If your sprayer can deliver good spray coverage at hull split, with a little work it can deliver good bloom spray coverage faster and cheaper. How is this possible? With no leaves in the canopy, air movement is less restricted at bloom than hull split. Also, there is less surface area to cover at bloom than hull split so volume needed to cover the susceptible tissue per acre (Gallons per acre, GPA) are less at bloom than hull split.
How could this work? Assuming your hull split spray set up is for 100 GPA (or more) and 2 miles per hour (MPH), at bloom you can increase ground speed, GPA and reduce power to the sprayer (less tractor engine or sprayer engine RPMs). All this means less time and diesel burned per acre and more acres per tank with no change in pest control. The exact settings should be worked out on the farm, but here are some general guidelines to use before bloom starts. [I am assuming that anyone trying this has a good knowledge of sprayer calibration. For the sake of space in the newsletter, I will not go into all the calibration details. Check the Almond Production Manual for details or call me at 530.218.2359. We do need an airblast sprayer extension publication.]
-Increase speed and reduce RPMs. Reduce engine RPMs by 15-20% from full speed and shift up a gear or two so that tractor and sprayer speed is somewhere around 3-3.5 MPH. For a PTO sprayer delivering 540 PTO RPMs with engine RPM at 2200, the target is somewhere around 1800 RPM for the tractor engine. This is quickly checked with a GPS unit or a quick pass down a row in the orchard counting trees (2 MPH=176 ft/min, etc.).
-Check that there will be enough upward air movement at this new speed. Readjust as necessary. Put a length of PVC pipe with a 1.5-2’ long length of flagging tape tied on the end up through the tree so that the top of the pole is roughly 3-4 feet above the top of the tree. Run the sprayer down the row with the fan on, water in the tank but nozzles turned off. Check how much the flagging tape moves as the sprayer goes by the tree? (I use the video function on my phone to capture the flag movement as the sprayer goes by.) If the tape flutters out to 45-90o off the vertical, that is enough sprayer fan air movement to give good coverage. If the flagging kicks straight up, you can speed up more and try it again until the desired 45-90 o movement is reached.
*If you spray every-other-row (EOR) at bloom, check air movement through the tree (next section) very carefully to make sure spray gets all the way through the tree or don’t use the approach described in this article. Every-other-row spraying delivers acceptable disease control at pink bud, but ineffective on the far side of the tree from the sprayer after 40% bloom. Every row spraying gives the best possible coverage. If you do spray EOR, do it carefully.
-Figure out the flow rate you’ll use based on your new speed and the product’s recommended GPA. Use your new tractor speed and row spacing to figure out the acres per minute you’ll cover at that speed. Using the measured acres per minute and the gallons per acre you want to spray, calculate the gallons per minute (GPM) needed from the sprayer.If you are using an air shear/electrostatic sprayer (Lectroblast, Windmill, etc.) make sure the system pressure is set to that required by the manufacturer, set the flow rate on each side of the sprayer and you are ready
-Adjust your nozzles to favor upward movement at this new speed. The general rule is that roughly 70% of the sprayer output (GPM) should come out of the top half of the open nozzles. Because of faster ground speed, larger nozzles will be needed and/or swirl plates changed (45’s used instead of 25’s). Large nozzles (D8-12) are a better choice in my opinion as the obvious nozzle exit hole difference between a D6 and a D8 make it easier to use the right nozzle for the right job if you are using rollover nozzle bodies (Rears or Nelson) or 2-3 nozzles/vane (AirOFan). In the table at the bottom of the page is an example of how a set up might go for a sprayer with two nozzle options per location on the spray boom.
In the orchard, place the disc/cores on the nozzle bodies that point at the tree. You may need to skip a nozzle body or two along the spray boom to make sure the spray targets the tree. For example, the first (very top) nozzle body on many sprayers basically points straight up and the second body is inches away and slightly angled into the canopy. I usually skip the top one. Lower on the sprayer you may skip a nozzle site, turning off the nozzle body. The goal with fungicide spraying is to aim high; rainwater will recycle the fungicide down through the canopy if it’s placed up high.
-Make sure your actual flow rate matches your desired flow rate. Ground truth the sprayer output by filling it to overflowing with clean water, running it for a set amount of time (a minute or two minutes) and then refilling it with a hose attached to a flowmeter or buckets marked with gallons/quarts/pints. Calculate gallons per minute sprayed to use in the following equation to check your actual sprayer output and determine how much material to put in the spray tank:
𝐺𝑎𝑙𝑙𝑜𝑛𝑠 𝑝𝑒𝑟 𝑎𝑐𝑟𝑒 =𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑝𝑒𝑟 𝑚𝑖𝑛𝑢𝑡𝑒/𝑎𝑐𝑟𝑒𝑠 𝑝𝑒𝑟 𝑚𝑖𝑛𝑢𝑡𝑒
-Double-check your coverage in the canopy. A final step in the calibration process is to check coverage with water sensitive paper either placed on poles or attached to the canopy.
If you are interested in this bloom sprayer set up concept and want some help with the setup, please give me a call 530.218.2359. — By Franz Niederholzer, UCCE Advisor, Colusa and Sutter/Yuba Counties