The subtropical climate of Florida allows for a wide range of crops to be grown, often as an expanded or extreme geographical range. With the removal of hemp (
Grain hemp cultivars are plants that produce seed that can be used for food items, animal feed, and cosmetics (Cherney and Small, 2016). These plants do not grow as tall as fiber plants, usually averaging 1 to 2 m in height. Dual-use cultivars tend to produce many seeds like grain hemp cultivars, but they also have a stalk that is suitable for use in fiber hemp production. Producers harvesting hemp grain would also harvest the remaining stems for fiber, and this is the most common example of a dual-use hemp crop.
Hemp that is cultivated and bred in order to process flower parts for cannabinoid extracts are usually shorter and have a more brachiate or bushy appearance as compared to fiber and grain. CBD, or cannabidiol, is the non-psychoactive compound commonly extracted from hemp flower and closely resembles THC. CBD can be obtained from the plant by extracting the oil from the flower or by burning or vaporizing the dried flower material. CBD products include topicals, edibles, and smokable products, and is used medicinally to curb pain and muscle spasms (National Academies of Sciences, Engineering, and Medicine, 2017). Cannabinoids are highly concentrated in the trichomes of the bracts and nearby leaves of unfertilized female flowers, much lower in the root and plant tissue, and are at even lower concentrations in hemp pollen and seeds. CBG, or cannabigerol, is another non-psychoactive cannabinoid found in cannabis. Just like CBD hemp, CBG hemp is bred and cultivated for production of the unpollinated female flower.
To support the future viability and sustainability of hemp and considering the importance and prevalence of plant-parasitic nematodes in Florida, it is critical to collect information on the interaction of hemp and nematodes. Plant-parasitic nematodes (PPN) are extremely prevalent in Florida, and many different species are found that can potentially cause damage to many of the crops grown. The most important PPN in Florida in terms of damage potential are root-knot nematodes (
The trials were done during 2019 and 2020 at three different field locations in Florida, (1) the North Florida Research and Education Center (NFREC) in Quincy (North Florida); (2) the Gulf Coast Research and Education Center (GCREC) in Wimauma (West-Central Florida); and (3) the Tropical Research and Education Center (TREC) in Homestead (South Florida) (Table 1). To support the future viability of hemp and considering the importance of PPN in Florida, it is critical to collect information on PPN associated with hemp in Florida.
Experimental site description.
Hillsborough | 31 m | Myakka fine sand | 27.76° N, 82.23° W | |
Miami—Dade | 1 m | Shallow Krome gravelly loam | 25.47° N, 80.50° W | |
Gadsden | 63 m | Orangeburg loamy fine sand | 30.58° N, 84.59° W |
GCREC, Gulf Coast Research and Education Center, Wimauma, FL.
TREC, Tropical Research and Education Center, Homestead, FL.
NFREC = North Florida Research and Education Center, Quincy, FL.
Nematode soil samples were taken at the end of each crop/experiment, and roots were visually examined for nematode damage (no preplant samples were collected). Nematode soil samples were taken as four cores per cultivar plot with a locally made cone sampler (3.0 cm-diam. × 25 cm-deep). The four cores were composited for each plot. Soil samples were sealed in plastic bags and were stored at 4°C and nematodes extracted within two weeks. Nematodes were extracted at the GCREC nematology lab by taking a 200 cm3 soil sample from each composite sample. A modified Baermann method using a salad spinner (Henrik Preutz, IKEA® USA) was used (Viglierchio and Schmitt, 1983).
Plant-parasitic nematodes (PPN) were identified to genus or species level and by feeding group. Morphological identification was performed using a compound Zeiss AXIO Scope A1 microscope (Carl Zeiss, Göttingen, Germany). Plant-parasitic nematodes (PPN) were identified to genus, and depending on the morphological complexity of the species, the nematode was also identified into species level by using the pictorial key proposed by Mai and Mullin (1996). When root galls were observed on roots,
Hemp cultivar trials at the Gulf Coast Research and Education Center farm in Wimauma, FL were conducted in October 2019 (season 1, fall) and February 2020 (season 2, spring) in the same location. The soil type in this area is classified as Myakka fine sand (95% sand, <1% organic matter). The experimental area was adjacent to an experimental hops (
Eight selected hemp cultivars (Table 2) were planted in a randomized block design consisting of four plants of the same cultivar per plot, and each plot was replicated six times (two replicates in each row), for a total of 192 hemp plants. Hemp seedlings were grown in a growth room for two months prior to transplanting in the field. Seeds were sown into 128-cell seedling trays filled with PRO-MIX HP growth medium (Premier Horticulture Inc., Quakertown, PA) on August 16, 2019, and December 29, 2019. Seedlings were grown under supplemental lighting (16-h light and 8-h dark) to maintain vegetative growth. Irrigation was supplied as needed using overhead irrigation. Uniform seedlings of each variety were transplanted to the field on 16 October 2019, and 23 February 2020. Plants measured on average 15–20 cm at the time of transplanting. Watering and fertilizing were administered via in-bed drip tape in both areas. Watering consisted of four one-hour cycles every five hours each day and a soluble fertilizer (N-P2O5-K2O: 5-2-8) was applied with irrigation twice a week throughout the season, based on an accumulated rate of 103 kg N ha−1.
Hemp cultivars with their specific use, country of origin and year(s) planted at each location.
Fiber/Dual | China | 2019 | |
Fiber/Dual | China | 2019 | |
Fiber/Dual | China | 2019, 2020 | |
Fiber/Dual | Poland | 2019 | |
Fiber/Dual | Italy | 2019 | |
Fiber/Dual | Italy | 2019 | |
CBD | US | 2019 | |
CBD | US | 2019 | |
CBD | US | 2019 | |
Fiber/Dual | Canada | 2019 | |
Fiber/Dual | China | 2019 | |
Fiber/Dual | Italy | 2019 | |
Fiber/Dual | China | 2019, 2020 | |
Fiber/Dual | Italy | 2020 | |
CBD | US | 2020 | |
CBD | US | 2020 | |
CBD | US | 2020 | |
CBD | US | 2019 | |
CBD | US | 2019 | |
CBD | US | 2019, 2020 | |
CBD | US | 2019 | |
CBD | US | 2019, 2020 | |
CBD | US | 2020 | |
CBD | US | 2020 | |
CBD | US | 2020 | |
CBD | US | 2020 | |
CBD | US | 2020 | |
CBD | US | 2020 |
GCREC, Gulf Coast Research and Education Center.
Planting at GCREC was done in fall 2019 and spring 2020, and at TREC and NREC in summer 2019 and summer 2020.
TREC, Tropical Research and Education Center.
NFREC, North Florida Research and Education Center.
Both trials were terminated after three to four months, depending on the cultivar.
Hemp cultivar trials at TREC in Homestead, FL (25.4687° N, 80.5007° W) were conducted in summer 2019 and summer 2020 on two different fields that were adjacent to each other. The soil type is a shallow Krome, a gravelly loam soil series (loamy-skeletal, carbonatic, hyperthermic, Lithic Rendoll) containing 58% sand, 19% silt, 15% clay, and 8% gravel (Li and Zhang, 2002). Its plowed surface layer, largely crushed bedrock, is 15–20 cm deep with 34% to 76% of limestone fragments (≥ 2 mm in diameter; Bryan and Lance, 1991).
A total of 17 different hemp cultivars (fiber, dual, and CBD) were planted at this location: 13 in 2019 and six in 2020 (Table 2). All cultivars were direct-seeded in the field, and planting densities differed according to their usage. All fiber/dual cultivars were sown by hand in eight rows measuring 1.8 m long and were spaced 30 cm apart within a 5.58 m2 (1.83 m × 3.05 m) rectangular plot. For dual cultivars, 900 seeds were planted per plot with an intended planting density of 161 plants/m2, while 1500 seeds were planted for fiber cultivars to achieve 269 plants/m2. CBD cultivars were planted to establish a density of 11 plants/m2 by sowing 60 seeds in the experimental plot and after germination thinning to 11 plants. All plots were fertilized once before planting at 112, 56, and 300 kg/ha of N, P, and K, respectively, using a 6-3-13 slow-release granular fertilizer. Due to early indications of N deficiency, there was an additional N application in mid-July, which was top-dressed using 46-0-0 conventional urea at a rate of 56 kg/ha. Irrigation was provided as needed by overhead sprinklers.
Hemp cultivar trials at NFREC in Quincy, FL were conducted in summer 2019 and summer 2020. Soil type at NFREC is an Orangeburg loamy fine sand. The experimental design was a randomized complete block design with four replications. Three DLS cultivars, including Cherry Blossom (CBL), Cherry × T1 (CT1), and Cherry Wine (CW), and two day-length-neutral (DLN) cultivars, including Kayagene 9201 (KG9201) and Kayagene 9202 (KG9202) were evaluated in 2019. In 2020, cultivars evaluated were CBL, CW, Berry Blossom, Cinderella Story, Cherry Blonde, Cloud Berry, Hot Blonde, and Queens Dream (Table 2). Seeds were sown in the greenhouse using the same methodology as for Location 1, on 14 June 2019 and 2 May 2 2020. Uniform seedlings of each cultivar were transplanted to the field on 3 July 2019 and 12 June 2020.
Agronomic practices were similar between 2019 and 2020. The field setup was similar as for vegetable production in the area, which is plastic-mulch raised beds that were 20-cm high and 30-cm wide with a single drip tape underneath the plastic mulch. The spacing between rows and between plants within a row was 1.8 and 1.5 m, respectively. Therefore, the plant density was ~3600 plants per hectare. Irrigation was supplied daily through the drip tape. Fertilizer (N-P2O5-K2O: 10-10-10) was applied at a rate of 112 kg ha−1 immediately prior to transplanting and disked into soils. A soluble fertilizer (N-P2O5-K2O: 4-0-8) was applied with irrigation as needed throughout the season based on an accumulated rate of 56 kg N ha−1.
At the GCREC, by the end of the first season, stubby root nematodes (
Nematode soil populations (no./200 cc soil) at harvest of eight different hemp cultivars for two consecutive seasons, GCREC, Fall 2019 (trial 1) and Spring 2020 (trial 2)a.
49 | 31 | 12 | 31 a | 0 | 0 | |
117 | 18 | 7 | 21 ab | 0 | 0 | |
120 | 32 | 12 | 32 a | 0 | 1 | |
70 | 30 | 7 | 6 b | 0 | 0 | |
121 | 30 | 9 | 12 ab | 0 | 1 | |
89 | 19 | 7 | 11 ab | 0 | 0 | |
121 | 32 | 5 | 23 ab | 0 | 1 | |
72 | 25 | 7 | 15 ab | 0 | 1 | |
- | - |
- | - | - | 18 abc | 16 | 15 | |
- | - | - | 62 ab | 437 | 3 | |
- | - | - | 62 ab | 610 | 13 | |
- | - | - | 11 bc | 289 | 14 | |
- | - | - | 11 bc | 9 | 16 | |
- | - | - | 8 c | 117 | 9 | |
- | - | - | 65 a | 100 | 8 | |
- | - | - | 24 abc | 315 | 32 | |
- | - | - |
Numbers listed describe the number of a type of nematode found in 200 cc of soil collected from the root area of the hemp cultivars listed. There are multiple types/uses of hemp here.
Nematode soil populations in the hemp trials at TREC consisted of several PPN: reniform nematodes (
Nematode soil populations (no./200 cc soil) at harvest of different hemp cultivars for two consecutive seasons, summer 2019 and summer 2020; TREC soil survey resultsa.
116 | 42 | 0 | 5,564 a | 112 | 176 | 12 | 0 | |
70 | 74 | 0 | 1,987 ab | 156 | 221 | 26 | 0 | |
28 | 52 | 0 | 574 abc | 32 | 92 | 2 | 0 | |
22 | 26 | 2 | 762 abc | 8 | 26 | 14 | 0 | |
52 | 100 | 8 | 4,872 a | 80 | 84 | 12 | 0 | |
68 | 48 | 2 | 648 abc | 24 | 48 | 0 | 0 | |
80 | 116 | 8 | 480 abc | 40 | 54 | 6 | 0 | |
54 | 21 | 0 | 319 c | 178 | 286 | 0 | 0 | |
83 | 27 | 0 | 333 bc | 15 | 373 | 0 | 0 | |
39 | 29 | 2 | 636 abc | 119 | 524 | 1 | 0 | |
25 | 12 | 1 | 195 c | 11 | 266 | 0 | 0 | |
42 | 25 | 0 | 989 abc | 38 | 119 | 0 | 0 | |
36 | 52 | 1 | 844 abc | 30 | 216 | 14 | 0 | |
141 | 31 | 1 | 78 | 79 | 148 | 73 | 41 | |
173 | 43 | 1 | 101 | 81 | 109 | 65 | 74 | |
180 | 42 | 4 | 214 | 216 | 409 | 17 | 62 | |
73 | 19 | 2 | 22 | 54 | 256 | 59 | 20 | |
215 | 50 | 2 | 69 | 108 | 686 | 447 | 57 | |
111 | 32 | 1 | 32 | 53 | 289 | 35 | 18 | |
Numbers listed describe the number of a type of nematode found in 200 cc of soil collected from the root area of the hemp cultivars listed. There are multiple types/uses of hemp here.
At NFREC, nematode soil populations consisted of the same PPN as at TREC, although at lower numbers (Table 5). Reniform nematodes (
Nematode soil populations (no./200 cc soil) at harvest of different hemp cultivars for two consecutive seasons, summer 2019 and summer 2020; NFREC soil survey resultsa.
139 | 40 | 0 | 41 | 1 | 0 | 0 | 3 | |
158 | 47 | 0 | 92 | 4 | 2 | 0 | 5 | |
312 | 74 | 1 | 127 | 3 | 0 | 1 | 4 | |
307 | 80 | 0 | 239 | 1 | 6 | 0 | 65 | |
304 | 68 | 1 | 191 | 2 | 3 | 0 | 16 | |
309 | 52 | 0 | 67 | 0 | 2 | 0 | 9 | |
212 | 32 | 1 | 40 | 2 | 0 | 0 | 3 | |
119 | 61 | 0 | 103 | 1 | 2 | 0 | 38 | |
441 | 86 | 0 | 328 | 2 | 4 | 0 | 4 | |
320 | 75 | 2 | 101 | 3 | 0 | 2 | 33 | |
167 | 50 | 0 | 53 | 1 | 1 | 0 | 41 | |
319 | 115 | 0 | 453 | 1 | 9 | 0 | 28 | |
224 | 64 | 1 | 90 | 2 | 1 | 0 | 83 | |
Numbers listed describe the number of a type of nematode found in 200 cc of soil collected from the root area of the hemp cultivars listed. There are only CBD hemp cultivars here.
RKN, root-knot.
Bacterivorous, fungivorous, and omnivorous nematodes (NPPN) were prevalent at all three locations and showed no difference between cultivars or seasons.
Seven different PPN were found on hemp in Florida. Most common were root-knot nematodes, which were found at all three locations, and reniform nematodes, which were found in North (NFREC) and South Florida (TREC).
Root-knot nematodes were the dominant nematode in Central Florida (GCREC) after the second season, despite the fact that none were found in the same field at the end of the first season. This shows our limited ability to quantify nematode populations and how difficult it can be to detect the presence of root-knot in a newly planted field. Probably, the deep sand soils that are common in Central Florida harbor significant amounts of root-knot inoculum in its deeper layers (Noling, 2019). It also indicates that in the presence of a good host, root-knot nematodes can build up rapidly in the subtropical climate of Florida. Recent reports from the US and China have shown that hemp can be a good host to various root-knot nematodes, including
Stubby root nematodes (
Cultivar differences were limited, and none of the 26 cultivars that were planted across the different locations showed a consistent response. More controlled experiments are needed to verify potential cultivar and genetic differences with regard to their host potential to root-knot and other PPN. This will allow us to tell which cultivars are best suited for which location. At TREC, hemp cv. Wife, which was previously reported to be resistant to the RKN species
The above results show that many different PPN can be associated with hemp in Florida, and that populations will vary by region. In North Florida, root-knot and reniform nematodes were the most common. In South Florida, in addition to reniform and root-knot, also spiral, stunt, and ring nematodes were abundant. In Central Florida, root-knot, sting, and stubby root nematodes were found. These regional differences in nematode populations are likely correlated with the different soil types. Sting and stubby root nematodes seem to prefer the almost pure sandy soils in Central Florida, while reniform and spiral nematodes are more common in North and South Florida, where soils are less sandy, having a higher loam and silt content.
Root-knot nematodes are of most concern due to their statewide distribution and high damage potential to many of the crops grown in Florida. A literature review by Bernard et al. (2022) on nematode interactions with hemp also reported that
Hemp production is still very new in Florida and for it to become profitable much more research will be needed. The lack of an earlier soil sample date that would enable comparisons between transplanting and harvest is a weakness in this study and cannot be corrected. Nevertheless, this study provides a “first look” and gives new information on which PPN are associated with different hemp types and cultivars in three different regions of Florida. It is a first step, and it is hoped that this research can form a basis for more focused nematode research in terms of nematode management. Such information would be very valuable to current and future hemp growers in Florida.