نشریه دانش علفهای هرز
سال پانزدهم شماره 2 (پاییز و زمستان 1398)

Conservation agricultural systems may considred as a solution to loosing arable soil in conventional system. We studied the effects of conservative agricultural systems compared to conventional systems on chemical weed control efficacy at the farm of Jolgeh-Rokh research station, Khorasan Razavi province, during 2014-2017. Crop rotaton was sugarbeet-barley-corn-wheat. The experimental designe was randomized complete block design aggranged in split-split plot with three replacations. Treatments were three types of tillage (conventional, reduced and no-tillage) as main plot; crop residue percentage (left on the ground from previous crop in rotation; 0, 30 and 60 percent) as sub plot and methods of weed control (hand weeding, recommended herbicide and check plots) as sub-sub plot. The results showed that application of herbicides significantly decreased weed dry matter (57%) and weed density (31%) and increased sugar beet root yield (64%) compare to the weedy check; however, weed reduction was not enough to prevent root yield loss in conservational tillage systems. Residue levels showed no significant effects on root yield of sugarbeet. The effects of tillage systems, levels of residues and even chemical control did not affect the grain yield of barley, despite the effects on weeds. Tillage in corn significantly decreased the weeds (83% to no-tillage); as a result, corn grain yield increased significantly in conventional and reduced tillage systems (3.53-ton ha-1 and 4.33-ton ha-1, respectively) compared to the no-tillage system (3.14-ton ha-1). Different levels of plant residues had no effect on corn yield, but chemically weed control caused a significant increase of yield (23%) as much as manual weeding treatment. Reduced tillage system with 30 percent of the residues and the chemical control of weeds was the best treatment for grain yield of wheat.

Willowherb (Epilobium ciliatum), a common weed in fields and gardens, is often controlled by diquat, paraquat and glyphosate herbicides, but reports showed appearance of resistance in this species to both groups of above herbicides. Due to this purpose, an experiment was performed in the University of Cordoba ,2017, as an alternative to control this weed using four groups of herbicides including glufosinate (GS inhibitor), MCPA and Fluroxypyr (synthetic auxin), flazasulfuron (ALS inhibitor) and pyraflufen-ethyl and Carfentrazone (PPO inhibitor). To investigate the effect of the mentioned herbicides, each herbicide used at eight doses and eight replicates. Finally, the lethal dose (LD50) and dry weight loss (GR50) were measured 21 days after treatments. The results showed the different degree of resistance between sensitive and resistant biotypes of willowherb in terms of the fresh weight and number of survivals after treatment with each herbicide. Also the except for fluroxypyr which needed 365.05 gr h-1 higher dose than the recommended dose (300 gr h-1) to control resistant biotype, the rest of the herbicides controlled both the resistant and sensitive biotypes well at lower doses than recommended ones. As a result, the resistant species needed more herbicides, therefore, all studied herbicides could be used with more caution in the proper management of this herb.

A split-plot experiment was conducted during 2016 with 3 replications to determine the optimum time and dose of tank mixture of Nicosulfuron and Bromoxynil+MCPA for weed control in maize (Zea mays) in Karaj. Main plots were four application times (different maize growth stages: 2-3, 3-4, 4-6, and 6-8 leaves) and subplots were five doses of herbicide mixture (0, 25, 50, 75, and 100 % of the recommended dose). Doses of herbicides and weed biomass relations were described with the standard dose-response model at each application time. Parameter estimates suggested that delaying in herbicides application increased ED 50 parameter (herbicide dose required for 50 percent reduction in weed biomass) from 6 to 54. In general, parameter estimates showed that Chenopodium album was more sensitive to herbicide mixture compared to Solanum nigrum and Amaranthus blitoides. Relationship between the doses of herbicide mixture and maize yield and total dry matter were described with a linear model. Delaying in herbicides application decreased the effect of each percent of the recommended dose of herbicide mixture on increasing maize yield and total dry matter (parameter b 1 ). For example, in the case of maize forage yield, it was 0.45 at first application time and reached 0.15 at the last application time. In general delaying herbicide mixture application time to 6-8 leaf stage of maize reduced herbicide efficacy for weed control and there was a need for higher doses to achieve an acceptable yield.

The effects of crop seed densities on mallow weed (Malva rotundifolia) suppression and grain yield of wheat cultivars was investigated at two separate (weedy and weed free conditions) factorial experiments with randomized complete block design with four replications. Four spring wheat cultivars (Atila 5, Yavaros, Zagros and Koohdasht) were sown at four densities. Mallow weed was sown at constant density of 10 m-2. Increasing wheat density significantly increased the grain yield, kernel per spike, spike number per m-2 and plant height. Under weed free conditions, the highest and the lowest grain yield belonged to Atila5 (3721.7 kg ha-1) and Zagros (3040.3 kg ha-1) cultivars, respectively. Yavaros cultivar had the highest ability to withstand competition (AWC) and competition index (CI). Increasing wheat density up to 500 plant m-2 reduced 8.5% of grain yield in competition with mallow compared to 18% in 350 plant m-2. Individual weed biomass was differed among wheat cultivars and crop densities. Mallow had higher and lower biomass when compete with Yavaros and Zagros cultivars, respectively. In general, the results showed that the wheat cultivars were different in yield stability and competition with the mallow and increasing the crop density up to 500 plants m-2, increased the competitiveness of wheat cultivars with mallow.

Purple nutsedge is one of the most problematic weeds of onion fields. To investigate the management practices of this weed, an experiment was conducted in the Agricultural and Natural Resources Center in Southern Kerman in 2017-2018 as a randomized complete block design with three replications. Treatments included twice disk + glyphosate, heavy plow + disk, metribiuzin, pendimethalin (Stomp), hand weeding, soil solarization, soil solarization + glyphosate, Control (no control), pendimethalin (Prowl), three times plowing, and twice disk + two times glyphosate. The results showed that the effect of different treatments was significant on shoot and underground dry weight and density, neck diameter, number of leaves and yield of onion. Twice disk + twice glyphosate decreased shoot and underground dry weight and density by 86, 87, and 87.2 %, respectively, and yield of onion increased 83 %. Therefore, combination of disk and glyphosate was desired in purple nutsedge control and this treatment is recommended.

The use of cover crops before planting the main plant along with selecting the type of tillage can be considered as one of the effective methods in sustainable agriculture. In order to show the efficacy of this system, an experiment was conducted in a no-tillage system and with six treatments, barely (Hordeum vulgare L.), rye (Secale cereal L.), rape (Brassica napus L.), vetch (Vicia villosa L.), crimson clover (Trifolium incarnatum L.) and control, in a randomized complete block design with three replications, at the farms of agriculture and education research center and natural resources of Ardabil Province (Moghan) during the 2015-2017. Variance analysis showed that the effect of the treatments on the total weed density was significant. On average, in four sampling stages, total control of winter and spring weed at barley, rye, rape, vetch and clover treatments were 83.5,77.25,66,25,51, and 26.25 respectively. The results also showed that the soil cover percentage was significantly

To evaluate the effect of rimsulfuron and oxadiargil and also rimsulfuron and metribuzin combinations on weed biomass and tuber yield of potato, a factorial experiment based on a randomized complete block design with 3 replications performed in 2016. Factors consisted of herbicide mixture ratio (0:100, 25:75, 50:50, 75:25 and 100:0), herbicides time of applications (pre-plant and potato emergence stages) and herbicide mixture of rimsulfuron and oxadiargyl and also rimsulfuron and metribuzin. In all treatments, a weedy plot as semi control and a weed free plot as control were considered. Results showed that the maximum reduction percentage of total dry weight of weeds obtained in 25% oxadiargyl + 75% rimsulfuron and also 25% metribuzin + 75% rimsulruron at potato emerge stage. Also, after weed free treatment which increased total potato tuber yield compared to herbicide mixtures by 1.33%, the maximum total potato tuber yield obtained from 25% oxadiargyl + 75% rimsulfuron at pre-plant stage witch increased 69/16% total tuber yield of potato compared to weedy control.

Weeds normally grow as patches and spatially distributed in field. Patch spraying to control weeds has advantages such as cost reduction, herbicide saving and reduction of environmental pollution. Machine vision system should obtain and process digital images to make control decisions. Proper identification and classification of weeds are the key steps to make control decisions and use of any spraying operation performed. In this study, a robust method based on image processing and computational intelligence was developed for segmentation from other parts of image and classification of weeds. Large crabgrass, common lamb’s quarter, velvetleaf, common barnyard grass, European black nightshade, red-rooted pigweed and European heliotrope were the weeds in the experiment. Results showed that this algorithm was precisely separated weeds from the soil. In the next step, the feature vector, which includes shape features and color features, was composed. Finally, classification of seven classes of weeds was carried out by artificial neural network (ANN). Among different ANN structures, the most optimum classifier was the 43-15-15-7 topology with accuracy 88/71 %. The results of this research indicate that the proposed system has the ability to accurately detection of weeds.

To study the effect of castor oil combination with different doses of Lumax (mesotrion + s-metolacholor + terbuthylazine) on physiological behavior of common cocklebure (Xanthium strumarium L.), a greenhouse factorial experiment was conducted in randomized complete block design with 3 replications in Agricultural Faculty of University of Tabriz in 2017. Results showed that by increasing the herbicide doses, area above the OJIP curve between minimum and maximum fluorescence, maximum Fluorescence, variable fluorescence, maximum quantum yield of photochemistry (Fv/Fm), water-splitting complex on the donor side of PSII and maximum electron transport flux per PSII reaction center, decreased 35, 15/6, 23/6, 11, 43 and 83%, respectively and minimum fluorescence and thermal dissipation quantum yield increased 14 and 60%, respectively. Castor oil had synergistic effect on Lomax and enhanced its efficacy on X. strumarium. A good relationship was observed between Fv/Fm parameter evaluated 2 days after herbicide spraying (DAHS) and dry weight measured 28 DAHS. The finding of this study showed that evaluating chlorophyll a fluorescence is a good, non-destructive and fast to survey the effect of Lomax, soon after spraying and before the visual symptoms appear in treated weed species.

A field experiment was conducted to evaluate the effect of barley (Hordeum vulgare) and berseem clover (Trifolium alexandrinum) cover crops, and their cutting time on black seed (Nigella sativa) weed management in 2016-2017 at research field of the College of Aburaihan, University of Tehran. The experiment designe was randomized complete block design with 3 replications. Treatments were: T1, no cover plant-weed free; T2, no cover plant- weed infest; T3, barley-first cutting; T4, barley-second cutting; T5, clover-first cutting and T6, clover-second cutting. The first and the second cutting were done after Black seed establishment and before flowering stage of cover crops, respectively. Results showed that the highest weed biomass was 444 gr.m-2 obtained from T2 treatment at t the second sampling time and the lowest weed biomass was 28 gr m-2, related to first cutting clover treatment (T5), at the first sampling time. The highest grain yields were 527 and 446 kg.ha-1, observed in treatment (T5) and control treatment (T1) respectively and the lowest yield was obtained from control (T2) with a mean of 100 (kg ha-1). Overall, results showed that T5 treatment at the second sampling time reduced weed biomass 90.4% compared to without weeding control. In addition, the berseem clover plant not only did not compete with black seed, but also increased yield compared to the without cover plant control (T1).