Tuesday, July 2, 2019

Dealing With Weeds At Harmony Valley Farm

By:  Richard de Wilde

“What we call a weed is in fact merely a plant growing where we do not want it.”
 —E.J. Salisbury, The Living Garden, 1935

Leeks after cultivation using "The Lilliston"
As organic farmers we do our best to understand and work with the natural world.  Nature is wise and knows the value of keeping soil in place and covered with plants which maximize each day of sunshine, capturing carbon and nitrogen from the air while exhaling oxygen that we need to live.  In nature, soil is never left bare to be wasted or eroded by wind and water.  Weeds have a purpose, and it really is a good one!  So why are we so set on killing and eradicating them from our fields?  Weeds can be very aggressive and can inhibit the potential of a crop by competing for sunlight and nutrients.  They impede our harvest efficiency and produce thousands of seeds which will haunt us for years.  Most weeds have accompanied agriculture from its beginning.  They moved around the world as early settlers brought their grain seed along with some tag along weed seeds and today they hitchhike with the global grain trade and then further spread by way of wind, animals, equipment, etc.

Potato field cultivated with "The Lilliston" 
Weed plants are very adaptive.  They can lie dormant in soils for 10-30 years, just waiting for their time of need to germinate.  Some weed seeds  only germinate at certain times of the year, such as in cool spring or fall temperatures.  Others are triggered in times of excess moisture, while others only germinate in summer heat or extreme drought.  Weed seeds are also triggered to geminate by exposure to light, usually caused by tillage.  Tillage is any disruption of the soil, which in our case could be cultivation or other work to prepare the soil for planting.  As the soil is stirred and disrupted, even just a flash of sunlight is enough to trigger some weeds to germinate!  In fact, I’ve read that in Europe some farmers even started cultivating at night to avoid triggering weed seeds!  Weed seeds may also be triggered by fertility needs in the soil.  Some weeds have the ability to correct soil nutrient deficiencies.  For example, if soil is deficient in phosphorus, a seed for a plant that has the ability to scavenge phosphorus may be triggered to germinate and grow.  As we try to minimize weeds in our crop, one thing we do is to provide balanced nutritional needs for the soil to prevent the need for weeds to correct the deficiency.

Cilantro:  Cultivated with "Basket Weeder" with shields & Kult Kress Duo.
There are really only two kinds of weeds, annual or bi-annual weeds and perennial weeds.  Annual or bi-annual weeds grow rapidly from seed, but only under the right conditions.  In order to thrive once they germinate, they need to grow and develop their green structures above ground to capture sunlight and utilize photosynthesis for energy.  When these types of weeds die at the end of the season, they are dead and won’t grow again.   Thus their main way to propagate themselves is to produce seeds that drop back into the soil and are available for a future season.  In contrast, perennial weeds survive from year to year and their main strength and the key to their survival is their underground root storage system which holds nutrients and energy.  When a new year rolls around, they don’t have to wait for the right conditions to germinate a seed and start photosynthesizing, rather they draw their energy from their roots.  The key to eradicating these types of weeds is depleting their root reserves.  Up until the plant is six inches tall, it is drawing its energy from its root reserves.  When it is about six inches tall, it starts utilizing photosynthesis to put energy back into the roots and replete the reserve.  One way we can battle this type of weed is to repeatedly mow it off when it is about six inches tall. This takes persistence, but after time the root reserves will be depleted and the plant will die.

Rafael using disc cultivator in the cilantro field.
By now you may be wondering if there is a silver bullet for weed control.  Valid question and one farmers have been asking for years.  In a recent article in Acres U.S.A. written by Anneliese Abbott, she commented about the onset of agricultural herbicide use.  “It seemed so easy:  forget about plowing…and just spray chemicals to kill the weeds.  No tillage, no erosion and no weeds:  what could be better?  Unfortunately, herbicides caused as many problems as they solved. They polluted water, harmed non-target organisms and sometimes posed a threat to human health.  Worst of all, they only worked well for a short period of time.  Weeds quickly evolved resistance to every major type of herbicide, forcing farmers to spray more and more chemicals with less and less success every year.”   Sadly, as organic farmers there is no easy way to deal with weeds.  Rather we try to understand how weeds work, the conditions they thrive in, and then we utilize multiple methods to kill them and prevent their growth.  Aside from the occasional use of 30% vinegar, chemicals are not our answer.  So lets talk about the methods and tools we can use.

New weed control technique:
Low growing cover crops between rows of melons.
One of our weed control tools is planting cover crops of grains, grasses and clovers.  If we can satisfy the need to cover the soil, there’s no need for dormant weed seeds to germinate.  It helps that most grasses and cereal grains, such as rye, also exude chemicals to inhibit other seeds from germinating.  Historically we have planted most of our cover crops in the fall, which can serve to prevent the growth of bi-annual weeds.  Bi-annual weeds germinate in fall, but do their growing in the spring.  If we can inhibit germination with a fall cover crop planting, we won’t have those weeds in our spring planted crop.  We are also perfecting a new and exciting technique we’ve developed for controlling weeds that grow in the space between the beds where crops are planted.  Immediately after preparing the beds, we plant two very fast germinating cover crop plants, creeping red fescue and white Dutch clover.  Both grow fast and inhibit weeds.  They are also short in stature, only 6 inches tall at most, so they do not compete with our crop for sunshine.

Using Flame Weeder to kill small weeds before crop emerges
We can also deplete the “weed seed bank” in the soil by triggering weeds to germinate, then killing them when they are small with very shallow cultivation or flaming.  We typically utilize this method before we plant the crop, but it requires us to prepare the beds one week ahead of planting.  Then, just before we plant, we “basket” the beds.  A “Basket Weeder” is an implement mounted on a small tractor.  It has horizontal wires that flip small weeds out as they roll across the surface of the bed.  We can also utilize a “Flame Weeder” to kill weeds that germinate and emerge after the crop has been planted, but before it comes up.  In order for this to work, the timing and conditions have to be just right.  The flame weeder is a tank of propane mounted on the back of the tractor with burners that carry just over the surface of the bed.  The flames burn the weeds off, thereby killing them.  If you flame too soon, you won’t maximize the number of weeds you kill.  If you wait too long, the crop may start to emerge and you risk burning off your crop.  We utilize flame weeding for crops such as cilantro and dill that we plant every week for over twenty weeks.  Typically we have to time the flaming about 4-8 days after the crop is planted, depending on temperature.  We also use this technique on carrots and parsnips and the difference between a crop that has been flamed and one that has not is dramatic!!  We have a significant reduction in weeds with timely flaming.  When we do get weeds in our field, it is critical that “bad” weeds to go to seed in the field or areas around our fields.  If they do, they’ll make a deposit into the “weed seed bank” that we’ll pay for in years to come!

Vicente using "The Lilliston" to "hill" sweet corn
We have a few more tools in our collection of things for weed control.  Sometimes we use a tool called “The Lilliston” which aggressively throws dirt in one direction and can be used to smother weeds by throwing dirt on them.  We use this to smother weeds within the rows of crops such as potatoes, leeks and sunchokes when the plants are big enough to get partially covered by dirt without damaging them.  Another tool we use is called a “Lely Tine Weeder.”  This tool has little tines that rake out very small weeds.  This is a more gentle tool and can be used on small transplants and fast growing crops that are direct seeded, as long as the crop is larger than the weeds.  The “Basket Weeder” is also extensively used with tunnel shields that we put on the implement to carry over the rows of crops to protect them from dirt flying into the row and smothering the crop when the crop is too small.  While this method preserves the crop and kills weeds in between the rows, it doesn’t do anything to remove weeds that are in the row.  Later, when the crop is bigger and can take a little more aggressive cultivation, we remove the shields.

Jaime and Felix G using "The Kult" in celeriac
In more recent years we’ve started using a steerable cultivator that we call “The Kult.”  It requires a team of two people to operate it.  One person drives the tractor and the other rides on the cultivator to steer the machine.  This tool is more effective at killing weeds within the rows of crops and it is indispensable at killing new weeds in larger, more established crops where we have to be careful not to disturb the crop’s root system or damage the plants.  It’s also adaptable and can be set up in a variety of ways to best meet our needs.  We have even more cultivating tools, but I think you can see we try to utilize mechanical options as they are our most efficient and cost-effective means of killing weeds.

Ascension using a hoe and his hands to remove weeds
in the strawberry field
We can also smother weeds by covering the soil with plastic or straw mulch.  Some of our crops are planted on plastic covered beds.  We use the plastic mulch for a variety of reasons, one being weed control.  As a last resort, when we’ve exhausted all other methods, we turn to old-fashioned hand weeding.  Yes, we do still do more than our fair share of hand weeding and this too is a skill.  We try to avoid weeding by hand because it is time consuming, but sometimes that’s the only option.

Will we ever kill all the weeds in our fields?  No, but the sum total of all our efforts will pay off this year and in years to come as we minimize the impact weeds have on our crops.

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