Are High Water Rate Applications Necessary?

by Alan McCracken

A high flying Air Tractor avoiding trees during a fungicide application. There is confusion in many technical advisors’ minds regarding the need for high volumes of water to obtain good coverage with several still believing this is the only way. In my opinion, many labels tend to be misleading by specifying high volumes that could result in “run-off” and soil contamination. I would like to provoke open thinking that may lead to new ideas for the future. This article has been written to clarify that low volumes do work, although they may not be the answer for all situations.

I fully agree that small droplets are more subject to evaporation loss or can be carried upwards by rising thermals causing drift. For this specific reason, all low volume applications must contain oils and adjuvants to obtain consistent results. For low volume spraying to be successful, those involved require a higher level of technical expertise for accurate adjustment and calibration of equipment.

Years of trials and experience on many millions of hectares have proven it is necessary to always add oil and/or adjuvants to the spray solution to obtain consistent good results, especially under conditions of high temperature and low relative humidity. There are numerous oil-type adjuvants on the market with labels that claim to enhance performance and to control evaporation using low dosage rates. Unfortunately, none of these low dose products control evaporation at the labelled rates. The best option is a combination of a vegetable oil with adjuvants to provide a double function with the oil providing protection against evaporation and the adjuvant to reduce surface tension to produce more uniform droplets and enhance coverage.

In many areas, growers using high volume applications generally deliver wheat with a significant fusarium level. Growers using low volume spraying in North Dakota and Canada are delivering wheat with practically zero level of fusarium and thereby obtaining a premium price for their commodity. It is often necessary to fly at 40-50 foot heights applying fungicides that are sometimes difficult to fly lower due to trees and other obstacles. However, there is no problem at these altitudes with low volumes using oil to control evaporation. If high volumes of water are used, a significant amount of product does not reach the crop due to evaporation.

Many growers in Brazil have been controlling for several years the psyllid that transmits greening HLB (Huanglongbing) using ULV spraying. It was a salvation to its citrus industry when spray volumes were reduced to 5 lts/ha (½ gal/ac) and subsequently reduced to 3 lts/ha (0.3 gal/ac) for control. But yet, USA growers are controlled by labels specifying 10-15 gals/acre that have been proven to be ineffective.

So, the question bears answering, why has the USA government in the past financed a major aerial spraying campaign to eliminate the boll weevil using ULV applications, if high volumes of water were better? There is currently a major locust outbreak in Africa, Argentina and Pakistan. I suggest high volume experts should go there and try drowning locusts with water.

There are over 300 aircraft and helicopters operating each year in the USA making ULV mosquito applications. Typical application volumes used are 150-200 mls/hectare (0.02-0.05 l/ac / 2-3 oz/ac). ULV methods have been used successfully controlling the aforementioned pests for over 50 years!

A grower located in a hot desert region of Mexico had very poor cicada control using high volumes of water at 100 lts/ha (10 gal/ac) treating asparagus. He requested my support to obtain better control. On arrival in the area, I immediately noted the high temperatures of 35-45°C (95- 113F) combined with low humidity of 15-25%. I advised my client the only way to control the pest was by using the ULV technique with oil. After aircraft modifications and careful calibration, a total spray volume of two liters/ ha (0.2 gal/ac) with one liter of insecticide plus one liter of oil per hectare was applied with excellent results and an immediate kill of the pests. He has been using this technique now for several years and continues to obtain excellent control Forestry applications of the Bt DiPel are applied using ULV since the early 1990s. Typically, doses of 40-90 BIU/ ha or 16-36 BIU/acre (Billion International Units) are applied undiluted in volumes of 1.8 to 4.7 l/ha (24 to 64 oz/acre). The use of undiluted Bt provides adequate foliar coverage and increases aircraft production. No water carrier is required proving another spectacular use of low volume applications for better coverage (Source:https://www. fs.fed.us/foresthealth/technology/pdfs/btmanage.pdf).

It is obvious to me that drift control has taken first ➤ place in some technical people’s minds who have obviously lost focus of the main objective being the control of pests and diseases. Practically all drift problems occur not because of high wind speeds, but problems of inversion and evaporation with thermals. Surely, it is past time to seriously question why labels are not being updated to reflect the advantages of LV and ULV. One herbicide label from a multinational company even specifies a three MPH maximum wind speed limitation, which in my view is a recipe for disaster that is encouraging applications when there is a higher risk of an inversion.

Another very clear example of a low volume application success is on soybeans in Brazil. In the early 1970s, there were only a few thousand acres of production there. In 2018/19 crop year, Brazil moved into first place as a soybean producer with 92 million acres planted, overtaking the USA; and with yields higher than in the USA. Brazilian exports of soybeans are expected to exceed 75 million tons in 2019/20. This growth is even more dramatic since disease and pest pressure in Brazil is much more intense than in USA, where most of the chemical applications are made using low volumes of 5 lts-15 lts/ ha (0.5-1.5 gal/ac). Fortunately for farmers in Brazil, they can use the best methods available and add oils and adjuvants to control evaporation. Most growers are using rotary atomizers of which there are at least six different types in the Brazilian marketplace.

During January and February of this year, I worked with a number of farmers in Brazil who rarely, if ever use, their ground sprayers. They apply 90-100% of fungicides and insecticides by air using spray volumes of 2-10 liters/ha (0.2-1 gal/ac).

Many “experts” insist the operator should follow the label on the premise that if the product does not work and the label was not followed, the chemical company will not accept liability. Plus, it is illegal to apply off-label. All this is true. However, the problem of Asian Rust control is a case in point. At the outbreak of this disease, experts insisted on following labels and also on using high volumes of water 30-50 lts/ha (3-5 gal/ac) for good coverage! This is false, as the only method that effectively controls the disease is by using smaller droplets and low volumes of 5–10 lts/ha (0.5-1 gal/ac) with the addition of oil to control evaporation.

Another clear example of the benefits of using LV or ULV is the control of spider mites. Many labels specify high volumes of 50-80 lts/ha (5-8 gal/ ac) and yet the proven most effective method is with low volumes of 3-8 lts/ ha (0.3-0.8 gal/ac) with crop oils. I have been working with low volumes worldwide and remain absolutely convinced that it is the only method for reliable pest and disease control under adverse conditions.

I’m not advocating applications being made off-label. Instead, I am pointing out that LV and ULV applications work with no more risk to drift than high volume applications if made properly. That being said, it would be prudent for chemical companies to provide the aerial application industry with LV and ULV application labels.

On a more humorous note, a significant number of applicators and clients who work with me in Argentina promoting low volumes are often referred to as “Martians” with proven ideas that are poles apart from others who are referred to as “Dinosaurs”. We all know what happened to them.