the soil. This paper reports the results of the first 4 yr of a long-term study. A cultural practice is repeated on the same plot year after year. Since the experiment was begun, no velvetleaf plants have been allowed to produce seed in any plots. The number of viable velvetleaf seeds is monitored by yearly soil sampling. In 1978, after 4 yr of a fallow treatment involving intensive tillage (two plowings per yr plus monthly tillage throughout the growing season), only 10% of the original seed population remained. However, that 10% was 1,300 viable seeds per m2 (to a depth of 23 cm). Four other practices that involved tillage gave generally similar results. Under undisturbed, continuous alfalfa, 56% of the original seed population remained after 4 yr, and under undisturbed, continuous chemical fallow, 37% remained. The results thus far demonstrate the extreme difficulty of eradicating velvetleaf seeds from the soil, and generally agree with reports in the literature, which primarily include studies conducted under more artificial conditions than we used. Our results also suggest that, in soil, velvetleaf seeds that have become water permeable (nonhard) may later again become water impermeable (hard).

The decline in the natural soil population of seeds of wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler ♯ SINAR] under nine cultural and chemical practice treatments was studied under field conditions. Wild mustard plants were not allowed to produce seeds in any treatment. After seven growing seasons, treatments in which the soil was not disturbed (continuous grass sod or continuous chemical fallow) had approximately 50% of the original population of wild mustard seeds remaining. In contrast, less than 3% of the original population of wild mustard seeds remained in a treatment that involved plowing three times a year with additional tillage throughout the growing season. This 3%, however, was equivalent to 2.4 million seeds/ha in the plow layer. Eradication of wild mustard from an infested field may be impractical with currently available techniques.

Field experiments, conducted from 1991 to 1994, generated information on weed seedbank emergence for 22 site-years from Ohio to Colorado and Minnesota to Missouri. Early spring seedbank densities were estimated through direct extraction of viable seeds from soil cores. Emerged seedlings were recorded periodically, as were daily values for air and soil temperature, and precipitation. Percentages of weed seedbanks that emerged as seedlings were calculated from seedbank and seedling data for each species, and relationships between seedbank emergence and microclimatic variables were sought. Fifteen species were found in 3 or more site-years. Average emergence percentages (and coefficients of variation) of these species were as follows: giant foxtail, 31.2 (84%); velvetleaf, 28.2 (66); kochia, 25.7 (79); Pennsylvania smartweed, 25.1 (65); common purslane, 15.4 (135); common ragweed, 15.0 (110); green foxtail, 8.5 (72); wild proso millet, 6.6 (104); hairy nightshade, 5.2 (62); common sunflower, 5.0 (26); yellow foxtail, 3.4 (67); pigweed species, 3.3 (103); common lambsquarters, 2.7 (111); wild buckwheat, 2.5 (63), and prostrate knotweed, 0.6 (79). Variation among site-years, for some species, could be attributed to microclimate variables thought to induce secondary dormancy in spring. For example, total seasonal emergence percentage of giant foxtail was related positively to the 1st date at which average daily soil temperature at 5 to 10 cm soil depth reached 16 C. Thus, if soil warmed before mid April, secondary dormancy was induced and few seedlings emerged, whereas many seedlings emerged if soil remained cool until June.

Research was conducted from 1979 through 1982 in east-central Alabama to monitor changes in sicklepod (Cassia obtusifolia L. ♯ CASOB) seed numbers in the soil under various cropping and weed management systems in soybeans [Glycine max (L.) Merr.]. Significant declines in sicklepod seed numbers were attained only when mechanical summer fallow each year prevented replenishment of seed in soil. Repeated disking favored germination and emergence of sicklepod seed and thus caused a reduction in seed numbers. Chemical summer fallow, which relied on postemergence control of emerged sicklepod, did not result in a disturbed seedbed and was less effective in reducing seed numbers. Permitting subcompetitive densities of sicklepod, 0.45 and 0.90 plants/m2, to reach maturity each year resulted in increases in seed numbers in the soil. Increases were more dramatic in conventionally planted soybeans than in no-till culture. Sicklepod produced more pods per plant in tilled culture than in no-till. Sicklepod seed distribution in the upper 30 cm of the soil was not affected by the type of primary tillage.

Quality discounts and premiums for rough rice in Texas rice bid/acceptance markets are analyzed. The most important quality factors determining the value of rough rice are head yield and peck. A one percentage point reduction in peck damage raises the price received per hundredweight of rough rice by $.13 to $.68 across markets and years. Since peck damage can be reduced by controlling the rice stinkbug, evaluation of alternative methods for better control of this pest in Texas rice fields is needed.

A model has been developed to simulate the annual dormancy cycle of seeds of light-requiring species in the seed bank and the germination of exhumed seeds after irradiation. Simulation of dormancy and germination is based on a physiological model concerning the action of phytochrome in the seed. Dormancy is related to the amount of a hypothetical phytochrome receptor, which fluctuates in an annual pattern. Relief of dormancy is equivalent to an increase in the amount of receptor, and induction of dormancy is equivalent to a decrease in the amount of receptor. Annual changes in temperature are the driving force for annual changes in the amount of phytochrome receptor in seeds that are buried in the seed bank. From the average amount of phytochrome receptor in the seeds of a population, the model calculates the germination percentage that is reached when a seed sample from the population is exhumed, irradiated and incubated at a given temperature in darkness. In the model, relief of dormancy results in a widening of the range of temperatures over which germination can occur, and induction of dormancy results in a narrowing of this range. Model parameters were estimated by fitting the model to data from a burial experiment with seeds of Polygonum persicaria L., Chenopodium album L. and Spergula arvensis L. At regular time intervals during 3 years, subsamples of these seeds were exhumed and tested for germination in the laboratory. The simulation model gave a good description of the observed cyclic changes in germinability of exhumed seeds.