The recent intense rainfall events in some areas have made pest management much more challenging. Pesticide residues will be affected by this much rain.
We previously posted on rainfastness of pesticides: https://onfruit.ca/2024/07/10/pesticides-rain-ensuring-strength-in-storms/. In a nutshell, products that are designed to stay outside host tissue (contacts) are more prone to wash-off. But a product being locally systemic does not prevent degradation of residues.
All the studies in the literature max out rainfall amount at 50 mm(2″). In the past couple storms we’ve had well over that and in a very short period of time in Niagara. Regardless of whether a contact or locally systemic product was applied before the storms, protection will have been decreased enough to require application of a product (fungicide and insecticide).
Because of the delay accessing flooded orchards and vineyards, pathogens will have time to start sporulating. For fungicide resistance management, rotate to a different locally systemic fungicide group than the last spray plus another group, preferably a compatible contact (folpan, sulphur, some of the biologicals, Diplomat, ProBLAD, or Oxidate), to eliminate any sporulation that has occurred. Since not all of fungicides cover the spectrum of potential pathogens present (downy mildew and Botrytis bunch rot are the key diseases in grapes and brown rot in stone fruit), choose tank mix partners to cover the spectrum of diseases. Make sure to consult product labels for restrictions on tank mixing. Make sure that any tank mix partners have the approved Pesticide Regulation Division (formerly PMRA) tank mix statements. If you are using a tank mix that you haven’t used previously, contact the company to confirm that it is safe.The table below summarizes some tank mix compatibilities and cautions.
Product | Caution |
Oxidate | See compatibility table . Note these are American products. Consult the Crop Protection Hub or individual product labels for active ingredients. |
MilStop | No not tank mix with any product that cannot tolerate high pH (9). See compatibility table for some tank mixes. Note these are American products. Consult the Crop Protection Hub or individual product labels for active ingredients. |
Folpan | Maintain agitation of tank mix Avoid mixes with oils, EC formulation or products containing oil (Fontelis) |
Diplomat | No compatibility issues |
ProBLAD | Avoid the specific pH of 5.5 as the BLAD protein can denature as this is the very specific iso-electric point. Above or below this pH is fine. |
Serifel | BASF has a compatibilty table for some fungicides. |
Serenade | Buffer tank mix to a pH of 6 with Aliette as it is very acidic. |
Insecticide residues will also be affected by rainfall and should be reapplied. With oriental fruit moth and grape berry moth sprays forecast for next week, insecticides for these pests do not have to be reapplied but this should be a consideration should the pattern of heavy rainfall persist after those sprays have been applied.