| Understanding Protected Spray Applications |
| In the last decade new developments in nozzle spray technology has improved spray deposition while reducing driftable fines. The new generation of spray tips has made hooded sprays almost obsolete. Still there are two types of spray protection devices being used today.
One type uses spray shields (figure 1) to defend the broadcast sprays against wind and chemical drift. The second type uses spray hoods (figure 2) and works on containment of the spray cloud to defend the crop against contact with the herbicide being sprayed. |
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Figure 1: Flexible spray shield is designed to prevent drift of broadcast sprays |
| In recent times more growers have experienced new infestations of weeds that are resistant to glyphosate and ALS inhibitor herbicides. In combination with resistant weeds are extreme weather conditions. A series of successive rains, or in its extreme opposite, drought and extreme heat are all weather conditions that can delay an application which then dictates what herbicide application crop producers must utilize to control weeds and maximize their efforts to achieve greater yields. |
Figure 2: Spray hood uses directed sprays under a hood to keep sprays from direct contact to crop. |
| When selecting nozzles for spray hoods and shields it is important to follow recommendations of the manufacturer and your local crop expert/extension agent. Spray hoods because of their shape further define what spray tips can be used to meet the physical shape of the hood. |
General Recommendations
| 1. Use off-center or flat fan tips (Ultra Low-drift, Low-drift, Extended Range) with limited angle for directed spray under hood. 2. Select nozzle with low operating pressures (15-30 PSI) to decrease driftable fine droplets and fogging that could escape from the hood. Spray patterns should not impact on hood—this causes dripping along edges. 3. Directed spray patterns should not extend out of hood except those for intended applications. 4. Each tip should employ a check valve to limit crop damage on end rows. 5. Operate at low speeds (< 6MPH) to prevent skipping of hood, loss of spray containment and crop damage. |
Limitations
| 1. Slow speed of operation requiring high carrier rates to meet minimum flow rates of small nozzle. 2. Bulky shield or hood is subject to physical damage. 3. Hoods are too large to be employed on sprayers and do not allow booms into folded position. 4. Large hoods dragged through crops break stems and leaves reducing yields. 5. Operator cannot see when a nozzle is plugged: need to use flow monitors. |
Hood Configurations
| Single nozzle in hood
Useful for post-emerge herbicide application and in-season fertilizer applications that keep sprays off crop. | Twin herbicide application
One nozzle is centered in the hood and two additional side nozzles are located for directed spray of a second herbicide under canopy and outside the hood. This application is used in crops like cotton where spray under the canopy to attack weeds outside hood’s protected area is necessary. |
| Triple nozzle in hood
Three nozzle configuration is preferred over single nozzle for post-emerge herbicide application. Three nozzles provide more effective coverage because of multiple spray angles and targeting over the tops of weeds. Remember the mode of action may not be the same as glyphosate products and may require more deposition of product on the leaf surface. |
Sizing Nozzle
| When sizing your nozzle for hooded sprays follow recommendations outlined for band spraying. |
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Band Spraying
| Standard U.S. | ||||||
| Volume of Chemical Solution Required | = | Band Width (inches) | X | Label Rate of Carrier | X | Field |
| [Band Width + Spacing between Bands] | ||||||
| (Gallons) | (inches) (inches) | (GPA) |
| (Acres) |
| Height Requirement for Band Spraying | ||
| Band Width | Height over Target | Height over Target |
| 8” | 5” | 3” |
| 10” | 6” | 4” |
| 12” | 7” | 4” |
| 15” | 9” | 5” |
| 18” | 11” | 6” |
| 20” | 12” | 7” |
| 30” | 18” | 11” |
| To find GPA in the band, use the following equation: | |||
| Band GPA | = | 5940 X GPM X N |
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| MPH X W |
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| GPM needed per tip: | |||
| GPM | = | GPA X MPH X W |
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| 5940 X N |
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| GPA = Gallons per acre GPM = Gallons per minute MPH = Speed in miles per hour W = Band width in inches N = Number of tips spraying in each band |