Hemp Disease And Pest Management - UT Extension
W 916Hemp Diseaseand Pest ManagementZachariah Hansen, Assistant Professor and Extension Specialist;Ernest Bernard, Professor;Jerome Grant, Professor;Kimberly Gwinn, Associate Professor;Frank Hale, Professor and Extension Specialist;Heather Kelly, Associate Professor and Extension Specialist;and Scott Stewart, Professor and Extension SpecialistDepartment of Entomology and Plant PathologyOverviewHemp acreage has increased dramatically in Tennessee in recent years. In 2019, approximately 3,400 licenseswere granted for hemp production in Tennessee, composed of more than 46,000 acres, with an estimatedhalf of those acres planted. Nearly all hemp produced in Tennessee in 2019 was for cannabidiol (CBD),although hemp can also be grown for grain and fiber. An overview of hemp production in Tennessee can befound in the University of Tennessee Extension publication “W 777 Status of Industrial Hemp in Tennessee.”Hemp is defined by the USDA as “the plant species Cannabis sativa L. and any part of that plant,including the seeds thereof and all derivatives, extracts, cannabinoids, isomers, acids, salts, and salts ofisomers, whether growing or not, with a delta-9 tetrahydrocannabinol [also commonly written as 9-THC]concentration of not more than 0.3 percent on a dry weight basis.” More information on thedistinction between hemp and marijuana can be found in the USDA Interim Final Rule on U.S. DomesticHemp Production.Hemp is susceptible to several diseases and insect pests that can cause economic loss. In Tennessee, wherehumid conditions tend to favor disease development, several of these issues have resulted in significantyield losses for Tennessee hemp growers. Leaf spots, southern blight and corn earworm have been the mostdestructive pest and disease problems over the past several seasons, but other issues have also occurred.The purpose of this publication is to describe the most common hemp diseases and insect pests observedin Tennessee in recent years and to outline strategies to manage these problems. With very few pesticidesregistered for use on hemp in Tennessee, growers must take an integrated pest management (IPM) approachfocusing on cultural practices to reduce losses.Common Diseases of Hempin TennesseeLeaf spot diseasesLeaf spot diseases were common and widespreadin Tennessee in 2018 and 2019. Several fungalpathogens may be associated with hemp leaf spotdiseases in Tennessee including Bipolaris spp.and Cercospora spp. (Figures 1 and 2). Leaf spotsymptoms range from small circular lesions with tancenters and brown margins to larger lesions withHemp Disease and Pest Managementdark centers and brown/purple margins. Lesionsmay coalesce (grow together) and cause blightingto large portions of the leaf area. Leaves may turnyellow and premature defoliation may occur undersevere infections. The fungus Periconia spp. is oftenobserved on dead hemp tissue, but it is most likelya saprophyte and not the cause of disease(Figure 3). Curvularia spp., a recently confirmed leafspot pathogen of hemp, have also been associatedwith hemp leaf spots in Tennessee. Leaf spot mostlikely spreads through wind and rain splash, but1
research is needed to better understand how hempleaf spot epidemics start and progress. Significantdifferences in cultivar susceptibility to leaf spotwere observed in field trials across three locationsin Tennessee in 2019 (Table 1). Growers whoexperienced significant leaf spot disease pressurein 2019 should consider avoiding highly susceptiblecultivars, while still considering yield components.Examples of high-CBD-yielding cultivars with lowleaf spot susceptibility include ‘OG’, ‘Sweetened’and ‘Carolina’. See UT Extension publication“W 900 Hemp Variety Trials in Tennessee 2019”for a summary of yield data from 2019 hemp-foressential oil field trials.ABFigure 2. A) Cercospora leaf spot on hemp appears as darklesions, which may be surrounded by a yellow halo. B) Cercosporaspp. spore (conidium) viewed under a compound microscope.C) Cercospora leaf spot lesions viewed under a dissectingmicroscope. Photos courtesy of Alan Windham, Extensionspecialist and professor, UT Department of Entomology andPlant Pathology.ABDCCEFigure 1. Hemp leaf spot symptoms and signs. A) Hemp leafspot caused by Bipolaris spp. on field-grown hemp showing lightbrown/tan lesions with tan borders. B) As leaf spot progresses,lesions coalesce and cause leaf yellowing and prematuredefoliation. C, D) Bipolaris spp. spore structures (conidiophoresand conidia), indicated by arrows, viewed under a dissectingmicroscope. E) Bipolaris spp. spores (conidia), indicated by thearrow, viewed under a compound microscope.Hemp Disease and Pest ManagementFigure 3. The fungus Periconia spp. is often associated withdead hemp tissue, although it is likely a saprophyte and not thecause of disease. The image shows long, darkly pigmented sporestructures (conidiophores and conidia) of Periconia spp. Photocourtesy of Alan Windham, Extension specialist and professor, UTDepartment of Entomology and Plant Pathology.2
Table 1. Leaf spot susceptibility ratings based on hemp-for-essential oil cultivar trials at threelocations in Tennessee in 2019.Leaf spot e SueIndoor Growers Worldlow--T-RexPWPlowlowlowFranklinMMHlowlowlowCBD TherapyMMHlowlowmoderateSuper CBDMMHlowlowlowOGPWPlow--Cherry sted Lime³Oregon Hlow-modmoderatelowCB DawgOregon CBDmoderatelow-mod-Siskiyou GoldOregon dmoderateCarolinaBlühenmoderatelowmoderateHawaiin HazeCorbin uver HazeBlühenmoderatemoderatemoderateCherry⁴South Central Growersmoderate-moderateCherrySouth Central uth Central Growershighmod-highhighT1⁴South Central Growershigh-highCherry TartPWPhigh--CherryPWPhigh--Hemp Disease and Pest Management3
-TangerineCorbin Scienceshighhighhigh¹Leaf spot susceptibility ratings based on 2019 disease incidence and severity ratings averaged across four replicatesat each experimental location. Trial locations were the University of Tennessee AgResearch and Education Center atGreenville, TN; UT Highland Rim AgResearch and Education in Springfield, TN; and an on-farm location in Jackson, TN.²Indoor Growers World, Goodlettsville, TN; PWP Greenhouses Inc., Pall Mall, TN; MMH, Athens, TN; Oregon CBD,Independence, OR; Blühen, Knoxville, TN; Corbin Sciences, Springfield, TN; South Central Growers, Springfield, TN.³‘Frosted Lime’ showed high phenotypic variability among individuals. Only the predominant phenotype was rated.⁴Cultivars were topped prior to transplanting.Southern blightSouthern blight has been the most damagingdisease in Tennessee hemp production in recentyears. The disease is caused by the soilbornefungus Athelia rolfsii (also called Sclerotium rolfsii).The most obvious symptom of southern blight isdramatic wilting that does not improve followingirrigation (Figure 4A). Wilt may be associated withleaf yellowing. Infections are often sporadic withina field, and affected plants may be surrounded byhealthy plants. Affected plants show white fungalgrowth, easily observed with the naked eye, at thebase of the plant near the soil line (Figure 4B).Small, round, tan/brown balls, called sclerotia,resembling mustard seeds will be embedded in thewhite fungal growth (Figures 4B and C). The whitefungal growth and sclerotia may extend beyondthe plant stem to surrounding plant residue on thesoil surface. Sclerotia are the pathogen’s hardyoverwintering structures and are responsible forinitiating disease each season. These sclerotia canoverwinter for several years without a host. Thepathogen does not produce spores, and so a plantmust be in close physical proximity to one of thesesclerotia to become infected.Southern blight has a wide host range and cancause disease on numerous other crops includingseveral vegetable crops. Grasses are consideredthe best crop rotation partners to reduce southernblight. Some fields that have been fallow orin pasture for several years preceding a hempcrop have had high incidence of southern blight,illustrating the wide host range and challengeof relying on crop rotation for southern blightmanagement. Deep plowing can reduce diseasepressure by physically burying sclerotia, but theact of working the soil may also spread inoculumthrough the field. Diseased plants, and the soilimmediately around them if practical, should becarefully removed to reduce overwinteringinoculum. Bud material can be harvested fromplants that become infected near or at maturity.This disease is favored by low soil pH. Hemp plantsare susceptible at any age from seedling to fullmaturity. The question of whether plasticultureincreases incidence of southern blight has beenHemp Disease and Pest Managementraised by growers, but research is needed todetermine if this is an important factor.Once a plant becomes infected with southernblight there is no cure. More research is needed todetermine if hemp cultivars differ in susceptibilityto southern blight.ABCFigure 4. Southern blight on hemp. A) A well-established plant inthe field displaying wilt and leaf yellowing resulting from southernblight infection (note: surrounding plants remain healthy).B) White fungal growth and tan/brown sclerotia are observednear the soil line on a hemp plant infected with southern blight.C) A close-up view of the hardy overwintering sclerotia, whichresemble mustard seeds.4
Hemp rustPowdery mildewHemp rust is a fungal disease caused by Uredokriegeriana (Figure 5). Little is known aboutthis pathogen’s life cycle and mechanisms foroverwintering. Hemp rust was first confirmed onsamples collected in East Tennessee on August26, 2019, at the UT Soil, Plant and Pest Center.Following the initial observation, the diseasebecame widespread and was observed in West,Middle and East Tennessee as well as surroundingstates. Symptoms of hemp rust begin as yellow/orange spots on the leaf surface, and eventuallyclusters (pustules) of orange spores (uredospores)become visible to the naked eye on the leafunderside. Lesions eventually become dark orange/brown and may coalesce. More research is neededto determine if hemp cultivars differ in susceptibilityto rust.Powdery mildew is a foliar disease of hempcaused by the fungal pathogen Golovinomycescichoracearum. This pathogen also causes powderymildew on cucurbits such as squash, cucumbersand melons. As the name implies, the most obvioussymptom of powdery mildew is white, powderyfungal growth on the upper leaf surface(Figure 6). Symptoms may also include leafdistortion, necrosis and premature defoliation.Powdery mildew is often a problem on hempgrown in protected culture, such as high tunnels orgreenhouses, where leaf wetness is limited. Powderymildew thrives under humid conditions but issuppressed by leaf wetness. However, leaf wetnessencourages several other diseases, including leafspots, and therefore should be reduced as part of ahemp IPM program. Powdery mildew has also beenobserved on field-grown hemp in Tennessee. Thepathogen is spread through airborne spores thatmay be dispersed long distances. More researchis needed to determine if hemp cultivars differ insusceptibility to powdery mildew.ACBABCDDEFigure 5. Hemp rust caused by the fungal pathogen Uredokriegeriana. A) The underside of a hemp leaf showing orange rustspore pustules. B) Hemp rust lesions on the upper leaf surface.As disease progresses, lesions become darker orange/brown andmay coalesce. C) Lesions start as yellow/orange spots with poorlydefined margins on the upper leaf surface. D) Orange sporeclusters (pustules) containing spores (uredospores) can be seenwith the naked eye on the leaf underside directly beneath leaflesions (image shown viewed under a dissecting microscope). E)Hemp rust spores (uredospores) under a compound microscope.Hemp Disease and Pest ManagementFigure 6. Powdery mildew on hemp caused by the fungalpathogen Golovinomyces cichoracearum. A) Powdery mildewappears as a white powdery fungal growth on the leaf surface andis easily seen with the naked eye (note: the brown circular lesionsin panels A and B are due to leaf spot, not powdery mildew).B) Powdery mildew on field-grown hemp. C) Powdery mildewon a greenhouse-grown hemp leaf. D) Leaf distortion caused bypowdery mildew on a greenhouse-grown hemp leaf.5
Fusarium wilt and Fusarium crown rotFusarium wilt and crown rot of hemp may be causedby several fungal pathogens in the genus Fusarium.In the field, fusarium diseases may be confusedwith southern blight, but disease caused byFusarium will not produce the brown sclerotiaresembling mustard seeds that are characteristicof southern blight. The exact specie(s) responsiblefor these diseases in Tennessee are not yet known.Fusarium crown rot is characterized by wilting thatdoes not recover following irrigation. The stemtissue near the soil line shows brown discolorationif cut lengthwise, rather than the white color ofhealthy stem tissue (Figure 7). Fusarium species aresoilborne pathogens and can likely survive in thesoil for several years. The host ranges of Fusariumspecies affecting hemp are not known, but croprotation should reduce disease pressure. Moreresearch is needed to determine if hemp cultivarsdiffer in susceptibility to diseases caused byspecies of Fusarium.AFigure 7. Fusarium crown rot is characterized by plant wiltingand brown discoloration of the vascular tissue (stem tissue) nearthe soil line. Brown discoloration can be seen by cutting the stemlengthwise near the soil line and is easily distinguished from thesurrounding healthy white tissue with the naked eye.Damping-offDamping-off has been observed on greenhousegrown hemp seedlings and clones (Figure 8). Thisdisease kills seedlings and is caused by several fungiand oomycetes (fungi-like organisms called watermolds), including Rhizoctonia and Pythium. Priorto seedling death, plant may show wilt, a brownlesion near the soil line, and roots may show browndiscoloration. Damping-off is worsened by overwatering and poor drainage. Greenhouse sanitationand the use of pathogen-free irrigation water areimportant practices for managing damping-off.Hemp Disease and Pest ManagementBFigure 8. Damping-off of greenhouse-grown hemp clones.Damping-off is often caused by inadequate greenhouse sanitationand is worsened by excessive irrigation.6
Nematodes on hempA wide range of plant-parasitic nematodes havebeen associated with hemp, but little is knownabout their ability to develop and reproduce on thecrop, or to cause yield loss. The only nematodesso far studied experimentally are the root-knotnematodes (Meloidogyne spp.) (Figure 9). Thesenematodes are common pathogens on manycrops and in home gardens and are consideredthe most important plant-pathogenic nematodesin the world. The female nematode resides withina root gall it induces, feeding on nutrients fromaltered plant cells and producing hundreds ofeggs that hatch into juveniles, which will invadegrowing root tips. In susceptible crops, root-knotnematodes can cause wilting, slow growth andreduced yield due to interruption of nutrient flowbetween roots and leaves. Two species of economicimportance occur in Tennessee, both of which canattack hemp. Meloidogyne incognita (southernroot-knot nematode) is ubiquitous and can beexpected nearly anywhere a susceptible plantspecies is grown. Meloidogyne hapla (northernroot-knot nematode) has a spottier distribution.Both species can attack hemp. The main symptom isdevelopment of small, hard, white galls on the roots,each of which normally contains a single female.Susceptibility varies, but most hemp cultivars andselections tested so far in greenhouse conditions aremoderate-to-good hosts of M. incognita andM. hapla. However, the cultivars ‘Wife’ and ‘SiskiyouGold’ appear to be resistant to M. incognita on thebasis of very limited testing. There appears to beno correlation of resistance to type of hemp (fiber,seed, CBD). Hemp has not been experimentallychallenged with root-knot nematodes in the field,and significant field infestations have not yet beenreported in the state.ABCDFigure 9. Meloidogyne incognita (southern root-knot nematode)on roots of ‘Delores’ hemp. A) Galled root system. B) Enlargementof box in A, close-up of typical galls produced on hemp, indicatedby arrows. C) Egg masses stained pink to show extensivenematode reproduction (nematode inside gall), indicated byarrows. Each egg mass contains about 500 eggs. D) Gall on hempshows swollen nematode inside, stained pink (indicated by arrow).Feeding cells are in the center of gall; phloem and xylem surroundfeeding cells. Egg mass has fallen away.Keys to Integrated DiseaseManagementThe disease triangle is a concept related to plantdisease management that helps illustrate the waysin which growers can manage plant diseases.The disease triangle includes a susceptiblehost, a virulent, or infectious, pathogen, and anenvironment favorable for disease development(Figure 10). If all three factors are present at thesame time, a plant disease will occur. Diseasesare managed by eliminating one or more of thesefactors. This concept underlies how wecan approach plant disease management.Hemp Disease and Pest Management7
Sanitation is especially important in greenhouseproduction. Below are resources that discuss thistopic in more detail. Sanitation Guidelines for Management of Pestsand Diseases of Greenhouse VegetablesHost PB 1825 An Overview of Systems-based PestManagement for Nursery Production Avoid working with plants while they are wet.Disease Avoid moving soil between fields to limit theintroduction of pathogens. Crop rotation can reduce disease pressure bylimiting the amount of overwintering inoculum inthe soil.PathogenEnvironmentFigure 10. The plant disease triangle includes a susceptiblehost, a virulent, or infectious, pathogen, and an environmentfavorable for disease development, and helps illustrate the waysin which we can manage plant diseases. If all three factors arepresent at the same time, a plant disease will occur. Diseasesare managed by eliminating one or more of the three factorsincluded in the triangle.HostChoosing disease-resistant cultivars is one of thebest ways to manage plant diseases. Research isneeded to evaluate hemp cultivars for differencesin susceptibility to diseases commonly observedin the Southeast. As indicated in Table 1, severalcultivars show strong resistance to leaf spotdiseases. However, it is not clear how leaf spotaffects overall CBD yield; therefore, growersshould select cultivars with good CBD yield andlow-to-moderate leaf spot susceptibility. Cultivarevaluations for susceptibility to the remainingdiseases described here have not been done,although there may be significant differences.Growers should record observations of diseasesand pests along with cultivar information to helpinform future cultivar selections until detailedcultivar disease susceptibility informationbecomes available.PathogenUnderstanding the spread of pathogens is anintegral part of disease management. Limitingpathogen spread can slow the rate of diseasedevelopment. The following steps can limit theintroduction and movement of pathogens. Weed management can reduce disease pressurebecause weeds can serve as disease reservoirs. For southern blight or fusarium diseases, removeinfected plants to reduce overwintering inoculum. Untreated surface irrigation water shouldbe avoided if possible because it can harborpathogens like Pythium. This is especially true forgreenhouse production. Municipal or well waterare preferred, or surface water may be treated toeliminate pathogens.EnvironmentManaging the crop environment can reduce diseasepressure by making conditions less favorable fordisease
Hemp Disease and Pest Management 5 Hemp rust Hemp rust is a fungal disease caused by Uredo kriegeriana (Figure 5). Little is known about this pathogen’s life cycle and mechanisms for overwintering. Hemp rust was first confirmed on samples collected in East Tennessee on August 26, 2019, at the UT Soil, Plant and Pest Center.
i. Hemp extract or CBD in milk and dairy products j. Restaurants / Bars / Cosmetics k. Report a problem with a hemp product for human consumption l. Hemp and CBD smoking and vaping 7. ANIMAL FOOD AND FEED (DOG TREATS) 8. HEMP SEED 9. ADDITIONAL INFORMATION LINKS . SECTION IV: LAW ENFORCEMENT ISSUES . 10. PERSONAL POSSESSION OF HEMP PRODUCTS 11.
insect infestations, and notify management when dead rodents and or birds are found. b) Management should immediately contact the pest management provider for assistance. 1.3.1. Pest Sighting Log a) Maintain a Pest Sightings Log which informs the pest control service technician of pest sightings or pest activity in the facility.
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accounting purposes, and are rarely designed to have a voting equity class possessing the power to direct the activities of the entity, they are generally VIEs. The investments or other interests that will absorb portions of a VIE’s expected losses or receive portions of its expected residual returns are called variable interests. In February 2015, the Financial Accounting Standards Board .
