Do Fungicides Have a Role in Alfalfa Hay Production?

Author: Carol A Frate

If you read national magazines covering hay and forage topics you may have seen some articles discussing the use of fungicides in alfalfa hay production to control leaf diseases.

Until recently, almost all fungicides registered for alfalfa hay were for seed treatments. It used to be the value of alfalfa didn’t justify the cost of applying foliar fungicides, but that has changed! In the past few years Headline, Quadris and Pristine have been registered in California for use on alfalfa hay. I conducted trials with these fungicides for efficacy against Sclerotinia stem and crown rot (“white mold”) but at a time of the year when foliar diseases are not widespread and, even if present, are minor compared to frost and insect issues. In the Midwest they have been looking at Quadris and Headline to control foliar diseases. These diseases result in the loss of lower leaves which, when severe, can reduce yield and quality.

Some of the foliar diseases prompting treatment in the Midwest are the same ones we have here. Common leafspot, Stemphyllium leafspot, Stagonospora leafspot, downy mildew and spring blackstem are fungi-caused diseases that occur in the Central Valley during spring and fall. These diseases are more common during these seasons because temperatures are moderate and dews provide the moisture needed for spore production, dispersal, germination and infection. Rain will also contribute to increased foliar disease levels but, as we too well know this year, rain is sometimes hard to come by. Currently, variety resistance and some management techniques are used to minimize losses from foliar diseases. Other than that, we just live with them.

The efficacy of these fungicides on specific diseases and the levels of disease are the two factors that decide whether or not fungicide applications pay for themselves. In Midwest studies they have good evidence that disease levels are reduced by fungicide applications, but measurable increases in yield and quality often do not occur. It depends on how serious the disease is in a particular cutting and weather has a lot to do with that.

My colleague Rachael Long in Yolo County and I will each be conducting a trial this spring evaluating fungicides for foliar diseases. I strongly suspect that we will see reduced disease levels with fungicide use but yield and quality differences will be hard to measure unless we get a lot of rain (which should increase disease levels) and cutting schedules are delayed (which will allow the leaf disease to infect more leaves). But that is why we conduct trials - to have facts and not opinions!