AGCSATECH UPDATE AGCSATECH UPDATE
Spraying 101 Whether it’s a hand sprayer, small pedestrian sprayer or a large boom sprayer, correct calibration of spray equipment is essential
AGCSATech senior agronomist Andrew Peart looks at some of the key considerations to ensure you get the best results from your spray applications.
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Nozzle selection is critical to obtaining maximum spray efficacy
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espite great advances in pesticide formulations, gaining acceptable control of pests, or in this instance weeds, seems to be getting more difficult in recent times. The term resistance is seemingly becoming more and more common and with certain species such as Poa annua this may well be the case. However, as turf managers are we doing as much as possible to ensure we are getting the best result from our spraying applications? There are many aspects that must be considered to gain successful weed control. Among them are correct identification, selecting the appropriate herbicide, the timing of application and ensuring the equipment used is operating at its optimum. It all starts with the correct diagnosis of the weed. In turf situations this can be difficult, especially if it is a grass weed which may not produce a visible seed head due to mowing frequency. If this is the case, a plug should be taken of the suspect plant, potted up and then allowed to produce a seed head to make identification easier. Grasses can also be identified through the use of a taxonomic key which uses specific plant characteristics and parts (such as vernation, auricles, collars and ligules) to identify them. Broadleaf weeds generally are identifiable by their foliage characteristics and it is rarer that a flower is needed for identification.
AUSTRALIAN TURFGRASS MANAGEMENT 19.1
Once correctly identified, selecting the appropriate turf-registered herbicide is crucial and where possible taking into account its chemical group to try and limit the possibility of resistance. With herbicides, the chemical groups (modes of actions) are represented by a capital letter. Any herbicide with the same letter has the same mode of action and their continual use should be avoided. For example, the herbicides containing the active ingredients trifloxysulfuron (Monument®), rimsulfuron (Coliseum®), foramsulfuron (Tribute®) and iodosulfuron (Destiny®) are all Group B herbicides and rotating between these chemicals will not avoid resistance of the weed trying to be controlled. The other crucial component of the chemical selection is the quality of water that it is to be mixed with. The pH level of the water is most critical and ideally should be between 5.5 and 7.5. The use of buffering agents should be incorporated into the water if it is outside this range. The use of dirty water, or that with a high percentage of suspended solids, should also be avoided particularly when using glyphosate as this can bind to the colloidal particles and be far less effective on killing the weeds. The timing of chemical applications is also crucial. Many chemical labels, under the heading ‘Direction of Use’, state that the product should not be used on turf or weeds that are under stress. Others state not to be used on waterlogged soils. Some may even state that applications should not be made if heavy rainfall is forecast in the following 24 hours. Taking note of these directions is crucial in obtaining spraying efficacy. Of most importance though is not spraying when plants are under stress. When a plant is under stress its stomata will be closed and not receptive to herbicide applications which are foliar absorbed.