Weed control in nut orchards is always an issue for growers and farm managers. With the impending increased regulation and practical loss of the valuable contact herbicide gramoxone, alternative products and alternative control methods are being explored.
Justin Nay, president and CEO of Integral Ag Inc. and a Certified Crop Consultant & Pest Control Adviser (PCA) and Joseph King a PCA also of Integral Ag Inc. have been working on an herbicide delivery system that will allow glyphosate use in sensitive crops.
Nay said that because of the systemic activity of glyphosate drift, it is not recommended in almonds or walnuts for two years and pistachios for up to three years. However, he said that during that time weed species including bindweed, knotweed and nutsedge can become problematic.
Nay and King’s solution to preventing drift is a $100 modification with over the counter irrigations parts to turn a normal herbicide application rig into a herbicide dripper.
The parts include 30 feet of poly irrigation tubing, a couple of poly connectors and end caps, 100 one gallon per hour pressure compensating drip emitters or 200 0.5 gallon emitters and zip ties.
Construction involves disconnecting pressurized tubing and spray nozzles (do not need to remove from booms) and connecting poly irrigation hose, running out to the tip of the boom. Attach 10-15 zip ties to hold tubing tight to boom and crimp, loop or plug. Next, install emitters facing down at the number of emitters to fit, filling the desired bandwidth. Nay said he used 50 emitters, moving at 4 miles per hour (mph) to achieve about 25 gallons delivered per acre. This allowed an 8-foot band. The 1-gallon per hour emitters left a larger gap both down the row and between the emitters, but at 2.5 mph it tightened up the patterns to over application and cutting back the rate was necessary.
The 0.5-gallon per hour pressure compensating emitters at a higher density allowed maintaining the desired speed and gave a better pattern. More tubing and an end loop can get the numbers of emitters if necessary.
Nay said the disadvantages of the modification is if a bandwidth change is desired it is difficult to go smaller. When the poly hose is not tight and flat on the boom drip emitters tend to roll down to the lowest spot instead of drip and you get a more concentrated stream. You cannot get the top of the berm and it does have gaps in the pattern and so some extra work will need to be done. Nay said it is not known how long each one of these systems can last before emitters are worn out.
The benefits are tree safety and fuel savings. With this system there was not drift to the trees even in high winds and a good kill on glyphosate sensitive prostrate weeds was achieved. Running the motor at a much lower revolutions per minute (RPM) because the pounds per square inch (PSI) needed for drip emitters is much less than for pressurized nozzles saves fuel.