June? Cool/Wet Returns, Pythium Root Rot, Bipolaris Leaf Spot, Cyst Nematode and KBG Divot Research

Is it June? After a hot Memorial Day weekend we saw the first full of week of June feel less summer-like. Instead it felt (and looked) like the penalty box of April or early spring. On certain days, Chicago’s lows were in the 50s. Cloudy conditions with persistent rains would darken our daylight. But on the days it didn’t rain? The conditions would warm and it was absolutely perfect. Perfect. If you love the outdoors, this week offered a few days that we dream about (in winter). In the landscape and on the golf courses one tree began asking for attention. That’s right, the eastern cottonwood, Populus deltoides, began releasing its seeds. Each is attached to what seems like a thread of cotton. When floating by in the outdoors it can feel like something is crawling on you. Or, if you inhale some of the cotton fluff, well that’s another experience. Usually you then look up and around. Eureka, you’ll see a very large tree (up to 100 feet) with distinctive heart-shaped (deltoid) leaves attached to flat petioles which undulate in the wind. Yes, cottonwood (the official state tree of Kansas) offers yet another sign that summer is near— June 21st is day one.

Image 1. A Pure Distinction creeping bentgrass green isn’t covered with disease (dollar spot). No, its just the day that a lot of tree seed was released and landed everywhere — cottonwood trees (Populus deltoides) grow along the edge of the Bob Berry Sunshine Course in Lemont, IL. Settle, Jun 7, 2022

On the golf course things are looking more and more balanced. Turfgrass color, density and uniformity is now or is about to be as good as it gets. For example, when rating creeping bentgrass visual quality in research studies this week we were saying 8, 8, 8, 9, 8, 7, 9. As good as it gets on a scale of 1–9. And then there’s roots. Out of sight and out of mind. Not so fast. June is a key month for root establishment. Roots are growing, reaching for both water and nutrients. That same root biomass will later serve as a carbohydrate reserves when the going gets tough (July). Our current conditions mean we have now increased our regular ‘scouting’ of plant health both above- (dollar spot, leaf spots et al.) and below-ground (fungal root rots). Superintendents and crew are officially back in the saddle. All caught up with the ancillary mowing of the rough. And the greens? They are already rolling just fine for summer — June 21st day one.

Weather Recap (June’s first 10 days) by Shehbaz Singh, MS

Air Temperature. The weather for first 10-days of June in Chicago was pretty mild. The air temperature ranged mostly from 58 to 78°F. The highest temperature of 81°F was recorded on June 3rd. This is actually in the normal range at this point of the month for Chicago. Last year in 2021, the air temperature at this time was on the higher-end and ranged from 70 to 89°F.

Figure 1. Current Chicago air temperatures (blue bars) versus normal range (brown band) in June, 2022.

Precipitation. Total accumulated rainfall so far in June is 1.2 inches. This is close to what the normal accumulated rainfall should be which is 1.4 inches. Periods of rainfall included 0.3 inches on June 6th and rainfall and 0.7 inches on June 8th. Last year in 2021, no rainfall was experienced in the first 10 days of June except from trace amounts.

Figure 2. Accumulated rainfall in Chicago (green line) versus normal (brown line) in June, 2022.

Weather forecast. Weather at the start of week will be cloudy to partly cloudy. Sunny to mostly sunny conditions can be experienced for most days and so it will be warmer. The air temperature is predicted to be from 59 to 90 ° F. Chances for rain will be highest early in the week

Pythium Root Rot Arrives

One of the chronic issues that creeping bentgrass greens can suffer from is a disease called Pythium root rot. More than one Pythium species can be the causal agent. The problem occurs when conditions are wet (Chicago’s spring in 2022) and then when conditions become hot which drives up plant water use via evapotranspiration rates or ET (Memorial Day weekend in 2022). It is most associated with golf greens. They are necessarily maintained at low mowing heights. That is enough additional stress to make this a problematic disease of golf greens that is becoming more and more common.

Aboveground symptoms are variable. It is impossible to diagnose this way. Obviously, midday wilt stress results from any root rot. Also an off-color look occurs to the affected turfgrass. It can look chlorotic (yellowish). Stressed creeping bentgrass often looks bronze (reddish). This is because turfgrass plants are unable to normally “mine” for nutrients like nitrogen with their roots. In the end we are talking about loss of root function and what it then causes = a weak plant.

Image 1. In creeping bentgrass, Pythium root rot is associated with darkened roots that appear damaged (layers of root cells slough off). Root hairs either disappear entirely or are reduced. Roots are short. Settle, Jun 8, 2022
Image 2. Presence of oospores (Pythium resting spores) are used to help confirm Pythium root rot. Settle, Jun 8, 2022

Bipolaris Leaf Spot of Creeping Bentgrass

Bipolaris leaf spot (B. sorokiniana) on creeping bentgrass greens at two locations in the Chicago District was another early arrival. Again due, in part, to the HOT Memorial Day weekend. This is an interesting foliar fungal disease because it is closely associated with certain creeping bentgrass varieties. For example, Penncross is highly susceptible as are probably some others. We just don’t know which varieties are more prone to it until we run into it. This isn’t a common disease of creeping bentgrass, but when it does occur it is problematic.

Bipolaris development is usually during conditions of frequent rainfall (now) and when conditions are warm (we’ve had some of that early). Control can be difficult because this fungal pathogen produces spores and so we have to keep an eye on the potential for development of resistance to certain groups of fungicides. For example, QoIs or strobilurins do not always provide adequate control of leaf spots. One possible explanation could be fungicide resistance.

Image 1. Bipolaris leaf spot of creeping bentgrass. The infection appears to be localized on a clone (dark green patch) of what is likely Penncross. Note: It was raining = ideal conditions for this disease! Settle, Jun 8, 2022
Image 2. Presence of multi-celled conidia/spores is used for positive diagnosis of Bipolaris leaf spot. To see this you must incubate a sample for 24–48 hours. Settle, Jun 8, 2022

Turfgrass Cyst Nematode (Heterodera iri)

Occasionally we find something out of the ordinary. Recently, we identifed the presence of cyst nematodes (likely Heterodera iri) from a root zone sample that represented an unhealthy area of a creeping bentgrass/Poa annua green. A healthy root zone sample (a check) from the same green did not contain cyst nematodes. It suggests that this endoparastic nematode may be part the story. For example, a different Heterodera species is a major nematode problem in soybeans. It’s part of an ongoing survey of golf course nematodes in the Chicago District area that uses a sucrose floatation with centrifugation to extract nematodes from soil samples. Historically (c. 2005), Dr. Randy Kane found cyst nematodes were associated with patches of wilt in sand-based greens during midsummer in Chicago. The occurrence of cyst nematodes in golf green is thought to be relatively rare. More to come.

Image 1. A juvenile (J2) cyst nematode from the root zone of a creeping bentgrass/Poa annua sand-based green. Settle Jun 1, 2022
Image 2. An enlarged female cyst nematode containing eggs from the root zone of a creeping bentgrass/Poa annua sand-based green. Settle Jun 1, 2022

Divot Research on a Kentucky Bluegrass Tee by Shehbaz Singh

A second divot study in collaboration with Zach Nicoludis, USGA, is yielding similar results as we are finding in the creeping bentgrass tee. This study is on an HGT Kentucky bluegrass tee at the Bob Berry Sunshine Course in Lemont, IL. The divot mix treatments have now seen seven weeks of turfgrass recovery.

  1. If a golfer is able to use an intact sod piece they should. But the success of this divot repair method may be influenced by time-of-year.
  2. Adding Leeward chewings fescue seed as a ‘nurse grass’ is improving divot recovery versus a divot mix alone.
  3. The two best treatments so far are: Compost + chewings fescue seed & 8:1:1 mix + chewings fescue seed.
Fig 1. Visual recovery (%) of HGT Kentucky bluegrass given 8 different divot treatments in 2022, Bob Berry Sunshine Course, Lemont, IL. Fig 2. Visual quality (1–9, with 6 acceptable and 9 best) of HGT Kentucky bluegrass given 8 different divot treatments in 2022, Bob Berry Sunshine Course, Lemont, IL.
Fig 3. Normalize Difference Vegetation Index (NDVI) of HGT Kentucky bluegrass divot treatments in 2022, Bob Berry Sunshine Course, Lemont, IL. Fig 4. Images taken 7 weeks after initial divots were made to a HGT Kentucky bluegrass tee at the Bob Berry Sunshine Course, Lemont, IL. Singh, Jun 9, 2022

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CDGATurfgrassProgram

Dedicated researchers and turf pathologists working for golf course superintendents in the Chicago area.