Ministry of Agriculture, Food and Rural Affairs

Rainfastness of insecticides on fruit

The following information has been adapted from an article posted May 30, 2017 by John Wise from Michigan State University Extension. Note that some products listed in this article may not be registered for use in Canada. Check with your local supplier or refer to the 2016-2017 Publication 360: Guide to Fruit Production and 2017 Supplement for a complete list of registered products.

In view of the frequent rains in recent weeks, this information is important for growers. 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, while 2 to 6 hours is sufficient drying time for many insecticides, 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.

Table 1. General characteristics for insecticide chemical classes

Insecticide Group	Rain-fastness ≤ 0.5 inch Fruit	Rain-fastness ≤ 0.5 inch Leaves	Rain-fastness ≤ 1 inch Fruit	Rain-fastness ≤ 1 inch Leaves	Rain-fastness ≤ 2 inches Fruit	Rain-fastness ≤ 2 inches Leaves
Carbamates (1A) Lannate, Sevin, Vydate	M	M/H	M	M	L	L
Organophosphates (1B) Cygon, Imidan, Lagon, Lorsban, Malathion, Pyrinex, Warhawk	L	M	L	M	L	L
Pyrethroids (3A) Ambush, Capture, Concept, Decis, Mako, Matador, Perm-Up, Pounce, Pyganic, Silencer, Up-Cyde	M/H	M/H	M	M	L	L
Neonicotinoids (4A) Actara, Admire, Alias, Assail, Calypso, Clutch, Concept	M,S	H,S	L,S	L,S	L,S	L,S
Spinosyns (5) Delegate, Entrust, Success, TwinGuard	H	H	H	M	M	L
Avermectins (6) Agri-Mek	M,S	H,S	L,S	M,S	L	L
IGRs (15 & 18) Rimon, Confirm, Intrepid	M	M/H	M	M	L	L
Diamides (28) Altacor, Exirel	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 Group	Persistence	Penetration	Rainfast rating
Carbamates (1A) Lannate, Sevin, Vydate	Short	Cuticle	Moderate
Organophosphates (1B) Cygon, Imidan, Lagon, Lorsban, Malathion, Pyrinex, Warhawk	Medium-long	Surface	Low
Pyrethroids (3A) Ambush, Capture, Concept, Decis, Mako, Matador, Perm-Up, Pounce, Pyganic, Silencer, Up-Cyde	Short	Cuticle	Moderate-high
Neonicotinoids (4A) Actara, Admire, Alias, Assail, Calypso, Clutch, Concept	Medium	Translaminar, acropetal	Moderate
Spinosyns (5) Delegate, Entrust, Success, TwinGuard	Short-medium	Translaminar	Moderate-high
Avermectins (6) Agri-Mek	Medium	Translaminar	Moderate
IGRs (15 & 18) Rimon, Confirm, Intrepid	Medium-long	Translaminar	Moderate
Diamides (28) Altacor, Exirel	Medium-long	Translaminar	Moderate-high

*Tables adapted from "Rainfast characteristics of insecticides on fruit" by John Wise, Michigan State University Extension

Based on simulated rainfall studies to combine rainfastness with residual performance after field-aging of various insecticides, including carbamates (Lannate), organophosphates (Imidan, Malathion), pyrethroids (Capture), neonicotinoids (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 for Japanese beetle and Malathion, Delegate and Assail on blueberries for spotted wing drosophila (SWD), 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 all products but Assail, Rimon, Delegate or Altacor on apples.
• 1-inch rainfall: In general, most products would need re-application following a 1-inch rainfall with 7-day old residues, whereas Delegate and Altacor could withstand this amount of rain on apples and would not need to be immediately re-applied. Some products such as Imidan on apples and blueberries (SWD), Assail (cranberry fruitworm), Delegate (cranberry fruitworm) and Lannate (SWD) on blueberries could withstand 1 inch of rain with 1-day old residues.
• 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 included in this study are registered on fruit crops and/or for these particular pests in Canada. Refer to the product label or Publication 360 for a complete list of management options.