| VULNRABILITY TO CLEMATIS WILT IN LARGE FLOWERED CLEMATIS
by Dr John Howells |
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First published in The Clematis, 1994. p51.
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INTRODUCTION
That clematis wilt is caused by one or more fungi has been demonstrated in a number of countries - USA (Gloyer, 1915), UK (Ebben & Last, 1965), The Netherlands (Blok, 1963, 1964; Rattink, 1970), New Zealand (Sith et al, 1991). A review of the literature on clematis wilt is available (Howells, 1993).
Some clematis are immune to wilt; others are vulnerable. This paper studies vulnerability in a number of popular large flowered clematis and gives the findings:
I. Of a number of Dutch studies on vulnerability to clematis wilt.
II. Of the views of a group of English clematarians on vulnerability to wilt in the clematis used in the Dutch studies.
III. Of the estimations of the same group of English clematarians as in II above on clematis of high and low vulnerability.
The findings will be a useful guide to both the grower and buyer of clematis. A related study (Howells, 1994) analyses the genetic background of samples of clematis of high and low vulnerability to clematis wilt in an attempt to draw conclusions on the source of the vulnerability.
I. DUTCH STUDIES ON VULNERABILITY TO CLEMATIS WILT
Method
The Dutch studies were conducted over the three years 1971-1973 at Proefstation Boomkwekerij, Boskoop, Holland. Thirty two clematis were studied. (Steckelenburg Van, 1971, 1972; Slavekoorde, 1973). This paper reports on thirty one clematis; X durandii was excluded because it is not regarded as a large flowered clematis. The researchers conducted two surveys: A. they reported the amount of natural wilting in samples of the thirty one clematis in each of the three years 1971-1973, ie these were clematis grown in the field in the usual fashion. B. In the last two years of the research, 1972 and 1973, they introduced a fungus - conethyrium clematis rectae to samples of the same clematis; from previous studies it was known that this fungus was very harmful to clematis. The method chosen was to infect the ground around the clematis with the fungus in June. The plants were not damaged.
Results
Figure 1
WILTING IN CLEMATIS
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A. % wilting in
Natural Group
3yr
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B. % wilting in
Infected Group
2 yr
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Avg %
Wilting
Both
Groups
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1971
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1972
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1973
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Avg
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1972
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1973
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Avg
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Barbara Jackman
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8
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6
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28
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14
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9
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11
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10
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12
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Bee's Jubilee
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18
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25
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11
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18
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42
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50
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46
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32
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Comtesse de Bouchaud
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0
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8
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10
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6
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0
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17
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9
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7.5
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Duchess of Edinburgh
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9
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14
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66
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29.5
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11
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20
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15
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22.5
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Ernest Markham
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52
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3
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49
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35
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3
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15
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9
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22
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Gipsy Queen
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10
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11
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61
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27
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19
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20
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20
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23
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Hagley Hybrid
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48
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15
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28
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30
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0
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4
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2
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16
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Henryii
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70
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3
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18
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34
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25
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46
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35
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34.5
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Hybrid Sieboldii
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57
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0
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43
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33
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17
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33
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25
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29
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Jackmanii
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83
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15
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no rec
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33
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30
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no rec
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30
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24
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Jackmanii 'Superba'
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56
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17
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57
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43
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20
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0
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10
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26
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Kathleen Dunford
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21
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14
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38
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24
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13
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46
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30
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27
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Lady Betty Balfour
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67
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20
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41
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43
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36
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50
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43
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43
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Lasurstern
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5
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18
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23
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15
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39
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10
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25
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20
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Lawsoniana
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68
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13
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63
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46
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21
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0
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10
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28
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Lord Neville
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43
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6
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38
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29
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32
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62
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47
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36
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Mme Le Coultre
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47
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13
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36
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32
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12
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16
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14
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23
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Miss Bateman
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22
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5
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11
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12
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3
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42
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22
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17
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Margot Koster
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55
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54
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45
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51
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0
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16
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8
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30
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Mme Baron-Veillard
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5
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9
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58
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24
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27
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10
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19
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21
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Mrs Cholmondeley
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30
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6
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50
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28
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9
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61
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35
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31
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Mrs N Thompson
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46
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44
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22
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37
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21
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50
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35
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36
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Nelly Moser
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5
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29
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11
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15
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23
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57
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40
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27
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Rouge Cardinal
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50
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0
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0
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17
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13
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0
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6.5
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12
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Sealand Gem
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67
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34
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43
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46
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25
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0
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12
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29
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Souv. J L Delbard
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30
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6
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73
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36
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0
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0
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0
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36
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The President
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27
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19
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40
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28
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17
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16
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16
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22
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Ville de Lyon
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33
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11
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26
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23
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9
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14
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25
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24
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Voluceau
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29
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3
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22
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18
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0
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8
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4
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11
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William Kennett
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20
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3
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18
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14
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23
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76
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50
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32
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Xerxes
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28
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9
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33
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23
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34
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75
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54
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39
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Av % wilting per year
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35.6
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13.96
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35.4
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-
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17.19
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27.48
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-
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No. of Plants
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12-59
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8-52
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4-32
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-
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8-42
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4-26
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-
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The first three columns of Figure 1 show the incidence of natural wilting in each of the three years of study. In the fourth column the results for the three years are averaged in percentages. Columns five and six show the incidence of wilt in the infected clematis group in the last two years of the study. Column seven averages in percentages the results of columns five and six. Column eight averages the results for columns one to three and five and six.
Comment
There are some reservations about these results by the researchers. The researchers comment that the findings show that more clematis wilted naturally in the first and third year than when infected with the fungus; they state "this is difficult to explain". Perhaps the method chosen for infection was ineffective. Again, the infected group may have been protected by greater care, e.g. careful watering. Perhaps some destructive other agent was present in the natural group or it may have received less care. Detailed comment is as follows:
SURVEY A
1. There is often inconsistency in Survey A from one year to another in the findings for a particular clematis.
2. The second year, 1972, gave much lower wilting than 1971 and 1973. There may be years when, due to natural factors, clematis may be more prone to wilt.
SURVEY B
1. There is often inconsistency in the findings between the two years for a particular clematis e.g. 'Mrs Cholmondeley'. But there is less inconsistency than in Survey A.
TOTAL TABLE
1. The rate of wilting is greater in the natural group in the two years 1971 and 1973 (35.6% and 35.1%) than the highest year 1973 (27.48%) in the infected group.
2. There is inconsistency between the results of Survey A and Survey B. For example 'Gipsy Queen' (Survey A - 35%; Survey B - 9%); 'William Kennett' (Survey A - 14%; Survey B - 50%).
3. There were also consistent findings between the results of Survey A and Survey B, e.g. in the case of 'Barbara Jackman'; 'Comtesse de Bouchaud'; 'Henryii'; 'Lady Betty Balfour'.
4. There were some surprises e.g. 'Margot Koster' regarded as a viticella and a low wilter showed a wilting of 51% in Survey A. 'Ville de Lyon' which Morel, its raiser, said never wilted showed 24% on average for the two surveys. This raises the possibility that some other factor, or factors, other than wilt may also be operating in the study.
5. The number of plants in a trial clematis group could be as low as four making results unreliable in that group.
6. It is important to exclude the possibility that factors other than wilt may be responsible for the damage observed, e.g. insufficient watering, physical damage, frost damage, vine weevil, poor clones, etc. However the researchers were skilled at the diagnosis of wilt and would be able to differentiate between wilt damage and other damage.
7. The highest rate of wilting (30%-43%) was seen in the following fifteen clematis: 'Lady Betty Balfour' (43%); 'Xerxes' (39%); 'Lord Neville' (36%); 'Mrs N Thompson' (36%); 'Souv. J L Delbard' (36%); 'Henryii' (34.5%); 'Bee's Jubilee' (32%); 'William Kennett' (32%); 'Mrs Cholmondeley' (31%); 'Margot Koster' (30%); 'Hybrid Sieboldii' (29%); 'Sealand Gem' (29%); 'Lawsoniana' (28%); 'Kathleen Dunford' (27%); 'Nelly Moser' (27%).
The least rate of wilting was seen in the following clematis: 'Comtesse de Bouchaud' (7.5%); 'Voluceau' (11%); 'Barbara Jackman' (12%); 'Rouge Cardinal' (12%); 'Hagley Hybrid' (16%); 'Miss Bateman (17%); 'Lasurstern' (20%); 'Mme Baron-Veillard' (21%); 'The President' (22%); 'Ernest Markham' (22%); 'Duchess of Edinburgh (22.5%); 'Gipsy Queen' (23%); 'Mme le Coultre' (23%); 'Ville de Lyon' (24%); 'Jackmanii' (24%); and Jackmanii Superba' (26%).
8. Comparison of the two groups of wilters shows striking differences in relation to time of flowering. In the high wilting sample 13 of the 15 clematis (86.6%) belong to the Early Flowering Group of large flowered clematis while only two (13.4%) belong to the Late Flowering Group of large flowered clematis. In contrast, in the low wilting sample the reverse ratio is seen. 10 out of 16 clematis of the low wilters (62.5%) belong to the Late Flowering Group of the large flowering clematis. 6 out of the 16 (37.5%) clematis belong to the Early Flowering Group of the large flowered clematis. Flowering in the Early Flowering Group comes from growth made the previous year. Flowering in the Late Flowering Group comes from growth made in the year of flowering.
9. The Dutch researchers report that there is no difference of incidence of wilt in the established three groups, i.e. patens, lanuginosa and florida groups. This is understandable; clematis should not be classified according to habitus but by genetic constitution. For example, lanuginosa and patens crossed can produce seedlings of different habitus. Those of patens habitus are put into the patens group. Those of lanuginosa habitus are put in the lanuginosa group. But the genetic background of the two groups may be similar. While there may be no difference between the traditional three groups it is notable that the heavy wilters are all from the Early Flowering Group of large flowered clematis - with the exception of 'Lady Betty Balfour' and 'Margot Koster' and the Late Flowering Group has a preponderance of low wilters.
10. Despite some inconsistencies in the findings there is still strong correlation between the findings here and the next two studies to be reported. Nevertheless, the inconsistencies of detail and small samples exclude elaborate statistical analysis.
II. THE FIRST BRITISH STUDY
Method
The list of the thirty one clematis used in the Dutch study were sent to a random sample of 19 experienced growers and gardeners in the UK. They were invited to score each clematis as low wilter (1 point), medium wilter (2 points) and high wilter (3 points). The scorers were unaware of the Dutch findings. The scores were added up for each clematis.
Results
See Figure II.
Figure II
CLEMATIS
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TOTAL POINTS
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NO OF ORBS
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CORRECTED % POINTS
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Barbara Jackman
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26
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17
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29
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Bee's Jubilee
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25
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16
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29.69
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Comtesse de Bouchaud
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22
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18
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23
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Duchess of Edinburgh
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34
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17
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38
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Ernest Markham
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24
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18
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25.3
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Gipsy Queen
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26
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18
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27.4
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Hagley Hybrid
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20
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18
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21.1
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Henryii
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32
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18
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33.7
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Hybrid Sieboldii
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20
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13
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29.2
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Jackmanii
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29
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18
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30.6
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Jackmanii 'Superba'
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29
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18
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30.6
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Kathleen Dunford
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20
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14
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27.1
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Lady Betty Balfour
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22
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16
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26.1
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Lasurstern
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27
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18
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28.5
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Lawsoniana
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22
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13
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32.1
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Lord Neville
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23
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15
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29.1
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Mme Le Coultre
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36
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18
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38
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Miss Bateman
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24
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19
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24
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Margot Koster
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18
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17
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20.1
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Mme Baron-Veillard
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18
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17
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20.1
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Mrs Cholmondeley
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29
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19
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29
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Mrs N Thompson
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34
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18
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36
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Nelly Moser
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29
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18
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30.6
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Rouge Cardinal
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26
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18
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27.5
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Sealand Gem
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19
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15
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24
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Souv. J L Delbard
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|
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The President
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29
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18
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30.6
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Ville de Lyon
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22
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19
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22
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Voluceau
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11
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26
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26
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William Kennett
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28
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19
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28
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Xerxes
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27
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17
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30.2
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Column 2 of Figure II gives the total points for each clematis. Column 3 gives the number of observers and Column 4 gives the score after correcting for the number of observers. There was no comment on 'Souv. J L Delbard' as it was not known to the observers.
Comment
1. The 15 estimated high wilters in order of severity were (points in brackets):
'Madame Le Coultre' (38); 'Duchess of Edinburgh' (38); 'Mrs N Thompson' (36); 'Henryii' (33.7); 'Lawsoniana' (32.1); 'Nelly Moser' (30.6); 'Jackmanii' (30.6); 'Jackmanii Superba' (30.6); 'The President' (30.62); 'Xerxes' (30.2); 'Bee's Jubilee' (29.69); 'Hybrid Seiboldii (29.2); 'Lord Neville' (29.1); 'Barbara Jackman' (29); 'Mrs Cholmondeley' (29).
2. The fifteen estimated low wilters in order of least severity were (points in brackets):
'Margot Koster' (20.1); 'Mme Baron-Veillard' (20.1); 'Hagley Hybrid' (21.1); 'Ville de Lyon' (22); 'Comtesse de Bouchaud' (23%); 'Miss Bateman' (24); 'Sealand Gem' (24); 'Ernest Markham' (25.3); 'Voluceau' (26); 'Lady Betty Balfour' (26.1); 'Kathleen Dunford' (27.1); 'Gipsy Queen' (27.4); 'Rouge Cardinal' (27.5); 'William Kennett' (28); 'Lasurstern' (28.5).
3. Two very experienced growers did not complete the questionnaire as they held that all large flowered clematis wilted.
4. There is some correlation with the results of the Dutch studies:
The following are agreed to be high wilters in the Dutch and First British Study. There is agreement between the First British Study and A and B surveys in the Dutch Study on 'Mrs N Thompson', 'Henryii' and 'Jackmanii'. There is agreement between the First British Study and either A or B surveys in the Dutch Study on 'Madame le Coultre', 'Duchess of Edinburgh', 'Lawsoniana', 'Nelly Moser', 'Jackmanii Superba', 'Xerxes' and 'Bee's Jubilee'.
The following are agreed to be low wilters in the Dutch and First British Study. There is agreement between the First British Study and both A and B surveys in the Dutch Study on 'Comtesse de Bouchaud'. There is agreement between the first British Study and either survey A or survey B of the Dutch Study on 'Margot Koster', 'Hagley Hybrid', 'Miss Bateman', 'Sealand Gem', 'Ernest Markham' and 'Voluceau'. In the first British Studay, 'Lady Betty Balfour' is assessed as a low wilter; in the Dutch Study 'Lady Betty Balfour' is rated as the highest of the wilters.
5. The striking difference between the high and low wilters in their placement in the Early or Late Flowering Groups of large flowered clematis is present here. Of the high wilters 13 out of 15 (86.6%) belong to the Early Flowering Group; the same percentage as in the Dutch study. In contrast, of the low wilters 9 out of 15 (60%) belong to the Late Flowering Group. 6 out of 15 (40%) of the low wilters belong to the Early Flowering Group.
II THE SECOND BRITISH STUDY
Method
Here 19 experienced clematarians, groweres and gardeners, were asked to select the five clematis with the highest record for wilting and the five clematis with the lowest record for wilting. The clematis were then listed in rank order for the number of mentions by the observers. Some of the clematis mentioned were not in the Dutch studies; it was thus hoped to extend the area of research to a topical and larger sample of large flowered clematis.
Results
Occasionally, a clematis would be selected both as a high and a low wilter by different evaluators. If a clematis rated as a high wilter had a mention as a low wilter then an adjustment was made in that clematis's number of mentions - and vice versa, i.e. in the case of a high wilter the number of mentions as a low wilter would be subtracted from the total of mentions as a high wilters. In the findings the number of mentions is given in the brackets.
The highest wilters, with more than one mention, were estimated to be: 'Vyvyan Pennell' (7); 'Countess of Lovelace' (4); 'Mrs N Thompson' (4); 'Moonlight' (4); 'General Sikorski' (4); 'Henryii' (3); 'William Kennett' (3); 'Duchess of Edinburgh' (3); 'Sylvia Denny' (2); 'Mrs Cholmondeley' (2).
The lowest wilters were estimated to be:
'Hagley Hybrid' (9); 'Ville de Lyon' (5); 'Gipsy Queen' (4); 'Comtesse de Bouchaud' (4); 'Perle d'Azur' (4); 'Dr Ruppel' (4); 'Nelly Moser' (3); 'Miss Bateman' (2); 'Huldine' (2); 'Mme Edouard André (2); 'Star of India' (2); 'Haku Ooken' (2); 'Lady Northcliffe' (2).
Comment
1. The correlation with the First English Study was high, as might be expected, as the same observers were employed.
2. There is also the same correlation with the Dutch study as in the First English study.
3. The striking trend noticed in the first two studies was present here. 10 out of 10 (100%) of the high wilters belong to the Early Flowering Group. 8 out of 13 (61.50%) of the low wilters belong to the Late Flowering Group. This finding strongly correlates with the findings in the Dutch Study and in the First English Study.
CONCLUSIONS
Wilt is widespread as can be seen by the incidence of natural wilting in the samples in the Dutch study and the views of experienced British clematarians.
The high wilters invariably came from the Early Flowering Group of large flowered clematis. The low wilters tended to come from the Late Flowering Group of large flowering clematis. All three studies agreed about this finding.
The tables in figures I and II may be a general guide to a grower of the susceptibility to wilt in his plants and a guide to the gardener in his purchasing.
It is also noted that some of the clematis shown to be low wilters are among the most popular of clematis. Presumably, low wilting has led to the purchasers being pleased and this has stimulated demand for that particular clematis. In this connection it is seen that 'Gipsy Queen' is a lower wilter than the rather similar 'Jackmanii Superba' or 'Jackmanii'; this may help to explain that 'Gipsy Queen' is often sold as Jackmanii. A recent survey shows that the first six clematis in the list of low wilters to follow are in the list of ten most popular clematis in the surveys of 1989 and 1994. (Brooks 1994.)
In the findings there is a paradox 'Vyvyan Pennell' rated the highest wilter of all, is still arguably the most beautiful of all clematis, indeed the Queen of Clematis. Anyone who knows the plant would still grow it because of its outstanding beauty. Thus large flowered clematis are still worth purchasing as effective measures can be taken against the clematis wilt. Unfortunately the control methods are unlikely to be known by new purchasers who are put off buying clematis by the deaths that ensue. Thus clematis wilt is the "Achilles heel" of clematis.
It is useful to have a list of indubitably high or low wilters. This list of high and low wilters is attempted herre. It is made up of the findings of the Second British Study which brought in clematis is not considered in the First British Study, the findings that correlated between the Dutch Study and the First English Study and the outstanding findings in the Dutch Study - 'Lady Betty Balfour' and 'Barbara Jackman'. The figure in brackets is the number of mentions in the Second English Study, and with the ranking in the First British Study, allows ranking to occur here. A clematis of only two mentions in the Second British Study is not included unless it has strong support in the other two studies.
High Wilters in rank order of severity of wilting:
'Vyvyan Pennell' (7); 'Countess of Lovelace' (4); 'Madame Le Coultre'' 'Duchess of Edinburgh' (3); 'Mrs N Thompson' (4); 'Moonlight' (4); 'Henryii' (3); 'Lawsoniana'; 'William Kennett' (3); 'Jackmanii; 'Xerxes'; 'Bee's Jubilee'; 'Mrs Cholmondeley' (2); 'Lady Betty Balfour'. It should be noted that 12 out of 14 (85.7%) listed come from the Early Flowering Group and 2 out of 14 (14.3%) from the Late Flowering Group. There is strong disagreement between the Dutch and First British study over the status of 'Lady Betty Balfour'. It is assessed as a low wilter in the First British Study.
Low Wilters in rank order of least severity of wilting:
'Hagley Hybrid' (9); 'Ville de Lyon' (5); 'Gipsy Queen' (4); 'Comtesse de Bouchaud (4); 'Perle d'Azur' (4); 'Dr Ruppel' (4); 'Margot Koster'; 'Sealand Gem'; 'Ernest Markham'; 'Voluceau'; 'Barbara Jackman'; 'Nelly Moser' (3); 'Miss Bateman' (2); 'Huldine' (2). It should be noted that 9 out of 14 (64.31%) come from the Late Flowering Group and 5 out of 14 (35.7%) come from the Early Flowering Group.
These samples will be the basis of a related study comparing the genetic background of the two samples.
REFERENCES
BLOK, I. 1963. Verwelkingsziekte in clematis. Jaarboek Proefstation Boomkwekerij Boskoop 1963, pp.86-89.
BLOK, I. 1964. De Verwelkingsziekte van clematis. Netherlands Journal Plant Pathology, Vol.70, pp.67-68.
BROOKS, R. 1994. Clematis Analysis. The Clematis 1994.
EBBEN, H.S. and LAST, F.T. 1965. Clematis wilt. Report Glasshouse Crop Research Institute, pp.128-131.
GLOYER, W.O. 1915. Iascochyta clematidina, the cause of stem-rot and leaf spot in clematis. Technical report No.44, New York Agricultural and Experimental Station, Geneva, N.Y.
HOWELLS, J. 1993. Clematis wilt. A Review of the Literature. The Plantsman. 15. p.148
HOWELLS, J. 1994. The Genetic Background of Wilting Clematis. The Clematis 1994. p.62.
RATTINK, H. 1970. Verweklingsziekte in clematis. Jaarboek Proefstation Boomkwekerij, Boskoop, 1970. p.79.
SLAVEKOORDE, S.M. 1973. Verwelkingsziekte in clematis. Jaarboek Proefstation Boomkwekerij, Boskoop, 1973. pp.82-85.
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ACKNOWLEDGEMENTS
My thanks for response to questioonaires to: Pat Gawler, Frank Cadge, G S Greenway, Vince Denny, Harry Caddick, Mike Adams, Ruth Gooch, Derek Cox, Margaret Morris, Jerry and Jenny Earl, Malcolm Freeman, Everett Leeds, Arthur Steffen, Nick Hall, Denis Bradshaw, Christopher Lloyd, Mike Brown, Fred Wein and for constructive comment to Jim Fisk, John Fopma, Richard Pennell, Ian Sayer and Robin Savill.
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