Giuseppe Zanin

Ecological interpretation of weed flora dynamics under different tillage systems

In northern Italy, on soil managed with three different tillage systems (conventional tillage, ridge tillage, and no-tillage) and submitted to standard cultural practices (crop rotation, and chemical weed control), the weed vegetation was assessed at the beginning of the trial (1987) and after six, and eight years. The aims were to evaluate (1) the effect of tillage systems on the weeds; and (2) the possibility of linking the floristic changes under reduced disturbance to the theory of ecological succession. The weeds were categorised according to life-forms (biological groups), periodicity types (ecophysiological groups), dispersal types and seed longevity. Data were analysed using Sorensons Indices of Similarity, the Independence test, and Principal Components Analysis. The tillage systems profoundly altered the weed community: in undisturbed soils the importance of the geophyte and hemicryptophyte species, and among the annuals, Digitaria sanguinalis, Conyza canadensis and Kickxia elatine increased, as well as that of the wind-dispersed weeds. The species linked to disturbance were annuals and in particular Amaranthus spp., Chenopodium album and Echinochloa crus-galli. After eight years the floristic evolution in the reduced tillage system can be interpreted on the basis of ecological succession. The community that has formed assumes, from the quantitative point of view, characteristics of a pioneer community of secondary succession with a predominance of annual species and a large number of wind-dispersed plants. Qualitatively there is a movement towards a more mature community that could become similar to that of the woodland edge, with more perennial species, shrubs, and bird-dispersed plants. The implications of these conclusions are discussed in terms of weed management.

A fugacity model of pesticide runoff to surface water : development and validation

Abstract Real field data for pesticide release to surface water are compared with data obtained by simulations of a fugacity-derived model. This was done for several herbicides, applied on to two basins, characterized by different soil properties. The basin were hydraulically isolated and data for water input (rainfall and irrigation), output (outflowing surface water) were recorded, together with concentration of the investigated pesticides in the outflowing water. A fugacity model was developed to take into account the unsteady-state condition of the actual field treatments, since pesticides are typically applied once or twice on the same area. The model allows for several pesticide applications on different areas of the basin at different times and for different reaction half lives, that may change during the simulation time, depending on environmental conditions. A “user friendly” program for Windows® was written, allowing for calculations and plotting of the results. The comparison between predicted and measured concentrations indicated that the model is a useful tool for the prediction of surface water concentration.

WeedTurf: a predictive model to aid control of annual summer weeds in turf

Abstract Predicting weed emergence is useful for planning weed management programs. Unfortunately, our ability to anticipate initial emergence and subsequent levels of emergence from simple field observations or weather reports is often inadequate to achieve optimal control. Weed emergence models may provide predictive tools that help managers anticipate best management options and times and, thereby, improve weed control. In this study, the germination characteristics of four annual grass weeds (large crabgrass, goosegrass, green foxtail, and yellow foxtail) were investigated under different temperatures and water stresses to calculate base temperatures and base water potentials. These parameters were used to develop a mathematical model describing seedling emergence processes in terms of hydrothermal time. Hydrothermal time describes seed germination in a single equation by considering the interaction of soil water potential and soil temperature. The model, called WeedTurf, predicted emergence with some accuracy, especially for large crabgrass (lowest efficiency index [EF] value 0.95) and green foxtail (lowest EF value 0.91). These results suggest the possibility of developing interactive computer software to determine the critical timing of weed removal and provide improved recommendations for herbicide application timing. Nomenclature: Goosegrass, Eleusine indica (L.) Gaertn. ELEIN; green foxtail, Setaria viridis (L.) Beauv. SETVI; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; yellow foxtail, Setaria glauca (L.) Beauv. SETLU.

Temperature and Water Potential as Parameters for Modeling Weed Emergence in Central-Northern Italy

Abstract Predicting weed emergence dynamics can help farmers to plan more effective weed control. The hydrothermal time concept has been used to model emergence as a function of temperature and water potential. Application of this concept is possible if the specific biological thresholds are known. This article provides a data set of base temperature and water potential of eight maize weeds (velvetleaf, redroot pigweed, common lambsquarters, large crabgrass, barnyardgrass, yellow foxtail, green foxtail, and johnsongrass). For five of these species, two ecotypes from two extreme regions of the predominant maize-growing area in Italy (Veneto and Tuscany), were collected and compared to check possible differences that may arise from using the same thresholds for different populations. Seedling emergence of velvetleaf and johnsongrass were modeled using three different approaches: (1) thermal time calculated assuming 5 C as base temperature for both species; (2) thermal time using the specific estimated base temperatures; and (3) hydrothermal time using the specific, estimated base temperatures and water potentials. All the species had base temperatures greater than 10 C, with the exception of velvetleaf (3.9 to 4.4 C) and common lambsquarters (2.0 to 2.6 C). All species showed a calculated base-water potential equal or up to −1.00 MPa. The thresholds of the two ecotypes were similar for all the studied species, with the exception of redroot pigweed, for which the Veneto ecotype showed a water potential lower than −0.41 MPa, whereas it was −0.62 MPa for the Tuscany ecotype. Similar thresholds have been found to be useful in hydrothermal time models covering two climatic regions where maize is grown in Italy. Furthermore, a comparison between the use of specific, estimated, and common thresholds for modeling weed emergence showed that, for a better determination of weed control timing, it is often necessary to estimate the specific thresholds. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; common lambsquarters, Chenopodium album L. CHEAL; green foxtail, Setaria viridis (L.) Beauv. SETVI; johnsongrass, Sorghum halepense (L.) Pers. SORHA; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; redroot pigweed, Amaranthus retroflexus L. AMARE; velvetleaf, Abutilon theophrasti Medik. ABUTH; yellow foxtail, Setaria pumila (Poir.) Roemer & J. A. Schultes SETLU.

Estimation of economic thresholds for weed control in soybean (Glycine max (L.) Merr.)

Abstract The competitive ability of 10 major soybean weeds (Abutilon theophrasti Medicus (ABUTH), Amaranthus cruentus L. (AMACR), Chenopodium album L. (CHEAL), Datura stramonium L. (DATST), Panicum miliaceum L. (PANMI), Polygonum persicaria L. (POLPE), Setaria viridis (L.) Beauv. (SETVI), Solanum nigrum L. (SOLNI), Sorghum halepense (L.) Pers. (SORHA), Xanthium strumarium L. (XANST)) was studied for two years in northern Italy. The economic thresholds for soybean weed control have been determined for different herbicides and mixtures. Economic thresholds were very low in 1989, when only SOLNI and PANMI showed a threshold higher than 1 plant m−2, while in 1990, values varied between 0.05 plants m−2 for XANST and 4.3 plants m−2 for ABUTH. The seed production — weed density relationships for five species (ABUTH, AMACR, CHEAL, DATST and XANST) were also determined and the long-term evolution of the potential infestations deriving from subeconomic threshold populations were calculated. The results of the calculation demonstrate the inadequacy in the medium-long-term of weed control decisions based on single year economic thresholds.

Effect of vegetative filter strips on herbicide runoff under various types of rainfall.

Narrow vegetative filter strips proved to effectively reduce herbicide runoff from cultivated fields mainly due to the ability of vegetation to delay surface runoff, promote infiltration and adsorb herbicides. A field trial was conducted from 2007 to 2009 in north-east Italy in order to evaluate the effectiveness of various types of vegetative filter strips to reduce spring-summer runoff of the herbicides mesotrione, metolachlor and terbuthylazine, widely used in maize, and to evaluate the effect of the rainfall characteristics on the runoff volume and concentration. Results show that without vegetative filter strip the herbicide load that reaches the surface water is about 5-6 g ha(-1)year(-1) for metolachlor and terbuthylazine (i.e. 0.5-0.9% of the applied rate), confirming that runoff from flat fields as in the Po Valley can have a minor effect on the water quality, and that most of the risk is posed by a few, or even just one extreme rainfall event with a return period of about 25-27 years, causing runoff with a maximum concentration of 64-77 μg L(-1). Mesotrione instead showed rapid soil disappearance and was observed at a concentration of 1.0-3.8 μg L(-1) only after one extreme (artificial) rainfall. Vegetative filter strips of any type are generally effective and can reduce herbicide runoff by 80-88%. Their effectiveness is steady even under severe rainfall conditions, and this supports their implementation in an environmental regulatory scheme at a catchment or regional scale.

Application of decision-support software for postemergence weed control

Abstract GESTINF is a decision tool for postemergence weed control based on the equivalent density approach. Using observed weed densities just before treatment, the program estimates the economic return from the treatment, thus indicating whether to treat or not and, if a treatment is needed, the most economical weed control solution. Each treatment is also characterized by an environmental pollution index. GESTINF has been tested in wheat and soybeans on a farm in northeastern Italy with a total cropping area of 60 ha of wheat and 40 ha of soybean. For both crops, weed control followed the suggestions of GESTINF, whereas the remaining cropped areas were treated according to standard farm weed control practices. To compare the two weed control systems, weed control efficacy, average crop yield, and the extra time required for scouting and treatments were measured. In both crops, the treatments suggested by GESTINF showed good efficacy, and yields proved to be no different from those obtained in the fields treated with standard farm weed control practices. In most cases, GESTINF selected treatments with a lower environmental effect. The most critical point was the time required to scout the weed population that, in low-value crops or when very cheap treatments were available, reduced the weed control economic return. In wheat, GESTINF indicated that fewer fields needed to be treated than did the conventional system. However, extra costs due to both scouting and more expensive treatments balanced the savings obtained from nontreated areas. For soybean, the treatments adopted by the farm were based on a combination of pre- and postemergence practices. In this case, GESTINF identified cheaper but still efficacious treatments, significantly reducing the total cost of weed control. Nomenclature: Soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L.

Estimating ecotoxicological effects of pesticide drift on nontarget arthropods in field hedgerows.

When hedgerows grow in orchards where pesticides are applied, they can play a double role: Providing a barrier for chemical spray drift and as a refuge for beneficial arthropods such as pollinators and predators. Effectiveness of hedgerows as barriers to drift depends mainly on canopy density (that can be estimated through optical porosity) and wind speed. When optical porosity is low, the hedgerow can intercept a significant amount of spray drift and act as an effective barrier, but the intercepted pesticide can negatively affect the beneficial arthropods living there. A drift model was used to simulate drift in a hedgerow- vineyard system, and a deposition distribution model was used to calculate the pesticide spatial pattern distribution on a hedgerow with different optical porosity and wind speed conditions. The possible ecotoxicological effects were estimated for 28 active ingredients with different median lethal rates for two nontarget arthropods, Aphidius rhopalosiphi and Typhlodromus pyri. A spatialized risk assessment for a hedgerow is suggested to improve procedures based on application rate, standard drift, and vegetation distribution values, as in the hazard quotient approach. An alternative method for calculation of the exposure is also proposed, with a step-by-step example of a toxicity/exposure ratio calculation. The results highlighted the importance of the spatial pattern of drift and proved that a hedgerow can be an effective barrier against spray drift. Analysis of the toxicity/exposure ratio values showed that a hedgerow can continue its shelter and feeding function for nontarget arthropods when low-toxicity pesticides are used, there is no significant wind interference, or both.

Weed–Corn Competition Parameters in Late-Winter Sowing in Northern Italy

Abstract In recent years, interest has increased in late-winter sowing of corn in northern Italy because of many agronomic advantages. However, cold and rainy weather slows initial crop growth, which can favor weed infestation. There is, therefore, a need for appropriate timing of weed control tactics based on an understanding of the competitive relationship and dynamics between crop and weeds. Five experiments were conducted over 4 yr, with a series of treatments increasing either duration of interference or length of weed-free period. Yield data were fitted with sigmoidal equations to find the critical point (CP) and critical period of weed control (CPWC). Although the CP is determined only by the competition between weed and crop, the CPWC is also market dependent. To quantify the effect of weed flora on the CP, a multiple regression model was tested, taking into account weed density, inflection point, and slope parameter of the Gompertz model of the cumulated infestation. The results confirmed that the late-winter sowing date increases the importance of late winter– and early spring–emerging weeds. In general, the precompetitive period was longer in the late winter–sown corn than in traditional midspring-sown corn. The delayed start of the CPWC makes control more difficult with a preemergence herbicide, which raises questions on the utility of this agronomic technique. Multiple regression analysis showed that the position of CP can be estimated with the density, earliness, and competitiveness of the infestation. Furthermore, the slope/inflection point ratio of the Gompertz model appears to be independent of sowing date. Results suggest that the weed–crop competition mechanism can be represented with simply the weed flora dynamic parameters and that a combination of crop–weed competition studies and emergence prediction models can predict the position of CP and give useful information about the CPWC and weed management. Nomenclature: Corn, Zea mays L. cv. ‘PR33 J24’

Modeling Weed Emergence in Italian Maize Fields

Abstract A hydrothermal time model was developed to simulate field emergence for three weed species in maize (common lambsquarters, johnsongrass, and velvetleaf). Models predicting weed emergence facilitate well-timed and efficient POST weed control strategies (e.g., chemical and mechanical control methods). The model, called AlertInf, was created by monitoring seedling emergence from 2002 to 2008 in field experiments at three sites located in the Veneto region in northeastern Italy. Hydrothermal time was calculated using threshold parameters of temperature and water potential for germination estimated in previous laboratory studies with seeds of populations collected in Veneto. AlertInf was validated with datasets from independent field experiments conducted in Veneto and in Tuscany (west central Italy). Model validation resulted in both sites in efficiency index values ranging from 0.96 to 0.99. AlertInf, based on parameters estimated in a single region, was able to predict the timing of emergence in several sites located at the two extremes of the Italian maize growing area. Nomenclature: common lambsquarters, Chenopodium album L.,CHEAL; johnsongrass, Sorghum halepense L. Pers, SORHA; velvetleaf, Abutilon theophrasti Medik., ABUTH.