Mixed Growth with Weeds Promotes Mycorrhizal Colonization and Increases the Plant-Availability of Phosphorus under Maize (Zea mays L.)

(1) Background: Weed control decreases the competition for nutrients, but also the potential of increased phosphorus (P) mobilization in soils caused by higher plant diversity. (2) Methods: Impacts of weed species under maize on mycorrhizal colonization and plant-availability of P were investigated in two pot experiments. Plant traits and P mobilization were tested in weed-free maize and in mixed growth with six annual weed species. (3) Results: Growth of maize decreased in treatments with weeds, while P concentrations in its shoots increased in mixed growth with C. album, E. crus-galli and P. convolvulus. Mycorrhizal colonization of maize without weeds was low (<20% of root length), but increased in mixed growth with C. album, E. crus-galli and V. arvensis up to 40%. The activities of Pmobilizing hydrolytic enzymes (phosphatases, ß-glucosidase) and plant-availability of P were occasionally higher under mixed growth with weeds. The dimension of weed impacts on P cycling under maize differed significantly between both experiments. (4) Conclusions: Weeds potentially promote P mobilization and mycorrhizal colonization under maize, but this impact is not guaranteed. The weed-based improved P supply of maize should be defined under field conditions to allow a controlled weed tolerance in maize cropping systems.

EVALUATION OF CASSAVA VARIETIES FOR WEED TOLERANCE ABILITY

SUMMARYMany types of weeds occur in cassava fields causing enormous yield losses due to competition for nutrients, light and space. The purpose of this study was to evaluate the growth and yield of four traditional varieties of cassava (Bonoua Blanc, Tambou, Yassé and Six mois) produced in Côte d'Ivoire and select the highest tolerant variety to weed competition. Six treatments were induced by varying the period in which cassava varieties were grown with weeds. Varieties and exposure time to competition with weeds significantly affected the productivity of cassava. The number of leaves per plant (NLP), the number of tuberous roots per plant (NTRP) and the weight of tuberous roots per plant (WTRP) declined with increasing duration of weed presence. After an initial period of weeding, the first four months of grassing proved critical for the four varieties. Despite the presence of weeds, Bonoua Blanc has higher growth and yield than Tambou, Yasse and Six mois. This suggests that Bonoua Blanc was more tolerant to weed competition than the others from planting to harvest, being a suitable variety in intercropping systems.

Genotypic stability of weed competitive ability for bread wheat (Triticum aestivum) genotypes in multiple environments

Weed control in broadacre cropping systems is becoming increasingly difficult owing to widespread evolution of herbicide resistance in major weed species. The importance of crop competition in weed management is often overlooked but it can play an important role in cropping systems. Competitive ability of 86 wheat (Triticum aestivum L.) genotypes varying for early vigour was investigated at two sites over two growing seasons against cultivated oats (Avena sativa L.) as a weed mimic. There were significant (P < 0.001) treatment effects of weed, wheat genotype and weed × genotype interaction at the different sites. Mature crop height and early crop vigour were strongly correlated with improved weed suppression and tolerance. Negative correlation between early vigour (normalised difference vegetation index and visual score) and weed-free yield indicates the presence of some yield penalty in high-vigour (HV) lines. Wheat genotypes with high grain yield under weed-free conditions tended to suffer high yield loss from weeds (low tolerance) and allowed greater production of weed seed (low weed suppression). However, many of the HV lines produced significantly higher grain yield than the tested commercial cultivars under weedy conditions. The use of the Finlay–Wilkinson regression approach for assessing cultivar stability revealed a strong association between genotype mean weed suppression and stability across the four environments. Several HV lines showed consistently greater weed suppression than the wheat cultivars investigated. Genotypic variation was much greater for weed suppression than weed tolerance, suggesting greater opportunity for the selection of improved weed suppression in wheat. However, strong positive correlation between weed suppression and tolerance (r = 0.79, P < 0.001) suggests that wheat lines selected on the basis of high weed suppression may also exhibit improved weed tolerance.

Potential new tool for weed control in organically grown agronomic crops

Field experiments were conducted during summer 2007 to determine a baseline information on crop and weed tolerance to broadcast flaming utilizing different rates of propane. The species evaluated were: maize (Zea mays), sorghum (Sorghum halepense), soybean (Glycine max), sunflower (Helianthus annuus), barnyardgrass (Echinocloa crus-galli), green foxtail (Setaria viridis), velvetleaf (Abutilon theophrasti) and redroot pigweed (Amaranthus retroflexus). The propane rates applied were 0, 12.1, 30.9, 49.7, 68.5 and 87.22 kg/ha. The response of the plants to propane rates were described by log-logistic models. Plant response to flame varied depending on the species, growth stage and propane rate. Broadleaf weeds were more susceptible to flames than grasses. Field maize and sorghum were less susceptible, while soybean and sunflower were severely injured. Of all crops tested, broadcast flaming has the most potential for use in field maize.

Comparison of weed management methods in organic carrot

14 combinations of mechanical and also physical (thermal) weed management techniques are compared for organic growing of carrot. Crop of our weed management research is carrot because of its difficulties in weed management (long growing period, poor weed tolerance) and because carrot needs to be important product of organic farming. Herbicide treatment is used as control — cultivator, brush hoe, hand hoeing and hand weeding are mechanical control tools and flame weeder is used for thermal control. Measured parameters are the weed cover, cover of the crop and dry mass of them. Result of the two appraisable years shows contradictory results, which contradiction can be justifiable with different weather conditions of these two vegetation periods. In 2000 brush hoe was significantly the best in interrows but in the year 2001 cultivator combined with hand weeding in rows seemed to show the best result. We can see in this example that agriculture and weed management depends very much on the weather of the year, so that is why it is so difficult to develop a method, which can be generally used for organic weed control of carrot.

Specific Weed Tolerance of Wheat (Triticum aestivum L.) Varieties - A Key to Non-chemical Weed Control

Six wheat varieties representing different genotypes were tested under exposed and protected conditions in a three year herbicide provocation field trial at Nagygombos, Hungary. Three types of herbicide treatments (fluroxipir, bromoxynil and dicamba ai.) were applied in comparison with untreated and mechanical treated controls. Weed populations were sorted into two major groups according to the level of their occurrence. The result of experimental treatments were evaluated and weed tolerance of varieties was determined. The magnitude of weed populations has shown significant differences. All weed control treatments, including chemical and mechanical applications, had an influence on weed development. Herbicide treatments had about fifty per cent, while mechanical applications had a nearly hundred per cent effect concerning weed reduction. The latter can be considered as a level of total weed extinction. High weed canopies were observed in the case of untreated controls only. Wheat cultivars have shown a variety specific yield response. The results obtained suggest varietal differences concerning weed tolerance. The extent of yield losses between wheat cultivars ranged from 4 to 18 per cent of grain yield. In the trial Martonvásári 19 and Martonvásári 21 wheat varieties were proven to have the best weed tolerance abilities.

Edina Goes Green Part III: A Survey of Consumer Lawn Care Knowledge and Practices

Homeowners in Edina, Minn., were surveyed in conjunction with a low-input lawn care community educa- tion project. Surveys were sent at the start and finish of the yearlong project, and asked questions pertaining to the respondent's lawn care knowledge, practices, and environ- mental attitude toward lawn inputs. The responses from before the program, compared with those afterward, show overall that homeowners lawn care did not change signifi- cantly by the end of the educational campaign. Responses are useful, however, in targeting future educational efforts. For example, while >80% of respondents were aware of the benefits of leaving mowed clippings on the lawn, <6% knew how much fertilizer is needed yearly for a medium mainte- nance lawn. Participants indicated a 10% weed tolerance was acceptable, but 25% was not; and disagreed with the state- ment &quot;pesticides are not harmful to the environment.”