TECHNICAL
fungus Pyricularia spp.; the highlight of the spread being at the beginning of September. The NDVI measurements indicate that the grass plants were under signifi cant stress between the period of July to September and this stress was not uniform across the entire fi eld. In comparison with the climate data during this same period, it could be surmised that the high temperatures during the summer months, between the end of June and early September, were a major stress factor for the grasses, specifi cally in the older turfed area. The heat tolerance of the diff erent grass species would appear to be diff erent and, if we look at the areas on the pitch which were most strongly stressed, the high temperatures seemed to put more pressure on the older areas which contained a high percentage of Poa annua. On August 5, 2019, the multispectral data on this older turf illustrates the severe decline in vitality of the overall grass sward containing a high percentage of Poa annua.
On the other hand, the newly sodded area in the centre of the pitch shows a signifi cantly better vitality up until August 5, despite the stress signs due to the pressure of heavy use. Only the northern area towards the side line shows an anomaly, due to unknown factors, but which may be the fi rst signs of a general change in the vitality of the Lolium perenne cultivars (signs which are visible in the NDVI index images). Looking back, temperatures had risen sharply from June 22 and excessive artifi cial irrigation was necessary because of the lack of rainfall, creating conditions conducive
to the occurrence of Grey Leaf Spot (L.B. McCarty, 2005).
On August 6, these stressed areas were analysed on site and identifi ed by Bernhard Schenk (Division Manager at UFA-Samen PROFI GRÜN) as the turf disease Grey Leaf Spot.
By September, the area covered with sodded turf had been almost completely destroyed by the Grey Leaf Spot. The clear demarcation from the older area with a signifi cantly lower proportion of Lolium perenne is clearly visible, illustrating that Lolium is aff ected by Grey Leaf Spot, whereas Poa species seem to be less aff ected. Results which are corroborated by L.B. McCarty (2005).
Evaluation of weather data and maintenance measures
The weather data from the weather station BAS Basel/Binningen shows the last precipitation on June 20 with 26mm. After that time, the weather turned hotter and dryer with many hours of sunshine and only sporadic precipitation was measured between the end of June and the beginning of August. Due to the low rainfall, the pitches had to be irrigated daily in the early morning hours. The measured wind movements can be defi ned for the entire period of the measurement as a light breeze (2-9km/h) to a gentle breeze (10-19km/h), providing little air for surfaces to dry out following irrigation. During the same period, the greenkeeper cut less often and, on June 24 and July 27, fungicides were applied due to a summer
fusarium infestation. The site was over- seeded for the fi rst time on June 28. The hot, dry period continued into July and with total rainfall of only 80 mm the need for irrigation remained high. Relative humidity remained high, averaging 61%. On July 5, the entire site was over-seeded again and on July 8 it was aerated and then sanded. On July 10, the site had to be over-seeded a third time and on July 11 it was fertilised.
Analysis/discussion
By early July 2019, conditions in Basel were theoretically ideal for the Grey Leaf Spot. It was hot and humid and the turf was intensively irrigated and kept moist for a long time. The pitch had been freshly fertilised and there was no strong air movement on and around the pitch to dry it out following morning irrigation. Although the Grey Leaf Spot disease probably started at this time, the NDVI image from July 4 doesn’t necessarily reveal any particular indication that would point to a disease outbreak. The images indicated that much of the pitch was stressed, likely due to the hot dry conditions and wear and tear from daily practice. It was therefore diffi cult to diff erentiate between stress due to wear and tear or weather conditions and the beginnings of a disease outbreak. However, the August 5 image (below) does seem to show the beginning of some stress on the north-west corner of the central portion and, looking back, this is likely the fi rst signs of an infestation on the Lolium perenne cultivars of the newly sodded area, which was confi rmed
Overview of the NDVI measurements on Field 11 PC February/March 2021 117
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