Implications for Disease Control under Reduced Management Conditions
All reports are that courses are emerging from winter in fabulous shape…as long as you had a strong snow mold treatment down. This is obviously good news because recovery from winter injury means stimulating growth, which we want to avoid. For now, it’s fortunate that this crisis has come at a relatively low disease pressure time of the year. Relatively minor infections of leaf spot or Microdochium patch can occur but can also be tolerated without golfers present since it’s unlikely that they will cause any lasting effects. If the course closures last into late May and June that has larger implications for disease control, but for this article let’s assume that courses will be opening up by June 1st and maintenance will be returning to normal around that time.
For a June 1st ‘return to normal-ish’ date, the fungicide focus should be on diseases that aren’t effectively controlled with curative fungicide applications later in the season. This is true for diseases like take-all patch, summer patch, and fairy ring. If you have experienced these diseases in the past, preventative applications targeting these diseases should be the priority (and should be lightly watered in) when 2-inch soil temperatures reach 55-60°F. Applications for these diseases made much later than this, when soil temperatures are above 65°F, are largely ineffective and can lead to widespread damage later in the season that isn’t easily fixed.
Dramatic reductions in nitrogen fertility will lower growth rate but could also increase susceptibility to certain diseases later in the season, namely dollar spot and anthracnose. Rutgers has determined the optimal nitrogen fertility range for anthracnose to be between 2.5 and 3.5 pounds of nitrogen per 1000 sq ft per year. While the nitrogen range for dollar spot is less well-defined, our research has demonstrated that nitrogen fertility below 3 pounds of nitrogen per 1000 sq ft per year will lead to increased levels of dollar spot and slower rates of recovery. To account for nitrogen levels well below this, we recommend making a preventative fungicide application in mid-to-late May targeting primarily dollar spot. Products from the SDHI fungicide class (Posterity, Xzemplar, Exteris, etc) and newer products like Maxtima and Secure Action typically have longer reapplication intervals (21 to 28 days) and should be used instead of shorter duration products like chlorothalonil.
The products listed above have longer reapplication intervals, but in many cases might be too expensive for fairway applications given the reduced-revenue environment many superintendents currently find themselves in. Putting greens should be prioritized, and an increased willingness to accept some disease on fairways and tees is probably needed right now as well. Mild to moderate outbreaks of dollar spot can be brought under control in just a couple weeks with increased nitrogen and curative applications of a number of fungicides.