A good spray programs is not rocket science, and it shouldn’t be. There are millions of successful farmers around the world that get it right without having an agricultural degree. Pest management or pest control is about logic and simple easy to follow principles. It also requires you reading the instructions, not only of the chemicals, but also your equipment and understanding your crop.

Good spray program principles are as follows:

Always wear protective clothing

It does not matter how good or bad your spray program is, the danger of these chemicals stay the same. At the bottled concentrations, they are so toxic they can kill you even in small quantities! If these chemicals don’t kill, they can permanently harm you. Even if you don’t ready this article further, get the best protective clothing possible and keep it updated. Don’t use protective gear that have holes, cracks or don’t fit properly.

Just to get the dangers into perspective, you can read the article where Beyer has to pay nearly $2 billion in compensation due to the cancer risk of glyphosate herbicides.

Follow the instruction manuals

If you are in the habit of not reading instruction manuals and think you know how to do things, this will be the one time that you must forget that attitude. With chemicals that can kill you, you must read the instruction manual, not once, but a couple of times.

I am inclined not to read instruction manuals, but when it comes to things that are harmful to my health, I read them very carefully. It perplexes me that there are farmers that do not follow the instructions even if all the information is available. Would you dismantle a bomb without reading the instructions first? I guess not, apparently there are some that do.

Know the pest or pests you want to control

Never spray for the sake of spraying. Never spray just because you thought you saw insects flying around the land. There are good insects and problematic insects. Predators are good and plant feeders are ‘bad’. It is only the plant feeders that a grower must control and kill, not the predators since they eat the plant feeders for free.

If you spray the wrong pesticide it might not kill the right insect and you have wasted a lot of money. Not only that, you could also kill off most of the predators that control a lot of plant feeders. Now you have double the trouble as in a few days the number of plant feeders can grow exponentially compared to the past. This will cause more damage, lower marketable yields and higher cost to control them.

If you don’t know what pest is causing the problem ask your local chemical supplier. They are trained to identify the problem and advise you on the right chemical and or spray program for you specific crop.

Focused disease and pest control, even on a large scale saves a lot of money, but the equipment can be expensive

Know your target and the target area.

Don’t confuse the target with the pest and the target area with the crop or land. They are not the same thing but are very much related. The concept is best explained by the two images below. (Just a small disclaimer, the black and white image is edited just to clarify what I am trying to say, but the technology used is real and with software gives the same effect.) Plants under stress emit a different infra-red spectra (or colour range) than the plants that are healthy. It is possible to identify the infra-red range that specific crop emits with a specific insect infestation. Once that’s done, you can clearly see where the insect hotspots are, which is indicated by the read areas. That is also the target area of your spray program. There is no need going to other areas since the specific insect (the target) you want to control is nearly absent.

Infra-red technology is very expensive and is used on very big farms with big budgets. The same information can be gathered by scouting at least once a week.

Interestingly, the plant feeders (i.e. the insect that you want to control), is also found in high concentrations on neighbouring fields. This means, for effective control, you have to spray the field adjacent as well. That is why it is so important to grow plants between fields that attract predators as well as plant feeders. The plant feeders are lured by specific plants and their predators are close by for a good meal. Certified organic growers use this method extensively as they are not allowed to use harmful chemicals.

Image of a farm land using a drone with normal camera.1)Image by Pexels from Pixabay
Image of a calibrated IR image taken by a drone with Infra-red camera. Red areas show the insect infestation which represents the target area of the spray program.

The target area for fungicides and pesticides can differ. In most cases, the target area for fungicides are the leaves, so that’s easy. Pesticides are a little different since you get contact, stomach and systemic pesticides. A contact insecticide must be applied on the insect or on areas where the insect will come in contact with. Stomach insecticides must be applied on the areas on which the pest feeds and systemic insecticides must be applied on the whole plant so that it can be absorbed from an early stage.

When plants are young, spray a systemic formulation that will last a long time in the plant and control pests, fungi and bacteria. When the plants are older, use contact and stomach formulations to control pests.

Choose the correct product for your target(s)

The right choice of pesticide or fungicide depends on your spray program’s history. Choosing formulations on the spur of the moment is a guaranteed recipe for pest and disease resistance buildup.

Things can get a bit difficult when selecting a product. Each product is differentiated in three ways; the commercial name, active ingredient and the class or group. Using a pesticide in the same group throughout the whole year is not recommended as resistance will build up very quickly.

Table below: A random selection of some commercial formulations, their active ingredients and chemical groups. The most important column is the chemical group. The farmer must rotate the chemical group in the spray program and not the active ingredient or commercial name.

Commercial name Active ingredient Chemical Group
Cypermethrin, Doodskoot, Ripcord cypermethrin pyrethroid
Decis, Deltamethrin, Decis Forte deltamethrin pyrethroid
Mevinphos, Phosdrin mevinphos organophosphorus
Nemathorin fosthiazate organophosphorus
Primor Apid Killer, Aphox pirimicarb carbamate
Karbadust, Karbasol, Karbaspray, Kamikaze carbaryl carbamate

There are numerous reasons why a farmer will deviate from the original spray program. The weather is one of them. There might be a very wet period so applying a powder might be a bit difficult, especially if the wind is blowing (wet and dry conditions).

One of the most important ones is the days required between the chemical application and when you are allowed to harvest. For instance, controlling red spider mite with abamectin EC requires 3 days before you are allowed to harvest. But if you used diazinon EC, you have to wait 14 days. If you are treating nematodes with aldicarb GR you have to wait 90 days!

So saying choose the correct product is not that easy, you have to have a holistic approach that takes your whole spray program into consideration.

Know what time of day to spray

This is a tricky one since pests are active in the morning, so any other time will not be as effective. Never spray during the heat of the day. This applies especially to systemic types of formulations because they are absorbed through the stomata, which are closed during hot days.

Not only do insects hide later in the day, but droplets dry out in hot weather, leave the active ingredient behind which burn the leaves. See image below. Each formulation is thoroughly tested on the crop so that the recommended concentration will not affect the growth of the plant, just the target (pest, fungi or bacteria). If the droplets dry out, the concentration increases beyond the levels and the suppliers cannot be held responsible.

Classic chemical burn signs on a young spinach plant. This is not a disease. The fungicide was applied either on a very hot day or the concentration was too high, meaning the user did not read the manual. These leaves are unmarketable.

Do not spray in the rain or if the possibility of rain is very high. The active ingredient, which is very expensive, will wash away. It is possible to add adjuvants that increase the stickiness of the formulation but there is a limit. Rain and overhead irrigation is the same thing. Don’t switch the overhead irrigation on just after applying a pesticide or fungicide.

Working with chemicals

As i have said before, pesticides, fungicides and bactericides are harmful, so be careful. You are not a chemist so don’t try new things that you have no idea what the end result will be. If a chef follows recipes very closely so much more must you when working with hazardous chemicals.

Make sure that the pH and if you can the electrical conductivity (EC) of the water is within the specifications. pH is critical, each formulation has optimal pH levels between which they are most effective. In most cases, fungicides work at pH 7 and pesticides and herbicides between 4.5 and 5.5.

Do not make up cocktails. It’s the same as filling a room with political extremists from both sides, handing them guns and say have a little mingle. It ends up in tears. Mixing different pesticides and fungicides together to save money can actually cost you more, not just in health, but in damage to equipment and reduced effectiveness of the application.

It is good practice to use adjuvants. Now you can start making cocktails. Adjuvants are designed to help the chemicals do their work better. The most common adjuvants are stickers and spreaders. Less common is penetrators that are used with systemic fungicides.

Always use freshly mixed chemicals. Some chemicals can bond with each other forming insoluble precipitates that accumulate at the bottom of tanks. These newly formed compounds are useless and will clog up your spray nozzles, wasting valuable time and money.

Never spray in windy conditions. It is dangerous and ineffective. Not only will the spray or drift move to other crops that do not need it, it will also spread over the person applying it, which is dangerous. Just imagine the danger to other people if the drift spray goes onto a crop that must be harvested the same day!

There will always be some drift because there is always some air movement. Another type of drift is called endodrift, that is when the chemical falls onto the ground inside the target area. By changing the type and angle of the nozzles, endodrift can be minimized.

Spray volume

There are five types of spray volumes

  • High volume: more than 600 L/ha
  • Medium volume: 200-600 L/ha
  • Low volume: 60-200 L/ha
  • Very low volume: 5-60 L/ha and
  • Ultra-low volume: < 5 L/ha

The volume you choose will depend on your equipment and that depends on how big your farm is. What is important though, no matter what method you use, is that the chemical must reach the target at a lethal dose. The most effective methods is ultra-low volumes used with mist sprayers. They allow for a very fine even coverage which also penetrates the underside of the leaves. The grower can also use less active ingredient which makes it more environmentally friendly.


1 Image by Pexels from Pixabay