Controlling weeds in green beans

Given the high cost of labour, using chemicals is the only realistic option for weed control in most crops.

Good weed control in beans usually requires two different herbicides.
Photo: Bill Kerr

Green beans are no exception. A few registered products, and several unregistered ones, are available for beans. Most of these are for dry beans (belonging to the same species) as fewer varieties of dry beans are planted on much larger areas. The chemical companies do not see the market as large enough to justify the huge investment in registering them for green beans as well.

Take care, however, when using these products for green beans. Some green bean varieties mature very early and are more vulnerable to some herbicides. In addition, with the many green bean varieties coming onto the market today, chemical companies cannot ensure that their products are safe for all varieties.

In most cases, due to the number of weed species that exist, you will have to use two products for complete weed control. It stands to reason that if a single product could control all the weed species, it would most likely harm the bean crop too.
Over the years, I have found the following products to be effective:

  • Stomp and Treflan: Where there is no nutgrass, I use a pre-emergence application of Stomp at 1l/ha. This must be followed immediately by an irrigation. In the past, I also used Treflan as a pre-plant application (followed immediately by incorporation), but found that Stomp is more convenient to apply.
  • Eptam Super: For red nutsedge, I apply Eptam Super, which also has to be incorporated into the soil within minutes of application. Both Eptam and Stomp are more effective in controlling grasses than broad-leaf weeds.
  • Dual: If you have a problem with yellow nutsedge, Dual is a useful alternative. It must be applied early, however, not when the nutsedge is halfway from the bulb to emergence. Usually, a thorough tillage is necessary for the herbicide to be effective. Dual is effective against grasses and will control only some of the broad-leaf weeds. It is not effective against red nutsedge. It can be leached into the soil by irrigation soon after application.

The above products are mainly grass herbicides, so there will still be a broad-leaf problem. This is where the following herbicide comes into play.

Basagran
This product is registered to control broad-leaf weeds and suppress yellow nutsedge when applied at the full development of the first trifoliate leaf. The rate is about 3l/ha. Basagran has some disadvantages. In hot, dry weather, it kills the smaller weeds and merely sets back the larger ones. In cooler, wet weather it suppresses the crop slightly.

Tapered nozzles
After some trials, I made up a knapsack boom with two nozzles positioned in the middle of the two rows sprayed. I would spray at the early emergence of the second trifoliate leaf. At this stage, all the weeds are small enough to be controlled under any conditions.

I would calibrate my sprayer to apply only 1l/ ha. Using Teejet tapered nozzles, I would position the height so that the edge of the spray would just touch the dicotoledenous leaves only. Tapered nozzles apply less product at the edges, as this allows for overlap when positioned on a boom. With this small amount touching the plant, and only a small part of the plant at that, there would be no detrimental effect on the beans.

One 20l knapsack should cover 0,1ha. It goes rather quickly, so I suggest using one-third of the product. By doing this, you will save far more than the cost of the labour. The control is also much better and the risk of plant damage is virtually eliminated.

Spray pure water at a comfortable walking speed and see what area you cover. Then calculate how much herbicide to apply to each tank. This can also be done, albeit with some difficulty, with a boom, especially where GPS planting is used on very level soil.