Well, there are many reasons that make the weed control not effective. One of them is the time for spraying. Usually, the ideal time is early in the morning when the winds is not blowing.
Besides, factors such as season, weather, temperature and other things also take into account the herbicides efficacy.
Below is all the information about Best time of Year and Best time of Day to spray Weed killers, as well as best weather, and best temperature for an effective herbicide application.
Table of Contents
*This post may have affiliate links, which means I may receive commissions if you choose to purchase through links I provide (at no extra cost to you). As an Amazon Associate I earn from qualifying purchases. Please read my disclaimer for additional details.
Best time of years to spray weed killers?
Spring and fall are the two best seasons to spray.
The early spring
In this time, A pre-emergent spraying is an effective way to prevent unwanted weeds before they start. This will help control the germination of the seed. Hence, if the weed has already sprouted and is visible, pre-emergent spraying will be useless.
After 8 weeks, it is time to apply a post-emergent spraying. This is to destroy the hardier. Remember that it is more successful and beneficial to kill young and immature weeds.
Weeds are in storage mode and preparing for winter. They will be vulnerable at this time. So, hit them by a post-emergent herbicide will let them little surviving chance in the cold weather.
If you see the weeds are not wilting immediately, do not panic. It takes time to kill them. Be confident that a majority of them will not come back in the upcoming springtime. The best month to do this is October. You can spray 2 times with 2 weeks apart.
Besides, you can also spray in late summer before the weeds knock down their seeds. If the seeds land on the ground, new weed generation will grow. This spraying time can prevent them from spreading.
Also, it is important to identify the type of weed you are trying to kill. Choosing the wrong herbicides will waste your time and money.
Best time of day to spray weed killers?
Time of day can affect the effectiveness of spraying. The best time of day to spray weed killers is peak plant grow times during the day. Over the day, plants can grow fast or slow depending on light level, temperature and local clime.
1. Warm climate
In summer, in early morning and late afternoon, it is warm and not too hot, which is suitable for weed to grow fast. So, it is best time to spray.
You should not spray around middle or early afternoon – the hottest part of the day. At this time, the plants will grow more slowly, and therefore will absorb less herbicide. Also, the sun and hot will dry out herbicide on the leaves, which reducing the amount absorbed.
In winter, you can still spray if you want as the weeds often continue to grow. But this time, best time is the middle of the day when it is warmer.
2. Cool or cold climate
In summer, unlike the warm climate, the spraying now should be done in late morning, middle, and early afternoon. From dusk to the following morning (before sunrise), plants are less active.
Also, do not apply herbicide if you see dew on the leaves. If not, the spray will run off or it will become too diluted and hence, reduce the effectiveness. So, it is better to wait until dew has evaporated.
In winter, it is often covered by snow. So, it is good to tread weeds.
In fall, you can spray weeds during the warmest part of the day.
Best weather to spray weed killers?
Weather is also a factor that contributes to the effectiveness of the spraying. So how to treat with different types of weather?
It should not be too windy unless you want the spray to drift off the target. Usually, wind speeds which greater than 15 km/h can cause a loss of herbicide during spraying.
Drift is something you really need to avoid as you are more likely to inhale the herbicides fumes when spraying. This cause damage to your respiratory system. Moreover, drift is sometimes illegal.
Usually, in the morning and evening, the wind is calmer.
Following are things to consider in windy conditions:
- Read the herbicide label. It may indicate maximum wind speed to be allowed.
- Use methods to reduce drift, such as: using drift-mitigating nozzles, larger droplets, low nozzle height, slower forward speed, etc. But, remember no current method can eliminate drift.
- Do not spray if the wind blows faster than the speed you are spraying. You may contact the drift when spraying with the wind is behind.
- If there is a temperature inversion, drift can also be a problem in light winds.
- You should know the wind direction where the spray will drift. This can be an advantage for you in high wind.
- Sometimes, it is worth to spray in strong wind. For example, if you intend to spray a selective herbicide in wheat and down-wind there is another wheat field, spraying will be probably safe in strong wind.
Rainfall shortly after spraying can wash all the chemical off your plants before it has worked (a waste of money). What is worse, the chemical may end up in a local river, which can pollute the environment.
Allow at least 24 hours to let the rain dry. If raindrops are still on the leaves, you will need to wait more. If you plan to spray, remember to check the weather forecast to choose a suitable day.
If your area often receives a great deal of rain, there are certain weed killers which are rain fast in 2 to 4 hours of spraying. You can take this into consideration.
3. Extreme heat or cold
If it is too hot or cold, the herbicide will not be effective. Also, the weeds will not absorb the chemical as usual.
Besides, if it is too hot, the herbicide liquid can evaporate quickly before it is absorbed. Meanwhile, if it is too cold, it will freeze.
Best temperature to spray weed killers?
Well, herbicides usually have the best performance when the temperature is from 60 to 75ºF. This temperature range should not fluctuate for a few hours afterward.
If the temperature is under 60ºF, weeds will grow slowly, which leads to slower chemical absorption and translocation. This mean the onset of symptoms and herbicide efficacy will be slow.
If the temperature is under 40ºF, avoid spraying systemic herbicide such as glyphosate. Moreover, under cloudy conditions (and also below 40ºF), weed control should not be applied.
If a severe frost is forecasted after an intended weed-killer application, you also should not spray. If weeds are under stress, the efficacy of herbicide will drop.
It is best to wait for better weather conditions to come. However, for some conditions that your plans need treatment now, be careful in choosing herbicides that are best killer for the targeted weeds.
Sometimes, killing weeds just likes a chore which has no ending. They are just noxious and so frustrated to destroy.
Knowing what factors contributing the herbicide effectiveness as well as best time of year, of day, best temperature to spray weed killers, … is a good plan for success. Hope you will enjoy your garden and field throughout the year.