Last week was incredibly hot and humid. Precipitation totals across the region exceeded 100 mm of rainfall in select locations. These temperatures and precipitation totals are not optimal. Many physiological functions (cell strength, root function, photosynthetic efficiency) begin to rapidly decline with these environmental conditions. Alas, we have had our first full week experiencing summer decline.
Perhaps the physiological function we should be most concerned about is root function. Root dieback can occur when soil temperatures in the upper rootzone exceed 28°C. Saturated or poorly draining rootzones that deplete oxygen supply are even more prone to root dieback.
In addition to the abiotic maladies, root dieback can also occur due to biotic stresses including summer patch and Pythium root rot among others. The summer patch pathogen is active whenever soil temperatures exceed 20°C. Its’ activity, and resulting damage, tends to increase proportionally to the temperatures in that upper profile. Summer patch has been confirmed on annual bluegrass tees, fairways, collars, and putting greens. Researchers from NC State University have also discovered that summer patch can also cause decline of creeping bentgrass putting greens during peak summer stress.
Unfortunately for golf course superintendents, summer patch cannot be controlled by just one preventative fungicide application. Those with a prior history of summer patch are usually on a strong preventative program with two, three, and sometimes four applications. This is because fungicides DO NOT kill the pathogen; these materials simply force the pathogen into remission. When the persistence of those active ingredients drop considerably under high temperatures, the pathogen resumes infecting roots.
A good best management practice is to open up with rootzone with a minimally disruptive venting program. This can provide quick relief to rootzones that have lacked adequate oxygen in the past week. Venting with needle tines can also open up avenues to allow a fungicide application to reach the site of infection in the root system. It should be noted that there is a risk of needle tining during times of pathogen activity as the inoculum could spread to other areas. However, I believe the benefits of this practice outweigh the possible negatives.
A great Bayer solution for summer patch management is applications of Mirage Stressgard. This DMI has excellent summer safety and is among the most powerful antifungal compounds available in the Canadian market with excellent demonstrated efficacy against summer patch.
Pythium root rot is another disease that could have also been opportunistic last week. This disease occurs most commonly on poorly draining creeping bentgrass putting greens. Low lying areas on putting greens or areas near collar damns should be especially diligent with daily scouting.
Signature XTRA Stressgard would be a great Bayer solution as this product is the only fungicide in the Canadian market labeled for both Pythium root rot and anthracnose control. In a curative situation, I would recommend that Signature XTRA be watered in. In extreme high pressure areas, it may be beneficial to tank-mix Signature XTRA with Banol to control a broader spectrum of Pythium diseases.
It is widely known the active ingredient in Signature XTRA (Fosetyl-Aluminum) can transport into the phloem and enter the root system. However, in a curative situation where physiological functions have already declined, I would encourage the applicator to water in this product to the site of pathogen infection. Signature XTRA may also help facilitate new root growth to aid in recovery. Internal research in a controlled environment as demonstrated a positive impact of creeping bentgrass rooting in absence of visible disease pressure.
For further questions I would recommend you to contact your regional Bayer Territory Sales Manager. I hope that these solutions will help you deliver outstanding playing conditions that redefine normal for your golfing community.