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Mechanical weed control highlights

Author: Natalie Hoidal, Extension horticulture educator. 

This week I (Natalie) attended a mechanical weed control field day in Eastern Wisconsin. This is an overview of some of the tools that were highlighted and some reflections from the day. One of the most exciting things about mechanical weed control is that these tools are available on multiple scales, and there's a lot of room for mixing and matching. For example, finger weeder is an appropriate tool for a small-scale diversified farm using a two wheel tractor or even a wheel hoe, as well as field crop systems with much larger tractors. You also don't have to choose just one type of attachment - it's often more effective to attach multiple tools to your toolbar to achieve multiple functions (between row weed control, within row, deeper-digging attachments as well as those that just scratch the surface).

General tips for mechanical cultivation

  • Do it early and often. Mechanical cultivation is most effective when weeds are at the white thread stage. Many growers will cultivate every 5-7 days at the beginning of the season, and slow down as canopy cover improves. 
  • No one tool is a silver bullet. Just like you wouldn't use the same hoe for every task, having a few different cultivation attachments gives you versatility for weeding in different situations. 
  • Stacking tools (using multiple tools) is key. More aggressive tools like sweeps can be used within 2 inches or so of your crops, and will uproot larger and more aggressive weeds. Following a sweep with a less aggressive tool like a tine weeder or a more precise tool like a finger weeder can give you good between and within row weed control. 
  • Using a stale seedbed can improve the efficacy and efficiency of mechanical cultivation. 

What is a stale seed bed? 

Before talking about different equipment types, I want to talk about the concept of a stale seed bed. This technique is really important for organic weed control, especially for direct seeded crops, and will make the tools listed below more effective. Tilling the soil in the spring brings weed seeds to the soil surface. If you plant at the same time as you till and prepare your beds, your seeds will emerge at the same time as many of the weed seeds, leaving you with fewer options for management. By preparing your seed bed and waiting a week or two before planting, you're allowed a window of time where a shallow cultivation pass or using a flame weeder will allow you to remove germinating weed seeds before your crop seeds have emerged. The longer you're able to wait, the more weed seeds you'll be able to germinate before planting. This of course can be challenging in wet years like 2019, but it's something to strive for when possible.

False and Stale seed bed diagrams. Click on images for larger, clearer versions. 

Finger weeders

I asked quite a few farmers and other attendees "If you could only use one mechanical weed control tool for the rest of your life, what would it be?", and nearly everyone said they'd choose finger weeders. Finger weeders are made of soft polymer materials and consist of multiple "fingers" around a metal wheel (see below). As you move through the rows, they rotate, and the "fingers" lightly scrape the top layer of soil to uproot small weeds. Finger weeders are most efficient (as are all mechanical weed control tools) when weeds have just emerged. Ideally you'd use a finger weeder when weeds are at the white thread stage. They provide nice in-row weed control without scooping too much soil on top of young, fragile plants. Most people said that on a smaller-scale farm (~5 acre or less), the finger attachments shouldn't need to be changed more than every couple of years. Finger weeders are available in a variety of sizes and range from soft to hard plastic. You can adjust the spacing as well as the angle to accommodate crops as they grow.

Since finger weeders are usually soft, they don't always easily dig into the soil, especially in heavy or compacted soils. As such, it's common to use a side knife or spyder attachment in front of your finger weeders to break up the soil a bit and create a "shelf" that the finger weeders can get underneath (see photos below). Side knife attachments are the most common, but in situations where you have a lot of organic materials (sticks, un-decomposed plant debris), they may pick up and drag materials through the field. In such cases, a spyder attachment may be a suitable alternative.
Finger weeders with side knife attachments in front. 
Finger weeders (left) with spyder attachments in front. 

Basket weeders

While basket weeders do not provide within-row weed control, they are an excellent between-row weed control option for crops like head lettuce, where you want to completely avoid heaping dirt into your rows. They are also often used in conjunction with finger weeders to provide between-row weed control.

Tine weeders

Tine weeders are great for cultivating a stale seedbed, and for use when crops become slightly larger (think 3-4 leaf stage or larger) and sturdier. In a stale seedbed, they lightly scratch the surface and provide good soil coverage to uproot small weeds that have just germinated. However, when your crops are small, especially direct seeded crops, this tool is a bit less discerning than some of the others and you may end up uprooting your crop. We watched a demonstration of a tine weeder in a field of beets that were ~2.5 inches tall, and while some appeared to be fine, quite a few were uprooted. This is one way to thin your beets while eradicating weeds, but may not be the most precise approach... That said, when your crops have developed slightly deeper root systems, this can be an effective tool, especially for crops like beets or carrots with strong taproots.

Sweeps and knives

Sweeps and knives are some of the most rudimentary, yet still very effective cultivation tools. They essentially consist of small shovels that you can attach to your tool bar. They come in different shapes and sizes, and can be set to different depths. They work like a standard hoe, and can get a bit deeper and cut through more compact soil than some of the other tools. This means that they are more effective than other tools in compact or heavy soil, as well as on larger weeds.

More shoveling action, means you’re more likely to bury plants, so these are most suitable for between row weed control. However, sometimes you may actually benefit from the hilling effect. If crops are larger and sturdier, the hilling action can actually bury weeds within the row.

These tools will often be used between rows in conjunction with finger weeders for within row cultivation. If you scroll up to the finger weeder section, you'll see a photo where the farmer has put three different tools on their tool bar: they have sweeps between the rows for more aggressive between-row cultivation, knives next to the rows to break up compaction and create a soft "shelf" surface for the finger weeders, and finally finger weeders for within-row weed control. 

Manual approaches

Some farmers in Minnesota have invested in weeding systems that require a person to sit behind a tractor and manually maneuver a set of vertical tines (e.g. the ECO Weeder). These systems are very practical for a few specific purposes: The more mechanized tools above require straight rows, whereas the maneuverability of the ECO Weeder makes it more forgiving. If a plant is out of place you can move the tines out of the way so as to not hit your crops. Additionally, for vining crops like pumpkins, this type of cultivation tool may allow you an extra cultivation pass without damaging your vines. For straight rows and early season weed control, maneuvering these machines is tiring work and requires an additional person compared to the other tools listed above, which only require a tractor (or wheel hoe) operator.

Stacking tools

No tool is a silver bullet. Your choice of cultivation tools will depend heavily on your soil type and the types of crops that you're growing. In general, using multiple approaches (multiple cultivation tools as well as techniques like stale seed beds and flaming) is going to be your best bet. For a more comprehensive overview of these tools, see the SARE publication Steel in the Field. 
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