If a weed is defined as a plant growing where it is unwanted, then the worst kind of garden weed is that which both spreads rampantly and is also extremely difficult to eradicate. This article will focus on the "gang of four", which from my 20 plus years experience gardening in central Israel, are the most invasive and problematic of all. They are in ascending order of monstrosity:
(1) Bindweed – Convolvulus arvensis
2 Bermuda grass – Cynodon dactylon
3 Galingale – Cyperus rotundus
(4) Dodder – Cuscuta campestris
Prevention is better than cure
If you are building a new garden or just planting up a border, then it's advisable to ensure that the soil is free of these particular weed before before embarking on the planting. The first three species in the list, all develop extensive root systems which are all but impossible to remove manually. Mulch is ineffective in controlling them. They bought to be eliminated by use of a systemic herbicide such as Roundup. In order for the systemic properties of Roundup to work effectively, the weeds have to be growing actively and the shade temperature should be above 23-24c.
In cases where these weed types are not visible but their presence in the soil is nonetheless suspected, the ground has to be watered thoroughly in order to encourage their growth, so that they can be sprayed. This is a laborious process taking up to 12 weeks if carried out properly. Also if you are planting in the winter, do not be fooled by the non-appearance of these species. They grow actively in the summer and are dormant in the winter. Let's look at each one separately then and see what can be done in the event of an infestation.
Bindweed – Convolvulus arvensis
Bindweed is a creeping plant, common to heavy, clay soils. Its roots can reach a depth of 2 meters and more. It is extremely invasive and can ruin a flower bed or a carpet of ground covers. It is also resistant to Roundup when that is applied on its own, but can be eradicated when the Roundup is mixed with the hormonal types of herbicide. This is a very dangerous procedure and must only be performed by a qualified person. If growing in a bed or border, then tall stakes should be inserted in the ground to encourage the bindweed to climb and "bind" its way up the stake. The plant can then be carefully painted with the appropriate weed killers.
Bermuda grass – Cynodon dactylon
Bermuda grass is the source of many lawn varieties such as "Santa Anna," which are commonly grown in hot climates. The wild species though, as a perennial grass can be a highly noxious weed. It is generally killed by Roundup if applied at the suitable concentration. If growing in the flower bed, it can be sprayed by a selective herbicide, which damages plants belonging to the grass family, (Poaceae) without affecting species belonging to the other botanical families. From my experience, the selective weed killers only retard the perennial grasses for a season or two and do not eradicate them.
Galingale – Cyperus rotundus
Cyperus is grass-like in appearance but belongs to the sedge family. The anti-grass weed killers are there before useless against it while Roundup is only partially effective. Cyperus is responsible for major losses to farmers in tropical, sub- tropical and Mediterranean climates. However it hates shade and competition from other plants, so in such conditions, its threat decreases over time. If growing in the lawn, very frequent mowing (every 1-2 days) will cause it to stay dormant under the ground.
Dodder – Cuscuta campestris
This is the stuff from which Sci-Fi stories are created! Dodder weed may be an annual plant, but do not let that fool you into thinking it's easy to get rid of. It is in fact a parasite, wrapping itself round host plants (mostly soft herbaceous plants and low bushes) which sap it sucks out. It spreads from plant to plant in the summer by way of yellow, string-like filaments. Affected parts of a plant have to be cut down completely, because leaving even a tiny residual of filament, will allow it to re-grow and continue its work of finding a host and then strangling it. Dodder weed blooms and sets seed very quickly, thereby creating fresh generations for both the current growing season and for the following year.
Plants that have been attacked by it should never be thrown on the compost heap, as the seeds survive the heat of the compost pile. They are also hardy to solar sterilization.
So what can be done? By way of prevention, profuse watering on bare soil will cause the dodder seeds to germinate. On condition that there are no weeds or garden plants in the vicinity (2-3 meters) the seedlings will die as they need to find a host in a short period of time. In the event of an attack, you'll have to do as described in the last chapter. In extreme cases it may be necessary to totally remove all plant material, thereby preventing the parasite from finding host plants.