Chicken or the Egg? Weather. SAVE THE DATE: MU Turfgrass & Landscape Field Day - August 1

Transcription

1 Chicken or the Egg? SAVE THE DATE: MU Turfgrass & Landscape Field Day - August 1 Registration is open and the schedule is set for the 2017 Mizzou Turfgrass & Landscape Field Day! Come on out August 1 to our research facility at South Farms, and we ll give you the latest on our ongoing research and regional topics of interest. The entire schedule is at the end of the update. Registration for both attendees and exhibitors can be found at the site - For more information, feel free to contact me at turfpath@missouri.edu or Kevin Dern at mufieldday@gmail.com. Look forward to seeing you there. Weather Summer is here, bringing along high humidity and 90 F + high temperatures and expelling those comforting mornings in the mid and upper 50s. Those cool mornings last week were a nice anomaly to start the season, but considering the forecast and current trends the dog days of summer are here. Currently, June is running approximately 2-3 degrees above normal for the state. Although we endured an overall wet spring with the severe flooding in late April/early May, our current 30-day trend since mid-may has north of I-44 at an inch or two below normal, whereas in southern Missouri and Arkansas totals are 1-2 inches above normal.

2 Over the next week, forecasts indicate at or above normal temperatures, so expect the high 80s and 90s to continue. Also, of rainfall is expected through next Tuesday, mostly in the central and northern parts of the state where it is needed. Although needed, if this rainfall does come to fruition expect a bevy of disease activity should follow. Quick Hits Dormancy/Wet Wilt - In the central portion of the state, lawns and other unirrigated cool season turfgrass areas are going dormant as potential evapotranspiration nears three inches for the month. This dormancy is also partially due to the restricted root system caused by the earlier spring rains. On lower cut putting greens, we ve observed both localized dry spot and wet wilt occurring in this dry period. This is further evidence of the constraints this past wet spring put on proper root development, which on putting greens could spell considerable trouble as we enter the gauntlet of summer. Vent greens. Check drainage. Get water in when needed, but replace with oxygen as soon as possible. Use fans.

3 Rust Rust has been observed on several Kentucky bluegrass/tall fescue sports fields throughout the state. The pathogen in this case is Puccinia graminis, which also causes a more devastating black stem rust on wheat. The previous dry period tends to spur this disease, as does low nitrogen levels which is why late May/early June are the normal timeframe for disease occurrence. Outbreaks seem to be more common, as this is the second straight year that we have observed this disease. Newer Kentucky bluegrass cultivars are obviously impacted by rust, and since younger seedlings are more susceptible this could be a reason for the increased epidemic. Another interesting point about Puccinia graminis is that it requires a very specific alternate host, the barberry, to complete its life and disease cycle. For this reason, a nationwide barberry eradication program lasted from 1918 through 1975 that resulted in the destruction of over 100 million barberry bushes. Now that the eradication program is over, the common barberry has been making a comeback and may be spurring on this resurgence. Most ornamental barberry cultivars are resistant, but prior to planting one around your facility check the list for susceptible cultivars. For control, a small shot of nitrogen (which may require some growth regulation) and irrigation should take care of minor outbreaks. If a fungicide is warranted, a QoI + DMI class combination such as azoxystrobin + propiconazole (Headway) or similar should provide control. Rust populations can develop resistance so alternating fungicides and using the combination of two chemistries is necessary. Stubborn $ Spot The current heat wave should suppress new dollar spot infections, but some reports of tough to control dollar spot on putting greens have been heard over the social media airways in recent weeks. The mild temperatures and high humidity have been extremely conducive for this disease, so control intervals were strict this spring. Difficulty with controlling dollar spot with fungicides in the spring is a bit more concerning than in the fall, as it could mean a resident and set in fungicide resistant

4 population. This being said, some supers have stated their dollar spot pathogen may be resistant to chlorothalonil or other fungicides. I am unaware of any confirmation of field resistance to chlorothalonil, a fungicide that acts on multiple metabolic sites of the pathogen. Chlorothanil is not a systemic fungicide, however, and protection does not last very long (7 to 10 days at the most). Dollar spot scars are very slow to heal, due to the production of a root-damaging mycotoxin by the pathogen that needs to dissipate and allow for regrowth from the outside of the spot back in. Using chlorothalonil alone in an attempt at recovery will not happen quickly and will require very short application intervals to provide continued protection of non-infected plants. The newer fungicides with fluxapyroxad (Xzemplar and Lexicon) have provided extremely fast, curative recovery from dollar spot damage in our field experiments over the last two years. Since dollar spot is a low nitrogen disease, this recovery can be accelerated with a small (and reasonable) increase in nitrogen levels. Lastly, if fungicide resistance is a concern, fluazinam (Secure) is a new multisite fungicide that should be considered as a part of your management strategy. Algae Earlier wet conditions and high humidity has caused an increase in algae observations on putting green samples submitted to the lab. While in some cases these algae are simply filling in the voids of thinned turf, some of these species are known to produce toxins to gain a competitive edge over our desired bentgrass. When looking at these samples, algae either coating the leaf tips or present down in the leaf sheath of declining plants is normally cause for alarm even when not causing the typical yellow spot disease (click here for previous update). Regular applications of chlorothalonil and mancozeb will aid in algae reduction. Brown Patch on Tall Fescue warning Sweaty pants means it s brown patch time. We noticed brown patch starting on our creeping bentgrass fairway height trials yesterday

5 so brown patch outbreaks on tall fescue lawns can t be far behind. Do not use nitrogen at high rates in a fast release form, and water in the morning rather than at dusk to reduce brown patch severity. Zoysia bug warning Billbug and chinch bug damage is starting to be observed on infested zoysia fairways and lawns. On sites with a previous history of billbug damage, preventive insecticide applications (many are using a tank mix of bifenthrin and imidacloprid) should have been made in early May to knock back egg laying adults. Chinch bugs are a bit trickier since occurrence may be sporadic from year to year, particularly after previously being controlled. Rigorously scouting for presence and damage will allow for an early curative application and perhaps prevent unnecessary insecticide use. See this previous report for more information. Etiolation: The Chicken (Bacteria) or the Egg (Environment)? Our first observation of bacterial etiolation was submitted to the diagnostic clinic yesterday, and it brought to mind an interesting question does the cause stem from the chicken or the egg? In other words, is the bacteria itself doing the major lifting or is it the predisposition due to the environment? When we get into these dog days of summer, the argument is really a moot point since both are at play, but it is interesting that we can observe the etiolation at this point in the season but never get into the decline phase like was experienced in severe summers like 2011 and Prior to field day last year, we set up a small experiment aimed at finding the best treatment combination for dollar spot recovery. I know, some of you are sick of hearing about dollar spot, but bear with me. In the study, we had several different fungicide

6 chemistries represented that were split into two nitrogen treatments two applications of dissolved urea applied at 0.1 lb N/M vs. a single application of dissolved urea applied at 0.2 lb N/M + trinexapac ethyl (TE) as Primo Maxx at fl oz/m. A week after application, the result is shown above. On the left side of the dotted line, etiolation and chlorosis occurred on plots treated with the urea + TE, whereas on the right no etiolation occurred with just urea. Several of the plants were taken back to the lab, and bacteria was observed streaming like crazy from the veins of cut leaves. This effect with TE has been clearly demonstrated in recent peer reviewed research, but interestingly after the etiolation was mowed off and dissipated, the TE treated plots had the highest turfgrass quality ratings. In our trial, we had similar results as the yellowing and etiolation wore off in seven days and by the time field day rolled around three weeks later we had very little evidence of the effect. Holding to pattern in the recent observation, the greens had a heavy application of Nitroform down in spring,and a TE application was also applied the week prior. Perhaps the bentgrass is just temporarily confused by the nitrogen promoting growth, the TE restricting growth, while heat and/or humidity beat it over the head. I might turn a little yellow and etiolate too Based on the previous research, how much should we worry about this induced etiolation? Perhaps the occurrence should make the superintendent aware rather than worried. The pathogen is present as evidenced by the bacterial streaming, so if the intense plague of summer does come crashing down than the decline phase may occur. Fungicides such as the Action products with acibenzolar and/or Stressgard products like Signature should be put into the rotation to reduce this potential for advancement into bacterial decline. Back off temporarily on the TE and perhaps a little on the nitrogen. Switch to solid rollers, roll a little more often, and mitigate stress. Don t, however, switch into panic mode when etiolation occurs and contemplate the use of general sterilants or off-label antibiotics. That would be throwing the baby out with the bath water.

7 Lee Miller Follow on Like on Facebook! Mizzou Turfgrass Extension Turfgrass Pathologist - University of Missouri