May 30, 2017
Rainfast characteristics of insecticides on fruit reviewed

The rainfall events experienced in Michigan have prompted questions about the relative “rainfastness” of the insecticides used in fruit production. In 2006, AgBioResearch provided funds to purchase and install a state-of-the-art rainfall simulation chamber at the Trevor Nichols Research Center (TNRC), after which Michigan State University Extension (MSU) has conducted trials on fruit crops for a range of insecticides.

MSU’s John Wise said there are several critical factors that influence impact of precipitation on a pesticide’s performance. First is the plant-penetrative attributes of the various compounds. Some pesticide chemistries, like organophosphates, have limited penetrative potential in plant tissue, and thus are considered primarily as surface materials. Some compounds, such as carbamates, oxadiazines and pyrethroids, penetrate plant cuticles, providing some resistance to wash-off. Many newer compounds, such as spinosyns, diamides, avermectins and some Insect Growth Regulators (IGR), readily penetrate plant cuticles and have translaminar movement in leaf tissue. Others, like the neonicotinoid insecticides, are systemic and can have translaminar (moves from top surface to bottom of leaf) as well as acropetal movement in the plant’s vascular system (moves from center to growing tips of leaves). Penetration into plant tissue is generally expected to enhance rainfastness of pesticides.

The second factor is the inherent toxicity of an insecticide to the target pest and the persistence of the compound in the environment. In some cases, a compound may be susceptible to wash-off, but its environmental persistence and inherent toxicity to the target pest compensates for the loss of residue, thus delaying the need for immediate re-application.

The third factor is the amount of precipitation. In general, organophosphate insecticides have the highest susceptibility to wash-off from precipitation, but following light rainfall their high field-rate toxicity to most target pests overcomes the necessity for immediate re-application. Neonicotinoid insecticides are moderately susceptible to wash-off with residues that have moved systemically into plant tissue being highly rainfast, and surface residues less so. Carbamate, IGR and oxadiazine insecticides are moderately susceptible to wash-off and vary widely in their toxicity to the range of relevant fruit pests. Diamide, spinosyn, avermectin and pyrethroid insecticides have proven to be moderate to highly rainfast on most fruit crops.

For most insecticides, a drying time of two to six hours is sufficient to “set” the compound in or on the plant. With neonicotinoids, for which plant penetration is important, drying time can significantly influence rainfastness. For neonicotinoids, up to 24 hours is needed for optimal plant penetration, thus the time proximity of precipitation after application should be considered carefully. Spray adjuvants, materials intended to aid the retention, penetration or spread on the plant, can also improve the performance of insecticides.

Based on results from current studies, the following charts have been developed to serve as a guide for general rainfastness characteristics and re-application recommendations for certain insect pests (also printed in the “2017 Michigan Fruit Management Guide,” E0154). Note that these recommendations should not supersede insecticide label restrictions or farm-level knowledge based on site-specific pest scouting, but rather are meant to compliment a comprehensive pest management decision-making process.

Rainfastness rating chart: General characteristics for insecticide chemical classes
Insecticide class Rainfastness ≤ 0.5 inch Rainfastness ≤ 1.0 inch Rainfastness ≤ 2.0 inches
Fruit Leaves Fruit Leaves Fruit Leaves
Organophosphates Low Moderate Low Moderate Low Low
Pyrethroids Moderate/High Moderate/High Moderate Moderate Low Low
Carbamates Moderate Moderate/High Moderate Moderate Low Low
IGRs Moderate Moderate/High Moderate Moderate Low Low
Oxadiazines Moderate Moderate/High Moderate Moderate Low Low
Neonicotinoids Moderate, Systemic High, Systemic Low, Systemic Low, Systemic Low, Systemic Low, Systemic
Spinosyns High High High Moderate Moderate Low
Diamides High High High Moderate Moderate Low
Avermectins Moderate, Systemic High, Systemic Low,Systemic Moderate, Systemic Low Low

Highly rainfast = ≤ 30% residue wash-off
Moderately rainfast = ≤ 50% residue wash-off
Low rainfast = ≤ 70% residue wash-off
Systemic = Systemic residues remain within plant tissue

Apple insecticide precipitation wash-off re-application decision chart – codling moth. Expected codling moth control in apples, based on each compound’s inherent toxicity to codling moth larvae, maximum residual and wash-off potential from rainfall.
Insecticides Rainfall = 0.5 inch Rainfall = 1 inch Rainfall = 2 inches
*1 day *7 days *1 day *7 days *1 day *7 days
Imidan  Sufficient insecticide residue Insufficient insecticide residue  Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Asana  Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Assail  Sufficient insecticide residue  Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Proclaim  Sufficient insecticide residue Insufficient insecticide residue  Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Rimon  Sufficient insecticide residue  Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Delegate  Sufficient insecticide residue  Sufficient insecticide residue  Sufficient insecticide residue  Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Altacor  Sufficient insecticide residue  Sufficient insecticide residue  Sufficient insecticide residue  Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue

* Number of days after insecticide application that the precipitation event occurred.
Insufficient insecticide residue = Insufficient insecticide residue remains to provide significant activity on the target pest, and thus re-application is recommended.
Sufficient insecticide residue = Sufficient insecticide residue remaining to provide significant activity on the target pest, although residual activity may be reduced.

Grape insecticide precipitation wash-off re-application decision chart – Japanese beetles. Expected Japanese beetle control in juice grapes, based on each compound’s inherent toxicity to Japanese beetle adults, maximum residual and wash-off potential from rainfall.
Insecticides Rainfall = 0.5 inch Rainfall = 1.0 inch Rainfall = 2.0 inches
*1 day *7 days *1 day *7 days *1 day *7 days
Imidan Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Sevin Sufficient insecticide residue Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Brigade Sufficient insecticide residue Insufficient insecticide residue Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Actara Sufficient insecticide residue Insufficient insecticide residue Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Avaunt Sufficient insecticide residue Insufficient insecticide residue Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue

* Number of days after insecticide application that the precipitation event occurred.
Insufficient insecticide residue = Insufficient insecticide residue remains to provide significant activity on the target pest, and thus re-application is recommended.
Sufficient insecticide residue = Sufficient insecticide residue remaining to provide significant activity on the target pest, although residual activity may be reduced.

Blueberry insecticide precipitation wash-off re-application decision chart – cranberry fruitworm. Expected cranberry fruitworm control in blueberries, based on each compound’s inherent toxicity to cranberry fruitworm larvae, maximum residual and wash-off potential from rainfall.
Insecticides Rainfall = 0.5 inch Rainfall = 1.0 inch Rainfall = 2.0 inches
*1 day *7 days *1 day *7 days *1 day *7 days
Asana  Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Intrepid  Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Assail  Sufficient insecticide residue Insufficient insecticide residue Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Delegate  Sufficient insecticide residue Insufficient insecticide residue Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue

* Number of days after insecticide application that the precipitation event occurred.
Insufficient insecticide residue = Insufficient insecticide residue remains to provide significant activity on the target pest, and thus re-application is recommended.
Sufficient insecticide residue = Sufficient insecticide residue remaining to provide significant activity on the target pest, although residual activity may be reduced.

Blueberry insecticide precipitation wash-off re-application decision chart – Japanese beetles. Expected Japanese beetle control in blueberries, based on each compound’s inherent toxicity to Japanese beetle adults, maximum residual and wash-off potential from rainfall.
Insecticides Rainfall = 0.5 inch Rainfall = 1.0 inch Rainfall = 2.0 inches
*1 day *7 days *1 day *7 days *1 day *7 days
Imidan Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Mustang Max Sufficient insecticide residue Insufficient insecticide residue Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Sevin Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Provado Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue

* Number of days after insecticide application that the precipitation event occurred.
Insufficient insecticide residue = Insufficient insecticide residue remains to provide significant activity on the target pest, and thus re-application is recommended.
Sufficient insecticide residue = Sufficient insecticide residue remaining to provide significant activity on the target pest, although residual activity may be reduced.

Blueberry insecticide precipitation wash-off re-application decision chart – spotted wing Drosophila. Expected spotted wing Drosophila control in blueberries, based on each compound’s inherent toxicity to SWD, maximum residual and wash-off potential from rainfall.
Insecticides Rainfall = 0.5 inch Rainfall = 1.0 inch Rainfall = 2.0 inches
*1 day *7 days *1 day *7 days *1 day *7 days
Imidan Sufficient insecticide residue Insufficient insecticide residue Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Mustang Max Sufficient insecticide residue Insufficient insecticide residue Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Lannate Sufficient insecticide residue Insufficient insecticide residue Sufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Malathion Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Delegate Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue
Assail Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue Insufficient insecticide residue

* Number of days after insecticide application that the precipitation event occurred.
Insufficient insecticide residue = Insufficient insecticide residue remains to provide significant activity on the target pest, and thus an immediate re-application is recommended.
Sufficient insecticide residue = Sufficient insecticide residue remaining to provide significant activity on the target pest, although residual activity may be reduced.

Insecticide persistence, plant penetration and rainfastness rating
Compound class Persistence (residual on plant) Plant penetration characteristics Rainfast rating
Organophosphates Medium – Long Surface Low
Carbamates Short Cuticle Penetration Moderate
Pyrethroids Short Cuticle Penetration Moderate – High
Neonicotinoids Medium Translaminar & Acropetal Moderate
Oxadiazines Medium Cuticle Penetration Moderate
Avermectins Medium Translaminar Moderate
IGRs Medium – Long Translaminar Moderate
Spinosyns Short – Medium Translaminar Moderate – High
Diamides

 

Medium – Long Translaminar Moderate – High


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