Rainfastness of insecticides on fruit

Adapted from "Rainfast characteristics of insecticides on fruit for 2014" by John Wise, Michigan State University Extension

The following information has been adapted from an article posted June 10, 2014 by John Wise from Michigan State University Extension. For the complete article, refer to Rainfastness characteristics of insecticides on fruit on the Michigan State University website. Note that some products listed in this article may not be registered for use in Canada. Check with your local supplier or refer to Publication 360: Guide to Fruit Production for a complete list of registered products.

According to Wise, the impact of rain on an insecticide's performance can be influenced by the following:

  1. Penetration into plant tissue is generally expected to enhance rainfastness.
    • Organophosphates have limited penetrative potential, and thus considered primarily surface materials.
    • Carbamates and pyrethroids penetrate the cuticle, providing some resistance to wash-off.
    • Spinosyns, diamides, avermectins and some insect growth regulators (IGR) readily penetrate the cuticle and move translaminar (top to bottom) in the leaf tissue.
    • Neonicotinoids are considered systemic or locally systemic, moving translaminar as well as through the vascular system to the growing tips of leaves (acropetal movement).
    • For products that are systemic or translaminar, portions of the active ingredient move into and within the plant tissue, but there is always a portion remaining on the surface or bound to the waxy cuticle that is susceptible to wash-off.
  2. Environmental persistence and inherent toxicity to the target pest can compensate for wash-off and delay the need for immediate re-application.
    • Organophosphates are highly susceptible to wash-off, but are highly toxic to most target pests, which means re-application can be delayed.
    • Carbamates and IGRs are moderately susceptible to wash-off, and vary widely in toxicity to target pests.
    • Neonicotinoids are moderately susceptible to wash-off, with residues that have moved systemically into tissue being highly rainfast, and surface residues less so.
    • Spinosyns, diamides, avermectins and pyrethroids are moderate to highly rainfast.
  3. Drying time can significantly influence rainfastness, especially when plant penetration is important. For instance, neonicotinoids require up to 24 hours for optimal penetration prior to a rain event.
  4. Spray adjuvants that aid in the retention, penetration or spread will enhance the performance of an insecticide.

The following tables have been adapted from Wise's studies to serve as a guide for general rainfastness to compliment a comprehensive pest management decision-making process.

Based on simulated rainfall studies to combine rainfastness with residual performance after field-aging of various insecticides, including organophosphates (Imidan), neonicotinoids (Calypso, Assail, Actara, Admire), IGRs (Rimon, Intrepid), spinosyns (Delegate) and diamides (Altacor), Wise recommends the following re-application decisions for apples, grapes and blueberries. Among the crops, variation in rainfastness of a specific insecticide occurs since the fruit and leaves of each crop have unique attributes that influence the binding affinity and penetrative potential.

  • ½ inch rainfall: With the exception of Imidan on blueberries, all products with 1-day old residues could withstand ½ inch of rain. However, if the residues have aged 7 days, immediate re-application would be needed for Imidan (apples, grapes, blueberries) and neonicotinoids (grapes, blueberries), but not Calypso, Assail, Rimon, Delegate or Altacor on apples.
  • 1-inch rainfall: In general, Imidan, neonicotinoids and IGRs would need re-application following a 1-inch rainfall, whereas Delegate and Altacor could withstand this amount of rain on apples and would not need to be immediately re-applied.
  • 2-inch rainfall: For all products, 2 inches of rain will remove enough insecticide to make immediate re-application necessary.

It is important to note, not all products registered for the selected pests were included in this study. Refer to Publication 360 for a complete list of management options.

Table 1. General characteristics for insecticide chemical classes
Insecticide Class Rainfastness
≤ 0.5 inch
Fruit
Rainfastness
≤ 0.5 inch
Leaves
Rainfastness
≤ 1 inch
Fruit
Rainfastness
≤ 1 inch
Leaves
Rainfastness
≤ 2 inches
Fruit
Rainfastness
≤ 2 inches
Leaves
Carbamates (1A)
M
M/H
M
M
L
L
Organophosphates (1B)
L
M
L
M
L
L
Pyrethroids (3A)
M/H
M.H
M
M
L
L
Neonicotinoids (4A)
M,S
H,S
L,S
L,S
L,S
L,S
Spinosyns (5)
H
H
H
M
M
L
Avermectins (6)
M,S
H,S
L,S
M,S
L
L
IGRs (15 & 18)
M
M/H
M
M
Diamides (28)
H
H
H
M
M
L

H -highly rainfast (≤ 30% residue wash-off), M -moderately rainfast (≤ 50% residue wash-off), L -low rainfast (≤ 70% residue wash-off), S -systemic residues remain with plant tissue

Table 2. Insecticide persistence, plant penetration and rainfastness rating
Insecticide Class Persistence Penetration Rainfast rating
Carbamates (1A)
Short
Cuticle
Moderate
Organophosphates (1B)
Medium-long
Surface
Low
Pyrethroids (3A)
Short
Cuticle
Moderate-high
Neonicotinoids (4A)
Medium
Translaminar, acropetal
Moderate
Spinosyns (5)
Short-medium
Translaminar
Moderate-high
Avermectins (6)
Medium
Translaminar
Moderate
IGRs (15 & 18)
Medium-long
Translaminar
Moderate
Diamides (28)
Medium-long
Translaminar
Moderate-high

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