Haldor Fykse

Patch spraying of weeds in spring cereals: Simulated influences of threshold level and spraying resolution on spraying errors and potential herbicide reduction

Abstract A major obstacle to patch spraying of broad-leaved weeds in cereals is a cost-effective method to assess within-field heterogeneity of the weed population. One method could be a camera mounted in front of the spraying vehicle, online image analysis, and field sprayer shifting between ‘on’ and ‘off’ as the predefined weed damage threshold level is reached. Because such a camera will capture a very limited area (<1 m2) compared to the sprayer width (several m), success of this method requires that spraying decisions vary little within boom width, thereby causing few spraying errors. This approach was evaluated by simulations for varying boom widths and three levels of a weed damage threshold model. Potential herbicide reductions compared to blanket application were also simulated. The average potential herbicide reductions estimated as proportions of fields below the threshold, were 60%, 64% and 53% for the original, 25% increased and 25% reduced threshold levels, respectively. The simulated herbicide reductions were not influenced by boom width, but varied significantly between fields, and between threshold levels. As evaluated by spraying errors, the suitability of the suggested approach will increase by decreasing boom width, vary between fields, and in some fields vary between the threshold levels. For boom widths of 15 m and 24 m, the spraying errors were about 10% and 15%, respectively, where omission of spraying areas above the threshold constituted 5% and 8%, respectively.

Weed Development in Cereals under Different Growth Conditions and Control Intensities

The development of weed communities in cereals was investigated over 5 years at four locations in Norway. Each year the same plots were treated with 0, 1/3, 2/3 or 3/3 of the ‘normal’ dose of either of two herbicides. The weed species that emerged varied between years and locations, but were unaffected by treatments. The total number of weed plants and the frequency of individual species varied in all fields, but the changes differed greatly between fields, dosages and years. The seed bank was increased by the lowest herbicide dose and unaffected by the higher doses. The percentage of emerged weeds decreased with time, but varied between the fields. The per cent emergence was lower on untreated than on treated plots. The weed abundance in previous years and the size of the seed bank affected the plant number, but the air temperature after sowing was just as important. Even soil temperature in spring prior to tillage influenced weed emergence.

Regeneration of Canada Thistle (Cirsium arvense) from Intact Roots and Root Fragments at Different Soil Depths

Abstract In the present field study, the capability of Canada thistle to develop shoots from intact roots and root fragments at different soil depths was studied. The experiments were performed on four sites with high-density Canada thistle, with three or four replications per treatment. At each site, the soil in the plots was removed layer by layer (to 30 or 40 cm, depending on the site), within a 1 by 1-m quadrat, and spread out on a plastic sheet. All roots and other plant parts were removed, and the soil was either replaced without any root material (two sites), or the roots of the thistles were cut into 10-cm-long fragments and replaced into the source holes (two sites). The measured variables were shoot number and biomass. The number of shoots of Canada thistle decreased with increasing depth (P < 0.001) and increased with time. Additionally, the two factors interacted (P < 0.001) such that shoot development was slower from greater depths. Roots from ≤ 20 cm depth produced higher biomasses than did roots from below 20 cm depth. Replacement of root fragments did not affect the amount of biomass produced. It was concluded that the intact root system contributed considerably more to the total biomass produced by Canada thistle than did the root fragments in the upper soil layers. Nomenclature: Canada thistle, Cirsium arvense (L.) Scop.

Simulating the effects of mapping and spraying resolution and threshold level on accuracy of patch spraying decisions and herbicide use based on mapped weed data

Abstract A possible cost-effective real-time patch spraying implementation against seed-propagated broad-leaved weeds in cereals is a camera mounted in front of the tractor taking images at feasible distances in the direction of travel, on-board image analysis software and entire boom switched on and off. To assess this implementation, manual weed counts (0.25 m2 quadrats) in a 1.5 m×2 m grid, were used to simulate camera outputs. Each quadrat was classified into ‘spray’ and ‘not spray’ decisions based on a threshold model, and the resulting map defined the ‘ground truth’. Subsequently, ‘on/off’ spraying at larger control areas where sizes were given by the boom width and image distance, and spraying decision controlled by weed status at the single quadrat simulating the cameras view, were simulated. These coarser maps were compared with ‘ground truth’, to estimate mapping error (area above threshold not sprayed), spraying error (area below threshold sprayed), total error (sum of mapping and spraying error) and the herbicide reduction. Three levels of the threshold model were tested. Results were used to fit models that predict errors from boom width and image distance. Size of control area did not on average affect the magnitude of the simulated herbicide reductions, but the bigger the control area the higher the risk that the simulated herbicide reduction deviate from the reduction in ‘ground truth’. Mean simulated herbicide reductions were 42–59%, depending on threshold level. Only minor differences due to threshold level were seen for mean mapping and spraying errors at given spraying resolutions. Using original threshold level and image distance 2 m, predicted total errors for boom widths 2 m, 6 m, 20 m and 40 m would be 6%, 10%, 16% and 17%, respectively. Results indicate that control area should not exceed about 10 m2 if acceptable total error is maximum 10%.

Sensitivity of Cirsium arvense to simulated tillage and competition

Abstract Single and combined effects were studied of root length, burial depth, cutting and competition from a seasonal green manure crop on the growth and development of C. arvense from roots found in the upper soil layer. The experiment was performed under field conditions and partly repeated in a green house. The green manure consisted of a mixture of phacelia, common vetch, red clover and Italian ryegrass. Root fragments of 5 and 10 cm length were buried at 5 and 15 cm soil depth, simulating soil tillage. Use of green manure alone reduced growth of C. arvense more than any other single factor (81–99%), while root length and burial depth were more variable in their effect (0–96% reduction). Combined treatments involving both green manure, deep root burial (15 cm) and short root length (5 cm) reduced growth of C. arvense consistently by 95–100%. At the minimum regenerative capacity of C. arvense the number of leaves was 3–7 in plots with no green manure, at which time cutting had the greatest effect on regrowth the following year. The level for minimum regenerative capacity was not possible to decide for C. arvense growing in competition with green manure. Combined multiple treatments in spring, including use of green manure and mechanical operations in the upper soil layers, appear to be a potential means of reducing C. arvense infestations.

Production systems and plant protection requirements in cereals: a model analysis of long-term effects

The main models within the MILDRI modelling network for studying plant protection, PVNOR, a dynamic model which simulates the development of weeds and diseases in cereals, and FARMNOR, an economic analysis model for choosing and evaluating management practices, were used to predict the effect of different production systems on the need for plant protection measures, and the resulting yield and economic output in different climatic situations. The simulations were run for 22 years using historic weather data. The study showed that PVNOR reflected fairly well the changing plant protection problems and agricultural consequences which emerged during the simulation period, and that the model handled the interactions between the large number of variables involved in such perennial systems. The combination of PVNOR and FARMNOR proved to be a valuable analytical tool, which in addition to predicting plant protection problems and consequences, also allows the prediction of the economic outcomes arising from different cereal production systems.