As a professional turf manager, you routinely apply pesticides and fertilizers as part of your maintenance operation. You already know that proper selection of chemicals is critical, as is accurate diagnosis of the diseases and pests you are treating. However, if you're relying on these two elements alone, you probably are not getting the most out of your efforts. How the products are applied can influence their activity. To get the most from application, you have to consider all of the elements involved: Everything from calibration to pH of the spray solution to post-application irrigation and rainfall. And with each of these elements comes a subset of other elements. For example, calibration involves more than simply measuring and adjusting. You also have to consider walking speed, ground speed, pressure and nozzle type. Each of these can affect product performance.
Nozzles help control the rate, uniformity, thoroughness and safety of product application. Factors that influence nozzle selection include the target area, wind speed, the type of product you're applying, operating pressures, ground speed and application rate. There are many types of nozzles on the market today, and one nozzle does not work for all applications. So you may need to invest in several different types.
Flat fan nozzles are the most common type for boom sprayers. They commonly are used when the goal is to coat leaf surface. Flat fan nozzles are made in a number of styles (standard, even flat fan; air induction; and extended range), and offer spray angles of 65, 73, 80 and 110 degrees. Most manufacturers design nozzles that are color-coded according to a universally accepted ISO (International Organization of Standardization) standard color-coding scale. Each nozzle is color-coded to identify the gallons-per-minute output it produces at 40 psi. For example, an XR8008-VS nozzle will be white in color and output 0.80 gallons per minute, while an 11004 nozzle will be red in color and output 0.40 gallons per minute. When you use flat fan nozzles, overlap the spray pattern because output is less at the edges than in the center of the spray pattern.
Nozzles do not last forever. The best way to determine if a nozzle is worn is to compare the flow rate of the used nozzle to a new nozzle of the same size and type. Charts are available from manufacturers that list nozzle output at different pressures. A nozzle is considered worn and should be replaced when its output is +/- 10 percent of a new nozzle. Replace all of the nozzles on a boom sprayer when any of them become worn.
Spray nozzles are designed to output a specified amount of spray at a specified pressure. Refer to the manufacturer's charts for the specific recommended operating pressures of a nozzle. Change nozzles when you need higher output volumes. If you are looking to double the output from a nozzle, you would need to increase the pressure by four times, which is not practical. Therefore, you would need a different nozzle.
Spray pressure also affects droplet size. Spray droplets are measured in microns (1/1000 mm or 1/25,000 inch). An increase in pressure will reduce droplet size, while a decrease in pressure will increase droplet size. Most nozzle manufacturers produce charts that follow the ASAE (American Society of Agricultural Engineers) droplet size classification standard that indicates droplet size for a given nozzle at various pressures. (For an example of this, see Table 1, above.) Coarse spray droplets are acceptable for pre-emergence herbicides. Contact herbicides require a medium to coarse droplet size, depending on the target. Medium to fine droplets are preferred for fungicides and insecticides. You can adjust droplet size with pressure changes or by changing the nozzle. You should be aware that adjusting the droplet size will affect coverage. Reducing the droplet size by ½ will result in about 8 times more droplets per unit area. For example, a water volume of 0.50 gallons per 1,000 square feet from a nozzle that outputs a 400-micron droplet will apply about 360 droplets per square inch. A nozzle that produces a 200-micron-sized droplet will output about 2,900 droplets per square inch. Keep in mind that the potential for drift increases as droplet size decreases. You can match nozzles to achieve the droplet size and water volume you need.
Water volume is especially important for pesticide applications. Key factors to consider are the pesticide mode of action and the target pest. In other words, does the pesticide need to stay on the foliage, or does it need to get down into the lower canopy and root system?
A general guideline to follow for disease control products is to use a minimum of 1 gallon per 1,000 square feet for contact fungicides; 2 gallons per 1,000 square feet for systemic fungicides; and 0.50 to 4.0 gallons per 1,000 square feet for localized penetrant fungicides. You can control foliar diseases with 1 to 2 gallons per 1,000 square feet, while crown and root diseases such as summer patch and pythium require 3 to 5 gallons per 1,000 square feet. It is difficult to apply more than 2 gallons per 1,000 square feet through some nozzles, so fungicides typically require you to water them in after application to control diseases. One gallon per 1,000 square feet is 0.128 ounces per square feet, which is not very much water. Nozzles do a great job of helping apply products with low water volumes.
Water volume requirements for insecticides and herbicides are determined by the target pest. Most insecticides applied for root-feeding insects should be watered-in with 0.25 to 0.50 inches of water. This is also true for pre-emergence herbicides, as they require water to activate the herbicide barrier for weed control. Insecticides applied for foliage feeding insects and post-emergence herbicides work well at a rate of 1 gallon per 1,000 square feet.
Most pesticide labels will suggest a water volume per unit area for different applications. They also typically will state to water the pesticide in within 7 to 14 days after application. It is always best to water-in as soon as possible, as some products are subject to photo degradation. It is also important to know how much thatch is present because it can slow water movement and tie-up pesticides.
POST-SPRAY IRRIGATION OR RAINFALL
A common problem in pesticide application is determining if a foliar-applied product will still work if it rains soon after application. Generally, if the product has dried on the foliage before irrigation or rainfall, it will be effective. Products that contain sticking agents are less affected by post-application rainfall. Systemic fungicides should not be affected by moderate rainfall because, to be effective, they need to be taken up by the crowns and root system.
PH OF THE SPRAY SOLUTION
The pH of spray solutions are influenced by the carrier (water vs. fertilizer) and the products you add to the tank. Water quality varies greatly across the United States, resulting in a wide range in water pH and solutes present in the water. To maximize consistency of your spray mixtures, use water from a consistent source such as city or well water. Also, it is a good idea to have your water source analyzed so that you know your starting point when mixing products.
Often, you will want to combine chemicals to make the most out of your application efforts. If you know you need to treat some weeds but also a disease, doing so in one application will save you a lot of time — especially if you're treating a large area such as a golf course fairway. Most applications include one or more pesticides, as well as products such as fertilizers, micronutrients, adjuvants, etc. If the pH is out of line, one or more of the products can undergo chemical hydrolysis. If the pH is above 7.0, alkaline hydrolysis can occur. This is an irreversible reaction in which the hydroxyl ions in water interact with the pesticide to break it down into a non-toxic compound. Insecticides are more prone to alkaline hydrolysis than are fungicides. You can add buffers to the spray tank to adjust the pH, and many pesticide labels provide guidelines as to whether buffers are needed.
MSDS sheets provide technical information on each product, and pH values listed on the MSDS sheet are for that formulation. The MSDS information sometimes will list the product half-life at different pH values. The pH can also cause compatibility problems between the carrier and products in the mixture. The pesticide label will usually list other compatible products. The label will also offer directions for conducting a compatibility test (often referred to as a jar test) if there you have a question or have encountered a problem.
In general, if you spray the products within a few hours after mixing, and there are no compatibility problems, there should be little chemical breakdown to reduce efficacy. You should purchase a pH meter and keep records of the pH of all spray application mixtures. This may provide a clue if certain applications do not work as well as you expected. A pH range of 5 to 7 is generally recommended as the ideal spray solution pH to ensure efficacy and to reduce compatibility problems for most turf products.
The formulation of the pesticide is the key factor in determining the sequence in which you should mix different products. Compatibility problems can occur if you do not follow the proper sequence. Pesticide labels usually offer information on the proper sequence to mix different products. Check for compatibility between products before mixing them in the tank. Fill the spray tank ¼ to ½ full and start agitation. If the mixture needs a compatibility agent, add it first. Next, add products in water-soluble bags. Maintain agitation and allow the bags to completely dissolve and the products to disperse before adding other tank mix partners. Next, add water-dispersible granule and wettable powder formulations. Allow the products to disperse completely before adding other products. Add spray adjuvants and markers next, if needed. Then add flowable liquids and suspension concentrates. Add emulsifiable concentrates last. These are general guidelines and you should consult the label or manufacturers for additional mixing information on their products.
Turfgrass managers will commonly ask if the products can be mixed the night before application. Or, if the spray tank has problems, how long will the products remain stable? The best guideline is to mix products as close to the time of application as possible. How long they are stable will vary depending on the mixture. Some herbicides will re-agitate easier in a fertilizer carrier than in a water carrier. Consult the product manufacturer for information.
Turf managers should identify the class of chemistry and mode of action for each pesticide they use. This is especially true for fungicide use on golf courses where you're often applying two or more fungicides together to control multiple diseases. Ideally, you should rotate products with different chemistries and modes of action for continued disease control. Also, be sure that you know if the products are a contact, systemic or localized penetrant.
LABEL IS LAW
The best source of pesticide information is the label. Most application problems occur because the label directions were not followed. Product manufactures may spend many years and millions of dollars to develop new products, and the label is the law, but also a summary of how the product should be used. Read the label, follow directions, keep records and you will minimize application problems.
Dennis Shepard, Ph.D. and Michael Agnew, Ph.D. are technical support managers for Syngenta Professional Products. You can reach them by e-mail at email@example.com and firstname.lastname@example.org.
Table 1. Pressure effect on nozzle droplet size.
|Very Coarse||Extremely Coarse|
|Droplet size classifications are based on BCPC specifications and in accordance iwth ASAE Standard S-572 at the date of printing. Classifications are subject to change.|
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