Sensitivity of recently naturalised Digitaria spp. populations to 4-hydroxyphenyl pyruvate dioxygenase- and acetolactate synthase-inhibiting herbicides in maize

Until recently, Digitaria aequiglumis var. aequiglumis, native to South America, and Digitaria ciliaris subsp. nubica, native to Northeast Africa, were completely overlooked in Belgium due to their close morphological resemblance to Digitaria sanguinalis and Digitaria ischaemum. One of the possible reasons for their expansion in maize fields, besides for example the lack of crop rotation, might be a lower sensitivity to post-emergence herbicides acting against panicoid grasses. Dose-response pot experiments were conducted in the glasshouse to evaluate the effectiveness of four foliar-applied HPPD-inhibiting herbicides (mesotrione, sulcotrione, tembotrione, topramezone) and two foliar-applied ALS-inhibiting herbicides (foramsulfuron, nicosulfuron) for controlling Belgian populations of D. aequiglumis and D. ciliaris subsp. Nubica, as well as local D. sanguinalis and D. ischaemum populations. In another dose-response pot experiment, the influence of growth stage at time of herbicide application on efficacy of topramezone and nicosulfuron for Digitaria spp. control was evaluated. In general, D. aequiglumis and D. ciliaris subsp. nubica populations were less sensitive to HPPD inhibitors than D. ischaemum and D. sanguinalis populations, except for D. aequiglumis treated with topramezone. Contrary to other herbicides tested, topramezone adequately controlled all D. aequiglumis populations at doses well below maximum authorised field dose. All species tested showed a progressive decrease in sensitivity to topramezone and nicosulfuron with seedling age. A satisfactory post-emergence control of Digitaria species in the field will require appropriate choice of herbicide and dose, as well as more timely application

Differences in growth and herbicide sensitivity among Cyperus esculentus clones found in Belgian maize fields

Cyperus esculentus is an invasive troublesome neophyte in many arable crops in Belgium. Applied weed control varies from field to field. One of the possible reasons for this variability might be a differential vegetative and reproductive behaviour among Belgian C.esculentus clones. In this study, growth characteristics and herbicide sensitivity of C.esculentus clones collected in Belgian maize (Zea mays) fields were evaluated. In a morphology Experiment, 25 clones were screened for growth characteristics and ability to set viable seeds under outdoor conditions. Dose-response experiments were conducted in the glasshouse to evaluate the effectiveness of two foliar-applied herbicides (bentazon and glyphosate) and two pre-sowing soil-incorporated herbicides (S-metolachlor and dimethenamid-P) for controlling 14 C.esculentus clones. Response variables were aboveground dry biomass, tuber number, tuber dry biomass and individual tuber dry weight. Clones exhibited large differences in shoot number (up to 3.1-fold), tuber dry biomass (up to 4.7-fold), tuber number (up to 3.4-fold), individual tuber dry weight (up to 4.8-fold), inflorescence number and capacity to set viable seeds. Large interclonal differences in herbicide sensitivity (up to 8.3- and 4.0-fold for aboveground dry biomass and tuber dry biomass, respectively) were observed. Contrary to foliar-applied herbicides, soil-incorporated herbicides were very effective and provided season-long C.esculentus control at doses below the recommended maximum field dose. However, low doses stimulated tuber formation. Future C.esculentus management strategies should take into account differential growth characteristics and herbicide sensitivity of C.esculentus clones

Weed suppressiveness of paving joint filling materials under diverging water regimes

Since 2015, chemical weed control on public pavements in Flanders has been banned. This necessitates alternative weed control strategies. In this study, growth chamber experiments evaluated the weed suppressive ability of different joint filling materials under various water regimes. The tested materials comprised five unbound standard fillers (white quartz sand, sea sand, limestone 0/2 mm, limestone 2/6.3 mm and porphyry 2/6.3 mm) and two innovative materials (Dansand (R) and Eco Fugensand (R)). Their weed suppressiveness was tested in pure and organically polluted states. Germination and biomass accumulation of two weed species that are abundantly found on public pavements (Lolium perenne and Taraxacum officinale) were investigated. Germination and biomass accumulation were lowest in both innovative materials, irrespective of organic contamination level, plant species and water regime. Weed growth in the standard materials was affected by plant species and water regime. Monthly biomass accumulation increased with increasing monthly water supply and number of irrigation days. Furthermore, the materials best capable of reducing weed growth, under all water regimes, even when organically polluted, were the innovative materials and sea sand. The results of this study show that the implemented water regime can influence weed suppressiveness (absolute as well as relative) of a joint filler. Hence, to fully assess weed suppressive ability, commercially launched joint fillers should be tested under diverging water regimes

Impact of wetting agents, time of day and periodic energy dosing strategy on the efficacy of hot water for weed control

To further increase the cost-effectiveness and sustainability of hot water weed control, the further optimisation of hot water efficacy is needed. Therefore, three dose-response experiments were carried out to evaluate the impact of wetting agents (an ethoxylated triglyceride, an esterified rapeseed oil and a liquid linseed oil-based soap), time of day (2, 4, 6, 8, 10 and 12 h after sunrise) and treatment frequency (1-6 treatments in a 12 week period) on the hot water sensitivity of prevalent weed species (Lolium perenne, Festuca rubra, Taraxacum officinale and Plantago major) on public pavements. Generally, wetting agents did not improve hot water sensitivity. Taraxacum officinale with large planophile leaves showed a higher sensitivity than grasses with an erectophile growth habit. Festuca rubra was more sensitive than L. perenne due to its high leaf dry matter content. The plant species were most sensitive to hot water in the afternoon. This variation in sensitivity during the day was related to the variation in leaf thickness and dry matter content. In general, hot water weed control was highly efficient when conducted four times in a 12 week period at an energy dose of 589 kJ m(-2)

Effects of soil and crop management practices and pedo-hydrological conditions on the seedbank size of Galinsoga spp. in organic vegetable fields

Galinsoga quadriradiata and Galinsoga parviflora are very troublesome weeds in many organic vegetable crops in Europe. A very straightforward method to keep Galinsoga infestations under control is by targeting the Galinsoga seedbank. To identify cropping systems able to reduce the seedbank size in vegetable-based cropping systems, the relationships between the seedbank size of Galinsoga species and prevailing soil/crop management practices and pedo-hydrological conditions were investigated. Hereto, the seedbank of the 0-20 cm topsoil layer was sampled in 50 organic vegetable fields and analysed according to the seedling emergence method. Field history data were collected for the past 5 years, and physical, chemical and microbial soil quality was determined. Galinsoga quadriradiata was the most frequent and abundant Galinsoga species in the weed seedbank. The genus Galinsoga was present in 90% of the soil weed seedbanks of organic vegetable fields but displayed wide variation in abundance. Smallest Galinsoga seedbanks were found in fields that were predominantly tilled with non-inversion implements or rotationally ploughed, and continuously cropped with competitive crops during the entire growing season (April 15-November 15). Contrary to G. quadriradiata, seedbank size of G. parviflora was closely related to soil organic carbon content and sand fraction. Remarkably, soils with a low level of easily plant-available phosphorus and concomitant high activity of arbuscular mycorrhizae had smaller G. quadriradiata seedbanks. To reduce Galinsoga infestations, fields should preferably be tilled without soil inversion, fertilised with organic amendments with low content of readily plant-available phosphorus and cropped with competitive crops all season long