Pesticide Use

Use of Adjuvants

Spray adjuvants are materials added to pesticides in order to enhance their effectiveness. Many insecticides and some fungicides are formulated by the manufacturers with their own adjuvants. Because of the breadth of conditions vegetable growers encounter in Utah, additional adjuvants may further enhance the effectiveness of the product. However, selection must be done with care, considering all the factors that may affect spray performance. Use of the wrong adjuvant for the conditions can decrease product effectiveness. Many pesticides will state the type of adjuvant that can be used.

There are many types of adjuvants, including surfactants (ionic or nonionic wetting agents/ spreaders that improve wetting of foliage), stickers, and emulsifiers, and agents that buffer, defoam, control drift, penetrate soil, filter UV, and more. Each type of adjuvant differs in the way it interacts with spray chemicals and water quality, and weather conditions further affect their potential use. Thus, no one adjuvant can or should be used under all conditions.

Remember that amount and type of the adjuvant needed will vary with the hardness and pH of the water. Use just enough spreader-sticker to break the surface tension and spread the spray uniformly over the leafy surfaces; excessive amounts of surfactants will increase spray runoff. Do not use spreaderstickers with growth regulators (unless specifically called for on the label).

Adjusting for Water PH

The pH of water used to prepare spray solutions is very important. Water in many locations in Utah is alkaline, ranging in pH from 7.4 to 8.5. The use of alkaline water for spray solution preparation can rapidly decompose many insecticides and decrease their activity. The following procedure is strongly recommended:

  1. Check the pH of your water supply.
  2. Read labels to determine whether water pH is important for that material.
  3. If necessary, adjust water pH to the needed level before adding any chemical or pesticide that is sensitive to pH; pH adjusters include Buffercide, Buffer-X, Unifilm-B, and LI 700 Acidiphactant.
  4. Apply spray solutions as soon as possible after mixing in the spray tank. Especially avoid leaving mixed spray solutions in the spray tank overnight.

Preparation of Small Spray Quantities

Label directions for mixing and applying pesticides come in two general scenarios: rate per volume (usually 100 gallons of water) or rate per area, (usually acre or 1000 sq. ft.) Mixing directions for small quantities of pesticide vary with the scenario.

If your pesticide mixing directions state an amount of material per 100 gallons, you should adjust the amount of pesticide to the volume of water you mix. Table 11.1 gives mixing rates for label instructions. If your label instructions state a final spray concentration, you do not have to calibrate the sprayer, but you must read the label to know how much spray material to apply.

If the pesticide mixing instructions state an application rate in an amount per area (usually acre, but sometimes 1000 sq. ft.), your sprayer must be calibrated.

Densities of solid pesticides vary with the formulation and the amount of shaking or settling within the package during shipping and in storage. An electronic scale should be used to ensure the correct weight of the dry product is used. These scales are readily available on-line and reasonably priced. Many of these scales measure down to 0.1 gram. The use of an electronic scale is essential for the solid form pesticides (e.g., wettable powders, dry flowables, etc.).

Do not use an ordinary teaspoon for measuring liquids as the common teaspoon varies from 4 to 10 ml. Instead, use a graduated medicine spoon. When measuring out small amounts you will need to use a syringe, which are available from your physician, veterinary supply, farm supply, or pharmacy. Graduated spoons and syringes used for a pesticide must not be used for anything other than that pesticide.

Conversion values for preparation of 1, 3, and 5 gallons of spray from the rate per 100 gallons.

  Amount per:
Material 100 gal 5 gal 3 gal 1 gal

Wettable Powders, & Dry Flowables

4 lbs (1,814.3 grams)
2 lb (907.2 g)
1 lb (453.6 g)
8 oz. (226.8 g)
4 oz. (113.4 g)
2 oz. (66.7 g)

90.7 g or 3.19 oz
45.4 g or 1.659 oz
22.7 g or 0.79 oz
11.3 g or 0.39 oz
5.7 g or 0.2 oz
2.8 g or 0.06 oz
54.4 g or 1.92 oz
27.2 g or 0.95 oz
13.6 g or 0.48 oz
6.8 g or 0.24 oz
3.4 g or 0.11 oz
1.7 g or 0.05 oz
18.1 g or 0.63 oz
9.1 g or 0.32 oz
4.5 g or 0.16 oz
2.3 g or 0.08 oz
1.1 g or 0.04 oz
0.6 g or 0.02 oz
Liquids: Liquid or Emulsifiable Concentrates, & Liquid Flowables 1 gallon (3,840 ml)
2 qt (1,920 ml)
1 qt (960 ml)
1 pint (480 ml)
1 cup (8 fl oz=16 tbs=240 ml)
4 fluid oz (120 ml) or 8 tbs
2 fluid oz (60 ml) or 4 tbs
1 fluid ounce (30 ml) or 2 tbs
192 ml, or 12 tbs + 2 tsp + 2.0 ml
96 ml, or 6 tbs + 1 tsp + 1.4 ml
48 ml, or 3 tbs + ½ tsp + 0.5 ml
24 ml, or 1 tbs+1 ¾ tsp+0.25 ml
12 ml, or 2 ½ tsp
6 ml, or 1 tsp + 1.0 ml 3
3 ml, or ½ tsp + 0.5 ml
1.5 ml
115 ml, or 7 tbs + 2 tsp
57.5 ml, or 3 Tbs + 2 ½ tsp
28.8 ml, or 1 tbs+2 ¾ tsp+0.5 ml
14.4 ml, or 2 ¾ tsp + 0.65 ml
7.2 ml
3.6 ml
1.8 ml
0.9 ml
38.4 ml, or 2 tbs +1 tsp + 0.9 ml
19.2 ml, or 1 tbs+¾ tsp+0.45 ml
9.6 ml, or ¾ tsp + 1.05 ml
4.8 ml, or ¾ tsp + 1.05 ml
2.4 ml
1.2 ml
0.6 ml
0.3 ml
The measurements in tablespoons and teaspoons are approximate. The use of an electronic scale and syringe will be much more accurate