I have a nice 8 x 10 sq ft patch of mature asparagus. Something has been killing the plants underground and I can see no outward sign of rodent holes, but there are small rocks around the patch and there may be access I don't see. It started in the middle of the patch with no growth, and now it has affected about 1/3 of the patch where I previously had the best growth. Help! What could this be and how can I stop it?
Thank you in advance.
Jan Haley, northern MN
Beltrami County Minnesota
Thanks for the question.
A common pest of asparagus in Minnesota are asparagus beetles. However they largely affect spears and cause them to bend over. It sounds as if this is not what you are seeing. Nevertheless, here is a publication dealing with them:
With respect to some critter causing these issues, the three most likely candidates are gophers, moles, and voles. I consider these as somewhat unlikely as moles do not eat plant materials, gophers generally go after underground vegetables, and voles generally eat seeds and grass above ground. Also with them some type of access holes would be visible. You indicated that you have not seen such. But just for completeness, here is some information about them.
So here’s what I think is going on. Your asparagus is experiencing some type of fungal disease that affects its roots and more likely what is called the asparagus crown. The is the portion of the plant that exists just at the soil surface. The two most likely candidates are Fusarium stem/crown rot (Fusarium moniliforme) and Fusarium wilt/root rot (Fusarium oxysporum). These are two of the most common diseases of asparagus in Minnesota. Often spores of these diseases can exist in the soil for several years and with time, asparagus is adversely affected. Common symptoms, especially seen towards the end of the season, include a drooping of the plants, browning developing, and decay of the roots. Here is some information about these two fungal possibilities:
With respect to treatment, be sure to remove all asparagus debris this fall, place in a trash bag, and discard appropriately. Next spring (early!!) consider transplanting your asparagus to a new area, as far away from their current location as possible. See:
While the use of fungicides would not hurt, most evidence indicates that they are of limited utility against these two fungal diseases. If you do want to employ a fungicide, be sure that on the label that it is effective against these two types of fusarium.
If you really want to get to the bottom of things and obtain a definitive answer, consider sending a sample of your asparagus to the Plant Disease Clinic of the University of Minnesota: