Whether you’re an organic or conventional orchardist — or anything in between — you need to know about the weeds that can harm your orchard and the various strategies for dealing with them before they take over. The best weed control strategy begins with knowing your weeds — the species, type (annual or perennial), location, and how they spread. Then, you can develop an integrated approach to preventing and managing citrus problems effectively in your orchard.
Why Weeds Are a Problem for Citrus
Having a little ground cover underneath your orchard trees isn’t always a bad thing. Certain herbs, legumes, and even cucumbers can provide a living layer of mulch, provide nutrients to growing trees, and encourage pollinator activity.
However, there are certain weeds that you simply don’t want growing in your orchard. These weeds compete with young citrus trees for nutrients and water and can provide a habitat for critters that you don’t want in your orchard — rodents, pathogens, and insects that cause the trees to become damaged or diseased.
Weeds to Watch Out For
The best weed control starts with knowing your weeds. If you simply try to kill or suppress anything that grows, you will not only create a toxic environment for pollinators, you might also cause an invasive weed species to spread even further. These are the main species that cause citrus problems in California, described with photos on the University of California website.
In California, there are three species of concern that have developed resistance to the citrus weed killer glyphosate. These species are:
- Horseweed (Erigeron canadensis)
- Fleabane (Erigeron bonariensis)
- Palmer amaranth (Amaranthus palmeri)
For these three resistant species, these are the best weed control options:
- Treat the weeds when they are still small.
- Use multi-action herbicides.
- Use the full label rate of herbicide application.
- Treat the targeted population as well as those adjacent to it, including roadsides and ditch banks so that the weeds don’t spread back into your orchard.
Aside from these basic guidelines, it’s essential to research the reproductive cycle of each species, how the timing of herbicides needs to coordinate with pollination, flowering, and the growth of fruit, and application methods that limit the spread of herbicides beyond the weeds.
Weed Species with a Long-Lived Seedbank
The next group of weeds that can be difficult to manage includes nutsedge (Cyperus esculentus and Cyperus rotundus) and Johnsongrass (Sorghum halepense). Johnsongrass seeds can remain viable in the soil for over five years and nutsedge spreads underground via tubers.
For both of these species, the best weed control strategy is to eliminate the weeds before planting out a new orchard. This can involve turning over the soil to expose the roots and seeds to the sun (and thus killing them) and/or using a citrus weed killer before the upcoming weeds have more than 5-6 leaves on the plant. Nutsedge is usually not a problem in established orchards because it doesn’t grow well in the shade.
Organic Methods for Managing Weeds
Organic growers often take an ecosystem approach to maintain a healthy culture on the orchard, and that means replacing invasive weeds with a more helpful species or suppressing their growth with mulch. For some growers, cover crops provide the best weed control with the least manual labor.
As mentioned near the start of this article, there are several different cover crops that you can grow to leave less space for weeds:
- Clover: Fixes nitrogen and attracts pollinators.
- Legumes like peas and alfalfa: Fixes nitrogen.
- Roman Chamomile: Useful in teas, doesn’t require mowing.
- Parsley: Nutrient-rich, edible annual.
- Cucumbers: Provides ground cover before the tree canopy grows, to shade the soil.
There is some concern that growing a cover crop between the rows might increase the risk of frost damage. Because of this concern, cover crops are recommended for the parts of California where temperatures don’t drop below 30°F or where the crops are harvested before frost damage is likely to become a problem.
The best weed control usually takes a multifaceted approach. In addition to (or instead of) cover crops, you could also try these chemical-free techniques:
- Implement an effective irrigation system that distributes irrigation water evenly.
- Ensure excellent soil drainage by improving the topsoil.
- Disk the areas affected by weeds.
- Remove larger weeds by hand.
Knowing about the citrus problems to watch out for can help you enjoy a healthier orchard and increase your yields. As we have seen, there are multiple approaches to the best weed control and which ones will be effective depends on your growing philosophy, location, and climate.
If you choose to use herbicides, please contact your local agricultural commission to find out which chemicals are approved, the timing of application, and how to protect surrounding crops (especially downhill crops), pollinators, and groundwater reserves from chemical damage. If you choose not to use herbicides, consider the pros and cons of the various strategies presented here.
As you prepare for another great citrus season, Fruit Growers Supply is here to support you with citrus weed killer, weeding tools, custom irrigation systems, and anything else you might need. Contact our team to plan for the best weed control in your orchard this year.