2022 Update on Ash Trees in Nursery Wood, the Nursery and Locally

Summer 2022 has been quite a contrast to Summer 2021. There was virtually no rainfall from mid-June to mid-August and the July heatwave saw temperatures reaching 40 degrees centigrade in the shade locally.

There have been virtually no new cases of Chalara infection here this year. This is possibly due to the spores requiring damp leaf surfaces to enable infections to get a toehold. The dry conditions also meant little new shoot growth on ash trees during July and August – the main time for Chalara infections. It is much easier for spores to establish when the ash leaves are young, damp and fresh than when they are mature, dry and leathery.

In Nursery Wood the dieback in the outer crowns caused by Chalara infections in 2021 was soon masked by fresh new growth. The only new infections were on epicormic shoots sprouting from the trunks of previously
infected trees. One ash tree had failed to come into leaf; an inspection revealed the tell-tale dark smudge at the base of the stem. Death caused by a fungal root rot, possibly honey fungus, Armillaria, but nothing to do with Chalara, which is a leaf infection.

Another ash tree had pale, thinning foliage and a rough feel to the bark. Several colonies of small, dark, spiny creatures were identified as the larvae of Kidney Spot Ladybird thanks to an id app on my phone. Some adult ladybirds confirmed the identification. Thanks to Louise Hill from DEFRA, the roughness of the bark was found to be large colonies of scale insects, coccids, which had plugged their mouth parts into the tree and were siphoning off the
sap.  Here was a new food chain for me – coccids feeding on the ash tree which were in turn being grazed by the ladybird larvae. Rubbing the bark of the ash tree made an orange stain produced by the squashed coccids.

In the nursery 2000 seedling ash trees that had not been sold were lined out to grow on for another year. 10-15 trees showed dieback caused by Chalara when they were taken out of the cold store. These were removed. The remaining trees grew well until the middle of June, the drought then caused them all to form a terminal bud and no further height growth was made. The leaves curled and turned partially brown. Not surprisingly, no Chalara
infections were noted on such inhospitable leaves. The trees have strong black terminal buds and should grow away fast when planted out.

About 5,000 ash seedlings have also been grown in the nursery from parent trees which themselves appear to be tolerant. Irrigation has enabled them to keep growing through the drought. In mid-September no Chalara infections have been noted. Let’s hope that these trees will also find a permanent home.

Locally, ash trees have suffered badly from the drought this Summer with sparse foliage and early leaf browning. Older trees which are already under stress from environmental causes will be expected to show extensive die back in summer 2023. But this must not be confused with Chalara dieback which has been scarce this year for the reasons described above.

Driving over to the APF show in Warwickshire in September allowed a wider view of the Chalara situation. The drought and high temperatures were not so pronounced further West. Patches of dead sapling ashes on the roadside were
evidence of last year’s infections, but generally the view from the motorway was of lush green growth. At Alcester the APF demonstration woodland was a well-managed mature ash wood. It looked great.