Practical Guide to Turfgrass Fungicides, Second Edition

A Practical Guide to

TURFGRASS FUNGICIDES Second Edition

Richard Latin

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Fig. 4.2. All agricultural nozzles are color coded according to flow rates at 40 pounds per square inch (psi), as established by the International Organization for Standardization. For example, all yellow, red, and white TeeJet nozzle tips have flow rates of 0.2, 0.4, and 0.8 gallons per minute (GPM), respectively, at 40 psi. (Courtesy R. Latin—© APS)

Factors That Influence Fungicide Performance

established by the International Organization for Standardization and is universally recognized. For example, yellow, red, and white TeeJet XR flat fan nozzle tips have flow rates of 0.20, 0.40, and 0.80 GPM, respectively, at 40 psi (Fig. 4.2). Regardless of the manufacturer or the type of nozzle, flow rates are the same at 40 psi for nozzle tips of the same color.

Some nozzles are engineered to produce very fine sprays; others generate larger droplets to limit drift. Droplet size is defined in terms of volume mean diameter (VMD), where half the spray consists of droplets smaller than the VMD and half larger than the VMD. The VMDs are used to characterize droplets as very fine (VF), fine (F), medium (M), coarse (C), very coarse (VC), and extremely coarse (XC) (Fig. 4.3). For example, medium-sized droplets have a VMD of 250–350 microns (one micron is one millionth of a meter).

Droplet-size categories are color coded (Fig. 4.3). Fine (150- to 250-micron) or very fine (<150-micron) droplets theoretically provide the most extensive and uniform surface coverage, but for application volumes greater than 1.0 gal./1,000 ft2, they are not efficient in terms of the time required to treat fairways. They also have a greater potential to drift away from the intended target, causing possible safety and environmental concerns. Although it is impossible to completely eliminate drift, decreasing pressure and increasing the nozzle orifice can minimize it. Very coarse and extremely coarse droplets are often associated with decreased surface coverage. In general, medium (250- to 350-micron) or coarse (350- to 450-micron) droplets provide the best coverage for the application volumes used for turf fungicide application. A variety of manufacturers make nozzles that produce droplets in those ranges.

Fig. 4.3. Droplet sizes are assigned to six color-coded categories. (Courtesy R. Latin—© APS)

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114 Chapter 4 For most standard nozzles, droplet size is influenced by spray angle and pressure. The spray angle represents the angle (measured in degrees) of the cone of spray that exits the nozzle tip. Increasing the spray angle results in a decrease in droplet size. Pressure influences droplet size in a similar manner. For example, the XR8004 (red) nozzle tips shown in Figure 4.4 produce coarse (C) droplets when applied at 15 or 20 psi and medium (M) droplets when applied at 30 psi or greater. It is important to note that when pressure is too low, the spray pattern collapses. If the spray angle is increased from 80° to 110°, the XR11004 (red) nozzles produce medium (M) droplets at 15–40 psi and fine (F) droplets at 50–60 psi. Each nozzle tip is identified by its spray angle and flow rate (Fig. 4.4).

Air induction nozzles reportedly offer the drift-reduction benefit of large droplets without sacrificing coverage. They produce large droplets filled with air that shatter into smaller droplets upon impact with plant surfaces. Figure 4.5 shows droplet sizes for a selection of TeeJet air induction nozzles. Note that the flow rate color code remains the same as in Figure 4.2, but the droplets produced by air induction nozzles are larger than those produced by standard (XR) nozzles with the same output. For example, the AIXR11004 (red) air induction nozzle with a flow rate of 0.4 GPM at 40 psi produces extremely coarse (XC) droplets (Fig. 4.5), whereas the standard XR11004 (red) nozzle (Fig. 4.4) produces medium (M) droplets at 40 psi. Turf-jet nozzles, which are often used for herbicide applications, provide excellent drift control and produce extremely coarse (XC) droplets at all flow rates and pressures (Fig. 4.6). In limited trials (discussed below), coverage and disease control did not suffer when the air induction nozzles were used. Dual fan nozzles represent a second generation of air induction nozzles. They distribute medium to coarse droplets at 80 psi or less. As the name implies, dual fan nozzles spray in two directions (forward and backward) in the same pass and are likely to result in improved coverage, especially on grasses maintained at heights above 1 in.

Fig. 4.4. Spray angle and flow rate are identified on each nozzle tip. In this example, both XR8004VS and XR11004VS nozzle tips have flow rates of 0.4 gallons per minute (GPM) at 40 pounds per square inch (psi), but different droplet sizes (C = coarse, M = medium, and F = fine) are produced by different spray angles. (Courtesy R. Latin—© APS)

Factors That Influence Fungicide Performance

Fig. 4.5. Air induction nozzles produce larger droplets for drift reduction. GPM = gallons per minute; psi = pounds per square inch; M = medium; C = coarse; VC = very coarse; and XC = extremely coarse. (Courtesy R. Latin—© APS)

Regardless of the nozzle type, nozzle tips require regular cleaning to keep orifices free of obstructions. Guidelines for nozzle tip maintenance are listed in Box 4.1.

Several nozzle types (turf-jet, raindrop, flat fan, and air induction) commonly used for turf applications were compared for their effect on dollar spot control with a contact fungicide (chlorothalonil) and a penetrant fungicide (myclobutanil) (Vincelli and Dixon, 2007). There were few differences in disease control among nozzle types for either fungicide. Where differences did occur, nozzles that produced medium-sized droplets resulted in less disease.

In another study, flat fan nozzles producing a range of droplet sizes were evaluated for their influence on the efficacy of two fungicides (chlorothalonil

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Fig. 4.6. Turf-jet nozzles produce extremely coarse (XC) droplets. GPM = gallons per minute, and psi = pounds per square inch. (Courtesy R. Latin—© APS)

and propiconazole) against brown patch (Shepard et al., 2006). Regardless of the fungicide, applications with fine, medium, coarse, and very coarse droplets resulted in equivalent levels of disease control. Disease control suffered only for applications with an extremely coarse droplet size (greater than 550 microns). A third paper on the effects of nozzle type and application volume for dollar spot control with chlorothalonil also concluded that disease

Factors That Influence Fungicide Performance

Box 4.1. Guidelines for nozzle tip maintenancea 1. Observe the output pattern frequently during every use. Foreign particles disturb the uniformity of the spray pattern.

2. Remove nozzles and clean tips regularly.

3. When cleaning nozzles, use clear, clean water and detergent.

4. Gently rub surfaces with a soft bristle brush to remove residues.

5. Use compressed air to remove obstructions from the nozzle orifice.

6. Clean and flip nozzle gaskets during maintenance.

7. Replace nozzle components that consistently cause problems.

8. Always wear personal protective equipment when changing or maintaining nozzles. a

Courtesy R. Latin—© APS.

control improved with surface coverage (Kennelly and Wolf, 2009). Finally, Kaminski and Fidanza (2009) observed that nozzle type and droplet size did not influence dollar spot control under low to moderate levels of disease pressure. Moreover, they observed excellent disease control under severe disease pressure with air induction nozzles that produced coarse droplets at a low water volume (1 gal./1,000 ft2).

In one study, water-sensitive paper was used to illustrate coverage achieved with two flat fan nozzles producing medium to coarse droplets at 40 psi (Fig. 4.7). By adjusting the ground speed of the sprayer, spray volumes of 1 and 2 gal./1,000 ft2 were applied with each nozzle. Almost complete coverage (95–97%) was achieved with the nozzle that produced medium (250- to

Fig. 4.7. Surface coverage differs with changes in flow rate and ground speed, as illustrated with water-sensitive paper. VMD = volume mean diameter. (Courtesy R. Latin—© APS)

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118 Chapter 4 350-micron) droplets (8004 EVS), regardless of application volume. By changing to nozzles that produced coarse (350- to 450-micron) droplets at 40 psi (8008 EVS), coverage was reduced to 65 and 85% for application volumes of 1 and 2 gal./1,000 ft 2, respectively. Whether or not 65% coverage results in adequate control depends on several factors, including the type of fungicide, the environmental conditions, the disease, the nature of the damage, and damage tolerance. Studies on the use of fungicides against crop diseases show that coverage below 50% often results in sufficient control to avoid significant yield losses, but disease tolerance is much lower for fine turf where aesthetics and playability, not yield, are the goal. Therefore, under environmental conditions that are highly favorable for infection, 65% coverage may not be adequate for satisfactory fungicide performance, especially with contact fungicides.

To summarize, superintendents are afforded ample latitude in selecting a suitable combination of spray nozzles and volumes for applying fungicides.

Research over several decades indicates that applications within a range of 1–2 gal./1,000 ft2 (44–88 gal./acre) with nozzles that produce medium to coarse droplets provide sufficient coverage while minimizing the amount of time required to complete the application. Within that range, good disease control can be expected, provided that the sprayer is properly calibrated and the appropriate fungicide, rate, and application interval are selected (Box 4.2). Coverage is more of an issue with contact fungicides than with penetrants, whose active ingredients move within the plant to suppress existing infections. Among penetrant fungicides, it is reasonable to assume that coverage is less of an issue for xylem-mobile fungicides (acropetal penetrants) than for local penetrants that move only across leaf surfaces.

Water Quality Since most fungicides are mixed with water and applied as dilute sprays, it is reasonable to consider water quality as a factor that affects fungicide performance. Water quality is defined in terms of three factors: pH (measure of acidity or alkalinity of an aqueous solution), hardness (measure of the number of positively charged ions—calcium, magnesium, and iron—in water), and turbidity (measure of the relative clarity of a liquid). Hardness and pH are known to alter the effectiveness of some organophosphate insecticides and select groups of herbicides. There also is ample evidence demonstrating the effects of pH and hardness on the performance of plant growth regulators (PGRs) and herbicides used to manage turfgrass. Only the pH factor has been implicated in affecting the performance of fungicides.

Reports of the influence of water pH on the efficacy of fungicides used against crop diseases are limited to captan, a fungicide commonly applied to prevent fruit rot and other fungal diseases. Captan has an aqueous halflife of 1 hour at pH 8.5 and is reportedly prone to breakdown (and loss of efficacy) when carrier water exceeds pH 7.0. Growers were advised to buffer their spray suspensions and avoid any delay between mixing and spraying.

Among fungicides applied to turf, product labels for some older formulations of iprodione and current formulations of thiophanate-methyl include warnings of product breakdown when it is mixed with alkaline carrier water (Fig. 4.8). From a turf disease control perspective, results of a single-season

Factors That Influence Fungicide Performance

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Box 4.2. Fungicide application equipmenta Results of fungicide trials may be biased by the application equipment. Handheld wands (A) and two- or threenozzle booms mounted on bicycle wheel sprayers (B) are common. Custom booms mounted on motorized vehicles (C) are rare in university fungicide trials.

a

Courtesy R. Latin—© APS.

trial on creeping bentgrass showed no season-long effect of water pH on the efficacy of fungicides (chlorothalonil, propiconazole, and a combination of propiconazole and azoxystrobin) against dollar spot (Fidanza et al., 2009a).

However, results of a second trial showed significant (detrimental) pH effects