You spray a herbicide with enthusiasm, then two weeks later find the same weed as green as before, or find neighboring crop leaves yellow and scorched. In both cases the problem is usually not the product but its selection: the weed type was not identified, the timing was wrong, or the product is not registered for the crop. Weeds compete with the crop not only for space but for water, nutrients and light, and may harbor insects and diseases and cut yield, but treating them wrongly may cost more than they do. In this guide we explain weed types, the difference between selective and non-selective, when a herbicide is used pre- or post-emergence, how to avoid damaging neighboring crops or soil, and how to delay resistant weeds.
In this guide we explain the types of weeds, the difference between selective and non-selective herbicides, when to apply a herbicide before or after weed emergence, and how to avoid damaging neighboring crops or the soil through incorrect use.
Weed types: broadleaf weeds, narrow-leaf grass weeds, and perennial root weeds that regrow from roots and rhizomes.
Selective: targets a group of weeds without harming the registered crop, so it can only be used where the label says so.
Non-selective: kills most plants it touches, so it is used on paths and bare ground, or with careful crop protection.
Common mistake: spraying in wind or on a crop the product is not registered for, which injures and damages nearby plants.
The rule: identify the weed first, then choose the herbicide and timing, and always follow the label.
How do you identify the weeds in your field?
Look at the leaf shape: broadleaf weeds have net-like veins similar to vegetable leaves, while grass weeds are narrow with parallel veins like turf grass. Weeds also differ between annuals, which finish their life cycle in one season, and perennials, which live for years and need a longer program.
Pre-emergence vs. post-emergence herbicides
- Pre-emergence: applied to the soil before weeds appear to prevent germination. It usually needs moisture to move into the top soil layer.
- Post-emergence: sprayed on growing weeds. It works best when weeds are young and actively growing.
- A systemic herbicide moves inside the plant down to the roots, while a contact herbicide only burns the parts it touches.
An integrated weed control plan
1) Prevention
- Use clean seeds and seedlings, and avoid moving soil or uncomposted organic manure that carries weed seeds.
- Use mulch or plastic cover between rows to reduce germination.
- Clean tools and machinery when moving between fields.
2) Mechanical control
Early hoeing and hand pulling work well on small areas. The key is to remove the weed before it sets seed, because a single weed can produce a large number of seeds.
3) Chemical control
Choose the herbicide according to the crop, the weed and its growth stage, and calibrate the sprayer for even coverage. Avoid spraying in strong wind or right before rain, and follow the dose and safety intervals stated on the label.
4) Follow-up
Check the results after a few days, and rotate chemical groups from one season to the next to delay the appearance of resistant weeds.
Common mistakes
- Using a non-selective herbicide next to a sensitive crop.
- Spraying after weeds have matured and produced seed.
- Using the same sprayer for herbicides and other pesticides without washing it thoroughly, which later damages the crop.
- Ignoring the waiting period before planting a new crop in the treated soil.
Why Do Weeds Become Resistant?
Repeating the same herbicide season after season kills sensitive weeds and leaves less affected individuals to multiply and dominate. To delay this, rotate the chemical group between seasons per the label, combine mechanical and chemical control, and do not rely on one product for years. If you notice one weed type remaining after spraying while others died, it is an early sign of a resistance problem.
Spraying Conditions That Decide the Result
Calm weather and moderate temperature are best: wind carries spray to neighboring crops, and extreme heat evaporates droplets before absorption. Avoid spraying right before rain, and spray when weeds are actively growing. Calibrate the sprayer and nozzle for even distribution, using our spraying equipment and calibration guide and the sprayer types guide. Dedicate a sprayer to selective herbicides if possible, or wash it thoroughly between uses.
Weeds in Farms and Gardens Here
In palm farms and orchards, weeds grow between trees and compete for water, and under drip irrigation they concentrate around emitters. In home gardens and lawns a selective herbicide that does not harm grass may be needed. Use shielding when spraying near young trunks, and take care that a non-selective herbicide does not touch green leaves.
Safety and the Environment
Wear gloves, a mask, goggles and skin-covering clothing, and keep children and animals away from the treated area until the period written on the label ends. Do not pour leftover solution into water channels or near wells, wash tools away from water sources, and read the label carefully before every use.
Available control products
In the agricultural pesticides section you will find products from well-known brands, and suitable spraying equipment in the agricultural equipment and sprayers section. Check the label to confirm the product is registered for your crop, and consult a specialist before use.
Frequently asked questions
What is the difference between a selective and a non-selective herbicide?
A selective herbicide targets a group of weeds without harming the registered crop, while a non-selective herbicide affects most green plants it touches.
When should I spray a herbicide?
When weeds are small and actively growing, in calm weather with no strong wind and no rain expected right after spraying.
Why do weeds come back after spraying?
They may be perennial root weeds whose roots the herbicide did not reach, or new seeds may germinate from the seed bank in the soil.
Does the herbicide harm the next crop?
Some active ingredients stay in the soil for a while, so check the label for the waiting period before planting a new crop.
Is hand hoeing enough?
It is enough on small areas if done early and repeatedly; on larger areas it should be combined with a suitable herbicide.