If you find
Weeds succeed each year despite all attempts to beat them with chemicals
Weeds on your land have developed resistance to all the chemicals that it is feasible to throw at them
Weeds seed before you have a chance to get ahead of them
Understanding the way the weed works may allow you to get ahead.
- you can understand why a weed has a particular characteristic or behaves in a particular way
- you have the chance to understand how that benefits the weed and therefore
- how you may be able to get ahead of it by applying an appropriate tactic to counter that benefit or to give that benefit to your crop plant.
Generally, weeds are more of a problem when your crop is having difficulty. When there is plenty of sun, water, nutrients and no limiting or damaging factors, weeds are not as much of a problem as when your crop is not performing optimally.
This is because weeds are better adapted than desirable plants (such as crops including pastures) are to almost any difficulty.
Most crop and pasture plants are fussy and less capable in any but ideal conditions.
Pioneer plants such as weeds are usually well adapted to hard soils and to soils low in moisture, nutrients or in any other way below ideal. If you let your soil deteriorate, you take the advantage from your chosen plants and give it to the weeds.
Plants have three main lengths of lifecycle: Perennial, annual and biennial.
ANNUAL plants complete their life cycle in a year or less, starting from seed and producing another generation of seeds before dying.
BIENNIAL plants take more than one year and often less than two years to complete their life cycle. The first year is often spent establishing and the second year is spent producing seeds. The plant generally dies after this.
PERENNIAL plants continue to live from one year to the next, often producing seeds each year.
Weed control is particularly important with perennial weeds because as well as weed seeds, you will have weed plants that may continue to set seed for years.
In theory, it is easier to eliminate annual and biennial weeds (than perennial ones) because they can be beaten by eliminating the seed phase. If you stop them seeding, there will be no weeds once the seed bank in the soil is exhausted. The existing plants will die after one or a few years and if they are not replaced, that weed problem ends.
Unfortunately, they are usually at least as well adapted to our farm systems as the perennial weeds are and they run through their cycle quicker than our crops and thus seed before harvest.
Plants have few opportunities to move. The best opportunity to move or spread is when they produce seeds and they have many mechanisms for getting seeds to move.
Some plants have ways to spread other than through seeds:
- HORIZONTAL runners cover a lot of ground for kikuyu grass, Pennisetum clandestinum, and couch grass/bermuda grass Cynodon dactylon
- CLIMBERS move up into trees and can move across and down to the ground to start new plants: Ivy, honeysuckle, jasmine and others
- Some plants grow to become huge clumps that droop to the ground and put down roots to get nutrients for the existing plant or to establish a new plant. One blackberry can take over a gully
Because plants have limited opportunities to move, this is often the easiest point to protect yourself from weed spread.
The points where you can beat weeds are:
- keeping weeds from arriving on your land
- removing existing weeds
- preventing weed seeds from germinating
- preventing weed seedlings from establishing
- preventing established weeds from seeding
- capturing weed seeds that are about to spread
If you can beat the weed at one or ideally at every one of these stages, you will have few weeds and weed problems.
Any weed infestation begins with at least a single seed or any other propagule — a part of a plant that is capable of developing into a full plant. If you can beat it when it is a seed, a seedling or before it has a chance to flower, you will only have a brief problem with it. If you allow it to set seed, it can turn into a major problem.
Remember that what matters is the relationships between things rather than the things themselves. If you can work out where the relationships fall down, you will find it easier to resolve the problem than if you focus on any single thing.
This table shows some
- Characteristics of the weed – what the weed has, does or is
- What these characteristics may mean for you (this varies from farm to farm) and
- Some approaches you could try that may assist you against the weed.
| Weed characteristic
|| What these characteristics may mean
|| Approach that may assist you against the weed
| Large numbers of seeds
|| Poor seedling establishment
Poor seedling survival
Low germination rates
| Make conditions (particularly competition) tough at germination and soon after
No bare ground around seeding and germination — maintain full Ground cover.
| Seedheads break off with multiple seeds attached
|| An effective method of dispersal with built-in insurance: If one of the seeds on the seedhead germinates but does not survive, there are several others that may when conditions are more favorable.
|| Use windbreaks to confine seeds to specific areas
Note: A windbreak need not be particularly tall, and it need not be permanent. It could just be a tall crop, such as corn (maize), to catch the seedheads and prevent them spreading
| Prickles on leaves or stems
|| The weed would be attractive to stock otherwise
|| Allow pasture to grow tall when the weed is starting to grow. The competition will beat some of the weeds. Others of the weed may survive by switching to upright growth and this usually means fewer prickles plus the weed will be softer and more palatable. A short hard graze at an appropriate stage may get rid of it
| Rosette at base
|| Weed is trying to commandeer nutrient, light and water, most likely for next year when it will seed
|| Vigorous crop or pasture may outcompete.
Allow pasture to grow tall when the weed is starting to grow. The competition for light will reduce the effectiveness of the large flat rosette at catching sunlight. The weed may survive by switching most of its effort to upright growth. A short hard graze at an appropriate stage may get rid of it
Make sure there are no bare patches
Grow a broad-leafed crop every few years
| Weed is tall compared to crop
|| The weed gets the light and shades the crop
|| Grow a taller crop, such as an older variety
| Weed grows from a crown or other underground store
|| Base of plant is providing nutrient to kickstart the aerial part
|| Exhaust reserves by hard grazing or slashing before any stem has returned the nutrient it took to grow it.
For example, if you slash blackberries before they get to about 1 m (3 feet) high, there is a good chance you will exhaust them, although it may take a few grazings or slashings
| Remains after hard grazing
Survives hard grazing
| Unattractive to stock
|| May need to graze the field hard to make the weeds stand out and then remove weeds individually.
You may be able to make the weed more attractive by spraying it with molasses or by providing some high protein feed such as lupins so animals can digest it
| Weed is able to get from a germinating seed to producing seed quicker than the crop is
|| Weed has quick lifecycle so it can reproduce even in a short season
|| Consider slashing the crop as a green manure or using it for grazing, silage or hay making before the weed gets to seed.
Grow a vigorous crop and beat the weed at its own game. Oats will beat most weeds or at least give them a run for their money. Plus it is well suited to taking the weed out by grazing or cutting the oats for hay.
Many oat varieties are suitable for grazing and regrowing to regraze as a Cut and come again crop.
So, if you let the oats regrow and conditions are right you’ll have a second chance at beating the weed by grazing or cutting the oats for hay. Then it might be time to sow a summer crop and have a third go at beating the weed.
If that is not suitable or sufficient, plant an out-of-season crop (a summer crop if the weed is in a winter crop and a winter crop if the weed is in a summer crop) and prepare the seedbed before the weeds get to seed.
| Weed is very vigorous
|| A tough competitor that needs an even tougher crop
|| Pick a suitable crop that can grow vigorously, preferably beating the weed at its own game.
For example, a vigorous variety of oats will beat most weeds or at least give them a run for their money. You may be able to take the weed out by grazing or by cutting the oats for hay.
Many oat varieties are suitable for grazing and regrowing to regraze. So, if you let the oats regrow and conditions are right you’ll have a second chance at beating the weed by grazing or by cutting the oats for hay. Then it might be time to sow a summer crop and have a third go at beating the weed.
| The weed looks and behaves in a similar way to your crop
|| The weed possibly evolved in a cropping system similar to yours
|| You will need to fine tune your management or find some particular weakness in the weed or strength in your crop.
For example, if you grow wheat or a similar winter crop and you have a problem with wild oats, you may have to delay sowing until the wild oats germinate. At this point, grazing, tillage or sowing the crop may kill a lot of wild oats.
You could also choose a tall variety of wheat that can outgrow the oats.
However, the best approach is probably to change crops and beat it with a suitable competitive crop that doesn’t match the weed’s patterns of growth.
| Weed has uses in other places
|| Weed may be an escaper from another farming or gardening situation and thus has had a positive value there, rather than being considered a weed
|| Take advantage of the uses it has in other farming or gardening situations by turning the weed into a benefit:
- Capeweed (Arctotheca calendula) is a very productive pasture plant and many a farmer in the south of Western Australia would be out of business without it. But it can give plenty of problems if you don’t manage it well.
- If you are willing to run goats, many thistles and woody weeds (blackberry, briar etc) make good grazing or browsing. Some goat farmers are willing to agist their animals on your property.
Applying this understanding of weeds
Pick a weed that matches well with one or more of the characteristics in the left column and check whether the middle column fits that particular weed in that situation on your farm.
If it does, then some of the approaches in the right column might work for you.