Fungicide Application Basics

Fungicide use appears to be the fastest growing segment of North American crop protection.  Here is some advice on how to get the best bang for the buck.

• Timing is the most important part of fungicide application. Diseases can develop and spread quickly.  Most fungicides cannot cure a disease infection, they can only protect against it.  If an application misses the window, yield is lost.  Remember your priorities – become familiar with disease symptoms, the susceptibility of your crop and key growth stages.  Make sure your sprayer is ready – your nozzles are installed, calibrated, and you can achieve the necessary boom height.  Hire an agronomist to help scout and make recommendations. Make the right decision about whether to spray or not.

• Water volume is the most important application parameter for fungicide application. In years of study, increasing water volume had a greater effect on fungicide performance than changes in droplet size or spray pressure.  More water is needed for fungicides than herbicides because of the greater amount of plant material present.  Getting coverage on leaf areas deeper into the canopy requires more water.  Although finer sprays can also help with coverage, this practice is riskier due to drift potential and higher evaporation rates.
• Double nozzles, in particular the asymmetric types, are becoming more popular with fungicides. Double nozzles are proven effective and recommended primarily for fusarium head blight, or any other disease where an exposed vertical part of the plant canopy is the primary spray target.  Double nozzles are also useful for preventing the spray quality from getting too coarse as higher flow-rate nozzles (which tend to have larger droplets) are used.

• Travel speed is important with fungicides. Canopy penetration sometimes improves with slower travel speeds, and this can be used as an advantage by eliminating the need for a special fungicide nozzle.  For example, assume a nozzle was used to apply 8 gpa of herbicide at 15 mph at 70 psi (this pressure assumes air-induced tips).  For fungicides, this same nozzle and pressure will deliver 12 gpa simply by slowing down to 10 mph.

Boom height and spray quality are both important for single angled sprays or double nozzles. The angle at which a spray leaves a nozzle diminishes quickly as air resistance and gravity exert their influence.  If the boom is too high, the initial forward  angle will be lost and the spray droplets will actually deposit with gravity and wind.  But if the spray is a bit coarser and the boom is low enough, the angle of attack is retained for long enough to make a difference in spray deposition.

Despite these suggestions for making the spray more effective, there is no substitute for an informed decision regarding fungicide use.  It’s possible that spraying is unnecessary for a number of reasons, and it’s best to have professional advice help make that call.  If you decide to go ahead, ensure that your sprayer is set up to deliver the fungicide to the part of the canopy that needs protection.