Final Report for FNE12-766
Project Information
Artemisia annua, otherwise known as “Sweet Annie” or “Sweet Wormwood”, is a large vigorous plant that is grown on many farms, primarily for decorative use. In addition to the common use, this plant produces a compound, artemisinin, which is used in anti-malarial therapy. Malaria is not a big problem in the United States, but in developing countries there is a strong demand for malaria medicines. This project investigates the possibilities of growing this plant as a crop, but also since the plant is very vigorous and generates a large amount of foliage during the summer season it could be used as a summer cover crop.
This project showed that, on a small scale test plot, the plant was very effective in preventing weed growth. Although allelopathy has been suggested, we found the primary mode of weed prevention was through shading. There is a weak allelopathic action that causes a delay in germination of some plants after the A. annua has been removed from the field, but the delay was only about a week. The plant was quite effective on 1 square meter test plots, but it has not yet been tested on a large field.
The possibility of growing A. annua as a crop is currently limited by the availability of cultivars that are heavy producers of artemisinin. The cultivar used in this study was effective, but the plants are only propagated vegetatively. A. annua grown from seed is quite variable in production of artemisinin and probably would not produce sufficient quantities of this compound to produce a saleable crop. Other people are working to produce a cultivar that could be seed-propagated and high in artemisinin production. On the other hand, a number of investigators have shown that oral consumption of the dried leaves of the plant provides a therapeutic response equivalent to or better than that provided by pure artemisinin, but at much lower delivered dose.
At present A. annua appears to be a viable summer cover crop for suppressing weeds. Seed production does not occur until mid-September in New England, so there is ample time for the plants to generate a lot of biomass before mowing the crop to prevent re-seeding. The biomass could be turned into the field for organic material. When a practical seed-produced cultivar becomes available, this crop would have the additional advantage of being saleable at harvest.
An illustrated version of this report is available at http://small-farm.org/SARE
A pamphlet describing this project was developed for outreach. It is online at http://small-farm.org/SARE/Pamphlet.pdf
Introduction:
Artemisia annua is a medicinal herb used extensively in the treatment of malaria1, and there are indications that it may have wider benefits for other health concerns. The active ingredient, artemisinin, is produced in and extracted from the leaves of A. annua and is reported to be allelopathic as well as providing a medicinal benefit. Artemisinin is already in short supply, and if additional medicinal uses are developed there will be increased demand. Furthermore, a growing body of evidence is showing that oral consumption of the dried leaves of the plant provides a therapeutic response equivalent to or better than that provided by the pure drug, but at much lower doses of delivered artemisinin2.
This project provided information on the possible use of A. annua as a new high value crop that can double as a cover crop with some weed control efficacy. The project measured the productivity of Artemisia annua and provided yield estimates. It also evaluated the effectiveness of the crop in weed suppression.
There were 3 main objectives in this project:
- to measure the biomass and artemisinin content of a clonal cultivar of A. annua after 1 growing season;
- to measure the biomass and artemisinin content of a clonal cultivar of A. annua after 1 growing season, but where a mid-season harvest of the leafy biomass was also taken;
- to compare the number and types of weeds that appear in A. annua plots with plots that were either left fallow, or amended with dried A. annua leaves.
All test plots were initially cultivated to disrupt/remove existing weeds in order to normalize each plot for weed comparisons. All plots received a pass with the flame weeder just prior to planting to remove emerged weeds and give all plots a common starting point.
Objective 1
A. annua grows 6-7 ft in a New England summer. Although it can be grown at a wide variety of different planting densities, in 2012 we set 12 plants per square meter using conditions recommended by Ferreira et al.3 (in four, one square meter plots randomized in their location with the other test plots in the project). Each plot had a 24 inch buffer zone between plots. These plots had a combined total of 48 plants. The Weathers lab at Worcester Polytechnic Institute (WPI) provided ~6 inch rooted cuttings of A. annua (Sam clone), which produces artemisinin at about 1.5% of dried leaf weight. They routinely propagate A. annua by cuttings and by tissue culture. Plants were planted in late May and equally spaced 6/row in 2 rows. Although this species can tolerate a soil pH of 5-8, 6-7 is preferred. An NPK fertilizer (115:35:65 kg/ha) was predrilled into the soil 75 mm deep in bands 150 mm wide between the rows. A soil test was performed to establish the actual nutrient requirements. After planting, no further weeding was done until harvest. Although the species is somewhat drought tolerant, young plants require adequate soil moisture until they are established, so for this study a drip line was built into the plots to avoid drought losses.
A. annua is thus far effectively pest free so no pesticides were used. After the plants set flower buds, about mid-September for this cultivar, plants were harvested. Material from individual plants in each plot was kept separate throughout the analysis process. Leafy biomass was dried on the stem, at about 25°C in light: artemisinin levels in the plant reportedly increase post-harvest if light is present. After drying, the leaves and flower buds were removed, and successively passed through 1.0 mm and then 0.6 mm brass sieves. This finely sieved material was then weighed, homogenized and analyzed at WPI for artemisinin using GC/MS. The Weathers lab has been measuring artemisinin in A. annua for >20yrs.
Plot preparation, planting and maintenance of the crop over the summer (initial weeding, watering etc.) was done at small farm, Stow, MA (http://small-farm.org/). Rooted plants were provided by the Weathers lab. Small farm measured weed population types and tracked A. annua growth (height) every 1-2 weeks during the growing season.
Harvesting, final plant biomass measurements and artemisinin and total flavonoid analyses were done by the Weathers Lab. A final report was prepared by the Weathers lab in consultation with small farm.
Objective 2
The methodology and number of plants were the same as detailed in Objective 1, but in this experiment plants were harvested twice in the growing season: once midseason when they were about 2.5-3 ft tall, and then finally when flower buds emerged as described for Objective 1. The goal here was to compare the overall biomass productivity and artemisinin yield per plot for pruned and unpruned plants. Each harvest was analyzed separately and then compared with the single harvest plots. Kumar et al.4 suggested that greater yields can be obtained from multiple leaf harvests in a single growing season.
Objective 3
Here we compared how A. annua leaf-amended soil affected weed growth compared to plots containing A. annua plants and fallow soil. Two groups of four plots each were prepared and analyzed: fallow soil or soil amended with dried A. annua leaves. The leaf amended soil had 400g/m2 lightly raked into the top inch of the plot. This amount of material was determined by a preliminary experiment in the Weathers lab (unpublished results) to delay the germination of beans and stimulate corn growth; 400g/m2 was also deemed a reasonable amount of possible leaf debris in an A. annua field (Bohren et al., 20045). The other four plots were left fallow as a control. After initially removing weeds from these plots, new weed growth was measured in all plots in the study as follows: type of weed (monocot vs. dicot) numbers were tallied, weight of each weed type was measured, and any specific weeds that either increased or decreased were measured (e.g. red root pigweed, Amaranthus retroflexus, is notoriously persistent on this farm, along with several types of grasses). The Weathers lab provided the dried leaves with which to amend the soil.
Cooperators
Research
First year work
The grant was approved 21 February, 2012 and we received the OK to spend money on the project. The test plot was chosen to be remote from the main farm fields in order to minimize disturbance by Pick-Your-Own customers. Soil samples were taken in March and sent for analysis (results can be seen in Appendix 1). Compost was spread on the test area and the ground was disked and flattened in early April. Since the ground is quite gravelly, a slightly heavier layer of compost was added than our usual practice to ensure adequate organic material. The compost and cover crop were rototilled to mix them into the upper layer of soil and the field was flattened.
Since production of artemisinin is one of the goals of this study, a cultivar of A. annua that exhibited a strong production capacity was used. These plants are clonally produced by cuttings and tissue culture in the Weathers laboratory.
Plants were delivered by Professor Weathers in mid-May. This cultivar is propagated by cutting, so 168 plants were received, more than necessary for this project, in order to enable us to select the most vigorous. When received, the plant roots did not fill the cell of the 32 cell tray, so the plants were held outdoors for a couple weeks in order to allow them to acclimate and develop more of a root ball.
Toward the end of May, four bags of dried leaf amendment were delivered by Professor Weathers for use in the leaf-amended plots. Each bag held 400 grams of dried leaves, chopped finely. The bags were stored in a closed metal barrel to keep them away from various rodents frequenting the barn.
At this time the plot layout was begun. The tractor was used with a bedshaper and fertilizer applicator and a drip line server. This implement drops fertilizer in the center of the row, stirs it into the soil, a drip line is installed three to four inches under the surface and the bedshaper then flattens the bed, leaving two marks, 12 inches apart, which define the planting rows. The implement could do the job in one pass if it were not for the fact that we lay down two applications of fertilizer in the row. This was because the maximum application rate of our tractor is too low for the organic fertilizer we use.
The soil tests showed the plot to be low to medium in phosphorus and slightly higher in potassium. Our standard fertilizer is 7-2-4, so in addition to fertilizer we added bone meal to increase the phosphorus a bit. Measurements on the fertilizer applicator indicate that we added 1500 lb/A (1650 kg/ ha) of fertilizer to the test plot (in a band), which is equivalent to 105 lb/A (115 kg/Ha) nitrogen, 30 lb/A (35 kg/ha) phosphorus, and 60 lb/A (65 kg/ ha) potassium. The addition of bone meal (6-9-0) supplied additional nitrogen to a total of 140 lb/A (155 kg/ ha), and additional phosphorus to a total of 80 lb/A (90 kg/ ha). We did not feel it necessary to increase the potassium application since Davies et al.5 reported that variations in potassium resulted in leaf potassium variations without variation in artemisinin production; nitrogen was more important (up to a point). We chose the nitrogen level based on our use on other crops, which appeared to be effective.
NOTE: conversion factors used: 1 ha =2.45 A; 1 kg=2.2 lb; 1 lb/A≈1.11 kg/ ha; numbers rounded to reflect typical measurement accuracy.
Once the beds were made, we defined the test plots based on the plan presented in the proposal. We added color coding to make it easier to differentiate the plots. Figure 1 shows the color coded plan. The plots were defined by three foot hardwood stakes painted with the appropriate color on the top. Since the plots were one square meter in area, and since the width of the beds formed was 30 inches, the length of each plot was about 51.5 inches. A buffer of 24 inches was left between plots. In laying out the plots, a 24 inch stick and a 51.5 inch stick were cut and used to position the stakes.
Once the beds were laid out, the dried leaf material was spread onto the appropriate plots and raked in. Small stones turned up by the raking were removed in order to keep the surface fairly flat for ease in measuring weed growth. The leaf material was incorporated to a depth of about an inch, deemed to be appropriate for most germinating weed seeds.
After raking the surface the plot was lightly packed with the back of a flat shovel so that soil contact would be maintained with the weed seeds. After packing the plots were watered and allowed to rest for a couple of days to allow weed seeds to germinate. All plots were then flame weeded to remove emerged weeds prior to planting and give the different components of the test plot an equal footing at the start of the test.
Finally the Artemisia plants were placed into the appropriate plots (May 27). Signs were erected to inform customers who might encounter the plots about the project, discouraging them from disturbing the plots. Several dogs frequently walked through the farm with local residents, so snow fence was erected around much of the area to discourage local dogs from romping through. At that time the plots already had several paw prints in them.
As soon as the Artemisia was planted, the field was watered using the installed drip line since we were in a fairly dry period. After the field was watered, several small rainstorms provided a reasonable amount of water to establish the crop. The drip line was used once more after 10 days without rain, but that was all that was necessary. By mid June the crop was fairly well established and significant growth was observed on the plants. By June 20, the plant heights ranged from 12 inches to 24 inches with an approximate average of 17 inches. Photographs were taken to document the weed growth in the fallow and leaf-amended plots. No significant difference was seen visually in the weed growth comparing the two plot types.
In late June Professor Weathers decided it was time to do the mid-season harvest. On July 2 she brought some of her students to the field and cut one set of A. annua plots to 12-18 in height. The cuttings were bagged, labeled and taken to WPI for drying, and later extracted and analyzed.
Also, at this time, a string was placed on the stakes to delineate the weed test plots and the weeds were pulled, separated into monocots and dicots, bagged, labeled, and taken to WPI for drying and weighing. Weeds were harvested if the root was within the area defined by the string. The monocots and dicots were counted separately, so there were two measures of weed growth for the test plots.
After the first harvest, the plots were allowed to proceed without intervention. In September, the plots were monitored for flower bud development, signaling the appropriate time for the final harvest. Around mid September the flower buds started to appear. By this time the plants in the single-harvest plots had grown to a height over seven feet.
The perimeter of the test plots had grown tall weeds by this time so a rough mowing was done to remove the worst of the weeds and improve access to the test plots. On September 18-19 a wind storm came through which bent over some of the taller plants. There was no damage to the plants, but it mixed the branches of the test plants and the weeds. On September 20, the weeds immediately adjacent to the test plots were removed and baler twine was run around the plants to pull the outer branches into the plot and make it possible to separate the weeds and the crop.
Having cleared the area next to the plants, the weed suppression efficacy of the Artemisia annua could be seen by the lack of weed growth under the canopy ince weeds grew well on the perimeter of the plot and since the weeds were reduced outside the plot and where the plants spread beyond the edges of the plot, the weed suppression in the plot was deemed to be primarily due to canopy shading.
One thing noted during the bundling process was the occurrence of fasciola, a deformity of the plant stem caused by a bacterial infection. Fasciola produces a wide, flat stem with short internodes, as opposed to the normal round stem with internodes of 1-2 inches (2-5 cm). This deformity was found on only three stems out of the 96 plants, representing less than 1% of the total plant volume. At that level, this growth irregularity will not impact the artemisinin production significantly. Indeed, although these abnormal stems produce stunted leaves they still contained artemisinin
On September 23 the plants were harvested. Since these plants are destined for laboratory analysis rather than a bulk sale, the harvest was different from the common cover crop harvest involving just cutting and packing. Individual plots were harvested separately and the material was kept separated for analysis. Individual plants were cut at the base and placed into a labeled bag. This kept the leaves from getting lost in transport since the leaves are the part of the plant that contains most of the artemisinin. Care was taken during harvest to ensure the plants were clean so that the leaves could potentially be used later for clinical trials if necessary.
The volume of bagged plants was much higher than the mid season harvest, so they were taken to a local greenhouse, where they were hung to dry. The plants need light during the drying process to fully develop the production of artemisinin. The bags were perforated to allow air exchange for drying.
Second year work
Although not originally proposed, we conducted a second trial in 2013. We had planned to use the other side of the field in which A. annua was planted in 2012, but were unable to produce a usable seedbed due to heavy rains just prior to planting time. We decided to use an adjacent field, with plots about the same distance from the 2012 planting as the area which we had planned to use. The replacement field was slightly higher and drier so we were able to produce a good seedbed for planting. We did not add any fertilizer or bone meal to this plot, nor did we install a drip line since the 2012 planting did not really require water beyond normal rainfall.
Rooted cuttings of the SAM cultivar were again produced by Professor Weathers at WPI. The planting density in 2012 was 12 plants/m2. In 2013 we tried 10/m2, 8/m2, and 4/m2. The seedbed was prepared June 6th, and flame weeded immediately prior to setting out the plants on June 12th. The 1 square meter plots were separated by wooden stakes as in the 2012 planting, but we did not leave a buffer between the plots. We did leave a small buffer between different density zones, just for easier identification of the zones.
Half-season harvest was done July 17th, but instead of harvesting 1 m2 plots, the harvest was done by pruning every other plant in each plot to half height (~12 in). As before, the plants were labeled at harvest so that the different density planting zones could be compared. These plants were taken to WPI and dried in the laboratory, where the leaves were subsequently removed, sieved, and stored for later analysis.
Final harvest was done September 21st, when the plants were just starting to develop flower buds. These plants were bagged, dried in the greenhouse and then transported to the laboratory for processing post drying.
Results of first year work
Artemisia Biomass Productivity:
Analysis of the 2012 harvest was done in 2013 by Professor Weathers and students at WPI. Leaves from individually harvested plants were used to extract artemisinin using the method of Weathers and Towler7. Flavonoids were also extracted8, since they seem to play a role in enhancing the therapeutic effect of the whole plant9. Artemisinin content was 13.96 mg/g dry weight leaves (1.4%) for both the half-season and final harvested plants. Flavonoids were about 35% higher in the half-season harvested leaves compared to leaves from the final harvest. This was attributed to the higher proportion of shoot tips in the smaller plants at half-season. The shoot tips contain proportionally about four times more flavonoids than mature leaves (Weathers and Towler, unpublished data). Although the flavonoid content may vary with harvest time, the artemisinin content was expected to be consistent for each harvest.
Plants were harvested at two points during the growing season: mid-summer (July 02), and fall (September 23). The July harvest was of only half of the eight A. annua plots and designated as 2H1 plants that were cropped to about 12-18 height from the soil surface. This was to test whether a mid-season harvest, when added to the harvest of the same plants late in the season, would result in larger overall biomass yields from the plants as suggested by others. The September harvest of all eight plots at soil line was after bolting and just at first emergence of blossom buds. The 2H1 plants had also grown out and were again harvested, but at soil line this time; they were designated as 2H2 plants. Plants that were harvested only in September were designated 1H1 plants.
The dry biomass yield of leaves and stems from each harvested plant group was compared and also measured the relative ratios of leaf to stem biomass of each group. There was no significant difference in leaf to stem ratio between the 2H2 plants and the 1H1 plants (Figure 2). On the other hand, the ratio for the early harvested material, 2H1, showed at least three times more leaf than stem tissue than either the 1H1 or 2H2 plants (Figure 2). When the harvest yield per plant was compared, the stems, leaves and sum of both were significantly greater for the single harvest plants (1H1) than either the 2H1 or 2H2 harvest group or sum of both harvests (2H1+2H2) of the other plants (Figure 3). These results showed that despite earlier reports of multiple cropping being a successful production strategy for A. annua, that approach did not give maximum biomass yield in this field study. Recognizing that there was an estimated 5-10% loss of leafy biomass during the harvesting, drying, and transportation steps, the maximum average dry biomass yield of leaves obtained per 1H1 plant was 72.71 ± 6.01 g. There were 12 plants per plot and each plot was 1 m2, so that is equivalent to a dry leaf yield of 872.4 g dry leaf mass/m2 and equal to 8,724 kg/ha, or 7,860 lb/A for this study.
Weed Suppression Results
When field plots that were fallow were compared to those treated with 400 g dry mass A. annua leaves per plot, no significant difference was observed in either the number of monocot or dicot weeds or biomass yield of those weeds (Table 1). On the other hand, plots where A. annua was grown and then harvested showed effectively no weeds except at each plot’s planting perimeter. This showed that there was significant shade suppression of weeds from the tall canopy of A. annua shoots. These results indicated that while A. annua leaf-amended soil offered no inhibition of weed germination, its use as a cover crop significantly reduced weed production under canopy.
In this study there was no significant allelopathic effect in the test, but since there were reports of allelopathy when growing Artemisia we decided to check whether there was any residual allelopathic effect after the plants were removed but the roots remained in the field, a situation likely to occur after harvest of a cover crop. About two days after the plants were removed in the final harvest four of the plots were cleared by flame weeding (which killed the few emerging weeds and eliminated debris remaining from planting) and radish seeds were planted. The selected plots were one from the untreated fallow group, one from the single harvest group, one from the two-harvest group and one from the leaf-amended group.
To check for allelopathy, we counted out radish seeds so we could check the germination rate. Twenty-five seeds were placed on a strip of paper masking tape at roughly equal intervals of approximately 3/4 inch. The tape strips were folded so the seeds would not fall off and three tapes were vertically planted in each plot.
The plots were observed every couple of days and after two weeks the number of emergent plants was recorded in each plot. Germination rates for the plots were about 63% for the two harvested plots, 63% for the leaf amended plot, and 70% for the untreated soil. Germination rates for a tray seeded in the greenhouse was about 90%. Statistical tolerances are about 12% for the field test and 7% for the greenhouse test. That means that there was no statistical difference between the germination rates in the field, but there was a difference between the germination in the field and in the greenhouse, which could be attributed to warmer temperatures in the greenhouse. It is interesting to note that emergence of radish plants was delayed by about a week in the leaf amended plot compared to the harvested and untreated plots. This is consistent with unpublished observations of delayed germination in lab tests by Professor Weathers at WPI.
Second Year Results
Combining data from 2012 and 2013 work we found that planting densities of 8 plants/m2 yielded the highest biomass per plant and per m2. Yield dropped off after 8/m2, with 12 plants/m2 giving the lowest yield per plant. The 4 plants/m2 zones gave yields per plant similar to 8/m2, but the total biomass per acre was reduced by half because of the lower number of plants (Table 2). Although there was inadequate USDA SARE funding to do the 2013 artemisinin and flavonoid analyses (not part of the original scope of work), WPI provided funds to support that effort. Artemisinin levels in each plant at each planting density and harvest time were different and not consistent with the 2012 data; values ranged from 9.95 to 15.64 mg/gDW (Table 2). Also unusual was the artemisinin level in pruned vs. unpruned plants mainly because 10 past harvests of unpruned A. annua (SAM cultivar) grown form rooted cuttings in a diverse variety of conditions (field, garden, lab at vegetative and reproductive stages) averaged 1.38 % ± 0.26 (w/w) artemisinin (unpublished results).
Although also not in the original scope of work for this SARE study, total flavonoid content of each harvested crop was also measured. Flavonoids have been shown to work synergistically with artemisinin against the malaria parasite9, and their presence in the dried leaves becomes particularly important for use of the dried leaves as an oral therapeutic. In both the 2012 and 2013 crops the flavonoid level was significantly greater in the July pruning than in either of the September harvests (Table 2), followed by the yield in both crops of the unpruned September harvests. Thus, although the artemisinin yield for both crops did not match productivity profiles, the flavonoid yields did. These results suggest that although flavonoids and artemisinin are both plant secondary metabolites, in the plant they do not seem to respond to the same external pressures affecting their productivity. Clearly more work is required to understand how these two secondary metabolites are differentially responding to external stimuli.
Part of the study was to determine the value of A. annua as a cover crop. As far as weed suppression is concerned, there was no evidence for any allelopathy in this study, as already noted. However, weed suppression was considerable by canopy shading, for all densities tried in this study.
The monetary value of A. annua as a crop is based on the value of extracted artemisinin putatively available from the crop. The global value of the dried leaves of A. annua for the extraction market varies considerably. At this point we should point out that the SAM cultivar used in this study was selected for consistently high artemisinin content. Moreover, this cultivar is currently vegetatively propagated. Work in other labs is ongoing to develop a cultivar that can be produced from seed and still maintain consistently high artemisinin content.
Education & Outreach Activities and Participation Summary
Participation Summary:
Several newspaper articles were written about the project and NECN ran a video interview of Dr. Weathers at the field. The NECN clip, ran September 20, 2013, is online and can be seen at: http://www.necn.com/pages/video?PID=KuAh8thre2mJRHTej3_qzwUZps3tOAt_
A Boston Globe article from September 23, 2013, is also online at: http://www.bostonglobe.com/news/science/2013/09/22/farm-stow-possible-cheap-and-effective-treatment-for-malaria-grows/usod9QpRKgrDZq77amUHjK/story.html
A local paper, the Stow Independent ran a story on January 3, 2014:
http://stowindependent.com/stow-crop-shows-progress-towards-potential-malaria-treatment
In addition, a pamphlet describing the results of this project was prepared and distributed at the annual meeting of the New England Vegetable & Berry Growers Association in 2014.
During the next year, Prof. Weathers will submit the results of the field study for publication in a peer-reviewed journal. This manuscript will cite this SARE award for its financial support of the study.
Project Outcomes
We plan to try A. annua as a fallow cover crop on a medium sized field to evaluate both the weed supression and the addition of organic material to the soil. We will publish results as available on our website, at http://small-farm.org/SARE
References:
- Elfawal MA, Towler MJ, Reich NG, Golenbock D, Weathers PJ, et al. (2012) Dried Whole Plant Artemisia annua as an Antimalarial Therapy. PLoS ONE 7(12): e52746. doi: http://dx.plos.org/10.1371/journal.pone.0052746
- Weathers, P., Reed, K., Hassanali, A., Lutgen, P., Engeu, P.O., 2014b. Chapter 4. Whole plant approaches to therapeutic use of Artemisia annua, L. (Asteraceae) in: Aftab, T., Feirrera, J.F.S. (Eds.), Artemisia annua- Pharmacology and Biotechnology. Springer Berlin, GDR, pp. 51-74.
- Ferreira JFS, Laughlin JC, Delabays N, de Magalhães PM. Cultivation and genetics of Artemisia annua L. for increased production of the antimalarial artemisinin. Plant Genet Resour. 2005;3:206–229
- Kumar S, Gupta SK, Singh P, Bajpai MM, Gupta D, Singh D, Gupta AK, Ram G, Shasany AK, Sharma S. High yields of artemisinin by multi-harvest of Artemisia annua crops. Indust Crops Products. 2004;19:77–90.
- Bohren C, Mermillod G, De Joffrey JP, Delabay N (2004) Allelopathie auf dem Feld: Artemisinin von Artemisia annua als Herbizid in verschiedenen Ackerkulturen. Zeitschrift für Pflanzenkrankenheit und Pflanzenschutz 19: 263-270
- Davies, Michael J., Christopher J. Atkinson, Corinne Burns, Jack G. Woolley, Neil A. Hipps, Randolph R. J. Arroo, Nigel Dungey, Trevor Robinson, Paul Brown, Ian Flockart, Colin Hill, Lydia Smith, and Steven Bentley, Enhancement of Artemisinin concentration and yield in response to optimization of Nitrogen and Potassium supply to Artemisia annua, Ann. Bot., 2009, Aug. 104(2), pp 315-323 (http://aob.oxfordjournals.org/content/early/2009/05/30/aob.mcp126.full.pdf)
- Weathers, P.J., Towler, M.J. (2012) The flavonoids casticin and artemetin are poorly extracted and are unstable in an Artemisia annua tea infusion. Planta Medica. 78:1024-1026.
- Arvouet-Grand A., Vennat B.,Pourrat A.,Legret P. (1994) Standardization of a propolis extract and identification of the main constituents. Journal de pharmacie de Belgique 49:462-468
- Elford, B.C., Roberts, M.F., Phillipson, D., Wilson, R.J.M. (1987) Potentiation of the antimalarial activity of qinghaosu by methoxylated flavones. Transactions of the Royal society of tropical Medical Hygiene. 81, 434-436.
Potential Contributions
Artemisia annua, otherwise known as "Sweet Annie" or "Sweet Wormwood", is a large vigorous plant that is grown on many farms, primarily for decorative use. In addition to the common use, this plant produces a compound, artemisinin, which is used in anti-malarial therapy. Malaria is not a big problem in the United States, but in developing countries there is a strong demand for malaria medicines. This project evaluated Artemisia annua as a weed controlling cover crop and also the possibility of selling the crop at the end of the season. The efficacy of A. annua in controlling weeds was shown to be primarily the result of shading. Reports of allelopathy were not confirmed in this study. A. annua is a vigorous plant that produces a lot of biomass which could be used for organic matter in the field.
The possibility of selling the crop at the end of the season is real, but there are limitations in that the cultivar selected for the crop has to produce enough of the medicinal compound to be valuable for extraction. Current cultivars grown from seed do not meet this requirement. The use of clonal cultivars that do meet his requirement is probably not economically feasible. Further pharmacological work on the theraputic use of the dried leaves of A. annua is needed, and may contribute to increased value of cultivars with lower artemisinin production rates, at which point it would become feasible to pursue sales of the crop.