Selection inCirsium arvense(L.) Scop. andSonchus arvensisL.: Susceptibility to MCPA on different types of farmland in Sweden

Abstract

During the past century, changes in cropping systems have led to selective pressure on weed flora. The number of competitive species with decreased susceptibility to herbicides has increased, at the cost of more susceptible species. For a long period, the economically important perennial weed species Cirsium arvense (L.) Scop. and Sonchus arvensis L. have mainly been controlled by the herbicide MCPA (phenoxy-acetic acid), which stimulates the weed plant to abnormal growth. However, it has been reported from Sweden, Great Britain, Hungary and North America that C. arvense has become less susceptible to MCPA since the 1950s. Therefore, two greenhouse experiments were performed at Uppsala, Sweden with clones of C. arvense and S. arvensis. The purpose was to study whether ecotypes (clones) from high input farmland, where herbicides had been used intensively and regularly for a long time, were less susceptible to herbicide (MCPA) treatment than ecotypes from low input farmland. Sixty clones of C. arvense and 36 clones of S. arvensis were treated with nine different doses of MCPA. The results supported the suggestion that a shift towards less MCPA-susceptible ecotypes of C. arvense had occurred on high input farmland. Clone material from such farmland had, on average, significantly higher dry matter content after herbicide treatment than ecotypes from low input farmland. Similar decrease in susceptibility was not detected for S. arvensis. This was probably due to S. arvensis generally being less susceptible to MCPA than C. arvense. Sonchus arvensis has therefore being exposed to a lower selection pressure than C. arvense.

Selective pressure onCirsium arvense(L.) Scop. andSonchus arvensisL. growth characteristics on different types of farmland in Sweden

“…From this collection, root fragments of C. arvense (60 ecotypes) and S. arvensis (36 ecotypes) were transplanted for multiplication (see Fogelfors & Lundkvist, 2008) which yielded roots used for the growth-characteristic experiments and the competition experiment in the field.…”

“…The pots were then moved to a greenhouse where they were randomly placed. For information on growth conditions in the greenhouse, see Fogelfors and Lundkvist (2008).…”

“…In the middle of spring, the pots were transferred to a greenhouse where they were randomly placed. For information on growth conditions in the greenhouse, see Fogelfors and Lundkvist (2008). When at least one of the shoots in each of the pots had ten fully developed leaves the growth-characteristic experiment was terminated.…”

“…Competition experiment in the field (Cirsium arvense' Hordeum distichon) Based on the growth and development differences observed between the 30 ecotypes from low-input farmland in (a) the greenhouse experiment 1 where the ecotypes were submitted to nine doses of MCPA (Fogelfors & Lundkvist, 2008) and (b) the growth characteristic experiment 1 (C. arvense) described above, a field experiment with C. arvense was established in central Sweden (598 39' N, 178 50' E) on a clay loam containing 3Á6% organic matter. The purpose was to study the selective pressure on different ecotypes of C. arvense originating from lowinput farmland when submitted to (a) various competition pressures from a crop and (b) herbicide treatments.…”

Sprouting and shoot development of Sonchus arvensis in relation to initial root size

“…Consequently, the key for a successful control strategy is the ability of the control measure to affect the above‐ground shoot dynamics in S. arvensis in such a way that resource acquisition and subsequent allocation from the shoots to seeds and roots is diminished. Chemicals may be used to control S. arvensis , but this species is considered to be fairly tolerant against many herbicides that target dicotyledonous weeds in a growing crop (Lemna & Messersmith, 1990; Fogelfors & Lundkvist, 2008). As many of the applied herbicides have a destructive effect on above‐ground biomass, but have a lesser effect on root systems, a combination of herbicides such as glyphosate, dicamba or phenoxyacetic acids and tillage (deep tillage cultivator) in a year of fallow is usually recommended to control S. arvensis (Lemna & Messersmith, 1990; Darwent et al.…”