Bent on Anthracnose. Weather

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1 Weather August to this point has mirrored much of July with cooler than summer temperatures, approximately 2 to 4 F below normal around with the state. Combined with frequent rains in central and northern MO, most cool season turfgrasses in lawns, sports fields, and golf course roughs are looking fairly green and lush for mid August. The two significant rain events over the last two weeks supplied anywhere from 2 6 of precipitation over the northern 2/3rds of the state, and have gotten much of Missouri out of any significant drought situation. As the above forecast map shows, we are set for a strong hit of summer towards the middle and later portions of this week. Forecasts indicate this span could bear the highest sustained temperatures of the summer season, with highs in the upper 90 s and lows in the mid 70 s. This spell could be a blessing for those still waiting on warmseason turfgrasses to perk up, but may bring the curse of a stressful environment for cool season grass species and a high potential for significant disease outbreaks. Rain chances are slated to be lower during the heat of the next 5 7 days, but are back at or above normal in the 614 day outlook.

2 Bent on Anthracnose Quick Hits: HEAT!: Just to reiterate the weather report, Missouri is set for the hottest temperatures of the season. Brown patch on tall fescue, Pythium blight (and perhaps summer patch) on Kentucky bluegrass, and a myriad of problems on creeping bentgrass putting greens could show during this heat spell, so keep your scouting eyes open and look at the bright side of having the intense heat at the end of the summer season instead of at the beginning. Early August Large Patch: High temperature warning out of one side of the mouth, and large patch reports out of the other side. A few superintendents in the central MO area (thanks for the pics gentlemen) reported large patch symptoms on zoysia on August 8th after the cool 70 degree F rain event of August 7th. While this isn t necessarily a call to arms against the disease in early August, it highlights our cool summer weather pattern, an overall poor warm season turfgrass growing season, and most importantly that turfgrass diseases heed the environment and host condition, and not a calendar.

3 What if?: Despite my pathologically displaced dismay over the cool temperatures, there has still been some significant disease pressure this summer. The pictures above represent a What if? scenario of applying no treatments to a diseaseprone bentgrass putting green. Nonfungicide treated creeping bentgrass plots on this Penncross disease green have been hammered by dollar spot, resulting in a Tetrislike appearance. Since the frequent rain events, we have also received a decent amount of brown patch pressure on these plots, with very prominent smoke rings shining through in the morning dew. Invoking a small smile, but only for research purposes. Dollar Spot on Lawns/Sports Fields: Dollar spot has been fiercely driven by the mild summer, and in the Plant Disease Clinic we are routinely receiving Kentucky bluegrass samples from home lawns and sports fields with significant outbreaks. In most cases, the homeowner is not aware they even have Kentucky bluegrass, which was probably seeded in a mixture with tall fescue. As the years, (and potentially the brown patch), wore on, the Kentucky bluegrass won the war with its strong rhizomes, and now dollar spot is the principal disease problem. This species/disease switch becomes important if a fungicide treatment is elected, as the main fungicide utilized for brown patch on tall fescue is azoxystrobin (i.e. Heritage), which will not control dollar spot. Dollar spot will require a DMI chemistry such as propiconazole or myclobutanil to at least be included in the treatment to achieve dollar spot control. Alternatively, a small shot of fertilizer can be used to grow out of the disease, but it would be wise to save this until early to mid September. Brown Patch on Tall Fescue: We have also noticed spotty areas of brown patch on tall fescue at the turf farm, which should get worse when the temperatures rise later this week. At this point in the season, it may be wiser to invest in reseeding and fertilization costs in September, rather then apply a curative fungicide for what should be a small window of necessity.

4 Bent on Anthracnose Anthracnose on Bent Anthracnose on bentgrass putting greens have got some superintendents bent on anthracnose. In the last two weeks, samples from both St. Louis and Kansas City of destructive basal rot anthracnose on Penncross and Pennlinks bentgrass have come into the lab. The disease is caused by the fungal pathogen Colletotrichum cereale, which is seemingly always present as a saprophyte or secondary pathogen on senescing leaves and decomposing thatch. At some point, the pathogen gets particularly lethal by invading the crown instead of just the foliage. As an anecdotal observation, I tend to notice a spike in lethal anthracnose on bentgrass in the fall when temperatures first plunge (~70F highs, or ~60F lows) after a normal summer heat event. This summer we have experienced a number of these events throughout July and early August. Most of the recent and ongoing anthracnose research has been conducted at Rutgers University under the programs of Dr. Jim Murphy and Dr. Bruce Clarke. They have teased apart the impact of different agronomic practices on the severity of the disease, and have greatly enhanced our understanding of its etiology. Although this research has been targeted towards the disease on Poa annua putting greens, much of the some tenets hold true on bentgrass. In the anthracnose cases reported in the last few weeks, one had nitrogen levels that were admittedly too low, and one relied on one particular fungicide chemistry (QoI) for control. The Rutgers group has prepared an updated white paper on the best management practices for anthracnose. If you have had anthracnose problems on a susceptible bentgrass

5 cultivar (i.e. Penncross, Pennlinks, Providence, Dominant, SR1020 ), the paper is a great read and can be found here. As alluded to above, rotating fungicides for anthracnose control is critical, since fungicide resistance seems to develop rapidly in this pathogen population. Fungicide resistance to the benzimidazoles (thiophanatemethyl) and the QoI (azoxystrobin, pyraclostrobin, trifloxystrobin, fluaxostrobin) chemistries has been found in anthracnose populations, and is thought to be widespread. Other chemistries proven effective against the disease include chlorothalonil, the DMIs, fludioxonil, fosetylal, and polyoxind. If a curative application is necessary, a tankmix of a contact such as chlorothalonil with a systemic plus a small shot of nitrogen (0.1 lb N/1000 sq ft) may aid in recovery. Extreme caution should be exercised with most DMIs if applied during and shortly before a summer heat stress event (like this week in MO). One notable exception is Briskway, a prepackaged mixture of azoxystrobin and difenconazole, which has not demonstrated stress related phytotoxicity in our studies. Have a good rest of the week, Lee Lee Miller Follow on Extension Turfgrass Pathologist University of Missouri