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Control of brome grasses ( Bromus L. spp.) in winter cereals
Summary
The complete article is written in German
The spread of brome grasses, in particular of barren brome grass (Bromus sterilis L.), caused among others by ploughless tillage, requires an optimal use of herbicides in winter cereals. In a study with 20 field trials, performed between 2000 and 2005, treatments with application sequences in autumn and spring turned out to be the most effective control measures. In autumn the herbicides Herold (a.i. flufenacet + diflufenican) or Atlantis (a.i. mesosulfuron + iodosulfuron) can be used. At spring treatment with Attribut (a.i. propoxycarbazone) or Monitor (a.i. sulfosulfuron) the effectiveness can be improved clearly by splitting application in mixture with a suitable adjuvant. With this herbicide strategy yield losses between 30 and 60 % can be prevented. Because of limited selectivity these optimal control measures can employed only in winter wheat.
Comparative benefit assessment of various broad-spectrum herbicides
Summary
The complete article is written in German
Important properties determining the use of broad-spectrum herbicides like amitrole, diuron, glyphosate, glufosinate, paraquat can be characterized by their weed spectrum, herbicidal activity in pre- and/or post-emergence, their uptake and translocation behaviour in plants, soil mobility, speed of action as well as duration and extent of their residual activity.
In standard experiments paraquat is showing a comprehensive activity spectrum in post-emergence treatments against most grass and broadleaf weeds, whereas this active ingredient shows no activity in pre-emergence treatments. Preplant incorporation of paraquat in mineral soil with differently adjusted clay levels led to complete inactivation even in soils with clay content below 2 % within 24 hours after treatment. After pre-emergence use crop selectivity to seedlings of wheat, maize, oilseed rape, field peas and sugar beets was dependent on the development stage of seedlings at the time of application after seeding, but independent of the clay content. The particular strength of paraquat results from a combination of different characteristics: superior weed spectrum to grass and broad-leaf weeds, lack of phloem mobility, rapid speed of action, exclusive post-emergence activity to green plant parts only, lack of residual activity, mode of action with potential use in resistance management to prevent development of resistance to other active ingredients. A comparative benefit assessment of herbicides should therefore consider and balance all these parameters.
Evaluation of trials on minimum effective dose related to the needed dose of herbicides
Summary
The complete article is written in German
For the authorisation of plant protection products data have to be submitted demonstrating that the applied dose is necessary to achieve sufficient efficacy. Fixing the minimum effective dose is an essential requirement laid down in the German Plant Protection Act in connection with Directive 91/414/EEC. Due to the reduction programme of chemical plant protection the minimum effective dose is of special relevance. Long-term practical experiences and investigations have indicated that in certain cases the needed dose is much lower than the authorised one. Therefore during the efficacy assessment a more extensive and systematic evaluation of the herbicide potential may be required in order to deliver information for the users. Trials on minimum effective dose are principally appropriate to quantify extend and conditions where doses can be reduced without a loss of effectiveness. Therefore a sufficient number of trials at different climatic and agricultural conditions is needed as well as a good documentation and evaluation. Corresponding requirements are stated in the EPPO guidelines, especially in PP 1/225 (Minimum effective dose). This paper suggests how to improve the process and evaluation of efficacy trials and how to implement the findings in order to specify the needed dose.
Reduction of herbicide inputs in winter cereals by the adjustment of herbicide mixtures and variation of dose to the target infestation – results of the trials in the states Brandenburg, Hessen, Saxony, Saxony-Anhalt and Thuringia
Summary
The complete article is written in German
At the usual weed control time in autumn, in the BBCH (EPPO) growth stage 10-11 of cereals, broad-leaved weeds and grasses have often not emerged. Herbicide application practice is often preventive. This evaluation consisted of 476 untreated plots of field trials in 1995-2004. The later assessment in untreated plots indicated that Apera spica-venti L. (silky bentgrass) required control in only 50 % of all the investigated cases. The broad-leaved weeds should be controlled in less than 30 %. In field trials in the five states herbicide mixtures were tested. The results show that despite the use of reduced application rates, good control of the target infestations was achieved. With these herbicide combinations the input of active ingredient/area can be better adapted to the treatment frequency index. The second treatment in spring is only necessary in exceptional cases of higher infestation of target weeds.
Field evaluation of an integrated Striga hermontica management in Sub-Saharan Africa: Synergy between Striga - mycoherbicides (biocontrol) and sorghum and maize resistant varieties
Summary
The root parasite Striga hermontica (Del.) Benth. constitutes a major biotic constraint to staple food production in Africa. Fusarium oxysporum Schlecht. (Foxy 2 & PSM197) proved to be highly virulent against their target weed S. hermonthica , host specific and they can be mass-produced. Thus, the antagonists offers a good prospect for Striga control in the future when incorporated into a long-term integrated Striga control program. This research focused on the development of an appropriate mycoherbicidal formulation, thereby reducing the amount of inoculum required for a practical field application. “Pesta” granules of both isolates were made by encapsulating their chlamydospore-rich biomass in a matrix composed of durum wheat-flour, kaolin and sucrose. Their efficacy in combination with Striga resistant and susceptible sorghum ( Sorghum bicolor (L.) Moench) and maize ( Zea mays L.) cultivars was tested under field conditions at two locations (Samaru & Bagauda) in Nigeria. 2.0 g of “Pesta” granules of each isolate were applied per planting hole in which 5 g of Striga seed-sand (1:20 w/w) were inoculated. Both granular mycoherbicides (Foxy 2 & PSM197) were very effective with same potential, in controlling Striga on both susceptible and resistant maize and sorghum cultivars tested. Cumulatively (on average), they reduced the number of emerged Striga plants per plot by 75.3 %, Striga dry weight by 74.4 %, Striga flowers by 83.6 %, and crop plant infested by 64.8 % compared to the controls. The resistant maize and sorghum cultivars enhanced clearly both mycoherbicides efficacy. For maize, the reduction in all Striga parameters assessed compared to the controls was clear and in most cases significant for both isolates while for sorghum the differences were small. When the different treatment x cultivar combinations were compared, the combination Pesta granules x resistant cultivar had the strongest suppressive effect on Striga Striga emergence and flowering as a result of combining mycoherbicides and host plant resistance is an important feature to prevent further Striga distribution and infestation. These findings are highly relevant to the realization of an integrated Striga control approach adoptable and applicable by subsistence farmers in Africa.
Impact of selective weeding on maize productivity in major and minor seasons – a comparative analysis from the Asian humid tropics
Summary
Weed management is vital in tropical food cropping systems to minimize competition for scare resources, especially under smallholder farming conditions, where hand weeding using family labor is a common feature. Hence, selective weeding could be practiced to maintain weed populations below economic threshold levels, and minimize competition. Field studies were initiated under rainfed conditions of Sri Lanka over the major and minor seasons that correspond to the two monsoons to determine the impact of selective weeding on growth and yields of maize (Zea mays L), the most popular highland cereal in these regions. The lack of weed control measures or the presence of the most abundant grass weeds reduced growth and yields of maize irrespective of the season. The adverse effects of the low number of sedges (Cyperaceae) was minimal, and that of broadleaves was lower than the impact of grasses. Comparative analysis of the effects of weeds in the two seasons highlighted the greater adverse effect in the minor season when the crop is subjected to water stress conditions. The weed numbers were greater, which affected the growth and yields of maize to a greater extent. However, the adverse effects of the different weed types did not change with seasons. The feasibility of adopting selective weeding to minimize adverse effects in rainfed farming systems of the humid tropics for procuring high yields is presented on the basis of this study. In contrast, clean weeding could develop other effects such as erosion
Factors affecting decision-making of farmers in weed management (case study of Tokat, Turkey)
Summary
This study analyses a weed management survey in Tokat province of Turkey. Four farmers did not use herbicides due to dry farming, unsuitable climatical conditions, low income, small-scale farms, etc. It was hypothesized that there is a relationship between factors taken into consideration while using herbicides and three variables of age, education and agroecological zones. Chi-square (x2) test results show that statistically significant relationships were found between education and dosage, destroying empty boxes or bottles of herbicides, knowledge about active ingredients of herbicides, and use of safety materials. There was also a statistically significant relationship between agro-ecological zones and dosage of herbicides and safety materials. A statistically significant relationship was found between age and destroying empty boxes or bottles and between age and safety materials. In addition, statistically significant relationships were found between weed management and farm size, ecological zones and crop rotation. On the other hand, no statistically significant relationship was found between weed management and irrigation possibility. 97 % of farmers do not have enough knowledge about the EU’s agroenvironmental policies (re-registration of agrochemicals). Farmers – scientists – extension staff – private pesticide dealer’s interaction is weak.
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