Perennial weeds

CgHjClaOj. M.p. 155°C. Used as a selective herbicide. It is made from 2,4,5-trichloro-pheno) and sodium chloroacetate. Ester sprays and combined ester sprays with 2,4-D are available. 2,4,5-T products are of particular value in that they control many woody species, and eradicate perennial weeds such as nettles in pastures. 

There is extensive evidence that allelopathy may contribute to patterning of vegetation in natural ecosystems (11). Distinct zones of inhibition are present under and adjacent to a variety of woody species, and often toxins from their litter are implicated (J2). One might speculate that aggressive perennial weed species quickly gain dominance by exploiting allelopathic mechanisms. 

Elmore CL, Roncaroni JA, Giraud DD (1993) Perennial weeds respond to control by soil solarization. Cal Ag 47 19-22... 

Pollen allelopathy can find utilization in field cultivations that could contain pollen of allelopathic crops or weeds. Pollen allelopathy could be an effective method for annual weed control that reproduce, at least in part, via wind pollination and flower concurrently with the allelopathic species. The effects of allelopathy should result in the loss of genetic variation and so in reduction of reproductive ability, but some plants are probably able to detoxify the pollen allelochemicals (Murphy and Aarssen 1995a, b). Murphy and Aarssen (1989) suggested possible delaying of weed flowering at later, less favorable times of the season or diurnal period, so decrease in weed pressure. However, infestation by perennial weeds can worsen due to compensation of pollen allelopathy through increase in the formation of rhizomes. 

Bedding from herbivorous pets—rabbits, hamsters, etc. Perennial weeds ... 

Perennial survival Perennial weeds make use of a range of mechanisms for their longterm survival and spread. This can include both seed and vegetative means such as runners, stolons, rhizomes and long, deep taproots. 

Take time to clear perennial weeds effectively before any permanent planting— even if this could take a year or more. 

A mulch membrane, weed barrier, or weed control fabric is simply a sheet of synthetic or biodegradable material that forms a physical and light-excluding barrier to weed growth. Membranes can be used to clear annual and perennial weeds from open ground and beds. They are also used to prevent weeds from growing on ground that has been cleared. 

Holes can be cut to allow planting through the membrane as appropriate. Membranes may be covered with a loose mulch, to hold them in place, extend their life span, and improve their appearance. A mulch membrane must be permeable, to allow air and water into the soil, unless it is only to be kept in place for a few months. However, to suppress the more vigorous perennial weeds (see also pp.80-81), the membrane may need to be in place for several years while there are several biodegradable choices of membrane material, a nonbiodegradable material is the more practical option in such situations. 

Where there is a severe perennial weed problem such as ground elder or horsetail, put the ground in grass, by either sowing seed or laying sod. Regular mowing for two or three years should solve the problem. 

Hie no-dig approach If your soil is in good condition, you can begin using the no-dig technique right away below left). If there are perennial weeds, a sheet mulch can be used to suppress them, again without any digging within two years it should be possible to sow seed of crops such as chard below right). 

On a no-dig plot, weeds are drastically reduced as dormant seeds are not brought to the surface by the soil s being turned over. A mulch further reduces weed numbers, but is not essential. Light hoeing is effective on bare soil and gradually depletes the reserve of weed seeds. Loosen any perennial weeds with a fork and lift them out, disturbing the soil as little as possible. 

As with all perennial plants, appropriate soil preparation, including removal of all perennial weeds, is essential before planting (see The Soil, pp.34-35, Weeds and Weeding, pp.76-79, and also Herbaceous plants, pp.190-191). 

It is much easier to improve soil structure and fertility before rather than after planting, and this is crucial to give trees, bushes, and canes a head start. A plant that establishes well soon develops an extensive root system that can forage for water and nutrients more efficiently than a weak plant. Details of appropriate soil improvement are given under individual fruits. Perennial weeds are awkward to remove from growing fruit, so clear the ground well before planting, too (see pp.78-8D. 

The product is a broad-spectrum, non-selective herbicide particularly effective against perennial weeds such as nutsedge and bindweed. Since the effect of changes in structure on biological activity is similar in several series of compounds, this topic will be discussed later. 

It is a broad-spectrum herbicide active both pre- and post-emergent. Studies with radiolabelled compounds ( ) show it to be rapidly translocated particularly to the meristematic regions. Translocation to the underground storage organs of perennial weeds prevents regrowth of these weeds. Most herbaceous and woody plants are controlled in the field at 0.4-1.0 kg a.e./ha whereas most woody plants require 0.7-3.0 kg a.e./ha (10). 

From the earliest greenhouse studies, it was obvious that AC 252,214 was an interesting compound. Remarkably, it was well tolerated by legumes, especially soybeans, yet showed a broad-spectrum of herbicidal activity, killing broad-leaved, grassy and perennial weeds. Further it was shown that AC 252,214 could be used both as a preemergent and postemergent herbicide. Rates for field application are 125-250 g/ha (12). 

D. The most widely used herbicide at present is 2,4-D. As far as the selective use of 2,4-D on cereal crops is concerned, the amine formulations seem perfectly satisfactory. As a translocated herbicide, results are not too good. In some localities, 2,4-D has been effective in treating perennial weeds, but in other places results have been disappointing. The differences seem related to the movement of the material after it gets into the plant, and here the physiology of the plant, as well as the nature of the chemical, is concerned. 

There are a number of other herbicides that affect photosynthesis indirectly. Pyrazole herbicides such as benzofenap, pyrazolynate and pyrazoxyfen interfere with chlorophyll biosynthesis and have found commercial application for the control of annual and perennial weeds in paddy rice and maize (Figure 2.4). 

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