Using allelopathic effect
Lucerne plant can be used for weed control
.I TOSSED out to you all, a suggestion and a challenge in last week’s issue of the Rural Weekly, of using other plants competitiveness against our burgeoning herbicide resistant weed spectrum.
In other words using more desirable plants as competitors against other undesirable ones.
We have streams of data in Australia that this competition angle with higher plant densities and narrower row spacing of wheat and barley really do limit the growth and seeding ability of other plants, that we class as weeds.
My local example was using buffel grass to compete successfully against galvanised burr, that I actually witnessed over a 12- month period back in the early 1980s.
The desirable plant that I mentioned last week was lucerne or alfalfa as it is known overseas. This highly productive perennial legume plant certainly is a producer of high quality feed for livestock or haymaking. What else it produces is this root exudate that is classed as having an allelopathic effect of surrounding plants.
So a few explanations here first about what is root exudate and the allelopathic effect?
Root exudate is a tiny liquid secretion of various compounds and metabolites that is released into the soil rhizosphere from the roots. The rhizosphere is that zero to 2mm area, where the root and soil interface or meet. Apart from impacting on the soil microbial community, this tiny amount of viscosey fluid can deter below ground pests and do many other complex duties, underneath the soil surface. For our purposes we would need to know how they inhibit other plant species, however that is a rather large technical topic that even defeats me.
Strangely enough this allelopathic effect on other plants can also affect other lucerne plants and is called aotopathy. For those lucerne growers who have ever tried to thicken up a straggly stand of lucerne by over sowing some more lucerne seed, have generally been sadly disappointed with the result and this aotopathy effect is the reason why. So these root exudates are full of the these different chemical compounds which may deter some plant species to not grow and others to be more stimulated in their growth pattern and this process is summarised by the term allelopathic.
So we do not exactly know if the lucerne plant roots exudate will have a positive or a negative effect as far as an allelopathic effect on a weed like feather top rhodes, however it is fairly safe bet that once our perennial lucerne plant gets established, it is going to hard work for an annual grass plant like feather top rhodes to establish and flourish in a dense patch of lucerne plants.
So the book is still to be written for this challenge to you all, about using desirable plants with high density numbers in those weedy areas, that you may have been using the same herbicide mode of action on, for many years. Lucerne was my choice from my experiences over the last 40 odd years of observing it compete very successfully over weeds like nut grass.
The end result of these deliberations is that we all need to consider and try these alternate weed control measures, so that we can still use effectively in the future, the current suite of herbicides available, if we so desire.