Organosilicone Surfactants – Use With Care
January 12, 2008
Organosilicone Surfactants are being actively promoted as excellent penetrators as well as good surfactants with superior rain-fastness properties.
They are definitely recommended for use with herbicides, which will have their effects considerably enhanced because of the properties of the organosilicones.
But then, nobody cares what happens to the weeds, and hopes that they die and disappear quickly and don’t come back!
Now, this is not the kind of approach for crops that we want to grow, nurture, and develop into quality, profitable products. And here are the reasons why:
- Organosilicones are so efficient at spreading materials, that they have been known to enter plant stomata and hydathodes - organs not normally penetrated by other surfactants.
Hydathodes are the tiny openings along the leaf margins that allow excess water to escape during the night. This type of action can lead to the penetration of unwanted bacteria that could cause serious plant disease problems1.
- Because of their rain-fastness properties: silicone type sealing of stoma, they would also act as anti-transpirants that would be detrimental to respiration, especially under warm and sunny growing conditions.
- Due to their enhanced penetration qualities, organosilicones would promote uptake into the stoma cells of spray materials that should remain on the surface(epidermis), hence possible damage or injury to the plant. They definitely should not be used in conjunction with oils or metals (fungicides).
Consequently, care must be exercised when selecting a surfactant or sticker/spreader, and one must first consider the safety and health of the crops.
Crop Protection, when promoted by commission and quota driven salespeople, can often turn into an "Oxymoron".
Auburn University: “researchers evaluated the use of an organosilicone surfactant to promote bacterial infection of leaves for biological weed control. The data indicate that a stomata-penetrating surfactant can facilitate bacterial infections in the absence of wounds and/or free moisture on the leaf surface. Further, in field experiments, high levels of infection were attained under hot, dry and sunny conditions.”
Spraying Speeds – Calculating Tractor Speed, Spray Speed and Coverage
January 9, 2008
Whether you’re spraying with a “Coupe”, Air-Blast sprayer, boom or even a hand-gun, you always want to finish the job as fast as possible. Yes…I know… spraying is not the most attractive or comfortable job a grower must do…
But, if we rush through the job to get it done quicker so as to be able to get out of our Tyvek Coverall that is like a set of “Fat-Farm Monkey Suits”, we are only kidding ourselves.
A spray job done to quickly is not an effective job and therefore we may have to come back and do it again.
Let’s do things well the first time. And that means spraying at a rate where the coverage is effective.
Speed has a lot to do with how far the spray travels. One of the comparisons I usually use when I’m teaching application techniques is the one of the steam locomotive stopped in the depot. When the engine is stopped, the steam from the chimney goes straight up.
When the engine is running at 50 miles per hour, the steam is pushed down against the engine. Take that and turn it on its side, and you have your sprayer. The faster you move the boom, volute or hand wand, the less the spray is going to travel in the direction you are pointing it.
Another thing to remember is with air-blast sprayers: for the spray and the air to reach the target, the air in-between has to be displaced and pushed out of the way. Think of this and try to visualize and you will realize that the more you “dwell” in one place, the further the spray patterns go. (this is a favorite of the sprayer salesmen, they always demonstrate the blower in a standing position and, of course, the wind carrying the spray displaces the air and goes quite far – very impressive!).
Try running your air-blast sprayer at a slower ground speed and you will get more reach and coverage and that way be able to do the job right the first time, even though it takes longer.
This will also apply to boom sprayers, especially if you want to get good under-leaf coverage in heavy foliage situations.
When hand spraying, wands should be held steady…let the vortex created by the spinners behind the nozzles, do the “swirling” for you.
Remember: when you slow down, cut down the rate so that you do not saturate and dribble a lot of chemical on the ground.
Calculating Tractor Speed.
Very often, when out in the field and somebody asks me about tractor speeds, I’m at a loss. Tractors do not have speedometers and those that have the little chart of speeds to RPM’s and Gear Ratios pasted on the console, the chart, of course is all scratched up and mostly illegible.
The simple way to calculate speed is by remembering (or having a little card handy) on how long it takes to cover distances in one minute. So here goes, and try to remember it:
I don’t recommend spraying at speeds higher than 2 mph. Again, I feel that doing it once properly is better than having to go back and do it again.
Remember to cut down your dosages accordingly.
Air-Assist Spraying of Crops
January 7, 2008
Much has been said and done over the past thirty years to improve the efficiency of air-blast spraying. Improved fans, oscillators, baffles, even electrostatics, have all contributed to better coverage and penetration especially in the orchard and tree-crop areas, where air-blast machines are the industry staple.
However, when it comes to spraying either horizontally or vertically down, as in the case of row-crops, vegetables and nursery stock, air blast sprayers generally lack the ability of delivering good coverage to the undersides of the leaves and many times are not effective in treating infestations.
Hence, they can be relegated to maintenance work such an application of nutritional and preventive fungicides and insecticides, but when eradication is needed, in come the old style boom sprayers!.
But take heart, several spray professionals (including yours truly), have been working over the years to develop systems that would delivery the spray material to the heart of the plant canopies and attain the coverage that could allow us to use air-blast machines to control infestations, especially in difficult to penetrate crops.
The Concept of Air-Assist Spraying Goes Way Back
The concept of Air-Assist spraying in which the droplet pattern is sprayed into an air-stream directed at the crop goes back before the development of the Air-Curtain (Degania/FMC) type boom sprayer. This machine was effective for open and simple canopy crops such as cereals, wheat, barley, corn, even cotton, where the cloud of spray could drop down into the crop and, through turbulence, cover most of the plant surfaces.
However, when you got into vegetables: cucurbits, melons, tomatoes, soy, beans and other tight canopies, the coverage just wasn’t there. The same held true for the “cannon” sprayers that delivered their pattern laterally and could not get the droplets to penetrate the canopies, much less cover the undersides of the leaves.
Cannon sprayers produced relatively small volumes of air at high speed, which reduced the inertia of the blast and therefore curtailed its ability to displace the air that was already in the way (between the sprayer and the target) in order for the spray material to reach its target. Consequently, forward speeds had to be lowered to increase the sprayer’s reach.
Growers were buying tractors with “crawler gears” and putting out higher volumes of spray than they had originally intended, in order to get the job done. And an extra added headache to all this was the considerable amount of uncontrollable pesticide drift that these machines generated.
Cannon Sprayers – Relatively Efficient Portion of Delivery
The cannon sprayers did have a relatively efficient portion of their delivery: those machines that had supplementary “horns” under the main cannon designed to reach the crops close to the sprayer, were getting good coverage on the plants sprayed by those “horns”.
The reason was that the “horns” were aimed into the crops at an angle and the air pattern coming out of them was relatively close to the targets and directed straight at them. Thus the spray was penetrating the foliage and covering most of it on both sides.
Three years ago, the writer developed a “directed spray” system for use on melons, by modifying a sleeve boom air sprayer into a duct boom sprayer with drops that ended in horns that were oriented directly at the crop. These horns held the nozzles so that the spray was injected into the air stream and the horns directed it onto the crop.
By orienting the horns at a 30 degree downward and 30 degree inwards (towards the crop in the bed) angles, the coverage obtained was far superior to anything attained previously with other systems.
This technique proved that the air assisted spray had to be aimed directly at the canopy and relatively concentrated so as to be able to penetrate the foliage and, once inside, create enough turbulence so that the droplets in the pattern reached all plant surfaces.
The Concept of “Directed Spray”
The concept of “directed spray”, long in use with standard boom/nozzle sprayers, has now been developed by several sprayer designers and manufacturers, including AirTech Sprayers of Winter Haven, Florida and is based on the use of directed “horns” that come off an “air-boom” which is a cylindrical duct that is held horizontally by the boom.
