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Author: François DROUET.
Photographs: François DROUET.
(unless indicated).
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Unripe figs individual bagging
This control method concerns the amateurs fig tree cultivation. For professionals, it generates a prohibitive labor cost, but I leave those who practice organic farming on small areas to think about it. I detail below the process, according to the following plan: principle, organza bags, implementation modalities, processing time, efficiency / possible improvements, figs varieties requiring pollination.
PRINCIPLE
Figs bagging prevents the Black Fig Fly female from depositing its eggs under the ostiolar scales or in the ostiolar canal of the unripe fig.
Silba adipata McAlpine laying eggs under an ostiolar scale of a tiny unripe fig.
(note the size difference between the two unripe figs).
Two types of bagging can be envisaged: bagging of the terminal part of the branch, where the figs groups to be protected are located, or individual bagging of each of the figs (one bag for one fig). Given the fruiting mode of the fig tree, which gives rise to figs as the upper part of the branch lengthens, bagging figs groups seems to cause difficulties. The bagging volume makes its resistance to strong winds problematic, even if this can be reduced by preparing the branch to be bagged by pruning certain leaves. The individual bag requires particular care for the closing system, which must be strictly fixed to the fig neck (or to the fig peduncle for certain varieties).
The protection of immature figs groups carried at the end of the branches of the year with large organza bags, or organza veil tied to the branch, gives good results (if some leaves are cut), according to Reuben CHETCUTI, a reliable correspondent who uses it in Malta, like one of his friends in Israel.
See the photograph below (espaliered fig tree).
Figs group protected against the Black Fig Fly with organza (espaliered fig tree).
Crédit: Reuben CHETCUTI
But I was never motivated to experiment this process, which seems to me less practical than indiviidually bagging the figs, in my orchard conditions (perhaps wrongly...). If the figs are collectively protected, the harvest is slower and more difficult. Maturity is staggered on each of the branches, and the protection must be many times widely opened and then closed (or removed and put back in place, if it is a bag).
I prefer to use individual organza bags, which, according to my experience, require a completely acceptable processing time in an amateur's orchard.
The photograph below shows a group of individually bagged unripe figs in my orchard (the internodes are almost non-existent).
Unripe figs individual bagging against Silba adipata McAlpine (organza bags)
ORGANZA BAGS
MATERIAL
It is not a question of bagging the figs with an opaque material, because this does not allow to know the figs maturity level, and does not let the sun pass through. The technique used for apples and pears, consisting in opening the opaque bag fifteen days before harvesting so that the fruit takes on a correct color, is unsuitable for figs, which have very staggered maturity on the same tree. In addition, this process would allow the Black Fig Fly to attack immature figs still on the tree. The ideal is the use of thin mesh bags, allowing air and sun to penetrate, but preventing the egg laying female from entering the bag. The objective of the chosen material is not to prevent the ovipositor from passing through thanks to a fairly thin mesh, but to keep the female away from the ostiole thanks to a certain rigidity, thus preventing it from laying eggs there. Organza (organdi) satisfies all of these specifications.
SIZE
The bag must be large enough to allow the maximum growth of the fig, even if the bags positioning is carried out on very small figs with a diameter of 1,1 cm (the minimum diameter that I measured for a fig attacked by Silba adipata McAlpine is 1.1cm). After various tests, I selected two bags models: one measuring 7 x 10 cm, for the small and medium-sized fig varieties; the other measuring, 8 x 12 cm, for the large fig varieties. In 2022, Marc SCHAISON, fig trees collector in Draguignan (Var), and contributor to this website, tested organza bags measuring 10 x 15 cm on the largest figs in his collection. At the end of the test, he recommends not to use bags of these dimensions, which he finds less practical, and to stick to bags of dimensions 8 X 12 cm even for very large figs.
CLOSING SYSTEM
The bag closing system is a very important point. II think that the choice of a bag with two draw strings is imperative. Care must be taken to choose a closure with a flat satin ribbon, and not with a little cord that, even if it is thin, thickens the part of the bag which must be inserted between the fig and the leaf petiole or the apical bud, or between figs almost touching each other due to very short internodes. According to my measurements, the fig neck has a diameter of about 5 mm when the immature fig reaches the size from which it can be attacked by Silba adipata McAlpine (about 1,1 cm in diameter).
The sliding links system satisfies the solidity criterion (installation and hold on the tree). With good quality bags, only one to two bags out of 100 have a defect in the seams or in the closing ties solidity, which leads to their elimination. But the bags manufacturing quality greatly varies from one supplier to another. With a poor quality product (green color bags directly sourced from China), I have experienced a bags eliminationl rate of over 10 %.
According to my practice on small and medium-sized figs, the closure by the two sliding ties tight around the peduncle or the neck of the fig does not constitute an obstacle to a proper development of this one. Even if I observe on some ripe figs a slight deformation in the upper part (only identifiable by a trained eye). In 2022, this point was tested, with the same positive conclusions, on large figs by Marc SCHAISON, fig trees collector in Draguignan (Var) and contributor to this website.
WEATHER RESISTANCE
According to my experience of individually bagging the unripe figs of my three fig trees (Biferous 'Grise de la Saint-Jean' variety, uniferous 'Bellone' and 'Col de Dame Noire' varieties), the two selected organza bags models meet the criteria of resistance to the sun, rain (no deformation), and strong winds (no bags falling).
RIGIDITY
My practice also made it possible to observe the permanence of the bags rigidity during the season, an essential factor in preventing the egg laying female from reaching the ostiole when it lands on them.
Unripe fig individual bagging against Silba adipata McAlpine (organza bag).
Protection against Silba adipata McAlpine: fig having reached the maturity stage in an individual organza bag.
Precaution to be observed: care must be taken to preserve the original bags rigidity, avoiding washing them. At the end of the 2022 season, I vigorously washed the organza bags removed from the second crop figs of my 'Grise de la Saint-Jean' fig tree, which were heavily stained by the remains of a mealybugs attack, and by sooty mold resulting from this attack. By soaking the bags in bleached water, rubbing them between the two hands, and letting them to soak for half a day in clean bleached water. This treatment caused the organza to soften, and during the 2023 season, I noticed that these bags no longer held straight, and folded in half when placed on small immature figs. The possible contact of the immature fig epidermis with the softened bag did not present a risk of egg laying. But having noticed that on some figs the bag collapsed at the ostiole level, I gave up using a large part of the softened bags.
REUSE
According to my experience, given their condition after the ripe figs harvest (figs detached with their protective bag), the organza bags can be used for several seasons.
Figs having ripened protected against Silba adipata McAlpine by an organza bag.
(uniferous 'Bellone' variety).
IMPLEMENTATION MODALITIES
START OF FIGS BAGGING
It is not a question of triggering the installation of the protective organza bags on a given date. To act effectively against Silba adipata McAlpine, it is necessary to act precisely according to the egg laying females behavior. It is therefore necessary to only take into consideration the diameter from which Silba adipata McAlpine can attack the fig (critical diameter). Knowing that the date of reaching the critical diameter varies according to the variety and the location of the fig tree, and, for the same fig tree, from one year to another according to climatic conditions.
The fig diameter that should trigger the bagging is 1,1 cm. Given that the smallest figs for which I directly observed an oviposition had a diameter of 1.1 cm. And that, according to my measurements, for certain figs varieties like 'Bellone', about 40 % of Silba adipata McAlpine attacks occur on immature figs with a diameter varying between 1.1 and 1.5 cm. In practice, I start bagging when the five largest figs on the tree have reached the critical diameter. Using, of course, a Vernier caliper to exactly measure the figs diameter (the sycone is not a regular sphere, so I usually measure the larger of its diameters).
And I include in the first batch of bagged figs all those whose neck is sufficiently individualized. But it exists a difficulty: if we bag figs with an individualized neck that are too small (0,8 to 1 cm), this most often leads to a physiological drop a few days later. It is therefore necessary to make a compromise and bag the figs only when they are just larger than 1,1 cm. The visual selection of figs to bag is acquired with experience.
Breba figs ('Grise de la Saint-Jean' variety) individually bagged against Silba adipata McAlpine.
(note that the leaves are not yet developed).
Breba figs ('Grise de la Saint-Jean' variety) individually bagged against Silba adipata McAlpine.
Breba figs ('Grise de la Saint-Jean' variety) individually bagged against Silba adipata McAlpine.
OPERATING MODE
During bagging, ensure that the bag contains only an immature fig. Therefore keep outside the bag the emerging leaf and the apical bud which can be next to the fig, depending on the case. Start by turning the top collar inside the bag on one side, in order to have a thinner side to insert between the fig and, depending on the case, the branch (breba fig ), the leaf petiole, or the apical bud.
Organza bag with collar turned inside on one side only.
To put the bag on the fig, it must be held pinched between the thumb and the index finger at both ends of the opening. Depending on the position of the fig on the branch, its orientation, and the place chosen for the insertion of the thinnest side (the one with the collar turned inside), the two thumbs are outside or inside the bag.
Before presenting the bag on the fig, ensure that the two sliding tightening ties are clear on either side of the bag opening, so that once the bag is placed, while we maintain this one in its position of insertion with the thumb and the index of the two hands, we can find them without difficulty with the other fingers. If the sliding tightening ties are turned on themselves, it is impossible to grasp them in the case of difficult bag positioning.
Insert the thin side (folded collar) of the bag opening, covering the fig, until it abuts on the branch, at the starting point of the fig peduncle. Do not hesitate to force if necessary, especially when the fig is almost contiguous to other figs themselves bagged.
Unripe fig bagging: insertion between the fig and the leaf petiole of the thin side (folded collar) of the bag opening.
(note that the bag abuts on the branch, at the starting point of the leaf petiole).
Then, position on the fig other side the bag side with the unfolded collar, up to its stop on the branch, at the peduncle starting point. Be careful, this causes the bag side with which we started to rise; therefore maintain its bottom against the branch during the positioning of the second bag side.
Unripe fig bagging: insertion between the fig and the branch of the second side (collar not folded) of the bag opening.
Finally, the two sliding ties must be tightened to close the bag, taking care to pull in the same movement in the direction that allows the bag opening to be crushed against the branch, in order to close the bag flush with the branch.
Unripe fig bagging against Silba adipata McAlpine: sliding ties tightening.
ERROR TO AVOID
The error to avoid is not to completely cover the fig neck (and the fig peduncle, for certain varieties) on one side or the other of the fig, by not making the bag stop at the starting point of the fig peduncle on the branch. This error has two harmful consequences: fig deformation during development (at the level of the neck, or even of the flank, if the bag, insufficiently tight, has slipped under the effect of the wind); Medfly (Ceratitis capitata Wiedemann) egg laying on the fig neck part remaining in the open air (when the fig is softened, at the maturity stage or just before).
Unripe fig bagging: error to avoid (bag not completely covering the fig neck).
Unripe fig bagging: protective bag incorrectly placed, or which has slipped under the effect of the wind.
(note that the fig neck is partially uncovered).
BAGS REMOVAL
According to my observations, the fig perfectly matures in its protective bag. It should then be harvested with its protective bag, in the same way as if it did not have one. During the harvest, the organza bag does not hinder the appreciation of the fig coloring, nor the possible evaluation of its softening degree by touch.
Breba figs of the 'Grise de la Saint-Jean' variety picked with their protective organza bags against Silba adipata McAlpine.
The fig extraction from the bag can be carried out once the harvest is sheltered. This is a quick operation, which is carried out by loosening the bag ties without raising any particular difficulties, and which leaves the bags intact for reuse. In my experience, figs bagged at the immature stage reach the same size as unbagged figs, and their organoleptic qualities are unchanged. The figs appearance is almost identical to that which they would have if they had not been bagged. If the protective organza bag has been correctly positioned, and with not excessive tightening (skill that is acquired with experience...), the ripe figs show only a slight deformation on the neck (slightly flattened on one side). This does not affect the figs aesthetics, and only a trained eye will notice it. See photograph below.
Breba figs of the 'Grise de la Saint-Jean' variety, the protective bags of which have been removed after the harvest.
TRACES AND DEFORMATIONS
If the protective bag has been incorrectly placed (opening not positioned at the peduncle starting point, at the level of the branch, on one side of the fig or on both), or if the wind has moved it (due to an insufficient tightening), we can see tightening traces on the ripe fig, or more or less significant deformations depending on the case. Without this altering the fruit capacity to reach maturity, nor its organoleptic qualities. See photographs below.
Second crop ripe figs ('Grise de la Saint-Jean' variety) deformed by the ties of the badly positioned protective bags.
Second crop ripe figs ('Grise de la Saint-Jean' variety) deformed by the ties of the badly positioned protective bags.
Second crop ripe fig ('Grise de la Saint-Jean' variety) deformed by the ties of the badly positioned protective bag.
Just ripe breba fig ('Grise de la Saint-Jean' variety) deformed by the ties of the badly positioned protective bag.
Fully ripe breba fig ('Grise de la Saint-Jean' variety) deformed by the ties of the badly positioned protective bag.
PROCESSING TIME
PROCESSING TIME - "Bagging all the figs" method
The first idea that comes to mind when hearing "bagging" for figs is that it is a huge amount of work, impossible to achieve. This is the case for professionals cultivating several hectares, but this is not the case for amateurs who own a limited number of fig trees. Particularly when the fig trees are trained in a tuft, or in an open goblet on a low trunk, 3.5 m to 4 m high, and that we can fairly quickly circulate around them. The best configuration is the fig tree trained in such a way that all the fruits are accessible from the ground, either directly, or by pulling the flexible branches towards us with the traditional instrument of the southern French regions, an iron hook fixed at the end of a Provence cane. In the case where the fig tree is grown in height, we can choose to treat only the figs located between the ground and the height of 3 to 4 m.
The timings of my individual bagging of several hundred figs (on trees of different varieties) show that, working at normal speed, I am able to individually bag 80 figs in one hour, making it possible to save in 5 hours of work the whole of a fig tree bearing 400 figs (which constitutes a significant crop for a single fig tree with pedestrian harvest). This treatment time is quite acceptable in an amateur's garden, knowing that, given the fig tree fruiting mode, the workload is spread over a few days.
Note: this is an average productivity for the treatment of all the figs, easy and difficult to access, carried by a 4 m high fig tree, bagged from the ground without recourse to the ladder, but using in some cases a Provence cane with an iron hook. Are taken into account in the processing time the movements around the tree and the handling of the branches, as well as various difficulties in positioning the bags. The three main ones are: figs in height or in the center of the tree, which require bringing the branch towards us and holding it with one hand, which is also used for bagging; figs tightly grouped because the internodes are practically non-existent; terminal figs of the branch which are stuck to the apical bud, between which and the fig it is necessary to insert the bag.
PROCESSING TIME OPTIMIZATION
The processing time can be significantly optimized if we take the option (on several fig trees, for example) of only treating the well-placed figs: those with easy access (which do not require twisting, to lean towards the center of the tree, make efforts in height, bring back the branches towards oneself), and which are single, or in a low number group and free from the branch. To bag an unripe fig that is easily accessible, and single or free from the branch, the time is less than ten seconds. This can give hope for a treatment of 6 figs per minute, or 360 figs per hour. But it is of course necessary to plan the bags replenishment (15 flat bags in each pocket, and a box with the bags near the fig tree to restock every 30 bags). We can then treat 300 figs in one hour. The aforementioned replenishment process, which is the one I practice, generates a loss of time due to the high replenishments frequency (every 30 figs). I think, without having tested it, that if we keep a basket filled with bags strapped across the chest, we should improve productivity.
PROCESS EFFICIENCY / POSSIBLE IMPROVEMENTS
PROCESS EFFICIENCY
In 2022, I individually bagged the immature figs from the two crops of my fig tree of the biferous 'Grise de la Saint-Jean' variety, and those of my fig trees of the uniferous varieties 'Bellone' and 'Col de Dame Noire' (in total, about 900 figs). I had tested all the technical constraints and defined the operating mode in 2021. I found that none of these figs were attacked by Silba adipata McAlpine, knowing that the harvest losses were until then at least 50% per fig tree, and regularly 98% for the 'Bellone' one. I can therefore assure that the process is 100 % effective (on the imperative condition of bagging the unripe figs when they are 1,1 cm in diameter, or a little more).
This is also what emerges from an experiment carried out the same year by Marc SCHAISON, fig trees collector in Draguignan and contributor to this website. He individually bagged (organza bags) several hundred figs on various fig trees, choosing the varieties most heavily attacked by Silba adipata McAlpine. He found no attack by this pest on bagged immature figs, whereas, for all the varieties included in the test, the not bagged crop part suffered significant damage.
POSSIBLE BAGS IMPROVEMENTS
Regarding the organza bags, three improvements should be tested: removal of the collar, green color, addition of thin and light raising elements on the inside of both sides. The removal of the collar would have the first benefit of facilitating the insertion of the bag around the fig in difficult cases. And, for second benefit, to eliminate the greenhouse effect generated by the collar (which I suspect...), which perhaps favors the parasites proliferation in the event of an attack of these (mealybugs, for example).
But it could be that the collar removal promotes the Medfly ovipositions on the very beginning of the fig neck, which is outside the protective bag that could not be perfectly placed. On a practical level, to experiment with the collar removal, it is not possible to cut out the one present on the bags, because, in my experience, the side seams no longer hold. It would be necessary to order bags without collar, whose side seam would be stopped just above the links. I have not spotted such organza bags on the market (they exist in other materials), and it might be necessary to ask for a specific manufacture.
The use of green-colored bags (currently on sale) could perhaps have a beneficial effect on bird attacks when the figs reach maturity. I have not tested this possibility, the birds attacks (magpies) on bagged ripe figs being weak in my orchard.
The addition of thin and light raising elements on both sides of the bag (glued on the inside) would prevent Medfly from laying eggs in the epidermis of the softened fig (at maturity stage, or just before), at the places where the bag rubs on the fig when this has reached a certain volume.
Imagine this unripe fig prtotected from the Black Fig Fly by an individual organza bag...
FIGS VARIETIES REQUIRING POLLINATION
PROBLEM
For Smyrna or San Pedro figs varieties, bagging the unripe figs prevents the blastophage (Blastophaga psenes L.) from entering the fig and carrying out pollination. However, in France, this types of figs are only found in the fig trees collectors' orchards. With the exception of the 'Dauphine' variety (San Pedro type, therefore for which only the second crop is concerned), the commercial fig cultivars and the thirty most planted fig varieties for amateurs are of the common type (parthenocarpic). In addition, the blastophage is absent in 75% of French territory, where it cannot whistand winter temperatures, while the fig tree is grown in amateurs' gardens and orchards in practically all French regions. Knowing that this last remark (drafted in 2021) will gradually lose its relevance in the years to come, given global warming.
CHANGING THE ORGANZA BAGS MESH
It was Bernard PEYRE, former fig producer and consultant-trainer for the figs commercial cultivation, who suggested that I study a modification of the organza bags mesh. So as to allow the blastophage to penetrate into the fig, while prohibiting Silba adipata McAlpine from having access to the ostiole. On reflection, it is true that the difference in size between the two insects (from single to double) should open the possibility of determining a mesh size modification of the bags allowing these objectives to be achieved. I observed under a binocular magnifying glass a ruler placed inside an organza bag, and I found that two stitches exactly fill the 1 mm interval. That means a mesh of 0.5 mm x 0.5 mm.
To determine the mesh modification, it is necessary to determine the width of the two insects bodies. I carried out a long search on the Internet (French, English) concerning the dimensions of the female blastophage. By examining the photographs of the female blastophage taken from above, I noted that it is the abdomen which constitutes the widest part. But I could not find mention of the abdomen width, and I am therefore led to deduce it from the photographs, using its ratio to the total body length.
For reasons that I do not know (curling up insect ?), the abdomen width / body length ratio can vary significantly from one photograph taken from above to another. In the photographs in which the abdomen is the widest compared to the body length, this ratio (excluding antennae and ovipositor) is around 33%. I did not take into account the possible wings overhang in relation to the abdomen, because the wings loss is frequent in the fig ostiolar canal, and would therefore not be prohibitive to cross the mesh. See examples below.
Female blastophage: estimation of the abdomen width / body length ratio (excluding antennae and ovipositor)
Credit: Glen Forister (BugGuide website)
Female blastophage: estimation of the abdomen width / body length ratio (excluding antennae and ovipositor)
Credit: H. Dumas (Le Monde des Insectes website)
The female blastophage length cited in several places in the specialized literature is 2 mm, and I base myself on the photograph below (Sorbonne University) to retain 2.30 mm (excluding antennae and ovipositor) .
Female blastophage: length estimation.
Credit: Roger Prat / Jean-Pierre Rubinstein (Fig tree page, Sorbonne University).
We can therefore estimate the maximum female blastophage abdomen width at 2.30 mm x 0.33 = 0.76 mm. This indicates that a mesh of 1 mm x 1 mm for the organza bags allows the female blastophage to pass (including individuals who would have a size significantly larger than the current size - up to 3 mm, if this size exists for some female blastophages…).
Concerning Silba adipata McAlpine body width, the measurement (at the thorax) carried out by Filippo SILVESTRI is 1.60 mm, for a 4 mm long individual. Reference: SILVESTRI F., 1917, Sulla Lonchaea aristella Beck. (Diptera : Lonchaeidae) dannosa alle infiorescenze e fruttescenze del caprifico e del fico, Bollettino del Laboratorio di Zoologia Agraria in Portici, vol.12, pp. 123 -146. It would be necessary to add the very small wings overhang in width, but I do not do it, taking into account the wings plasticity that I observed during the Black Fig Fly grooming sessions.
We deduce from the F. SILVESTRI measurements that the width / length ratio is 0.40. If we consider the minimum size of males and females of the species (3.5 mm) the minimum width to take into account is 3.5 mm x 0, 40 = 1.40 mm. This indicates that the 1 mm x 1 mm mesh of the organza bags retained to allow blastophage access prevents Silba adipata McAlpine from passing through, even in its minimum size.
To my knowledge, there are no organza bags with this mesh, and the manufacturers should be asked to make them, a special order generating a problem of order volumes and costs. It would also be necessary to ensure with the manufacturers that such a mesh does not cause the organza bags to lose the rigidity degree which is essential for the process efficiency. In addition, I have a question: would not the organza bag be a visual deterrent for the blastophage, despite the attractive volatile organic compounds emitted by the fig?
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