When Is the Best Time to Apply Post-Emergence Herbicide to Corn Seedlings? Detailed Guide to Methods and Precautions
As for post-emergence herbicides for corn seedlings, corn growers everywhere use them every year, but every year problems arise such as herbicide damage to corn and treatments having no effect. Sometimes, after applying a post-emergence herbicide to corn seedlings, the weeds do not die but the corn does, which gives farmers a real headache. So when is the best time to apply post-emergence herbicide to corn seedlings? How should it be applied? What precautions should be taken?
The best spraying time for post-emergence herbicide on corn seedlings
Because post-emergence herbicide for corn seedlings requires an absorption process of 2-6 hours after spraying, during these 2-6 hours, whether the herbicide works well (that is, whether the weed control effect is ideal) is very closely related to temperature and air humidity.
When spraying in the morning, at noon or in the afternoon of high-temperature, dry weather, because the temperature is high, light intensity is strong and the spray solution evaporates quickly, the solution will evaporate shortly after spraying, limiting the amount of herbicide that enters the weeds and making the absorbed amount clearly insufficient, thereby affecting the weed control effect; at the same time, spraying under high temperature and drought also makes corn seedlings prone to herbicide damage.
The best spraying time is after 6 p.m., because when spraying at this time, the temperature after application is lower and humidity is higher, the spray solution stays longer on the weed leaf surface, and the weeds can fully absorb the herbicide components, ensuring the weed control effect. Evening application can also significantly improve the safety of corn seedlings and make herbicide damage less likely.
How many leaves should corn seedlings have before post-emergence herbicide can be sprayed
The best period is when corn has 3 to 5 leaves and weeds are at the 2 to 4 leaf stage. In particular, a mixture of nicosulfuron and 2,4—D butyl ester must not be applied after the corn 5-leaf stage.
Spray when field weeds have basically all emerged and most weeds are at the 2~4 leaf stage. If the application period is too late, weed resistance increases and the weed control effect is affected. When spraying, the temperature should be 15~25°C, relative air humidity should be above 65%, and wind speed should be below 4 m/s. Select the spray equipment and nozzles as required and apply the herbicide according to the standard spraying operation specifications.
How to apply post-emergence herbicide to corn seedlings for good results
Let me tell you a method summarized from actual spraying practice: on the premise that the pesticide dose is sufficient, the more water the better (of course this does not mean adding water without limit, relatively speaking). For example, if you buy a herbicide, the recommendation is 1 bottle per 1 tank of water per 1 mu of land, that is, dilute with about 15 kg of water and spray it over 1 mu of land. But if you dilute it with 20-25 kg of water and also spray it over 1 mu of land, the effect will be somewhat better than with 15 kg of water.
To put it more plainly, change 1 bottle, 1 tank of water, 1 mu of land into 1 bottle, 2 tanks of water, 1 mu of land. Friends who are interested can try it, but note that the spray volume must be uniform, and there must never be a situation where one patch gets more and another gets less.
Look at weed size
When spraying post-emergence herbicide on corn seedlings, many farmers have a misunderstanding: they think the smaller the weeds, the lower their resistance and the easier they are to kill. In fact, this is not so, because if the weeds are too small there is not enough leaf area to receive the herbicide, and the weed control effect is also not ideal. The best weed age is from the 2-leaf 1-heart stage to the 4-leaf 1-heart stage. At this time the weeds have a certain area to receive the herbicide, their resistance is not great, and the weed control effect is significant.
Corn variety
Because most post-emergence herbicides for corn seedlings now contain nicosulfuron, and some corn varieties are sensitive to this component and prone to herbicide damage, corn fields planted with sweet corn, waxy corn, Denghai series and other varieties must not be sprayed, to prevent herbicide damage. For new corn varieties, please test first before extending them.
The issue of pesticide mixing
Within 7 days before and after spraying post-emergence herbicide, it is strictly forbidden to spray organophosphorus insecticides, otherwise herbicide damage is likely to occur. However, it may be mixed and sprayed with pyrethroid and carbamate insecticides. When spraying, try to avoid the heart leaf as much as possible to prevent the spray solution from pouring into the heart.
This year, Swedish fly and thrips occurred severely in some corn fields. To control these two small pests, imidacloprid or acetamiprid can be used to spray the heart leaf, but when spraying, do not mix them with post-emergence herbicide either, even though imidacloprid or acetamiprid are not organophosphorus compounds.
Because controlling these two small pests requires spraying the heart leaf, if mixed and used to spray the heart leaf, herbicide damage is likely to occur. They can be sprayed separately: spray the post-emergence herbicide in front, and immediately follow behind with imidacloprid or acetamiprid to spray the heart leaf.
The resistance of the weeds themselves
In recent years, because the stress resistance of weeds themselves has strengthened, in order to prevent excessive evaporation of water from within their bodies, weeds do not grow so lush and sturdy, but instead grow grayish-white and short, and their actual weed age is not small at all (the so-called “little old men”). Most of these weeds are covered all over with small white fuzz to reduce water evaporation.
In this way, when pesticide is sprayed, the spray solution is held up by these small hairs above the surface of the weed stems and leaves, and the weeds themselves absorb very little, which naturally affects how well the pesticide works. Therefore, under high temperature and drought, no matter what pesticide is applied, the amount of spray solution should be increased so as not to affect the pesticide effect. Farmer friends, when applying pesticide, please do not be stingy with water or with pesticide.
Precautions for using post-emergence herbicide on corn seedlings
1. Spray at the normal concentration according to the prescribed dose; do not arbitrarily increase the dose.
2. Use the “secondary dilution method”: first prepare a stock solution, then add water and spray evenly.
3. Generally, the suitable period for using post-emergence herbicide on corn seedlings should be after the corn shows 2 visible leaves and before it shows 5 visible leaves. If applying at the 5~7 leaf stage, it should be used between the corn rows to avoid spraying the solution into the heart leaf.
4. Some post-emergence herbicides for corn seedlings are relatively sensitive to sweet corn, seed production fields and inbred lines, so do not use them. Use strictly according to the herbicide label instructions.
5. Corn treated with organophosphorus pesticides is sensitive to post-emergence herbicide. The interval between the two pesticides should be at least 7 days.
6. When using a motorized sprayer to apply pesticide, do not increase the dose without authorization, and repeated spraying is prohibited.
7. Before using herbicide, be careful to clean sprayers that have been used for organophosphorus pesticides.
8. Applying pesticide after 4 p.m. gives good results; avoid applying pesticide during continuous high-temperature weather (temperature above 35°C).
If it rains after the corn herbicide is applied, should it be sprayed again the next day?
First, we do not recommend spraying post-emergence herbicide a second time.
So some farmers, afraid the weeds will not die, want to spray a second time. What should they do?
1. It rains immediately after the pesticide is applied.
2. Heavy rain or torrential rain lasting a very long time.
3. After 3-5 days for broadleaf weeds and 5-7 days for grass weeds, there is still no sign of poisoning, and the corn is also growing normally.
If the above 3 points are met, it can be sprayed once again.
Conversely:
1. The rain is not heavy and lasts a short time.
2. It rains after 6 hours of spraying the post-emergence herbicide on corn seedlings.
3. The weeds already show signs of poisoning.
If the above 3 points are met, then re-spraying is not recommended, to avoid herbicide damage.
Some friends may say, if I do not meet the above conditions, but when spraying the second time, I do not spray the corn, only the weeds, with directed spraying, is that okay?
Answer: Of course that is definitely okay!!
The above article has introduced in detail when it is safest to apply post-emergence herbicide to corn seedlings, how to apply it, what precautions there are, and other related information. In addition, a reminder to everyone: when applying herbicide under high-temperature weather, be sure to pay attention to your own safety and never let heatstroke occur.