As October comes to a close and Halloween pumpkins morph into compost or pies, one can still find a bit of orange sunshine on persimmon trees. The seedy fruits of this native attract deer, opossum, and raccoon as well as a number of bird species. Count humans among those appreciating the tree. In earlier days, the dense wood was used to make loom shuttles and the seeds were roasted as a coffee substitute as well as ground into flour for bread. Dried leaves were made into a tea, reputed to be high in Vitamin C. The fruit was converted to jellies, vinegar, syrup, and beer. Persimmon seeds are great ammunition in spitting contests and the unripe fruits initiate those unacquainted with their astringency into rural woodcraft. The late spring flowers draw many different pollinators.
Persimmon seeds are dispersed in the droppings of critters but the tree is frequently found in groves. Sprouts from the stolens, underground roots from the main tree, form dense thickets of genetically identical individuals. Persimmon trees are either male or female. Only a few male trees are required to fertilize the nearby female trees and you can quickly produce an orchard by thinning an all-male grove and grafting the remaining trees to a female cultivar. It’s common for grafted trees to produce fruit within three years. Persimmons are relatively pest-free although they are subject to twig girdlers, the persimmon borer, Phytophthora root rot, and fall webworms. The latter is the most distressing in appearance but, occurring late in the season, seldom causes damage to the tree.
One can argue the merit of the seeds as forecasters of winter weather but one legend that bears debunking is that the fruits require a frost before they are edible. Once the fruit softens and separates from the calyx “lid”, it’s ready to consume. Ripening dates vary among wild trees but cultivars, those individual specimens which have been grafted from trees with desirable qualities are more consistent. Larger fruit with fewer, smaller seeds typify Early Golden and Lena. Two hybrids, Nikita’s Gift and Rosseyanka are self-fertile crosses between Asian and American persimmons. They produce exceptionally large fruit with a few small, insignificant seeds and ripen very late in the season.
It’s unfortunate that commercialization of this abundant fruit is problematic. American and hybrid persimmon flesh is soft and sticky…a challenge to process. The consistency is much like that of the filling in Fig Newtons so picking them and putting them together in a basket results in a compact mass of fruit. Although abhorrent to those in the field of food safety, the easiest harvest technique is to spread sheets below the trees and pick up the fallen fruit daily, beating the other, night-active critters to the mother lode. The late Jerry Lehman, an Indiana persimmon breeder with a large grove, froze boxes of his improved persimmons and sold them to a winery. There are a few individuals who process and can the pulp. There is likely a market for selling the fresh fruit in individual egg carton cells, particularly if there is a specialty food store nearby. For the individual, making adult beverages for personal consumption is also an option. Removing the calyx caps and smashing the fruit, then mixing with a slurry of ground pears is the start of a great batch of wine. To produce a unique Christmas cordial, place the clean, capless fruit in half of a half-gallon container, top it off with vodka, and add the lid. Put it in the back of a dark cabinet, shake occasionally, and forget about it until Christmas Eve. Remember to leave a tumbler for Santa…the cookies may end up being left behind!
Chestnuts have been celebrated in song and verse, but the chestnuts of today don’t match the lore of the past. Rather than waiting for frosty days, the Chinese chestnut now planted in Missouri is harvested from mid-September through the following weeks, typically ending by early November. The village smithy would have been dodging large, prickly burs and quarter-sized (or larger) nuts. The American chestnut was a prodigious mast producer but those nuts were considerably smaller than The Chinese and Japanese nuts enjoyed by Asian and European cultures who now seek them in the United States.
The fist-sized burs of Chinese chestnut may contain three nuts, although it’s common for one or two of them not to develop. As the nuts ripen, the burs split open on the tree and the nuts fall to the ground. The burs drop as well, sometimes before they’ve fully opened and the nuts are still inside. Dry, warm, sunny days trigger the fall and a stiff wind can trigger a massive, continual drop throughout the day.
While mechanical harvesters exist, they are expensive. Some individuals will rely on large vacuums to gather the nuts while others will hire hand labor. A flexible back and a sturdy pair of leather gloves are basic equipment as well as separate buckets for burs and nuts.
Chestnuts grow quickly and frequently produce their first crop before they are 10 years old. That crop increases each year and, unless there is a problem during the pollination period or a late frost, it is quite reliable. Once they are too large to be browsed or rubbed by deer, the trees have few issues. Dealing with the nuts, however, is a different story. Daily collection is required if you don’t want the local deer, squirrels, and other rodents to commandeer your harvest. Once you’ve handled burs, you’ll have grudging admiration for the squirrels that go so far as to cut and carry the burs from the tree. Occasionally a pet dog will take an interest in chestnuts…first as a toy and then as a food item.
The most serious issue with chestnuts comes from weevils that infest the nuts. Again, one must have grudging admiration for an insect that can maneuver around the spines and lay eggs in the developing nuts. The weevil grubs, like those of hickory nuts, develop in the kernel and then emerge from the nut and enter the ground to pupate, emerging the following spring. Spraying is one control technique but the spring emergence finds them headed for the blooms, along with a host of other pollinators. The grubs are killed by extended temperatures above 117 degree and growers use hot water baths to kill the small eggs and larvae. Sanitation is critical in the chestnut orchard and removing all nuts and burning the burs is another technique to control weevil populations. Unfortunately, the nuts that squirrels bury serve as the source of future weevils. Many of these sprout so that once you have one chestnut tree you’re going to many chestnut trees.
Chestnuts are referred to as the “un-nut”, as they have no oils and become dry and hard if stored outside of the refrigerator vegetable drawer. That has made it difficult for new consumers to appreciate its rich flavor which is brought out by roasting or other heating. Scoring the shell of a dozen nuts with a sharp knife or box cutter and microwaving for 2 minutes cooks the nut and makes it easy to remove the shell and brown, papery coating on the nut (pellicle).
The MU Horticulture and Agroforestry Research Center will conduct its annual Chestnut Roast as a virtual event in 2020. They will release a set of novel videos on specialty crop production (pecan, Chinese chestnut, and elderberry), maple syrup production, and other topics. Presentations will be available at 8:30 a.m. on Saturday, Oct. 3, on the new Mizzou Agroforestry YouTube channel. Those who “subscribe” to the channel now will receive notifications as new content becomes available. The Chestnut Roast videos will also be linked through the Horticulture and Agroforestry Research Center Facebook page, the Center for Agroforestry Facebook page, and the HARC website.
The FDA recently opened up public comment for the rarely consumed raw exemption of the Food Safety Modernization Act. Walnut, Hickory, and Chestnut (along with many other tree crops) are not exempt from FSMA regulations. This is the opportunity to get them added to the Rarely Consumed Raw exemption. Aside from individual letters, it would be worth uniting with other growers/associations and presenting as an industry in regards to FSMA. The pecan industry did so back in 2015 and got a congressman to get pecans listed as exempt.
This will very likely be our last and only time to get many tree crops exempted from FSMA. Comments are due November 9th, 2020.
Can any school child find the Suwanee River on a map? If they’ve heard the song, do they have any idea of where they might find a pawpaw patch way “down yonder”?
Although few are actually familiar with the largest native fruit in North America, plenty of folks have claimed it as it is also known as the Hossier banana, the Missouri banana, the Michigan banana, and the West Virginia banana. Thanks to the efforts of a persistent group of school children, the pawpaw became the official state tree of Missouri in 2019.
Pawpaws ripen in late August and through mid-September. The green fruit gradually become more yellowish and soft under thumb pressure. Native Americans and early explorers relished the fruits once they turned black and had a butterscotch taste. Like overripe bananas, they were certainly edible but most modern taste buds and eyeballs prefer the freshly ripe fruit. The trees are frequently found in groves as they often propagate by forming new plants from root shoots. Unfortunately, fruit is seldom found in the most luxuriant patches of pawpaws. Because the tree can produce numerous shoots from its roots, these stems are all identical and, in order for fruit to form, the flowers must receive pollen from a genetically different pawpaw flower. Of course, there is competition from wildlife if you go seeking pawpaws. The flesh, which tastes like a mix of banana and pineapple, appeals to critters like raccoon and opossum and, in many situations, the seeds they consume would pass through their digestive tract and be sown at a different location. Because the large seeds in the fruit won’t germinate if they dry out, unless they somehow end up in a favorable setting, a new pawpaw patch cannot form.
Fewer and fewer young folks are going afield, splashing in creeks, building forts, in the woods, picking berries, and generally reveling in the outdoors so they seldom look for, know of, or discover pawpaws. With a bit of effort, the tree can become part of an “edible landscape” in your yard. Although characterized as a bottomland, understory tree, they perform well in most mesic settings. You can purchase potted or bare root stock from specialty nurseries: the potted trees will be far easier to plant. Young trees do best in partial shade, which can be provided with commercially available shade cloth or a discarded pair of sheer curtains. If you are fortunate enough to find pawpaw fruit, you can plant the seeds in the fall. Be forewarned that the seeds are slow to germinate, in some cases not sending up a shoot for two or three years. You’ll need two trees (if grafted, they must be the different cultivars) to produce fruit. It’s not unusual for the tree to die back to the ground and then resprout from the root, sometimes for several successive years, as it becomes established.
Once established, the pawpaw requires minimal care. If you have an established white-tailed deer population, protect the tree from rubbing in the fall and winter with a sturdy wire cage. Pawpaws are extremely sensitive to herbicides and some of the commonly used fruit tree sprays. The leaves are fodder for zebra swallowtail butterfly caterpillars but it is the Asimina webworm that is responsible for most concern, especially on young trees where it can reduce all the leaves to masses of brittle, dried foliage. Frequent dusting with BT dust can help to control this pest. There is also a pawpaw sphinx moth, the mature form of a hornworm caterpillar (similar to that frequently encountered on tomatoes) which feeds on pawpaw leaves.
The taste of pawpaw fruits can vary from tree to tree and some individuals detect an undesirable aftertaste. Pawpaws can be eaten fresh or the pulp, separated from the seeds and skin, can be used to replace banana in banana nut bread, baked in a custard pie, or frozen as an ice cream. The seeds and skin should not be consumed!
If you’re out an about in the woods this month, watch for the large, single, dark green leaves that smell like green pepper when crushed. You just found your pawpaw patch!
At one time, September was the official beginning of fall, but as school start dates have moved from immediately after Labor Day to mid-August, all those seasonal indicators, like cold weather clothes in retail stores, are appearing earlier. As if to get a head start on Halloween, the gossamer threaded nests of fall webworms are appearing in trees as well.
As their name implies, fall webworm colonies create a web. The caterpillars eat the foliage of a wide variety of hardwood trees, shrubs, and low plants. In contrast to the nests of the spring-announcing tent caterpillars, which set up housekeeping in the crotch where branches join the tree trunk, webworm tents cover the leaves at the branch tips. In both instances, the webs allow the caterpillars to feed in relative safety. A colony of fall webworms typically strips the foliage from the branches covered by the tent which increases in size as the caterpillars grow and their food needs increase. More than 100 species of trees, shrubs, and other plants have been recorded as food plants, including hickory, oak, maple, walnut, persimmon, cherry, elm, mulberry, willow, redbud, and sweet gum.
Fall webworms are native to the United States. The life cycle begins when the adults emerge, which may occur as early as May in Missouri. After mating, the female moth lays 900 to more than 1000 eggs on the underside of a leaf. These eggs hatch into tiny, hairy caterpillars that grow to about 1.5 inches long. When they have matured as caterpillars, the larva move to the ground and spin a cocoon. Missouri trees face two onslaughts from this insect as the adults emerge and lay eggs for the second brood. These caterpillars with spend the winter in their cocoons on the ground or under flaps of bark, where they remain throughout the winter and emerge the following spring to repeat the cycle. Although their nests are unsightly, fall webworm feeding does not harm large shade trees. Since the damage occurs in mid-late summer, the trees have had time to store energy since spring. Small trees can be weakened by large, enveloping nests of caterpillars and, conceivably, be killed by repeated defoliations. Fortunately, webworms are easily controlled on small trees: simply prune off the nests before they become large and submerge them In a bucket of soapy water. Residual insecticides are also effective but, if the problem is limited, pruning is certainly the cheaper solution! If you prefer an even more ecologically friendly route, use a stick or pole to open and break up the nest, exposing the caterpillars to predation by small mammals, birds, wasps, and hornets. The caterpillars themselves also become nurseries for the larvae of tiny, parasitic wasps and tachinid flies which lay their eggs inside the larvae. The caterpillar becomes both bed and breakfast for the invading larvae, dying in the process. Parasitic fungi also take their toll on fall webworm caterpillars, although, when the trees are draped in webs during the late fall, it appears that none of these sources of mortality is all that important. On the other hand, suppose the caterpillar populations went unchallenged?? Spiders and bats will eat the night-flying adult moths.
Although fall webworms are native to the United States, they were accidentally introduced to Yugoslavia in the 1940s. Since then, they have invaded most of Europe and spread to China, Korea, and Japan. This insect is a major pest in these introduced countries. In Europe, the fall webworm is more destructive than their native European gypsy moth caterpillar is in the United States. The gypsy moth was intentionally introduced to the United States in 1869, with the hope of interbreeding with silk worms to develop a silk industry in the United States. The interbreeding never occurred, but gypsy moths have spread from Massachusetts to west of the Mississippi River. States like Missouri, where gypsy moths are not firmly established, invest time and resources to identify and eliminate any potential population pockets.
Noted pecan specialist Dr. Bill Reid suggests that fall webworm control is warranted when there are more than five nest per acre in commercial orchards. This control is often combined with other sprays applied to control pecan case bearer and pecan scab. Because the caterpillars will expand their nests to access new foliage, a residual spray offer control.
You can read more about fall webworms in the University of Florida entomology department account at: http://entnemdept.ufl.edu/creatures/trees/moths/fall_webworm.htm as well as the Missouri Department of Conservation’s webpage: https://nature.mdc.mo.gov/discover-nature/field-guide/fall-webworm-moth and Dr. Bill Reid’s blog: http://northernpecans.blogspot.com/. Dr. Reid has made multiple entries on this pest so use the search function for fall webworm to see all of them.
It’s July…it’s summertime! Growers are out inspecting their trees to get an idea of the crop they will harvest later this year. This may be easy, as in the case of elderberries, where the white panicles of blooms are borne at the tips of stems and the green berries, ripening to purple are near eye level. Pawpaw fruits are large enough to be seen, even though tucked among the enormous green leaves. Persimmons are also visible, although require a keen eye as they are nearly the same shade of green as their surrounding leaves. Walnuts and pecans are readily visible at the tips of branches…if pollination was successful. Even during years with adequate pollination, trees may not produce a large crop if they made a lot of nuts the prior year. This on-again, off-again phenomenon, known as alternate bearing, is often triggered by boom crops, which drain energy from the tree as they ripen in the fall, leaving minimal energy to form female flowers for the next year. Chestnut burs are still tiny, but will grow quickly over the summer, maturing mid-September thru mid-October.
Spring pollination is only one hurdle faced in the marathon to produce a fall harvest. Summer thunderstorms with high winds and hail, can damage leaves, break branches, and even snap and uproot trees that have all that additional crop weight “upstairs”. It’s said that Missouri is only 10 days away from a drought as heat and plant needs pull the moisture from the soil and it is the water that is available at this time of year that is critical for nut sizing and the beginning of kernel fill.
Exploring details of water needed by pecan trees, known for their bottomland habitat, led me to the Noble Research Institute in Ardmore, Oklahoma. About 350 researchers from a range of disciplines and from 20-plus countries work at the Institute headquarters in Ardmore, Oklahoma, and on research farms in the surrounding area, to carry out the vision of Lloyd Noble. Lloyd Noble established the Noble Research Institute (originally named The Samuel Roberts Noble Foundation) in 1945 to help revitalize agriculture after the Dust Bowl. Today, the Noble Research Institute is the largest nonprofit agricultural research organization in the U.S. A paper written in 2006 summarized pecan water needs and I’ve summarized its contents in the following paragraphs. To read the full paper, visit: https://www.noble.org/news/publications/ag-news-and-views/2006/september/consider-pecan-trees-water-needs-during-drought/.
Many people have asked how much water a pecan tree requires and estimates have ranged from as low as 30 inches per year to as high as 72 inches per year. Of course, there are a number of other variables to consider, such as soil type and the physical location of the tree as well as timing, with moisture most critical during the growing season. Trees in a flood plain have a much different regime than those planted in sandy, rocky soil. A tree growing in a soil that is seven feet deep has the potential of 9000 gallons of available water per tree compared with a 7 inch deep soil, which has the potential of only 800 gallons of water per tree. Pecan tree roots range far beyond the canopy, as can be seen if you’re present during a tree shaking during the fall nut harvest. The folks at Noble figured that, on the basis of 55 inches of precipitation per year, with most arriving during the growing season, individual trees in a planting with 35 trees per acre, would need 190 gallons of water per day. By comparison, the standard recommendation for water requirements of pecan trees is 1 to 2 inches per week. At the same spacing, this amounts to 111 gallons per tree per day.
Here in St. Clair County, Missouri, the 2019 walnut crop on the farm was a good one, and harvested by energetic squirrels as other nuts were in short supply. This year a few trees have nuts so I will make my harvest in early July and intend to convert the nuts I can reach into Nocino, an Italian liqueur. If you’re interested and can find a few green black walnuts that haven’t yet hardened the shell inside the hull, here’s a link to a recipe I Googled: https://www.mountainfeed.com/blogs/learn/45965569-how-to-make-nocino-an-italian-walnut-liqueur. Perhaps it will prevent COVID-19 infections. For certain, overindulgence will mean that you won’t care!
July 2020 Persimmon
There are those special times of life…priceless moments like the unrestrained giggle of a baby and the day buds break on a scion grafted dormant, and seemingly lifeless save for the tinge of green as you saw as you made the cuts that you hoped would meld a superior tree onto a lesser root stock. The stars aligned, you did things right! Success, however, can be your worst enemy.
Removing buds and other growth from the root stock channels all the energy destined to go to many sites into the two or three buds on the scion and they grow rapidly. It’s likely you’ll see secondary buds continue to emerge on the root stock, both above and below the side graft. If your graft failed, you could take advantage of these secondary “backup” buds by pruning off the failed graft and leaving one or two of those new arrivals to form sprouts for your grafting efforts next year.
It’s common practice to leave only one bud of those that are viable on your successful scion, selecting the one that will most likely give the future tree a sound scaffold for future branches. Of course, this isn’t mandatory and a second option is to leave that second or even third bud to continue growing. These can help utilize all that excess energy, provide a second option should the “first choice” be damaged, and also serve as a source of scion material when pruned off the following year.
There are several threats to the new growth on a scion. The union of the scion with the root stock is tenuous, at best, at this point in time and needs to be supported. There is no reason to prune off the root stock growth above the side graft until later in the year. Add a “bird perch” that extends at least 18 inches above the graft. It’s common to trim your original pruned material and use electrical tape to attach it to the root stock at two points below the graft. If the rootstock didn’t have a well-defined leader, a bamboo stake works well. Birds perch on the highest point in relation to the surrounding vegetation. If you have protected your tree with a T-post or welded wire that extends above the graft, birds will use that as a perch rather than landing on the new growth…until the scion outgrows this protection. The “bird perch” is also a training stake and it’s important to lightly tie the lengthening stem to it as it grows. Summer storms are a major threat to the new stem and it’s a sad fact of life that the great growth you meant to tie to the stake in a day or two catches a gust of wind and is snapped at the union.
Browsing deer are yet another threat to the tender growth of a new scion. You would think that, given all the greenery available at this time of year, deer wouldn’t be so inclined to focus on your trees…but they will. If you have a large planting, an electric fence is probably your best temporary solution. If you are using individual welded wire cages, you can extend your protection by attaching the cage to the T-post12-18” above the ground. You’ll need to provide continued protection to young trees as what the deer don’t browse now bucks will likely rub this fall…and until the trees are about four inches in diameter.
….and you thought you were home free once that graft succeeded!!
Across Missouri, grafting knives are being sharpened and scion storage refrigerators are being opened as nut growers head to their orchards to graft material taken from high quality trees earlier this year to rootstocks of run of the mill trees.
Grafting has been practiced for thousands of years although its actual origin is up for discussion. The first definitive written account is attributed to writings from Greece dated 324 BCE but the descriptions detail a number of practices that were apparently commonplace. Grafting not only allows you to faithfully replicate a high quality tree but is also used to combine characteristics of the rootstock, such as dwarfing and disease resistance, with the high quality fruit produced by the scion.
There are a number of different grafting techniques which can be used. All focus on matching the cambium, a thin layer of growing cells just below the bark, of the scion and rootstock. Grafts can be used on everything from very small saplings to large trees, where bridge grafts are employed to save damaged trees, for example, where beaver have effectively freshly girdled a tree, disrupting the flow of nutrients up and down the trunk, but the tree hasn’t been damaged to the point that it will drop. About the only caveat is that the scion and rootstock must be the same or closely related species.
Many grafting techniques are demonstrated on U-tube videos, but not all provide good results when used on nut trees. The publication” Propagating Pecan and Black Walnut (available to download at: http://extension.missouri.edu/explorepdf/agguides/agroforestry/af1003.pdf) is a good introduction to those specifically recommended for nut trees. Another, more general but also helpful, grafting reference is the MU Extension publication titled “Grafting” (https://extension2.missouri.edu/g6971). The side graft, in Figure #4, is simple and also effective and can be accomplished using a pair of bypass pruners and a utility knife. The trimmed scion is inserted into a cut made into the side of the rootstock that is opened by pushing on the portion of the stem above the opening. When that pressure is released, the stem springs back, holding the scion in place. Of course, you must wrap the junction with grafting tape to reduce moisture loss from the cut edges. By cutting the rootstock about four buds above graft, you build in a bird perch without attaching a separate stick. Little details: the FLAT slope cut on each side of the scion should leave equal amounts of material on both edges, otherwise only one exposed cambium will contact the cambium of the rootstock. If the scion isn’t large enough to entirely bridge the width of the cut, all is not lost. You can trim another stick or simply match one side as this is often successful.
Followup care of the graft consists of monitoring rootstock buds above the graft and rubbing them off at the first sign of greening: if you don’t check carefully, that vegetation may lead you to think your graft has been successful when it has failed. Once the graft has begun to green, attach a second, taller stick to the rootstock to keep birds from landing on the tender sprouts.
The grafting techniques discussed here are best done in the spring, when the nut trees are breaking dormancy and before temperatures become excessive as grafts often fail once temperatures get above 90 degrees. Not all grafts will be successful but making certain that the scion material has been stored properly and is still dormant, careful alignment of the cambial layers of the scion and rootstock, and protecting the graft union from desiccation will greatly improve the likelihood of success. While the text and pictures referenced here will be helpful, nothing beats seeing the process in action and hearing the tips of an experienced grafter. The Missouri Nut Growers Association offers such an experience at its annual grafting and scion exchange meeting. Unfortunately, due to COVID-19 it was necessary to cancel the event this year. The 2021 event should take place in late April or early May, so revisit out home page after April 15, 2021, for an update.
As we prepare the Spring newsletter there are many concerns about the spread of the Corona virus. President Mike Lucas, in consultation with board members, has decided to cancel our May meeting. We are fortunate in having two medical professionals associated with the board and they concur that, given what we know at this moment and respecting current directives from local governments, that this action is appropriate.
You are urged to follow any updated CDC guidelines (visit https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/summary.html#anchor_1580064337377) and common sense. Wash your hands!
Scion exchange update...In light of the spring grafting meeting being canceled, I'll be facilitating an informal scion exchange. Several folks have offered up scion and there have been several request for scion - all of which is GREAT! The the following scion is available. Pecan - Kanza, Pawnee, Gardner, Shepherd, Yates 68, Lakota, Major, Meramec, Harc, Chetopa and Manson 1.
Black Walnut - Kwik Krop, Football, Hay, Emma Kay, Neel and Tom Boy
And some English Walnut.
Please feel free to contact me. I can be reached at 816-293-5819 (leave a message) or via email firstname.lastname@example.org.
I plan to do/coordinate the shipping the week of April 13.
Thanks, Mike Lucas
April showers bring May flowers…it’s a well known phrase but those who have an eye for detail, or a reason to look, know that trees have been blooming for several months. Bee keepers watch for willow, maple, and elm blossoms that may appear as early as February and serve as an early nectar and pollen source for their hives when the bees venture out on warm days.
For nut growers, dangling hazelnut catkins in early March are sometimes the best way to locate these shrubby plants along roadsides: their small nuts are usually claimed by mice and squirrels long before they can be gathered by humans. Swelling oak buds will soon have hanging catkins, and catkins of hickories, including pecans, and black walnut will become evident as spring progresses.
Catkins, however, are only part of the nut story. They are the male flowers which shed their pollen, carried by the wind to tiny female flowers that often go unnoticed until the nuts they produce begin to develop. You’ll have to look closely at other buds to find the tiny maroon filaments that are the female flowers. Pollination isn’t guaranteed, even given the volumes of pollen that are generated. The wet 2019 spring is blamed for poor black walnut production that year as many believe that the frequent rains basically washed the walnut pollen out of the air so that it never reached the female flowers. There can be other complications. There are numerous examples of trees that require a second specimen in order to achieve successful pollination and produce fruit. For example, in pecans the male catkins on some trees will mature and shed pollen before the female flowers on the same tree are ready to receive the pollen. Fortunately, there are other pecan trees where the female flowers mature before the males begin to shed their pollen. As long as there is a mix of those trees in the landscape, there will be pecans produced on all of the bearing age trees.
Chinese chestnuts, an increasingly popular crop in Missouri, rely on insect pollination and their showy pale yellow male catkin flowers are alive with activity. Ironically, the female flower, tucked at their base, doesn’t attract insects so perhaps it is the motion of those tiny feet that loosens enough pollen grains to cause fertilization. Hmmmm…I’m going to explore this question further in my chestnut orchard this spring!