Ullalena Boström

Earthworm populations (Lumbricidae) in ploughed and undisturbed leys

Abstract The extent of earthworm injury caused by rotary cultivation followed by ploughing of a meadow fescue and a lucerne ley was estimated. For comparison, parts of the leys were left undisturbed. One year later, earthworm biomasses in the ploughed leys and the undisturbed leys were estimated. The ploughed plots were under barley at the time. Rotary cultivation killed 61–68% of the earthworm biomass. The ploughing that followed increased the mortality by a further estimated 12% and 9% of the original biomass in the meadow fescue and lucerne leys, respectively. One year later, earthworm abundance in the ploughed treatments was similar to that in the undisturbed lucerne ley, while it was lower in the undisturbed meadow fescue ley. The difference in earthworm biomass between the leys was probably due to inferior food quality and drier soil conditions in the grass ley. More large adults of Aporrectodea caliginosa Sav. were found in the ploughed treatments than in the undisturbed leys, and this species also constituted a greater part of the earthworm biomass in the former compared with the latter (i.e. 85% and 60%, respectively). The biomasses of Lumbricus rubellus Hoffm. and juvenile Lumbricus terrestris L. were significantly greater ( P

Type and time of autumn tillage with and without herbicides at reduced rates in southern Sweden. 2. Weed flora and diversity

The design of integrated weed management (IWM) systems is essential in order to reduce the use of herbicides for crop production. By combining different weed management practices, herbicides may be used at lower doses than normally recommended, while still maintaining acceptable weed population levels. The purpose of this study was to develop tillage strategies, with and without herbicides at reduced rates, appropriate for different weed populations. The influences of type and time of stubble cultivation, harrowing and mouldboard ploughing on the weed flora were followed during 1988–1994 in eight long-term field trials situated in southern Sweden. Spring-sown barley (Hordeum distichon L.) and oats (Avena sativa L.) dominated the crop rotations. Herbicides were either omitted or used at ca. 50% of a full dose. The perennial species Sonchus arvensis L. was favoured by omittance of ploughing but was better controlled by late ploughing not preceded by stubble cultivation; the reduction in the latter treatment being 74%. Stubble cultivation succeeded by ploughing reduced biomass of Elymus repens (L.) Gould. by 90% compared with ploughing solely. Early ploughing reduced the biomass of the species by 50% compared with late ploughing. The species Cirsium arvense (L.) Scop. was highly favoured by early ploughing followed by late autumn harrowing, the biomass of the species being six-fold higher than in other treatments. Compared with other treatments, stubble cultivation favoured four annuals but efficiently controlled three others, while omittance of ploughing favoured six annual and two perennial weed species. Late ploughing not preceded by stubble cultivation favoured four annual and one perennial species, while early ploughing was more efficient than late ploughing in controlling two of the annual species. Influences of treatments on weed species were frequently moderated by interspecific competition resulting in inconsistent response at different sites. Herbicides reduced the number of species by three, from 11 to eight species, averaged across sites and tillage systems. Influences of treatments on diversity were not consistent, since weed floras differed between sites and since some of the species responded inconsistently to tillage and herbicides. This study shows that by utilizing appropriate tillage strategies it is possible at many sites to maintain acceptable weed population levels, although herbicides are used at 50% lower doses than is normally recommended. The timing and type of tillage have to be chosen for being as efficient as possible to the most troublesome weed species at a site.

Response of weeds and crop yield to herbicide dose decision-support guidelines

Abstract Today, the aim of weed management is to keep the weed community at an acceptable level rather than to keep the crop totally free of weeds. Satisfactory control of weeds may often be obtained when herbicides are used at lower doses than normally recommended. To facilitate the decision of what is an adequate dose in a specific field, the farmer needs support. In 1988 and 1989, a total of 10 field trials in spring cereals were initiated in Sweden with the objective of studying long-term effects of herbicide application according to recommendations from guidelines: the guidelines were developed at the Swedish University of Agricultural Sciences and consisted of printed cards designed for in-field use. Treatments also included a full and a half dose and an untreated control. As an average over the experimental time, i.e., until 1997, the dose used in the guideline treatment varied at different sites between 20 and 70% of a full dose. In 1998, i.e., 1 yr after the last herbicide application, the plant densities of annual weeds in the guideline treatment, the half and the full doses were 51, 57, and 67% lower, respectively, than in the untreated control when averaged over sites. At two and four sites, the half and full doses resulted in significantly lower weed densities than where guidelines had been used. Compared with the control, the full and half doses increased the proportion of difficult-to-control weed species significantly at five and four sites by 21 and 24%, respectively. In the guideline treatment the proportion of difficult-to-control weeds was increased at one site. In 1998, weed counts were higher where guidelines had been used than in the full dose for common lambsquarters and common chickweed at three sites each and for wallflower mustard, catchweed bedstraw, field violet, Galeopsis spp., and Lamium spp. at one site each. At three sites, no significant treatment effects on crop yields were found, whereas yields at the remaining seven sites were higher where guidelines had been used than in other treatments in several years. It is concluded that application of dose rates according to recommendations from guidelines can be a fruitful way to reduce herbicide use. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; common chickweed, Stellaria media (L.) Vill. STEME; wallflower mustard, Erysimum cheiranthoides L. ERYCH; catchweed bedstraw, Galium aparine L. GALAP; field violet, Viola arvensis Murr. VIOAR.

Long-term effects of herbicide-application strategies on weeds and yield in spring-sown cereals

Abstract Different herbicide-application strategies may serve as part of an integrated weed management (IWM) system. In 1987 and 1988, ten field trials were initiated in the south-central part of Sweden, with the objective of studying the long-term effects of herbicide-application strategies on the development of weed populations and productivity of spring-sown cereals. Each year until 1997, herbicides were applied at 25, 50, 75, or 100% of the full recommended dose. Treatments included herbicide exclusion every second year and herbicide application at 25 or 50% of a full dose during two out of three years, with a full dose applied in the third year. An untreated control was included. In 1998, weed densities in 25, 50, 75, and 100% of a full dose were reduced 43, 58, 64, and 67% compared with the control. At seven sites, the exclusion of herbicides every second year resulted in 43 to 178% higher weed densities than in 50% of a full dose, although the same amount of herbicide was applied when summarized over 2 yr. At four sites, herbicide application each year at 50, 75, or 100% of a full dose increased the density of difficult-to-control species by 24% compared with the untreated control. Averaged over sites, the untreated control contained 30% more weed species than herbicide application at 75 or 100% of a full dose. At three sites in 1996, the full dose resulted in 520 kg ha–1 (pooled over sites) higher barley yields than in the control. Neither in 1996 nor in 1997, was there any difference in crop yield between herbicide application at 25 and 100% of a full dose. This study demonstrates the potential of reducing the input of agrochemicals for weed control by using herbicides at reduced rates in competitive crops. Nomenclature: Spring barley, Hordeum distichon L.

Yield loss in spring-sown cereals related to the weed flora in the spring

Abstract Yield loss was related to weed species composition and density in permanent plots, recorded several weeks after sowing of spring cereals in southern Sweden. A range of agronomic situations was included by experimentally varying fertilizer application and sowing density in 33 field trials in different locations during 3 yr. Direct gradient analysis, using yield loss as the sole predictor, arranged weed community composition in the spring along a gradient of small to large yield losses. Yield loss could be explained, to some extent, by the species composition in the spring. Species associated with situations with large losses were hempnettle and wild radish, whereas several benign species were identified based on their association with lack of yield loss. The results suggest that possible predictive tools using spring species composition would be improved if they also considered soil type and seed rate. Some agronomically important weed species were not identified as associated with yield loss when assessed in terms of their abundance in the spring, which may limit the possibilities of basing management decisions on weed plant density in the spring. Nomenclature: Hempnettle, Galeopsis spp.; wild radish, Raphanus raphanistrum L. RAPRA; nightflowering catchfly, Silene noctiflora L. MELNO; scarlet pimpernel, Anagallis arvensis L. ANGAR; spurge species; Euphorbia spp.; Polygonum spp.; prostrate knotweed, Polygonum aviculare L. POLAV; wild buckwheat, Polygonum convolvulus L. POLCO; common lambsquarters, Chenopodium album L. CHEAL; field violet, Viola arvensis Murr. VIOAR; spring barley, Hordeum distichum L.; spring wheat, Triticum aestivum L.

Weeds and yields of spring cereals as influenced by stubble-cultivation and reduced doses of herbicides in five long-term trials.

The influence of herbicides at reduced rates and repeated stubble-cultivation on weeds and crop yields was estimated in five field trials with spring-sown cereals situated in the south of Sweden during the autumn of 1989 until the spring of 1997. Stubble-cultivation was accomplished during 1989–1996, while herbicides were applied at 0, 1/8, 1/4 or 1/2 of full dose during 1990–1996. In the spring of 1997, i.e. after 7 years without herbicide application, seedling densities 3 weeks after weed emergence were 68–340/m 2 at three sites and 535–610/m 2 at two sites when averaged over tillage treatments. Averaged over herbicide doses, stubble-cultivation reduced the plant density of annual broad- leaved weeds by 6–32% at three sites and increased the density by 25% at one site. At the remaining site, the density was not significantly influenced. Stubble-cultivation reduced the populations of two perennial and seven annual weed species, while one species was stimulated and nine species showed null, or inconsistent, responses. In the spring of 1997, i.e. one year after the last herbicide application, the densities of weed seedlings in 1/8, 1/4 and 1/2-doses were 34, 46 and 56% lower, respectively, than in the untreated controls. Stubble-cultivation increased crop yields at four sites by 200 kg/ha as a mean over herbicide doses. At these four sites, averaged over 1993–1995, herbicides increased yields in plots that were not stubble-cultivated by 7, 8 and 10% in the 1/8, 1/4 and 1/2 of a full dose, respectively, relative to the untreated control. In 1996, herbicides increased yields at only two sites. It is concluded that a fruitful way for weed management with a low input of agrochemicals is to combine the use of herbicides at reduced rates with repeated stubble-cultivation.

Regeneration capacity from buds on roots and rhizomes in five herbaceous perennials as affected by time of fragmentation.

Variation in seasonal sprouting pattern from roots and rhizomes of perennial herbaceous plants influence the success of plant proliferation ability, invasiveness and escape from weed control measures. The latter often rely on methods, which repeatedly fragment the underground system, thereby trigger adventitious and axillary buds to sprout, and consequently reduce the amount of stored energy. If carried out at times when no re-growth occurs, treatments will have little effect on weed populations, but cost much in terms of labour and energy. The purpose of this experiment was to determine the seasonal variation in bud sprouting capacity after fragmentation. Five troublesome perennial weed species, collected in northern and southern Sweden, were grown outdoors in Uppsala, Sweden (N 59°49′, E 17°39′), from May 2009 to January 2010. Cut root and rhizome fragments, taken at two weeks intervals from July to January, were used to evaluate bud sprouting capacity, which was statistically analyzed using generalized additive models. In Elytrigia repens from southern Sweden and Sonchus arvensis sprouting capacity was significantly impaired during a period from September to November. In Equisetum arvense and Tussilago farfara sprouting was low between July and November where after it increased. In contrast, Cirsium arvense and E. repens from northern Sweden sprouted readily throughout the period. Except for E. repens, a model by populations was significantly better than one based on latitudinal origin. The result suggests a species-specific timing of treatments in weed management, avoiding the non-effective autumn period for E. arvense, S. arvensis and T. farfara, and in some cases in E. repens.

Influence of Harvest Time and Stubble Height on Weed Seedling Recruitment in a Green Cereal

A long-term field experiment was conducted in southern Sweden to evaluate the effect of harvest before crop ripeness on weed infestation. In addition, two stubble heights, 10 cm and 30 cm, were compared. The aim was to determine the potential of the treatments in weed regulation. The harvests were performed on three occasions: milk-ripeness (I), which is the normal harvest time for a green cereal, yellow-ripeness (II) and binder-ripeness (III). In control plots, harvested at full ripeness, herbicides were used in all years. Weed density initially increased exponentially in all treatments except for the control, but had a tendency to level off after 4 years. In all years weed density was higher when harvest was delayed and the stubble was high. Harvest at milk ripeness (I) favoured short-season annuals such as Stellaria media (L) Vill and worked against late-maturing species such as Polygonum tomentosum (Schrank). Weed density differed between the treatment plots during the last year of the experiment. In the treatment harvested at stage I combined with low stubble height, weed density was only slightly higher than in the control. Thus, when harvesting a green cereal, herbicides can be avoided.

Growth Dynamics in Relay-Cropped Cereals in Relation to Weed Competition: a Greenhouse Experiment

ABSTRACT A greenhouse experiment was conducted to reveal whether it is possible to favour winter wheat by reducing the seed rate of spring barley in a relay-cropping system. Since crops sown at low seed rates may be less tolerant to high weed pressure the study also included weed competition. The experimental design was additive, the density of winter wheat being held constant while spring barley density was increased from 167 to 544 plants m−2. At four successive harvest times, the growth of the crops and weed was followed until barley maturity. The wheat plants remained at a vegetative stage during the study period. Seed rate of barley influenced both barley and wheat biomass less in the presence of weed than in the absence. Weed competition reduced wheat biomass significantly only at the lowest seed rate. The presence of weed also reduced barley biomass. The reduction decreased with increased seed rate. In weed-free stands, seed rate influenced barley biomass less and had no significant effect on barley grain yield, which was on average 772 g m−2. By contrast, in the presence of weed, barley grain yield increased from 242 to 646 g m−2 with increased plant density. The relative weight decrease per individual plant in response to barley seed rate and weed competition did not differ between wheat and barley, suggesting that wheat and barley responded equally to treatments. It is concluded that wheat performance is favoured by reduced barley seed rate. However, low seed rate will reduce barley grain yield if the weed pressure is high, while wheat may be less sensitive to the weed situation.