Guava Diseases
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Anthracnose of guava fruit
Fig. 1
Anthracnose of guava fruit

Cephaleuros parasiticus as a parasite of guava leaves and fruit in Hawaii, causing a leaf and fruit spot disease
Fig. 3
Cephaleuros parasiticus as a parasite of guava leaves and fruit in Hawaii, causing a leaf and fruit spot disease

Guava rust symptoms on fruit
Fig. 7
Guava rust symptoms on fruit

Fruiting bodies
Fig. 11
Mushroom root rot fruiting bodies

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The principal diseases affecting guava production in Florida include fungi and a parasitic algae. Anthracnose (Colletotrichum gloeosporioides) and leaf spot (Pseudocercospora psidii) are fungal diseases that affect guava production. Algal spot (Cephaleuros virescens) may become apparent in summer, and sooty mold is often present, though not considered a true disease of guava. Non-manageable diseases include mushroom root rot (Armillaria tabescens) and thread blight (Rhizoctonia solani). These diseases are controlled by selecting proper planting areas and pruning out diseased tissue, respectively. 2



Anthracnose

Caused by the pathogen Colletotrichum gloeosporioides

Anthracnose is the most commonly observed disease that affects both pre- and postharvest management of guava. This disease can cause considerable postharvest losses and can affect young developing flowers and fruit. It has been reported in all guava-growing areas around the world where high rainfall and humidity are present. 1
Symptoms of this disease are observed on mature fruits on the tree. The characteristic symptoms consist of sunken, dark colored, necrotic lesions. Under humid conditions, the necrotic lesions become covered with pinkish spore masses. As the disease progresses, the small sunken lesions coalesce to form large necrotic patches affecting the flesh of the
fruit (Fig. 1).
Conidia (asexual spores) are the fungal structures responsible for anthracnose infection. Conidia are produced on dead twigs, necrotic fruit lesions, inflorescences, and leaves. Inflorescences and young fruit are extremely susceptible and, if infected, may cause abortion and abscission. Conidia spread via rain splash and can cause infection; symptoms may develop shortly thereafter on any above ground host tissue. Latent infections are common with this disease and may remain quiescent for months. 1

Anthracnose symptoms on fruit
Fig. 2

Fig. 2. Anthracnose symptoms on fruit



Pseudocercospora Leaf Spot
Caused by Pseudocercospora psidii

Pseudocercospora leaf spot is prevalent in warm, humid and rainy guava producing areas of south Florida.
Symptoms may occur on leaves, stems and fruit. Small lesions (2-8 mm) appear as irregular to sub-circular, dark smokey brown on the upper leaf surface, with a darker brown, diffuse border. Under high humidity, sporulation of the causal fungus may be seen in lesion centers as greenish-gray, felty tufts of mycelium. Individual lesions may coalesce to form large areas of necrotic tissue. The fungi can infect fruit and cause lesions and fruit cracking which may lead to secondary infections of other opportunistic fungi and bacteria.
The source of inoculum most likely originates from infected leaves. The pathogens are capable of directly penetrating host tissues. Once infected, the fungus reproduces abundantly from the lower leaf surfaces.
Sporulation is greatest during warm, wet weather and most abundant from May thru September. Spores are disseminated via wind, splashing rain, insects and irrigation.
Very small fruit and those at or near maturity are less susceptible than those fruit which are one-fourth to three-fourth of full size. Copper based fungicides are labeled for the use on guava in Florida. 1

Further Reading
Pseudocercospora Leaf Spot of Feijoa from the Florida Department of Agriculture & Consumer Service pdf



Algal Leaf Spot
Caused by the pathogen Cephaleuros virescens Kunze

Disease symptoms are exhibited on both abaxial and adaxial leaf surfaces as orange, rust-colored, dense silky tufts ranging from 5 to 8 mm in diameter. Upon scraping away these spots, a thin, grayish white to dark-colored, necrotic crust remains on the leaf. These spots usually come together to form large irregular patches on a leaf. As the spots mature they take on a dull, grayish green color. Twigs and branches are also affected causing the bark to crack due to the growth and expansion of the pathogens filaments into the cortical tissues of the host.
Algal leaf spots proliferate under wet or humid conditions within the trees canopy. Infectious propagules such as sporangia and biflagellate zoospores are disseminated by water splash and wind; biflagellate zoospores are the primary infection stage of the pathogen. Quadriflagellate spores have not yet been identified as infection sources.
Algal leaf spot can be reduced by maintaining tree vigor with cultural techniques such as proper fertilization and irrigation, proper pruning to enhance air circulation within the canopy and sunlight penetration, managing weeds and wider tree spacing. Managing insect, mite and other foliar diseases increases tree vigor and lessens susceptibility to this disease. If chemical control is warranted, periodic applications of a copper-based fungicide will control the alga. 1

Algal leaf spot of gauva (Psidium guajava. Pathogen: Cephaleuros virescens Guava: Defoliation and fruit drop due to algal leaf spot Guava: Defoliation and fruit drop due to algal leaf spot
Fig. 4 Fig. 5 Fig. 6

Fig. 4. Cephaleuros parasiticus as a parasite of guava leaves and fruit in Hawaii, causing a leaf and fruit spot disease.
Fig. 5. Guava: Defoliation and fruit drop due to algal leaf spot
Fig. 6. Guava: Defoliation and fruit drop due to algal leaf spot

Further Reading
Cephaleuros Species, the Plant-Parasitic Green Algae from the University of Hawaii CTAHR pdf 6 pages



Guava Rust
(Fig. 7)
Caused by the pathogen Puccinia psidii G. Winter

The rust disease can be very destructive to guava producing regions around the world. The pathogen has been reported to occur in Central and South America, the Caribbean and in Florida. Aside from guava, the disease has been reported to affect other members of the Myrtaceae family. The pathogen can affect foliage, young shoots, inflorescences and fruit of guava. Typical symptoms associated with this disease include distortion, defoliation, reduced growth and if severe, mortality. On fully expanded leaves, dark bordered, roughly circular brown lesions with yellow halos develop (Burnett and Schubert 1985).
Infection of upper and lower leaves occurs in wet to moist environments within temperature ranges of 55 - 77° F (Burnett and Schubert 1985). Urediospores germinate at temperatures in the range of 18 - 22° C (64 - 71° F). Disease usually begins to occur at the onset and development of young shoots; leaves that are 40 days or more old have been observed to be more resistant to infection (Holliday 1980). Urediospore dissemination occurs via rainsplash.
Control of guava rust is based on the use of fungicides. Scouting trees for onset of disease or during the times of year when environmental conditions are favorable for pathogen infection are recommended so that proper and timely fungicide applications can be made. In addition, proper cultural tactics such as proper fertilization, irrigation, pruning and sanitation aide in achieving a healthy, vigorously growing tree less vulnerable to disease pressures. 1

Guava rust symptoms on leaves Guava rust symptoms on young leaves Guava rust (Puccinia psidii) symptoms
Fig. 8 Fig. 9 Fig. 10

Fig. 8. Guava rust symptoms on leaves
Fig. 9. Guava rust symptoms on young leaves
Fig. 10. Guava rust (Puccinia psidii) symptoms



Thread Blight

Caused by Rhizoctonia solani Kuen

Thread blight occurs on a wide range of host plants. The disease develops primarily in the spring and summer months when warm, humid conditions are present. Typical symptoms consist of circular to sub-circular leaf spots, tan to brown in color with alternating light and dark concentric rings dispersed throughout the canopy leaf spots eventually coalesce, resulting in a blight appearance. Leaves may be stuck together with tan to brown mycelium originating from the leaf margin.
Leaves, either on a new flush or an older flush, may appear water-soaked, necrotic, and the disease may eventually defoliate the plant. Leaves are held onto twigs by coarse brown threads of the causal pathogen. The fungus can invade leaves and twigs causing a dieback. It has been observed under warm, humid conditions, that the interior of the plant canopy is affected by the web blight disease (Benson and Jones 2001). Distribution of the disease is likely when plants are in close proximity to each other under ideal conditions.
Rhizoctonia spp. are among the most diverse of plant pathogenic fungi, causing root, stem, and foliar diseases of many subtropical and tropical hosts. Typically, Rhizoctonia spp. attack plants at the soil line causing root and stem rots. This pathogen can attack leaves as well, and is especially severe when trees are planted close together and the foliage remains moist for prolonged periods. 1
On guava, disease development can occur in less than one week. When humidity is high, the web-like brown mycelium of the fungus can cover portions of the foliage that are infected. The pathogen may invade the canopy from the ground level by means of mycelial webbing (Schubert and El-Gholl 1995). Under favorable conditions, the pathogen may produce a thin grayish or tannish-white hymenial layer consisting of mycelium, basidia and basidiospores of the telemorph, Thanatephorus cucumeris, on the zonate lesions (Schubert and El-Gholl 1995). The lesions produced may appear water-soaked and discolored (Benson and Jones 2001). The characteristic feature of R. solani is the tan to brown colored mycelium produced on the margins of infected leaves that will cause necrotic and abscised leaves to web or stick together. If the infection is severe, the center of the plant may become defoliated. Rhizoctonia may survive as hyphae and sclerotia associated with infected crop debris (Benson and Jones 2001). Once the pathogen is established in a plant canopy, it may spread to adjacent plants if plants are spaced in close proximity to each other. It has been observed that under moist conditions leaf infection occurs within 48 hours of inoculation (Benson 1993). 1
Cultural practices such as increased plant to plant spacing to promote air circulation, avoidance of overhead irrigation and irrigation regimens that extend leaf wetness periods, good sanitation practices (removal of infected plant debris, management of weeds that may be potential hosts, standing water, etc.) and proper nutrient management plans to maintain vigorous plants. 1



Mushroom Root Rot
Caused by the fungus Armillaria tabescens (Scop.) Emel

Mushroom root rot is a common and widespread disease that affects conifers and hardwoods in Florida. Aside from affecting Guava, the disease has been reported on over 200 species of trees and shrubs.
Infected trees will usually not show any symptoms until the disease has debilitated a significant portion of the root system. Diseased trees may exhibit a variety of symptoms, including: thinning of the crown, yellowing of foliage, premature defoliation, branch dieback, decaying roots, and lesions at the root collar. On some occasions, a tree may show symptoms of decline for several years before dying where as in other instances, trees may die rapidly without any visible symptoms. 1
Mushroom root rot, caused by the fungus Armillaria tabescens, can cause severe problems for guava producing areas if the pathogen is present in the field. The most notable sign of disease, if present, is the characteristic mushrooms which develop near the base of infected trees. The mushrooms usually appear in fall, but they can occur at other times as well. The mushrooms, when fresh, are tan to brown, fleshy, with gills beneath the cap, and lacking an annulus around the stem (Ash and Barnard 1994). The disease may not always produce fruiting bodies when guava trees are infected. When a tree is in decline, and the mushrooms are absent, the fungus can be identified by the characteristic cream – colored mycelium just beneath the bark of infected roots and tree bases (Ash and Barnard 1994). 1
Preventative measures to manage mushroom root rot such as the removal of diseased trees and their root system before re-planting should be taken in order to reduce the possibility of future infections. Cultural practices to maintain vigorously growing plants help to reduce the colonization of the fungus. These practices include keeping root damage to a minimum when planting or transplanting, planting at proper depths so that the root collar is not buried in the soil, keeping mulch away from the root collar, and maintaining an optimum growing environment (i.e., soil fertility, pH, irrigation) to alleviate any stresses to the plant. Currently, there are no known effective fungicides registered for the control of mushroom root rot on guava. 1

Symptoms on plum pine Symptoms on peach tree
Fig. 12 Fig. 13

Fig. 12. Symptoms of mushroom root rot on plum pine
Fig. 13. Symptoms of mushroom root rot on peach tree

Further Reading

Armillaria Root Rot from the University of Florida pdf 4 pages

Armillaria tabescens from USDA and University of Georgia pdf 4 pages




Nematodes

Nematodes are widespread and problematic in guava producing areas. Depending on soil type, different nematode species can proliferate and cause disease. A general decline in tree vigor is observed in response to high nematode populations.
Aboveground symptoms associated with nematode infection include chlorosis, stunting, premature wilting, and nutrient deficiencies. Below the ground, a reduction of fine root densities and root distortion is observed.
Causal nematode agents include reniform nematode (Rotylenchulus reniformis), burrowing nematode (Radopholus similis), ring nematode (Hemicriconemoides magniferae) and root-knot nematode (Meloidogyne spp.). While many species (M. incognita, M. arenaria, M. javanica, and M. hapla) of root-knot nematode cause disease in guava producing areas worldwide, Meloidogyne incognita, of races 1 and 2 are pests of guava in Florida.
The use of nematode free planting stock is the best control method. In Florida, there are no currently registered nematicides for the use on guava. 1

Further Reading
Reniform Nematode, Rotylenchulus reniformis Linford and Oliveira from the University of Florida pdf
Burrowing Nematode, Radopholus similis (Cobb, 1893) Thorne, 1949 from the University of Florida pdf 5 pages



Further Reading
2013 Florida Plant Disease Management Guide: Guava (Psidium guajava) from the University of Florida pdf 7 pages


Bibliography

1 Merida, Michael and Palmateer, Aaron J. "2013 Florida Plant Disease Management Guide: Guava (Psidium guajava)." edis.ifas.ufl.edu. This document is PP-232, one of a series of the Plant Pathology Department, UF/IFAS Extension. Publication date June 2006. Reviewed Apr. 2014. Web 10 Dec. 2014.
2 Mossler, Mark A. and Crane, Jonathan. "Florida Crop/Pest Management Profile: Guava and Wax Jambu." edis.ifas.ufl.edu. This document is CIR 1415 one of a series of the Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date, Sept. 2002. Original authors included O. Norman Nesheim, professor, Food Science and Human Nutrition Department. This publication was revised Aug. 2009. Reviewed Aug. 2012. Web. 10 Dec. 2014.

Photographs

Fig.Nelson, Scot. Anthracnose of guava fruit. 2008. flickr.com. Under (CC BY 2.0). Web. 31 Jan. 2017.
Fig. 2 Symptoms of anthracnose on fruit. N.d. University of Florida. edis.ifas.ufl.edu.  Web. 10 Dec. 2014.  
Fig.Nelson, Scot. Cephaleuros parasiticus as a parasite of guava leaves and fruit in Hawaii, causing a leaf and fruit spot disease. 2008. University of Hawaii at Manoa. flickr.com. Under (CC BY-NC-SA 2.0). Web. 3 Feb. 2017.
Fig.Nelson, Scot. Algal leaf spot of guava (Psidium guajava. Pathogen: Cephaleuros virescens, Hilo, Hawaii. 2008. flickr.com. Under (CC BY-NC-SA 2.0). Web. 3 Feb. 2017.
Fig. 5,6  Nelson, Scot. Guava: Defoliation and fruit drop due to algal leaf spot. 2008. University of Hawaii at Manoa. flickr.com. Under (CC BY-NC-SA 2.0). Web. 3 Feb. 2017.
Fig. 7 Hamann, Jonas Janner. Guava rust Puccinia psidii G. Winter. 2012. Universidade Federal de Santa Maria. bugwood.org. Under (CC BY 3.0 US). Web. 11 Dec. 2014.
Fig. 8 Guava rust Puccinia psidii G. Winter. 2007. Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services. bugwood.org. Under (CC BY 3.0 US). Web. 11 Dec. 2014.
Fig. 9 Starr, Forest and Kim. Puccinia psidii rust on young leaves. 2007. bugwood.org. Under (CC BY 3.0 US). Web. 11 Dec. 2014.
Fig. 10 Hamann, Jonas Janner. Guava rust Puccinia psidii G. Winter, symptoms. 2015. Universidade Federal de Santa Maria. bugwood.org. Under (CC BY 3.0 US). Web. 11 Dec. 2014.
Fig. 11 Stephens, David. Fruiting bodies, Armillaria tabescens. 2013. bugwood.org. Under (CC BY 3.0 US). Web. 11 Dec. 2014.
Fig. 12 Armillaria tabescens symptoms on plum pine. 2007. Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services. bugwood.org. Under (CC BY 3.0 US). Web. 11 Dec. 2014.
Fig. 13 Armillaria tabescens symptoms on peach tree. 2008. Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services. bugwood.org. Under (CC BY 3.0 US). Web. 11 Dec. 2014.

Published 10 Dec. 2014 LR. Last update 12 Feb. 2017 LR
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