Hemp Diseases And Pests Download Free
Donnell Simon
Historically, the fungal pathogens gray mold (Botrytis cinerea) and white mold (Sclerotinia sclerotiorum) have been reported to infect and impact hemp production. In Indiana, white mold, in particular, is expected to be a major disease north of highway 70, particularly when soybeans are grown in adjacent locales, or in rotation with hemp. Hemp is also prone to numerous fungal and bacterial leaf spots, viruses, and Pythium root rot and blight during establishment. Southern blight was reported on hemp in Indiana (2019), as well as rust on the leaves of hemp (2019). Downy mildew has been found in Indiana.
Disease pressure will vary based on weather conditions, but with wet springs, we typically see several seedling diseases, including Pythium, Fusarium, and Rhizoctonia. Indoor producers also have to manage diseases on hemp. Powdery mildew is a common indoor disease that can be managed through adjustments in humidity, selecting disease resistant/tolerant cultivars, removing infected tissue, and the use of registered fungicides.
Disease management is challenging with no labeled synthetic fungicides for use in hemp. There are biopesticides available for use in Indiana and can be found here (PDF). Proper sanitation is crucial to prevent plant infection.
This site is aimed at presenting information about Florida Hemp diseases and their management. New information will be provided as new diseases are identified and we learn more about their epidemiology. The University of Florida Pilot Program is instrumental in populating this information.
Making recommendations on how to manage the pathogens we discuss in this website will be forthcoming. Because this is a new crop and we have very little Florida data on how to manage them it will take a while to determine what is both effective and safe for the crop. We will use the FDACS Florida Pesticide List to determine which products we will evaluate. As you will see, there are 4 pages of products approved for use on hemp in Florida. This list will change over time, but it is all we have at this point. We can't evaluate all the materials listed and thus we will limit what we evaluate to products we have funding to evaluate or products that meet other criteria set my each of us who are planning to conduct such research.
Leaf spot diseases are common among hemp growers throughout the region, such as in Tennessee and Kentucky. Since the start of the (UF/IFAS) Industrial hemp pilot project there have been two confirmed fungal leaf spot diseases. Leaf spot (Curvularia pseudobrachyspora) and Cercospora Leaf Spot (Cercospora cf. flagellaris), the diseases were confirmed in June and March of 2020 respectively. As the project continues, we have seen more of these types of diseases, such as Septoria leaf spot and Bipolaris spp. The humid conditions of Florida favor the development of leaf spot diseases.
Symptoms of leaf spot diseases may vary, but are generally observed as small circular lesions with tan centers and brown margins to larger lesions to dark centers and brown/purple margins (UT Extension). Often, the lesions merge which can lead to blighting and in some severe cases can become yellow and cause defoliation of the hemp leaves.
More work is needed in this area to develop a better understanding of leaf spot diseases. It is important to remember that symptoms alone should not be used to diagnose, and you should always confirm with a diagnostic lab.
Photo Credit - Marin, Coburn, Desaeger and Peres. UF-GCREC, Wimauma, 2020. Infection of Curvularia pseudobrachyspora on hemp leaf and pathogen morphology. -03-20-0546-PDN
Septoria leaf spot is one of the most common leaf spot pathogens among the hemp leaf spot diseases. Like other leaf spot pathogens, the symptoms of this disease begin in the lower canopy as small brown spots with yellow margins. The leaf spots may continue to grow, turn brown and coalesce. More advanced symptoms may be observed, such as leaf yellowing, stunting, and plant death. This disease can progress quickly during the summer months when there is excess moisture, humidity, and the canopies are more dense.
Soilborne & seedling diseases are caused by pathogens that live almost exclusively in the soil. Some of the diseases in this section are caused by true fungi, such as Southern Blight, while others are caused by Oomycetes, such as Pythium Root Rot. These diseases are usually very difficult to manage because they often exist conspicuously in the soil and can develop survival structures that exist in a field for many years. Some of these diseases may be managed by sanitation or cultural controls, such as crop rotations, while others are best managed through disease resistance.
The most common symptom associated with the diseases in this section is wilting. While wilting is not a diagnosis for soilborne diseases, it should not be ruled out. If any of the following disease are seen in a field, the most important thing to remember is to prevent any further spread of the pathogen, and always confirm with a diagnostic lab.
This disease is observed mostly in field grown hemp, and can be particularly devastating. Symptoms of this pathogen are characteristic of other Fusarium spp. diseases, and are most commonly observed as yellowing of leaves, and wilting, which will not improve with watering. Additionally, the vascular tissue within the crown, or stem near the soil line, will often show a brown discoloration. This pathogen is particularly difficult as it can remain in the soil for many years. Other diseases of this pathogen exist, but have yet to be observed in Florida.
At this time, there are a few species of Fusarium spp. that are known affect hemp. Like other Fusarium spp. diseases, crop rotation and planting resistant varieties are the most effective strategies. Ultimately, an integrated approach will be needed to manage this disease, but more research is needed to provide specific details, such as rotational crops and resistant varieties.
Since this pathogen is omnipresent in the soil, cultural considerations are the most important factor in management of this disease. And since it can be present in both outdoor and greenhouse grown hemp, particular attention needs to be paid to sanitation. Close attentions should be paid to any contaminated soil and water, as well as preventing movement of infected plants from greenhouses and previous years. Since this pathogen moves through water, runoff and infected irrigation water should be prevented. The most important aspect of managing this pathogen is to stop the introduction or infection, and maintain good plant health.
Bacterial diseases are caused by bacterial microorganisms, which require free water for movement and to infect its host. Many bacterial diseases are observed as leaf spots, but they differ from fungal leaf spots in that the spots have a water soaked appearance, are generally vein limited, and often become necrotic and fall off the leaf.
Although relatively common on other crops, information regarding bacterial diseases on hemp is only minor at this time. Currently, in Florida, there is only one bacterial leaf spot disease being researched, Xanthomonas Leaf Spot caused by the pathogen Xanthomonas spp. More information will be provided as we learn more about these pathogens on hemp. If you suspect a bacterial leaf spot disease, always make sure to contact a diagnostic lab.
While viral diseases of hemp exist, at this time, viral diseases have been hard to determine as a causal agent. There have been reports of viral disease symptoms in hemp, but speculation still exists whether or not the virus is the cause of the disease. Additionally, those viruses that have been identified in hemp have been observed outside of North America. At this time, there is no conclusive evidence of viral pathogens causing diseases on hemp in Florida or North America.
Viral diseases of hemp are most likely to be transmitted by vectors, such as insects, so management of these insects will be the key in managing these pathogens. We expect more information as researchers begin to understand the transmissibility of hemp viruses in nature.
Hemp is enjoying a worldwide resurgence. This unique book combines a review of the hemp pest and disease literature published over the past 50 years with up-to-date information on modern biological control techniques. Each pest and disease organism is presented in the same format, covering economic impact, geographical and host-plant range, plant symptoms, taxonomic description, life history, and differential diagnosis. Important cultural, mechanical, biological and chemical controls are highlighted with charts, illustrations and explicit instructions. Easy-to-use keys are included for rapid identification of the most common pests. Introductory chapters describe the general principles of plant protection, requirements for healthy plant growth, and taxonomy of parasites and pathogens.
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