Asian Chestnut Gall Wasp
Copyright 1993 to 2013 University of Missouri. Published by MU, Extension, all rights reserved.
Photo: Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org
Distribution and hosts
The gall wasp, Dryocosumus kuriphilus Yasumatsu, was introduced into North America in 1974 on imported chestnut cuttings. A native of China, the gall wasp is also considered a major pest in Japan and Korea. The gall wasp has been identified in Georgia, Alabama, North Carolina, Virginia, Maryland, Pennsylvania, Maryland, Kentucky, Tennessee and Ohio. Although the gall wasp has not been found in the Midwest, it is likely to be found in additional areas as detection surveys continue. D.kuriphilus may be established in an area for some time before it is identified.
The distribution of this pest in the United States is primarily due to the transport of infested seedlings to new areas and the exchange of infested scion wood used to graft new trees.
Chestnut species affected:
Chinese chestnut (Castanea mollissima)
Japanese chestnut (Castanea crenata)
European chestnut (Castanea saliva)
American chestnut (Castanea dentata)
Chinquapin (Castanea pumila)
This insect pest lays eggs in the buds of chestnut shoots, and galls develop on the shoot tips, leaves and catkins. These galls greatly reduce nut production and suppress shoot growth. After adult insects emerge, the dried, blackened galls become woody and can persist on older limbs for several years. In cases of severe infestations, interior portions of the tree canopy die and trees are killed.
Female adult wasps, one-eighth-inch long, lay three to five eggs in a cluster inside chestnut buds in early summer. Multiple adults may oviposit in a bud, with as many as 25 eggs per bud. Eggs hatch in 40 days and the larvae remain dormant until the following spring. As buds growth begins, larvae induce gall formation on developing plant tissues. Larvae feed on the inner gall tissue for 20 to 30 days before pupating. Adult wasps emerge from the galls in late May and early June. Dispersal by wasp flight has been at a rate of 23 km per year, however, dispersal of adult insects has been augmented by prevailing winds.
Prevention of further pest dispersion
Because the dormant larvae are not easily detected on chestnut twigs, infested plant material, especially that used to propagate new trees, may escape detection. Pruning and burning infested plant material may retard further movement of this pest. Chemical controls are not feasible on trees where nuts are harvested for human consumption. Currently, University of Missouri researchers are studying insect monitoring, trapping and disinfestation strategies. The purchase of seedling trees or scion wood from nurseries where the gall wasp has been identified should be avoided to limit the spread of this serious pest.
Who to contact If you observe galls on chestnut trees in a previously non-infested site, please contact: Michele Warmund, MU Extension Horticulture Specialist, 1-31 Agriculture Bldg., Division of Plant Sciences, University of Missouri, Columbia, MO 65211, 573-882-7511 email@example.com
11 Sept: Paige Cousineau, Jim Ronson & John Sankey visited Earl Roffey on Burnstown Road to see the 10 shagbarks planted by his grandfather. One tree was loaded with nuts, and there were hundreds of seedlings sprouting under the trees; we collected about a hundred of them. Jim went back for two further visits to collect a total of 52 nuts. Seedlings have been distributed to Joanne Butler, Gordon Wilkinson, Dan Mayo and the Sawmill Creek plantation.
17 Sept: John Sankey and Gordon Wilkinson surveyed the Hardy Heartnut plot, with very encouraging results. We found many seedlings peeking up through the grass that we had missed in the spring. Germination was at least double that originally thought: perhaps 50% overall have survived their first winter and the July drought. We've run out of carpet squares for them, and will put out a call for more. Gordon collected his first harvest, 3 nuts from an Imshu graft, 2 from a seedling tree.
6 October: Joanne Butler and John Sankey joined Hidden Harvest Ottawa on Lemieux Island to show them how to collect and process black walnuts for individual use. 5 kg of hulled nuts were collected from the site to be shared among the 9 participants. They are adding the data from ECSONG's Inventree to a master map of all edible crops to be found in the Ottawa urban area, and are planting new food-bearing shrubs and trees throughout the city.
The heat and low rainfall this year in the Ottawa area has produced close to the lowest groundwater recharge since records began in 1890. Streams and rivers are mere trickles compared to their usual flow; most ponds and lakes are surrounded by dry black mud. Almost all City trees planted last year have been lost except where they could be watered; all new plantings have had to be provided with watering bags. Soil moisture has been maintained for deep-rooted trees however, so established nut trees seem to have no problems.
21 December: ECSONG has received a $500 grant from the City of Ottawa to provide protective stakes and surrounds for nut trees to be planted at the Sawmill Creek Constructed Wetland, in the same area as the Lavant shagbark planting of a few years ago.
ECSONG Winter Meeting & AGM
January 19, 2013 2p.m. Citizen Building, Ottawa ON
15 members & guests in attendance.
President's opening remarks by John Sankey. Review of the past year's happenings including the summer drought, City grant of land & planting materials.
Presentation by guests Katrina Siks & Jason Garlough of Hidden Harvest Ottawa on food use of urban nut trees & fruit trees on city-owned properties, inventorying and promotion initiatives.
Dan Mayo gift of children's CDs of songs & poems.
Jim Ronson presentation on Lavant/Burnside shagbark hickories; seed-gathering & planting activities.
Nutrition break for nutty snacks.
John Sankey's interesting nut cracker collection show&tell; history of nut cracking starting with the stone age.
Election of Board members. Nominations and acceptances:
John Sankey - President
Richard Viger - Vice President
Dan Mayo - Secretary
The Renfrew Shags: The mystery within a mystery
Jim Ronson, Perth
On a small patch on the French Line north of Hopetown in Lavant township there are 1000 Shags which are about 130 years old. They grow in random. Are they the last part left of an ancient forest of shagbark hickories? Did First Nations groups plant there? Or, did a single tree that was a genetic mutation multiply and thrive?
The Lavant Shags are almost certainly a subspecies. They do well on thin Canadian Shield soil on top of hills that have been extremely cold before Climate Change came in a big way. When planting the nuts, if you use mulch around the seedlings, the elevated moisture will kill them.
Recently, a surveyor working between Burnstown and Renfrew noticed a straight line of 10 planted shagbark hickories with excellent crowns that appear to be of similar age.
The Renfrew shags are on the Roffey farm. That fact may be important. There is a related Roffey family living on the French Line. Could there be some relationship between the Roffey family and the random trees in Lavant and the planted trees at Renfrew?
For now, my priority is to plant 50 nuts from the Renfrew shags into the Perth Wildlife Reserve. Permission has been given by the Rideau Valley Conservation Authority to do the planting this April or May.
If all goes well, there will be thousands of nuts each year for planting in Eastern Ontario and Western Quebec for edible nuts and wood.
Pecan Trees in Eastern Ontario
How are they faring?
Pecan trees are not native to Ontario and commercial production of pecan nuts is concentrated in the southern part of the United States, so why would anyone try to grow them as far north as Eastern Ontario? This article provides some answers to this question and summarizes the performance of pecan trees at two sites in eastern Ontario - the Dominion Arboretum in Ottawa and my nut tree plantation east of Rockland.
Where do pecans grow?
The native range of pecan trees (Carya illinoinesis) extends along the Mississippi River and its tributaries from the Gulf Coast of the United States into northeastern Illinois and southeastern Iowa and west into Texas, and central and eastern Oklahoma (Figure 1). Pecans are grown commercially in Alabama, Georgia, northern Florida, and the Carolinas. These areas are well outside the native range but the widespread establishment of commercial orchards in these areas show that growing conditions are as good as or better than the native range (Figure 2). With pecan trees growing over such a wide range of climatic zones, it is not surprising that considerable variation has been noted in the climatic requirements of pecans. The number of frost-free days required for maturing nuts ranges from as little as 140 days for cultivars growing in more northerly locations to as many as 210 days for cultivars growing in more southerly locations(1). Pecan trees in northern locations seem to be able to survive cold temperatures as low as -40 C(2). However, pecan trees require considerably more heat to mature their nuts than other types of nut trees (Table 1). This heat requirement appears to be more important than the length of the frost-free season as pecans fail to fill nuts in locations where the frost-free season is adequate, but the heat requirement is not met(3).
Pecans at the Dominion Arboretum in Ottawa(4)
Various exotic trees were introduced to Ottawa on a massive scale in the late 1890s when William Saunders, then Director of the Central Experimental Farm, started the Dominion Arboretum. Many European, Asian, and North American trees were planted to test their hardiness and suitability for cold climates. No pecan trees from the original planting survive, although another Carya species - Carya ovata, commonly known as Shagbark Hickory - still grow and produce nuts in the Arboretum.
Since the early twentieth century Ottawa has grown from a town to a big city. With urbanization, the Arboretum has figuratively "moved" from the outskirts of the town to the middle of an urban agglomeration where the climate is warmer, resulting in new plantings of pecan trees that have been successful.
One pecan tree, with an estimated height of about 35 feet or more, was planted in the 1980s at the lower part of a hill close to Dow's Lake, behind a wind break of large pines and spruce trees. Well protected from strong eastern and north-western winds, this specimen does not show any winter dieback and it flowers regularly, although fruits never grow to maturity. It is not clear why nuts do not develop. It may be infertile self pollination, asynchronous male and female flowering, or cold nights at the early stages of fruit development.
One more pecan tree, with an estimated height in excess of 18 feet, was planted about 7 to 8 years ago in a new nut tree collection at the southern end of the Arboretum. This tree grows on a relatively open slope yet does not have any winter damage and produced male and female flowers during the last two springs. Unfortunately, there are also no nuts on this tree and the reasons for this are unknown.
Ultra Northern Pecans
Over three decades ago Douglas Campbell and John Gordon harvested nuts and scion wood from early ripening pecan trees at Green Island, Iowa, which is the most northerly tip of the pecan's native range(5). Selections and seedlings from these pecan trees at Green Island are now growing in Southern Ontario and regularly yield nuts. The nuts are considered to be too small, however, to compete commercially with those harvested further south in the United States.
Pecans at My Nut Tree Plantation
My nut tree plantation is a hayfield a few miles east of Rockland, Ontario and extends about 900 to 2,800 feet south of the Ottawa River, hi 20011 purchased six ultra northern pecan seedlings from a nursery in the Niagara region. Except for one that was mowed down by a tenant farmer in its first year, the other five seedlings have survived. Growth, however, has been very slow, averaging only 4 to 6 inches every year(6). After 11 years, the trees range in height from only 5 feet 4 inches to 7 feet 4 inches (Figure 3). Except for pecan tree #5, the trunks of all the other pecan trees have experienced some degree of winter dieback in one or more seasons. For example, pecan trees #1 and #4 had so much trunk dieback during the winter of 2009/2010 that their heights were, respectively, 9 and 5 inches lower in September 2010 than one year earlier. The minimum low winter temperature of-23.3° C. was not more severe than usual, so the trunk dieback is a mystery. The absence of trunk dieback in tree #5 is also a mystery because it was planted in the Norway spruce windbreak where a spruce seedling had died and regularly faces cold north-westerly winds during the winter. Perhaps proximity to a drainage ditch, albeit plugged with vegetation, offers better soil drainage.
Although the latitude of my site is 236 miles further north from where the ancestors of these ultra northern pecan seedlings are located, there are a number of reasons why it seemed worthwhile to plant such seedlings at my site and observe how they perform. For one, these seedlings come from parent trees adapted to a continental climate similar to that found in eastern Ontario with wide daily swings in temperature, very cold winters, and hot summers. Northern pecans withstand temperatures that regularly drop to -30°C in the winter(7), so they are expected to tolerate the typical winter cold of eastern Ontario. Moreover, as noted previously, it seems that northern pecan trees can withstand temperatures as low as -40°C. Nevertheless, given the more northerly latitude of my site, low winter temperatures will typically be more severe than those prevailing in the ancestral habitat of these pecan trees. For instance, the record low temperature at some weather stations closest to my site (Chelsea, Quebec and Russell Ontario) was -40°C in mid-January 1957. At Dubuque, Iowa, which has the closest weather station to the Green Island site, the record low is only -33°C. But research involving differential thermal analysis (DTA), which is often used to evaluate cold hardiness in woody tissues, showed that a selection of 18 pecan cultivars originating from regions north of latitude 34° had low temperature exotherms ranging from -26.9°C. to -39.4°C. and averaging -35.4°C(9). Based upon this research and the climatic records for eastern Ontario and Iowa, it seems that ultra northern pecan trees should be able to tolerate typical low winter temperatures at my site, but it remains to be seen how well they perform during rare "test winters" when cold temperatures approach or drop below estimated low temperature thresholds.
Of course, surviving deep winter cold is not sufficient justification to plant a pecan tree if it never produces nuts. Insufficient summer heat or a frost-free period that is too short can jeopardise nut production. The average frost-free period estimated for my site is longer than the 140 frost-free days required for pecan cultivars maturing within the shortest of seasons (Table 2), but summer heat is likely to be insufficient for filling nuts. Cumulative growing degree days above 10° C. in eastern Ontario average lower than in Southern Ontario (Table 3), so one cannot expect these trees to produce mature nuts every season as many do in southern Ontario. At best, they may produce well-filled nuts during an exceptionally warm season, which is satisfactory for horticultural experimentation and, perhaps, home gardens, but totally inadequate for commercial production. In so far as some trade-off between summer heat and length of growing season might exist for some individual trees(10), the opportunity for maturing nuts at my site may not be as low as suggested by the number of growing degree days.
It is hoped that more regular applications of high nitrogen fertilizers and more frequent weeding and mulching will accelerate growth in the pecan trees at my site. Additional ultra northern pecan seedlings were planted in 2009 and again in 2011, but rates of mortality have been embarrassingly high - 80 per cent for both plantings. Only four of these seedlings remain alive and growth so far has been negligible, undoubtedly due to insufficient attention to weeding, mulching and fertilization. An additional 10 ultra northern pecan seedling trees will be planted this spring to replace those that died. This should provide a collection large enough to study the performance of pecan trees in eastern Ontario and to satisfy my curiosity about how far north pecan tree cultivation can be pushed.
TABLE 1 - Heat Requirements of Selected Nut Trees
|Nut Species||Growing Degree Requirements|
Above 10° C
TABLE 2 - Cumulative Growing Degree Days Above 10 C. at Selected Sites in Ontario (May to September, 30-year average)
|Site||Growing Degree Days|
Above 10 C
TABLE 3 - Estimated Frost-Free Days at My Site
|YEAR||Last Day of Frost|
|First Day of Frost|
|2004||May 31||October 3||125|
|2005||May 19||October 20||154|
|2006||May 7||October 7||153|
|2007||May 13||October 13||153|
|2008||May 1||September 19||140|
|2009||May 18||October 12||146|
|2010||May 10||October 12||154|
|2011||May 6||October 27||173|
References & Bibliography
1 Thompson and Madden (2003), p. 81.
2 Campbell (1995), p. 78.
3 Thompson and Madden (2003), p. 82.
4 This section was generously provided by Dr. Roman Popadiouk, who co-authored "For the Love of Trees - A Guide to the Trees of Ottawa's Central Experimental Farm Arboretum."
5 Grimo (2011), p. 109.
6 This calculation takes into account the average seedling height of 1.5 feet at the time of planting in 2001.
7 Reid and Hunt (2003), p. 109.
8 Converted to Celsius from data in Fahrenheit shown at: www.coolweather.net/statetemperature/iowa_temperature.htm
9 Volk et al. (2009)
10 Campbell (1995) pg.78
Campbell, R. D. 1995, "The Best Pecans for Ontario." Annual Report. Northern Nut Growers Association. 86:78-79.
Grimo, E. 2011. Nut Tree Ontario: A Practical Guide. Society of Ontario Nut Growers
Reid, W. and K.L. Hunt. 2003. "Pecan Production in the Midwest." A Guide to Nut Tree Culture in North America. D.W. Fulbright, ed. Vol. 1: 107 -115.
Thompson, T. E. And G.D. Madden. 2003. "Pecans." A Guide to Nut Tree Culture in North America. D.W. Fulbright, ed. Vol. 1: 79-104.
Volk, G.M., J. Waddell and L.Towill. 2009. "Variation in Low-Temperature Exotherms of Pecan Cultivar Dormant Twigs." HortScience Vol. 44 (2).
The information provided by Dr. Roman Popadiouk on pecan trees in the Dominion Arboretum and the editorial comments by John Sankey are much appreciated and gratefully acknowledged.
TABLE 2 was omitted in error from the print publication; that is corrected here
Provided by SONG. Feel free to copy with a credit.