Fungicide Programs in the Summertime

            I mentioned that some things, we can just count on, year in and year out.  One of those biological stresses is brown patch disease.  In my opinion, the fungi that cause brown patch and related diseases consume more bentgrass leaves in the summer in the southeast than any other disease.  However, other disease problems may need to be considered depending on the circumstance.  Dollar spot may be a problem on some golf courses, due to the culture of susceptible varieties and conducive environmental conditions.  Fairy ring, caused by Lycoperdon puffballs, may infest putting greens.  Anthracnose basal rot has been problematic on bentgrass greens in recent years.  And, Pythium blight occasionally rears its ugly head and reminds us of its reputation!

            For eight or nine months of the year, we can pretty well rely on curative approaches for disease control.  We might get some dollar spot development or brown patch development in cooler months, but chances are that the bent will recover relatively quickly if we can suppress the disease in question in a timely manner.  However, in the hot, humid summertime, preventive control programs are usually needed.  What should one consider when outlining a preventive program? Several things are important to remember.  For instance, fungicides vary in their effectiveness for particular diseases and in the potential for phytotoxic or growth regulating effects. Also, disease pressure from particular diseases varies through the summertime and, of course, is affected by weather patterns.

            Typically, brown patch starts to appear about mid-June.  Potential for disease increases as the frequency of days with temperatures of 85 or greater and nighttime temperatures above 68 F increase.  So, we see pressure increasing through July and a relatively high risk being present through August in most summers. Usually, night temperatures begin to decrease in September and brown patch pressure drops.  Dollar spot typically is more of a problem on bentgrass when temperatures are in the high 70’s, with persistent high relative humidities.  Anthracnose basal rot may occur in cool as well as hot conditions, but can be devastating when turf recuperative potential is lowest (mid-summer).

            Just because a particular disease is listed on a fungicide label, the different fungicides differ considerably in their effectiveness, residual activity, and potential for development of resistance among the dollar spot pathogens. Some characteristics of fungicides should be noted carefully:

Azoxystrobin – Heritage. Probably the best brown patch material available to date. No activity on dollar spot. No harmful growth regulation in summer.  Low potential for phytotoxicity. Decent suppression of Lycoperdon fairy ring. Moderate effectiveness against Pythium blight.  Excellent for anthracnose basal rot. Upwardly mobile penetrant. Short persistence of residues in soil.

Chlorothalonil – Daconil, Echo, etc. One of the best all-round fungicides available. Very good brown patch activity. Good dollar spot activity, if used preventively.  Slow to cure existing, severe dollar spot. Low potential for development of resistance to dollar spot fungi. No harmful growth regulation in summer. Low potential for phytotoxicity. Moderate effeciveness for anthracnose basal rot, if used preventively.  Poor for anthracnose if used curatively. Moderate effectiveness for algae suppression, when used preventively. Contact fungicide.

Flutolanil – Prostar. Good brown patch activity. Decent suppression of Lycoperdon fairy ring. Activity limited to basidiomycete fungi, so no control of dollar spot, anthracnose and other diseases not caused by basidiomycete fungi. Upwardly mobile penetrant fungicide.

Propiconazole – Banner Maxx. Excellent for curative and preventive control of dollar spot. Poor brown patch material if used alone. Under high heat conditions, at high or frequent use rates, can cause unacceptable growth regulation in bentgrass. High potential for development of persistent resistance to dollar spot fungi. Upwardly mobile penetrant fungicide.

Other DMI or SBI fungicides: Bayleton, Eagle, Sentinel (removed from market recently), Rubigan. All are excellent for dollar spot, with some differences in length of control achieved. All can cause unacceptable growth regulation in bentgrass under high heat conditions, at high or frequent use rates. High potential for development of persistent resistance to dollar spot fungi. All are upwardly mobile penetrant fungicides.

Mancozeb – Fore, Dithane, Junction.  Excellent brown patch fungicides, but with very low residual activity, particularly under high rainfall conditions. Poor for dollar spot. Excellent for leaf spot. Moderate curative for Pythium blight. Moderate effectiveness for algae suppression, when used preventively. No problems with phytotoxicity observed. Contact fungicide.

Iprodione – Chipco 26GT, 26019. Moderate effectiveness for brown patch. Excellent dollar spot activity, both preventive and curative. Moderate to low potential for resistance to dollar spot fungi. Excellent for leaf spots. Localized penetrant fungicide.

Vinclozolin – Curalan, Vorlan, Touche.  Moderate effectiveness for brown patch. Excellent dollar spot activity, both preventive and curative. Moderate potential for resistance to dollar spot fungi. Excellent for leaf spots. Localized penetrant fungicide.

Thiophanate methyl – Cleary 3336, Fungo, Cavalier. Very good for curative and preventive control of dollar spot, but high potential for persistent resistance to dollar spot fungi. Good brown patch activity. Upwardly mobile penetrant fungicide.

By reviewing some of these characteristics of the commonly used fungicides, you have important information that could be used to design a preventive program.  I have observed in our experiments that low rates of SBI fungicides (e.g. 1 oz of Banner Maxx) can be used to achieve excellent dollar spot control and augment the brown patch under low disease pressure (e.g. in late May or early June).  Using these materials in a short rotation on into the summertime increases the risk of growth regulation that may increase algae encroachment.  Late in the summer or early fall, these materials can again be utilized with moderation and have reduced risk of unacceptable growth regulation.  Chorothalonil has performed very well in experiments for brown patch control under moderate to high pressure.  Heritage has performed the best at extremely high pressure in my experiments (typically, late June, through July).  If used earlier, dollar spot may become problematic unless the Heritage is tank-mixed with chlorothalonil or some other fungicides or follows in rotation from a fungicide that provides good dollar spot control.  Disease control can be augmented with tank mixes.  A number of years ago, Dr. Leon Lucas discovered that Aliette + Fore was excellent for summer bentgrass decline.  Since then, it has been shown that Daconil + Aliette or Daconil + Chipco Signature is as good or perhaps better under certain conditions (more residual control under high rainfall conditions).  And so on…

An Experimental Approach to Preventive Programs

Last summer, we decided to test several fungicide preventive programs for summer disease control.  This project was a special problem class for a turfgrass student, John Royals. The programs were designed for brown patch, primarily.  The test was initiated on June 2, 1998, on Penncross creeping bentgrass that was being grown on native soil at the Pee Dee REC.  The turf was mowed daily, at 5/32”.  Plots were 3' x 10' each, in randomized complete block design, with 4 replications.  The sprays were applied with a shielded CO₂ charged sprayer with two 8002 ER nozzles and 35 psi at the boom, delivering 2 gal of water/1000 sq. ft.  Sprays were normally applied by 11:00 am.  All fungicides were applied on a 14-day schedule, at “preventive” rates.  The plots were not inoculated for brown patch because the plots had a good history of previous infestation.  One broadcast application for Pythium blight was made using Subdue 2E at 2 oz/1000 sq. ft. in late June.    There were 10 treatments in this test with the first treatment being the check and 9 fungicides programs.  Some of the programs came from local superintendents and the others were formulated based on our own experience. 

The plots were rated once a week for percent brown patch, percent dollar spot, and turf quality on a scale of 1 to 9 with 9 being the best.  A turf quality of 6.5 was considered good, 7.5 was very good and 8 was excellent, 9 being superb.  The plots were normally lightly irrigated 3 times per day to make the area conducive to brown patch development. Plots were fertilized every 2 weeks with 1/8 lb N/1000 sq.ft. from a liquid 16-8-8 with minor elements. The plots were mowed 5 times per week at 5/32-inch with a Triplex greens mower.  The plots were also rated for percent algae and percent Curvularia blight as the trial progressed. 

 Table 1: Spray Programs. Rates are in oz product/1000 sq.ft.; all were applied on a 14-day schedule.

Results

            The summer was very conductive for disease development.  Weather records were accumulated to document highly stressful conditions. In general, all fungicide programs performed better than the check as expected.  There were two times during the trial when brown patch pressure peaked.  The first occurring around July 9, and the second occurred near the end of July. At the beginning of the trial, brown patch pressure was low, but there was moderate dollar spot pressure.

Most of the fungicide programs, with a few exceptions, performed well until about one week after the fourth spray was applied.  This indicates that several fungicides perform well when disease pressure is moderate.  However, when disease pressure was high, only 3 programs provided acceptable control. Programs 5, 6, and 7 performed the best and had the smallest area under the disease progress curve. Area under the disease progress curve is an integration of the amount of disease present over the period of time during the entire “epidemic”.  Programs 5, 6, and 7 never had disease over 20% during the test, despite the very high pressure that was induced by over watering. The check had brown patch over 20% for 90 days.  These programs, 5, 6, and 7 were all sprayed with Heritage in the third spray and programs 5, 6 and 7 were also all sprayed with a tank mix of Al  Signature + Fore or Al Signature + Daconil Ultrex in the spray program at times of high disease pressure.  This indicated that the plots that were sprayed with Heritage during the third spray around the first of July faired better than those treatments where Heritage was applied earlier or later in the program, or not at all. Based on past research, the excellent efficacy of Aliette Signature + Daconil Ultrex cannot be discounted.

Discussion

 This research demonstrated that fungicides could be strategically implemented to take advantage of certain materials strengths, and avoid some of the weaknesses and still obtain superior disease control.  There are other considerations that must be addressed.  For instance, many golf courses experience problems with fairy ring, caused by a puffball, Lycoperdon.  Generally, damage from these infestations is worse in the summertime (due to dry patches and limited ability to recover).  Typically, we have observed this damage to begin to be evident around the first of May.  In other work, we have demonstrated suppression of these fairy rings with Prostar, as well as Heritage.  Prostar is labeled for diseases caused by basidiomycete fungi (e.g. Rhizoctonia), but does not control dollar spot.  Similarly, Heritage also does not control dollar spot, and this disease can become more problematic in programs that rely strongly on Heritage and don’t adequately control dollar spot with other fungicides as tank mixes or in rotations.  Prostar has not performed as well as Heritage for brown patch in trials at the Pee Dee Research and Education Center.  But the 2 fungicides have performed about equally well for fairy ring.  Superintendents with both problems might consider using Prostar early (perhaps also, Prostar Plus or equivalent) to suppress fairy ring and augment brown patch control, and rely on Heritage in mid-summer to control brown patch (and further augment fairy ring suppression).  Another consideration is that Prostar does not control anthracnose caused by Colletotrichum graminicola.  However, Heritage is outstanding for that disease.  Anthracnose typically is more damaging to bentgrass in the summer than at other times of the year; another reason to “save” this fungicide for high heat stress times.

            Superintendents should pay close attention to the patterns of disease and the specific diseases (identification is critical) that occur on their golf courses.  The programs we have evaluated might be considered as guidelines and not as programs that are “written in stone”.  There are many other combinations and programs that might work effectively. For instance, golf courses that occur at higher elevations in the southeast or further north in the country likely will have greater pressure from dollar spot.  For those courses more attention would be placed on utilizing fungicides with excellent dollar spot activity, such as Chipco 26019, and vinclozolin formulations (Curalan, Vorlan, or Touché) or one of the DMI fungicides.        A similar scenario should be considered for prevention of Pythium blight.  In the hot, humid southeastern coastal plain, Pythium is a threat.  Utilizing Subdue Maxx, Banol, Koban, Aliette Signature, and Heritage in certain rotations should be considered, depending on experience and on the Pythium pressure that is predicted.  Subdue can be tank mixed with Daconil or other chlorothalonil formulations at the start of the summer when Pythium pressure is low but higher pressure is impending. When the residual fungicide is diminishing, another fungicide such as Banol might be considered.  When brown patch is increasing, Heritage should augment the Pythium program, although the label indicates higher rates and shorter intervals for Pythium blight than for brown patch; thus, it may augment Pythium control but might not be the strongest material for this disease (more data is needed!).  Similarly, use of Aliette Signature with Daconil has been excellent over the years in our trials.  Perhaps, Aliette Signature is providing some preventive and perhaps some curative activity against Pythium fungi that may be impacting the health of the bentgrass.

            Finally, realize that these are preventive programs where the fungicides were used at low rates on a preventive schedule.  If active disease is allowed to develop, it likely will take higher rates and shorter intervals of a fungicide to get adequate disease control and then only if the disease is positively identified in a timely manner to make the right decision on fungicide choice.

            There are several ways in which to approach disease management, and one should always attempt as much as possible to reduce disease pressure with cultural methods, and by proper design of the landscape.  The programs we evaluated were conducted under very high disease pressure, where fungicides are absolutely necessary in order to culture bentgrass greens through the summer.  We will continue this line of research and investigate the influence of newer cultivars that should also provide some help with recuperative potential.  It may be possible to move toward more curative approaches, if the cultivar will provide a better “baseline” of heat tolerance, and perhaps utilize lower rates of fungicides and/or longer intervals of control.  This may only be possible at times of moderate disease pressure, but the research needs to be conducted.

First printed in the Carolinas Green, July-August 1999