Weeds are plants growing in the wrong place, which compete with the trees of interest for growth factors like moisture and nutrients. Some weeds are also alternate hosts of diseases, nematodes or insects pests. With this, it is therefore very important to keep the area under the canopy free of weeds.
Interference from weeds also causes labour inefficiencies, for instance, tall weeds at harvest, discomforts from allergies e.g. ragweed or skin irritations from stinging nettles, among others.
Common orchard weeds
A wide range of weeds (broadleaf or grass, annual or perennial, etc.) grow in orchards, and their population is highly variable depending on several factors like soil type and the type of trees.
They include;
| Broadleaf weeds | Grass & Sedge weeds |
| Blackjack (Bidens pilosa) | Couch grass (Digitaria spp) |
| Pig weed (Amaranthus spp) | Crab grass (Digitaria spp) |
| Sow thistle (Sonchus oleraceae) | Barnyard grass (Echinochloa crusgalli) |
| Mexican marigold (Tagetes minuta) | Nutsedge (Cyperus spp) |
| Devil’s thorn (Emex australis) | Wild oat (Avena fatua) |
| Thorn apple (Datura stramonium) | Johnson grass (Sorghum halepense) |
| Macdonald’s eye (Galinsoga parviflora) | Bermuda grass (Cynodon dactylon) |
| Black jack (Bidens pilosa) | Star grass (Cynodon spp) |
| Nightshade (Solanum nigrum) | Guinea grass (Panicum spp) |
| Oxalis (Oxalis spp) | Goose grass (Eleusine indica) |
| Thorn apple (Datura stramonium) | Sweet buffalo grass (Panicum schinzii) |
| Gallant soldier (Galinsoga parviflora) | Winter grass (Poa annua) |
| Double thorn (Oxygonum sinuatum) | Italian grass (Lolium multiflorum) |
| Purslane (Portulaca Oleraceae) | Rye grass (Lolium spp) |
Why is proper weed control in orchards important?
- Weeds directly compete with the fruit trees for growth factors like nutrients, space, and water. This makes the plants weak and susceptible to attack by pathogens.
- Weeds greatly reduce crop yield as well as its general performance.
- They harbor pests and diseases.
- Weeds that present late in the season cause severe harvesting problems.
- Some are parasitic, others are harmful when eaten by livestock.
- Some weeds are allelopathic and can cause damages to the trees by producing toxic substances (allelochemicals).
- Generally, plants in wrong places look ugly.
What is the benefit of early/timely weed control?
- It eliminates competition for light, nutrients and moisture, giving the trees the opportunity to establish well.
- It protects the nutritional potential of the fruits.
- It protects the yield potential of the trees
- It substantially curtails opportunities for pests’ establishment in the crop
- Young weeds are easier to control, e.g., they absorb and translocate herbicides better
Management & Control
Proper weed control is very crucial for improved quality and quantity produce (fruits). The following are the most commonly used management/control methods;
- Cultural methods
They include the following;
- Pulling/uprooting weeds before seed setting
- Using irrigation water that is free from weed seeds
- Mulching
- Mowing
- Weed flaming
- Felling the unwanted tree
- Slashing
- Mechanical Control
This involves the use of tools and equipment like jembes, spades, hoes, rakes, pangas, ploughs, among others, in weed control.
It should be done carefully in order to avoid damages to the shallow feeder roots or the trunk. Wounds promote penetration of pathogens which cause infections.
- Chemical method
This method involves the use of herbicides and is highly preferred because;
- It is a fast and an easy method
- There is no mechanical damage to the crop.
- It is cost effective
The following herbicides are recommended for use in orchards;
| Name of herbicide | Active ingredient | Mode of action | Application rate |
| Catapult® 480SL | Glyphosate – isopropyl ammonium 480g/L | Broad spectrum non-selective herbicide with enhanced systemic activity, which controls post-emergence broadleaf and grass weeds.
| 200ml/20L |
| Hurricane® 200SL
| Paraquat dichloride 200g/L | Very fast-acting broad spectrum non-selective herbicide with enhanced contact action which controls post-emergence broadleaf and grass weeds | 200ml/20L
|
| Forester® 150EC
| Fluazifop – p – butyl 150g/L | Highly selective systemic herbicide with fast contact action that effectively controls post-emergence annual & perennial grass weeds
| 50-75ml/20L |
| Deacon® 600WDG | Hexazinone 132g/Kg + Diuron 468g/Kg | Broad spectrum selective herbicide with enhanced systemic action that controls a wide range of broadleaf, sedge and grassy pre& post-emergence weeds.
| 100g/20L |
Tips!
- It is advisable to mix the herbicide with Integra® 3ml/20L, an adjuvant which improves the efficacy of the chemical by acting as a sticker, spreader and penetrant.
- Herbicides should be diluted with clean water.
- An integrated weed management strategy is highly encouraged.
- Equipment used in spraying the herbicides (e.g. knapsack sprayers) should be cleaned immediately after use.
