Jukka Salonen

Weed infestation and factors affecting weed incidence in spring cereals in Finland - a multivariate approach

Weed vegetation of spring cereal fields in southern and central Finland was analyzed by ordination methods to provide a community level description of weed populations. Attention was paid particularly to the relative importance of environmental factors affecting weed incidence such as crop management, soil properties and weather conditions. A data set of 33 weed taxa from 252 fields was subjected to both indirect and direct gradient analysis. Indirect ordination was obtained with correspondence analysis (CA), and direct gradient analyses were performed with redundancy analysis (RDA) and withcanonical correspondence analysis (CCA) relating environmental factors to the occurrence of weeds. Among several management factors, continuous herbicide use explained best the variation in the species composition of weed flora. Weed vegetation was also associated with soil type, moisture conditions and soil pHh 2oOrdination diagrams visualized the species-environment interactions and detected characteristic weed species for different geographical regions. In addition to ordination analyses of weed flora, the level and structure of weed infestation are described. The density of weeds averaged 170 plants m 2(median=l24) and the air-dry weight of weeds 320 kg ha I (median=lB3). The average weed density was the same in different soil types, but the weed biomass was lower in clay soils than in coarse mineral and organic soils.

Composition of weed flora in spring cereals in Finland - a fourth survey

Kevatviljapeltojen rikkakasvillisuutta kartoitettiin Etela- ja Keski-Suomessa 16 alueella Nivala-Vierema-Kitee -akselin etelapuolella vuosina 2007-2009. Tutkimuksessa oli mukana yhteensa 595 peltoa 283 maatilalta. Pelloista 523 oli tavanomaisesti viljeltyja ja 72 luonnonmukaisesti viljeltyja. Rikkakasvien tiheys laskettiin kymmenelta ja kuivapaino maaritettiin neljalta 0,1 m2 (40 x 25 cm) havaintoruudulta. Aineisto kerattiin heinakuun puolivalin ja elokuun alkupuolen valisena aikana. Rikkakasvillisuuden pitkaaikaiseen seurantaan liittyvat vastaavat kartoitukset on tehty 1960- ja 1980-luvun alussa seka viimeksi 1997-1999. Valtaosa tutkituista pelloista oli samoja kuin 90-luvun kartoituksessa.Kevatviljapelloilta loydettiin yhteensa 148 rikkakasvilajia, joista 128 oli levealehtisia ja 20 heinamaisia rikkakasveja. Tavanomaisesti viljeltyjen torjunta-aineilla ruiskutettujen peltojen yleisimmat rikkakasvit olivat pelto-orvokki (83 % tutkituista pelloista), pihatahtimo (65 %), pillikkeet (59 %), peltomatara (59 %), linnunkaali (57 %) ja kiertotatar (53 %) seka heinamaisista lajeista juolavehna (50 %) ja kylanurmikka (33 %). Luonnonmukaisesti viljeltyjen peltojen yleisimmat lajit olivat puolestaan jauhosavikka (96 %), pihatahtimo (94 %), pelto-orvokki (94 %), juolavehna (89 %), peltohatikka (89 %) ja pillikkeet (88 %). Luonnonmukaisesti viljellyilla pelloilla kasvoi keskimaarin 21 rikkakasvilajia ja tavanomaisesti viljellyilla ruiskutetuilla pelloilla 12 lajia. Ruiskutetuilla tavanomaisen viljelyn pelloilla kasvoi rikkakasveja keskimaarin 160 kpl/m2 (mediaani: 112) ja luonnonmukaisesti viljellyilla pelloilla 519 kpl/m2 (mediaani: 468). Rikkakasvien tuottama biomassa oli vastaavasti 167 kg/ha (mediaani: 82) ja 775 kg/ha (mediaani: 563). Rikkakasvien osuus kevatviljapeltojen kasvimassasta (vilja + rikkakasvit) oli ruiskutetuilla tavanomaisen viljelyn pelloilla keskimaarin 3 % ja luomupelloilla 21 %. Juolavehnan osuus rikkakasvien tuottamasta kokonaismassasta oli kummassakin viljelymuodossa suurin, tavanomaisen viljelyn pelloilla 28 % ja luomupelloilla 31 %. Rikkakasvilajiston kartoituksen yhteydessa otettiin myos peltomaan pinnasta (0-5 cm) maanayte rikkasiemenpankin maarittamista varten. Maanaytteista seulottiin ja tunnistettiin yhteensa 27 rikkakasvilajia. Viiden sentin maakerros sisalsi keskimaarin 1684 siementa neliometrilla runsaimpana lajina oli jauhosavikka. Rikkakasvien kasvutiheys ja kasvimassa olivat tavanomaisesti viljellyilla pelloilla suunnilleen samalla tasolla kuin 1990-luvun lopussa, jolloin edellinen kartoitus tehtiin. Yleisimmat rikkakasvit ovat tavanomaisessa viljelyssa paaosin samoja lajeja kuin 1990-luvulla, mutta esim. peltomatara ja peltoemakki ovat yleistyneet selvasti. Juolavehna on edelleen tavanomaisen viljelyn haitallisin ja eniten biomassaa tuottava laji, joskin sen osuus rikkakasvien kokonaismassasta on pudonnut alle 30 %:iin oltuaan noin 50 % kymmenen vuotta sitten. Glyfosaatin kaytto on kymmenen vuoden kuluessa yli kaksinkertaistunut, mika selittanee havaittua juolavehnatilannetta. Levealehtisten rikkakasvien torjuntaan hyvaksyttyjen valmisteiden valikoimaan on viime vuosina saatu uusia vaihtoehtoja, joilla parjataan nykyisen rikkakasvilajiston kanssa, mukaan lukien esimerkiksi peltomatara. Nykyinen keskimaarainen torjuntatulos takaa kevatviljojen riittavan ja laadukkaan sadontuoton. Luonnonmukaisesti viljellyilla pelloilla yleisimpia rikkakasvilajeja esiintyi lahes joka pellolla. Kymmenen vuoden aikana merkittavimmin yleistyneita lajeja olivat peltoemakki (+17 %), ukontatar (+ 15 %) ja peltolemmikki (+12 %). Rikkakasvien kasvutiheys ja kasvimassa oli huomattavan korkea ja haittaa merkittavasti sadontuottoa. Keskimaarainen rikkakasvimassa oli noin 100 kg/ha suurempi kuin kymmenen vuotta sitten, ja juolavehnan osuus on lisaantynyt. Jauhosavikka, peltohatikka, peltovalvatti ja pillikkeet olivat seuraavaksi tarkeimpia biomassan tuottajia. Yhdellakaan pellolla ei torjuttu rikkakasveja mekaanisesti kasvavasta viljasta, mika voisi olla osittainen ratkaisu rikkakasvien nykyista parempaan hallintaan.

Managing Sonchus arvensis using mechanical and cultural methods

Perennial sow-thistle (Sonchus arvensis L.) represents an increasing problem in Finland. Options for mechanical and cultural control of S. arvensis were studied in a field experiment on clay soil under organic production. The experiment consisted of different crop sequences: spring cereal (barley, Hordeum vulgare L., in 2001, oats, Avena sativa L., in 2002) with or without inter-row hoeing and/or stubble cultivation, bare fallow, fibre hemp (Cannabis sativa L.), and ley with mowing. In 2003 the entire field was sown to spring wheat. Crop plant and Sonchus shoot density and dry mass prior to cereal harvest and crop yield were assessed. The control effect was rated: bare fallow > ley > cereal with or without inter-row hoeing > poor growth fibre hemp. Bare fallow was an effective but costly way to reduce S. arvensis infestation. Introduction of a regularly mown green fallow or silage ley in the crop rotation is advisable. Mechanical weed control by inter-row hoeing in cereals limits S. arvensis growth. Infestation might also be reduced by stubble cultivation in autumn. When managing S. arvensis using mechanical and cultural methods, appropriate options, including a competitive crop, should be chosen for the specific field and rotation.

Weed flora and weed management of field peas in Finland

The composition of the weed flora of dry pea (Pisum sativum L.) fields and cropping practices were investigated in southwestern Finland. Surveys were done in 2002–2003 in 119 conventionally cropped fields and 64 fields under organic cropping. Herbicides were applied to 92% of conventionally cropped fields where they provided relatively good control but were costly. Weeds were controlled mechanically only in five fields under organic production. A total of 76 weed species were recorded, of which 29 exceeded the 10% frequency level of occurrence. The average number of weed species per field was 10 under conventional cropping and 18 under organic cropping. The most frequent weed species in both cropping practices were Chenopodium album, Stellaria media and Viola arvensis. Elymus repens was the most frequent grass species. The difference in species composition under conventional and organic cropping was detected with Redundancy Analysis. Under conventional cropping, features of crop stand and weed control explained 38.7% and 37.6% of the variation respectively. Under organic cropping the age of crop stand and field location (y co-ordinate) respectively explained best the variation. Weeds could be efficiently managed with herbicides under conventional cropping, but they represented a significant problem for organic production. Mixed cultivation of pea with cereals is recommended, particularly for organic cropping, as it favours crop competition against weeds.

Sowing time affects the abundance of pests and weeds in winter rye

Selection of an appropriate sowing time for some winter rye (Secale cereale) cultivars could reduce the need for crop protection measures. In this study the occurrence and status of pests and weeds in relation to sowing time and growth habit of winter rye was studied in southern Finland. This was done using three sowing times and four rye varieties in field trials conducted at three locations in 1999–2001. The early sown rye was severely affected by pests (Oscinella frit, Mayetiola destructor) and weeds, whereas postponing sowing for two weeks after the recommended sowing time in late August resulted in considerably less damage and the optimal establishment of crop stands. The German hybrid varieties Picasso and Esprit produced more tillers m -2 in autumn than the Finnish varieties Anna and Bor 7068. However, the number of pests and weeds did not differ among rye varieties. Late sowing of rye should be considered to minimize the need for plant protection. If rye is sown at the recommended time it may still require insecticide treatments promptly in the autumn whereas herbicide treatment need not be determined until spring, after recording the winter mortality of weeds.