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A field experiment was conducted at the research farm of the University of Tehran to evaluate the effect of cover crops and herbicide (nicosulfuron) dosage on corn (Zea mays L.) productivity. Cover crops suppressed weed biomass and density during the fallow period; however, there was no significant effect on weed biomass or weed density in the subsequent corn crop. A mixture of cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth.) was the most weed-suppressive cover in the fallow period. Nicosulfuron applied at different amounts suppressed weed biomass and density in corn when compared with weedy plots. Application of 40 g ai ha−1 of nicosulfuron was as effective on weed control as the recommended application. Cover crops did not affect corn growth; however, corn yield improved with herbicide application.
The genetic diversity of 39 clones of common reed originating from different geographical areas of Iran were evaluated using morphological and RAPD analyses. High level of morphological variation was observed among clones. The 16 primers used in this study amplified 149 scorable RAPD loci among which 123 were polymorphic (83.1%). A dendrogram was prepared on the basis of a similarity matrix of RAPD data using the unweighted pair-group method with arithmetic averages (UPGMA) algorithm and separated the 39 clones into four groups, which mainly were in accordance with geographical origins. The results of the morphological comparison mostly corresponded with the results of RAPD analysis. It is possible that these variations among clones will affect successful management of common reed using chemical or the other methods of control.
Intercropping is an eco-friendly approach for reducing weed problems through nonchemical methods. Intercrop effects on weed community structure have rarely been studied. A 6-yr study was initiated in 1999 and the response of aboveground weed flora (1999–2002 and 2005) and seed bank (2005) to the intercropping of saffron and black zira, two perennial crops was investigated. Mixtures consisted of 0/100, 25/75, 50/50, 75/25, and 100/0 saffron/black zira ratios, each planted at three densities: 30, 50, and 70 plant m−2. The effect of planting density on weed populations was variable and in most cases not significant. However, mixture ratios caused drastic species compositional changes in the weed community for which univariate and multivariate analyses explored four major associations: (1) weeds that favored a higher ratio of saffron in mixtures (e.g., grasses, field bindweed, pigweeds), (2) weeds that preferred a higher ratio of black zira in mixtures (e.g., Persian speedwell, Brassicaceae complex, Polygoaceae complex, and earthsmoke), (3) weeds that were more abundant in 50/50 mixtures (e.g., Caryophyllaceae complex), and (4) weeds that showed no specific pattern (e.g., common lambsquarterss). Pigweeds, prostrate knotweed, and common lambsquarters dominated the viable seed bank with relative densities of 48, 28, and 8%, respectively. The seed bank of most weed species responded to mixture ratios in a similar manner to those of their corresponding aboveground flora. Seed density decreased as soil depth increased, leading to the accumulation of 66, 22, and 12% of viable seeds in soil layers of 0–5, 5–15 and 15–25 cm, respectively. Greater weed and seed densities were found in more pure stands of black zira. These findings contribute to improving current understanding of crop–weed community structures and may help in developing weed management practices.
Information on the germination and viability of turnipweed seeds could be
helpful in developing appropriate management strategies for this weed.
Therefore, experiments were conducted to investigate the effects of light,
storage conditions, duration of storage or burial, and seed type (naked,
i.e., fruit wall was removed and encapsulated in siliques) on germination
and viability of turnipweed. The naked and encapsulated seeds (fruit) were
kept under five different storage conditions, including dry storage at 25 ±
2 C and 3 ± 1 C and outdoor environments (soil depths of 10, 20, and 40 cm).
All seeds were retrieved every 2 mo and tested for germination in light and
darkness. At each exhumation date, nongerminated seeds were treated with
triphenyltetrazolium chloride to test their viability. The germination of
seeds liberated from siliques (85%) was markedly greater than that of seeds
in intact siliques (20%). The germination response of naked and encapsulated
seeds to light varied between storage conditions and through time. Under
indoor conditions (room and cold), both seed types had greater germination
percentages in dark on most occasions than those in light. On the contrary,
the germination of siliques buried at soil depths of 20 or 40 cm was
considerably stimulated by light. Under indoor conditions, the percent
viability of both seed types only declined marginally, whereas seeds buried
in soil showed high rates of mortality. Seeds in intact siliques persisted
longer under either indoor or outdoor conditions than naked seeds.
Photocontrol of weeds requires knowledge about the response of weeds to light and its changes over time. Thus, littleseed canarygrass germination, as an important weed in winter crops, in response to the light environment was evaluated in seeds retrieved from different burial (10, 20, and 40 cm, under irrigated or nonirrigated conditions) or storage (room temperature 25 C and cold 3 C) conditions for 1 yr. Seeds buried in the soil showed a cyclical germination behavior when tested at 20 C, with high germination percentages (68%) occurring in August, October, and December and low percentages (12%) in February and April, with another late germination in June. Germination percentages were mostly higher for seeds incubated in light than in darkness and seeds were more likely to positively respond to light in June than at the other retrieval dates, with differences as great as 60% having been observed under irrigated conditions and at depths of 20 and 40 cm. The most outstanding effect of light as a germination stimulus was observed for seeds stored at room temperature where germination in light was always 20 to 35% higher than that in darkness. The viability of seeds did not change over time in seeds kept at room or cold temperature. However, the proportion of surviving seeds was reduced by 35 to 65% when buried in the soil. Littleseed canarygrass seeds tended to survive more when buried 40 cm deep and the differences between irrigated and nonirrigated conditions were only detectable at 10 cm deep, with higher seed mortalities under irrigated conditions. Information gained in this study would be useful in developing weed control programs for this species.
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