Calibrate, Calibrate, Calibrate!
Each spring equipment and nozzles should be calibrated using a tank of water. Spray for 30 seconds into a cup to check volume and/or drive the planned speed over paper calibration cards randomly spaces through the rows to check spray and drip patterns.
Dr. Richard Bonanno, Extension and GAP Educator with UMass Extension Agricultural and Landscape Program, in Amherst, Massachusetts recommends careful boom and nozzle calibration. Most nozzles should be spaced 20” apart on a boom. Nozzle tips should be 19” above the surface that is being sprayed. He uses quarter turn, quick release plastic nozzles with stainless steel tips. They last longer than brass nozzles and can easily be taken off for cleaning. Also, make sure that all the nozzles on the boom are the same size. (Do NOT use old brass tips that may have been cleaned out with wire.)
Spray Nozzles and Boom Settings:
The most common spray nozzles offer either 80o or 110o patterns. Boom spacing either allows a full overlap (110o) where all weeds or soil are hit by spray from two nozzles or a 20% overlap (80o) between the nozzles where the spray is weaker at the edges. Nozzle codes are simple: they start with 80 or 110 depending on their spray pattern. The next number refers to their delivery (at a ground speed of 3 mph and a pressure of 40 psi): “01” means 10 gallons per acre, ”02” means 20 gallons per acre, “03” means 3 gallons per acres and “04” means 4 gallons per acre. Smaller tips (01 and 02) can be used for liquid-based formulas. Larger tips (03 and 04) are commonly used for powder-based formulas to minimize clogs. Nozzle codes ending in VS work well at lower pressures. Nozzle codes ending in E spray evenly across their whole delivery width.
Ideally, boom heights should be set so that the nozzle tips are 19” above the surface to be sprayed. When spraying emerged weeds, the nozzle tips should be 19” above the top of the weeds. The proper height adjustment is crucial when spraying a post-emergent herbicide. If the boom is too low, more herbicide will be deposited under the nozzles. If the boom is too high, more herbicide will be deposited between the nozzles.
Another critical setting is the orientation of the nozzles over the crop row when spraying a post-emergent herbicide. It is important that the nozzles are NOT directly over the crop rows. This is especially important over crops like corn where the herbicide can run directly into the whorl. Crops may be stunted and yield reduction can be significant.
To adjust the amount of water you are using per acre, you can change the speed of the tractor. If you normally spray at 3 mph, doubling the tractor speed will result in half as much water being used. Do not drive too fast on rocky or uneven fields, as this will jostle your boom and send spray in random, less effective patterns.
Another way to alter the amount of herbicide delivered is to change the size of the nozzle tip being used. Using a smaller tip will reduce the amount of water sprayed per acre.
A final way to change output is to change the pressure in the spray tank. However, the relationship between pressure and delivery rate is not linear. To double the output you will need to quadruple the pressure and to cut the volume in half, you need to decrease the pressure by a factor of four. Dr. Bonanno did not recommended this because raising or lowering the pressure too much will change the pattern of the nozzle and result in either an uneven spray pattern or too much potential for drift.
Weed ID and Treatment Selection:
After identifying the weed to be controlled using a good field guide or the “New England Vegetable Management Guide,” determine what time of year and what treatment offers the best control. The Guide is available online and includes the crops an herbicide is registered for and any restriction on which crops can be grown afterwards.
Current registrations and approvals are shown in Table 18: Vegetable Herbicide Registration. Growers can learn what to expect with these herbicides using Table 19: Relative Effectiveness of Herbicides on Weed Species. Dr. Bonanno advised using controls that offer E (Excellent) or G (good) effectiveness.
“Herbicides don’t make weeds resistant; herbicides select for resistance,” said Dr. Bonanno. Sometimes these resistant weeds take years to gain numbers where they present a significant problem.
To reduce this risk, alternate herbicide applications, use varying herbicide choices combined with other options such as cultivation and crop rotation.
Greenhouse Weed Control:
Dr. Bonanno’s favorite weed control in greenhouses and high tunnels is weed cloth or landscape fabric. These cloths often last ten years so when holes are cut for certain spacing and growers rotate crops he recommended moving the cloth to the new location rather than cutting new holes and fighting weeds in each hole. This effort is faster and cheaper than weeding the weed cloth later.
In general, Dr. Bonanno recommended against using herbicides inside high tunnels or greenhouses. Having multiple crops in close proximity makes selecting a spray program difficult if not impossible. Chemicals can build up or volatilize in unexpected ways effecting plants and people working in closed spaces. The only exception would be mitigating weeds in an empty house before planting. Be sure to ventilate before and after but not during application to avoid movement of herbicides out of the greenhouse through exhaust fans. Wear all recommended protective clothing and respirators during application process as closed houses increase the risks to applicators. Dr. Bonanno advised Gramoxone be used instead of Roundup on existing landscape cloth or over sandy soils. Do NOT use Roundup on a soilless mix or sandy soil, as some clay is required to inactivate Roundup once it hits the soil. Roundup in soilless mixes or sand could pose a risk to future crops.
For more information, contact Dr. Richard Bonanno, Extension and GAP Educator with UMass Extension Agricultural and Landscape Program, Amherst, Massachusetts, via email or call 978-361-5650.
Printed copies of the “New England Vegetable Management Guide” and the “Northeast Vegetable and Strawberry Pest Identification Guide” may be ordered from state Extension publication offices or call the University of Massachusetts Extension Bookstore at (413) 545-2717. The Guide was created by the Extension Vegetable Programs of all six New England State Universities and is updated every two years. This Guide for commercial vegetable growers offers cultural practice recommendations, including soil fertility, organic production and irrigation as well as weed, insect and disease management. Organic and Integrated Pest Management (IPM) efficacy tables, biological controls, pesticide safety, transplant production and seed or root stock sources are also included. A recent grant allowed color photos to be included allowing accurate weed, disease and pest identification.
A similar story ran in the May 28, 2012 New England issue of “Country Folks.”