Entomology Logo

ISSUE 3    May 18, 2006


With the high cost of fuel, it is efficient (both money and time-wise) to combine control of weeds and insects when appropriate. However, it is important to know that some herbicide-insecticide combinations can increase crop injury. Efficacy data on herbicide-insecticide mixtures are limited because of the number of potential combinations. Non-registered tank-mixtures should be used with caution until experience or research has shown that the combination is effective and safe. The following information is based on label restrictions and/or research indicating crop injury or decreased control.

2,4-D: Wheat injury (not lower wheat yield) occurred with 2,4-D amine combined with Lorsban. 2,4-D, dicamba, bromoxynil+MCPA or Curtail mixed with Asana, Cygon, Di-Syston, Warrior or Lorsban caused no wheat injury in University of Wyoming research.

Assert: Use caution when tank-mixing organophosphate insecticides for use on barley and sunflower. Assert and Di-Syston caused barley injury in University of Wyoming research.

Dicamba: Oil-based insecticides increase risk of wheat injury.

Basagran: Basagran should not be tank-mixed with any organophosphate insecticides as crop injury may result.

Betamix/Betanex: Increased sugarbeet injury occurred from tank-mixtures with Lorsban, malathion, or Sevin XLR. Micro-rates of herbicides will reduce incompatibility problems. Oil-based additives increased risk of sugarbeet injury in herbicide-insecticide tank mixes.

Bromoxynil: Refer to label for directions on the order of adding products to the spray tank and for the complete list of insecticides that can be tank-mixed with bromoxynil.

Post Grass Herbicide: Assure II, Fusilade DX, Fusion, Poast, Prism, Select. Reduced grass control may result from tank mixes of Fusilade DX with Lorsban, malathion, Sevin XLR, or Pydrin; or Poast mixed with Sevin XLR or Pydrin. Poast tank-mixed with lorsban or malathion did not decrease grass control.

Glyphosate: No anatgonism or injury to resistant crops occurred when applied in combination with Warrior, Asana, Sevin, or Capture insecticides.

Sulfonylurea Herbicides (SU): Severe crop injury may result from tank-mixing SU herbicides with organophospate insecticides. Most SU labels do not allow addition of Lorsban or malathion. SU herbicides and insecticides should be tank-mixed only when experience or research indicated crop safety.

(Source: Prairie Grains, June 2006)



Under federal law, combining pesticides is legal unless the pesticide label contains instructions that you do not combine them. However, not all pesticides work well when mixed together. They must be compatible. Mixing pesticides together should not cause phytotoxicity or reduced efficacy. In general, the more pesticides that you mix together, the greater the chance of undesirable effects.

To test tank-mix compatibility of pesticides, use a large, clean glass container, such as a quart canning jar. Use the same water that you will used when making up the larger spray mixture. Add the water and each of the products in the same proportions as you will mix them. For example, each quart of pesticide that you add to 50 gallons of final spray mixtures is the equivalent of about 1 teaspoon per quart of water. Unless the pesticide labeling states otherwise, add pesticides to the diluent using the "W-A-L-E" plan:

- Add some of the diluent first

- Add Wettable and other powder and water-disperbile granules

- Agitate thoroughly and add the remaing diluent

- Add the Liquid products, such as, solutions, surfactants, and flowables

- Add Emulsifiable concentrates last

Shake the jar vigorously. Feel the sides of the jar to determine if the mixtures is giving off heat. If so, the mixture may be undergoing a chemical reaction and the pesticides should not be combined. Let the mixture stand for about 15 mintues and feel again for unusual heat.

If scum forms on the surface, if the mixture clumps, or if any solids settle to the bottom (except for wettable powders), the mixture probably is NOT compatible. Finally, if no signs of incompatibility appear, test the mixture on a small area of the surface where it is to be applied.

(Source: Prairie Grains, June 2006)

Resolving Incompatibility

Add 6 drops of compatibility agent and stir well. If mixture appears compatible, allow it to stand for 1 hour, stir well, and check it again. If the mixture appears incompatible, repeat one or two more times, using 6 drops of compatibility agent each time.

If incompatibility still persists, dispose of this mixture, clean the jar, and repeat the above steps, but add 6 drops of compatibility agent to the water before anything else is added.

If the mixture is still incompatible, do not mix the chemicals in the spray tank.

To overcome this problem, you might consider the following alternatives:

- Use a different water supply. Hard water can contribute to incompatibility.

- Change brands or formulations of chemicals

- Change the order of mixing.

Make only one change at a time, and perform a complete test, as described above, before making another change. Do not mix the chemical in the spray tank if incompatibility cannot be resolved.

(Source: Montana State University Extension Service)



Flea Beetles in Canola
Continue to scout spring planted canola fields in the seedling stage (susceptible crop stage) for flea beetle injury. Cool temperatures and dry conditions have delayed movements into spring planted canola fields in some areas. As temperatures warm up into 70s F, flea beetles move quickly and in large numbers out of overwinter sites. Foliar applications of insecticides are necessary when defoliation reaches 25% (economic threshold level). Foliar insecticides registered in canola in ND include: Capture, Sniper, Decis, Methyl parathion, Proaxis, Taiga Z, and Warrior.

Lilac as an Indicator of Grasshopper Emergence
Lilacs are blooming in most regions of North Dakota, and the beginning of bloom in common lilac is an indicator of the start of grasshopper hatch. Using plants as indicators can help the farm or range manager observe the influence of current weather on biological activity without using temperature-driven predictive models. The main variable influencing bloom time of common lilac, a landscape plant that often receives standard care, is temperature. On average, 10 days after common lilac were flowering 75% of the grasshoppers were first stage nymphs and 25% were second stage nymphs. Earlier hatching and faster development can be expected on southern facing slopes. If populations of newly hatched grasshoppers are threatening (more than 50-75 per square yard in field margins or 30-45 per square yard in field), control grasshoppers early while they are concentrated in grassy ditches, fencerows and weedy areas. Grasshoppers are also more susceptible to insecticides during the nymph (young grasshopper) stage. Continue scouting for young grasshoppers into late June. Peak egg hatch usually occur in mid-June in ND. Cool temperatures and wet conditions may delay egg hatch in the spring. Whereas, warm temperatures and dry conditions may increase the risk of grasshopper infestations.

Janet Knodel
Extension Entomologist

NDSU Crop and Pest Report Home buttonTop of Page buttonTable of Contents buttonPrevious buttonNext button