Using fluorescent dye and a UV light to show spray coverage on a grapevine leaf.
The aim of all spray operations is to get an even coverage of chemical on the target, whether that is a crop in the case of fungicides and insecticides, or a weed in the case of herbicides. But how do we know if we are achieving even coverage of the target, or whether we are getting enough spray onto the target, or indeed whether we are even getting the spray onto the target?
Coverage is particularly important in the following situations:
- In tree and vine crops, where the label specifies for Dilute Spraying that the canopy should be sprayed ‘to the point of runoff’.
- When spraying contact chemicals, that is, chemicals that do not move within the sprayed plant; as compared with systemic or translocated chemicals which can be absorbed by leaves and move around within the plant.
- Spraying young crop plants or weeds that are growing under a thick stubble, where the stubble may intercept much of the spray before it reaches the target.
- Where you are trying to get the spray to penetrate a dense canopy, eg spraying bunches of grapes in mature vines to protect them from infection with Botrytis.
Here are three techniques that can help us assess coverage:
- Put water sensitive paper in the canopy that you are spraying. The colour of the paper changes from yellow to blue when it gets wet. You may be able to purchase water sensitive paper from spray equipment dealers or chemical resellers. If there is also chemical in the spray tank, wear gloves when inspecting the sprayed paper.
- Put kaolin clay into the spray tank and spray the target under normal conditions. The clay will leave a residue on the target leaves. You may be able to purchase kaolin from chemical resellers. Make sure you mix it with water into a slurry in a bucket before adding it to the spray tank, and keep the mixture agitated to prevent settling out of the clay. As the clay may interfere with some chemicals, do not use in conjunction with chemical in the spray tank.
- Add a fluorescent dye to the spray tank, then inspect the target under UV light to check coverage. Inspect the target at night, or in a dark or shady area, for maximum visibility. Croplands® produce a kit with fluorescent dye and a UV torch, which is stocked by some agents. If there is also chemical in the spray tank, wear gloves when inspecting the sprayed target.
The same techniques can be used to assess spray drift onto non-target areas. If using the fluorescent day, get a mate to shine the UV torch on your face, hands and clothing at the end of the exercise, and see how good your hygiene practices are!
Smith & Georg talk about achieving good coverage when spraying, and reducing spray drift, in the Online Chemical Accreditation course.
Smith & Georg provides Chemical Accreditation training for users of agricultural and veterinary chemicals. Our Online Chemical Accreditation course covers legislation in all states. For more information go to www.smithandgeorg.com.au/onlinetraining or call us on 1800 991 985.