Three types of sprayers are commonly used for applying fungicides and insecticides to pumpkin and winter squash in New England. These are high pressure/high volume hydraulic (boom), low pressure/low volume hydraulic (weed sprayers) and air blast. The dense foliage of pumpkin and winter squash vines makes it difficult to achieve good spray coverage on all but the upper leaves. Depending on the sprayer type, there are several suggestions for improving spray coverage. These include:
- using a slow ground speed (two mph) to allow enough time for spray droplets to penetrate the foliage
- using a high volume (80+ gpa) to cover more surface
- using high pressure (100 psi) to force spray into the canopy
- on hydraulic sprayers, using solid cone nozzles which have better penetration that hollow cone nozzles
- turning horizontal booms of hydraulic sprayers so the spray pattern is about angled about 15o forward rather than vertical to stir the leaves
Low pressure/low volume or so called weed sprayers typically operate at about 40 or less pounds per square inch (psi), deliver 20 to 40 gallons per acre (gph) and are equipped with flat fan nozzles which are not designed for penetrating the foliage. These sprayers cannot be expected to provide adequate coverage.
High pressure/high volume hydraulic sprayers are capable of providing the recommended pressure and volume and typically are fitted with hollow or solid cone nozzles. This type of sprayer would be expected to provide reasonable penetration of the canopy.
Air blast sprayers utilize a strong stream of air to carry the spray to the target. It would be expected that this blast of air would carry spray droplets into the canopy.
Water sensitive cards can be used to evaluate spray coverage. The cards surfaces change color when contacted by spray droplets, clearly indicating the amount of coverage at that particular spot. Using clothes pins, cards can be clipped to leaves at various locations within the plant canopy. A spray of water only (to eliminate re-entry concerns) is applied and the coverage pattern is easily seen at the locations of the cards.
Water sensitive cards were used to evaluate spray coverage provided by four sprayers in three pumpkin fields in August, 1999. At this time, the leaf canopy was fully developed. For hydraulic sprayers, cards were clipped to the upper and lower surfaces of top leaves and those that were low in the canopy and well covered by upper leaves. Ground speeds of 2 mph and 4 mph were tested. Spray booms were operated so that nozzles pointed straight down (vertical) or angled forward about 15o. One of the sprayers is a low pressure/low volume unit with flat fan nozzles which delivered 50 gpa at 2 mph and 25 gpa at 4 mph. We also tested low pressure hollow cone nozzles. All treatments with this sprayer provided very little coverage of the lower surfaces of top and bottom leaves. The various treatments did affect coverage of the upper surfaces: 2 mph was always better than 4 mph; the boom generally provided better coverage when angled than when vertical; and the flat fan provided better coverage than the hollow cone, however, the flat fan delivered twice the gallonage of the hollow cone. Regardless of treatment, this sprayer provided poor coverage.
The high pressure/high volume sprayer has solid cone nozzles and was tested at 2 (120 gma) and 4 mph (60 gpa) with the boom vertical and straight. With the boom angled, this sprayer provided excellent coverage of the upper surfaces of top and bottom leaves at both ground speeds, but little coverage of the lower surfaces. When the boom was in the vertical position, coverage of the upper surfaces was reduced and was poor on the lower surfaces. There was little difference between ground speeds.
Two air blast sprayers were tested at 2 and 4 mph. They delivered 25 and 12.5 gph at these speeds respectively. Cards were attached to upper and lower leaf surfaces of top and bottom leaves as for the hydraulic sprayers. In addition, this was tested on the first, third and fifth rows from the sprayer. The coverage was somewhat better in the third row that in the first or fifth rows. Perhaps this could be improve, especially in the first row, by adjusting air patterns. With these sprayers, coverage of the lower surfaces was poor and fair on the upper surfaces at 2 mph. Coverage was reduced at 4 mph. Occasionally, a top leaf would flip over in the air stream, resulting in better coverage on the lower surface of the leaf.
None of these sprayers provided a desired level of coverage of lower leaf surfaces. Coverage of the fruit, especially the lower surfaces, would probably be marginal. The high pressure/high volume hydraulic sprayer with solid cone nozzles with the boom angled, provided the best coverage. The low pressure/low volume sprayer provided the poorest.
By: John Howell, Extension Vegetable Specialist, Dept. of Plant and Soil Sciences, University of Massachusetts
Originally published: Proceedings. 1999. New England Vegetable and Berry Growers Conference and Trade Show. Sturbridge, MA.
Reviewed by: T. Jude Boucher, IPM, University of Connecticut. 2012
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