Tips to Improve Rice Fungicide Application Effectiveness

Although the majority of the 2014 Mississippi rice crop hasn’t been planted, pre-planning for a mid-season fungicide application should not be far from our minds.  Recent mention of strobilurin-resistant Rhizoctonia solani in rice and soybean should remind us to weigh important fungicide application strategies before the season gets under way. Once the season gets underway, we all get busy and forget important decisions regarding fungicide applications.  Preventing fungicide resistance from developing remains an important goal for rice farmers since there are no commercially available sheath blight resistant cultivars.

Several factors should be considered when planning a fungicide application program in any rice production system.  Crop coverage (carrier volume), canopy penetration, adjuvant and product choice, and application rate are all important items to consider.  The majority of the fungicide products labeled for rice disease management are preventive and not curative.  Therefore, applying a fungicide to provide maximum plant coverage is of key importance since fungicides are “locally systemic”.  Spray droplets land on plant tissue and the activity of the fungicide allows the product to travel short distances; hence the terminology “locally systemic” used with most fungicide literature.  In general, a fungicide’s mode of action is one of prevention by protecting the additional spread of the fungus to non-infected plant tissue.

To make the most out of fungicide applications that can become rather costly, we suggest considering the following items to aid in increasing fungicide application effectiveness: to increase application effectiveness use a greater carrier volume; because most if not all applications will be made via air consider 5 rather than 3 gallons.  Canopy penetration can be more difficult to achieve, than simply increasing the carrier volume.  Generally speaking and similar to a herbicide application, fungicide applications should be made when the wind is low.  Reducing the application volume and applying a fungicide that doesn’t quite reach or penetrate the canopy is not an effective disease management practice.  In addition, reducing the amount of fungicide that reaches the plant canopy can increase the likelihood of fungicide resistance developing, due to greater selection pressure when using a reduced rate of active ingredient.

Adjuvants can increase tissue coverage as well as aid plant canopy penetration.  Read and follow label instructions regarding the use, rate, and specific type of adjuvant.  Choosing a fungicide product is not normally a major decision; however, most rice farmers use the same product annually.  In some instances product choice depends on the historical disease pressure on each farm.  In other cases the product choice may be based on price.  When selecting a  fungicide, choose a product that has performed well in efficacy trials within the Mid-South rice belt and keep in mind that for a disease such a sheath blight, members of the strobilurin class of fungicides tend to provide the best disease management.  Last, but not least, fungicide application rate is important for several reasons.  Fungicide application rates vary from farm to farm and producer to producer.  However, one thing is certain, resistance management suggests that applying full label rates will help protect against the development of fungicide-resistant fungi in the Mississippi rice production system.  Cutting the labeled rate may be a cheap short-term alternative, but ultimately that decision will reduce the amount of chemical that can effectively manage the disease and increase the potential for fungicide resistance and create a greater long-term issue that will be inhertitly more costly to the Mississippi Rice Industry.

See results from two rice trials conducted in 2013, one on Cocodrie (2013 Cocodrie trial) and one conducted on hybrid rice (2013 hybrid trial).