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- Author or Editor: Monica L. Elliott x
Since the mid-1990s, several new pathogens and diseases have emerged on palms (Arecaceae) growing in Florida. These include two formae speciales of Fusarium oxysporum, with f. sp. canariensis causing fusarium wilt of canary island date palm (Phoenix canariensis) and a new forma specialis causing Fusarium wilt of queen palm (Syagrus romanzoffiana) and mexican fan palm (Washingtonia robusta). The texas phoenix palm decline phytoplasma (‘Candidatus Phytoplasma palmae’ subgroup 16SrIV-D), which causes a lethal yellowing-type disease, has been detected in date palms (Phoenix spp.), queen palm, and cabbage palm (Sabal palmetto). New rachis (petiole) blight pathogens include Cocoicola californica on mexican fan palm and Serenomyces species on several palm species.
Foxtail palms (Wodyetia bifurcata Irvine) were grown in 6.2-L containers using a 3 calcitic limestone gravel: 2 coir dust (by volume) substrate to induce Fe chlorosis. Plants were treated initially and 2 and 4 months later with soil applications of FeDTPA, FeEDDHA, FeEDTA+FeHEDTA on vermiculite, FeEDTA+FeDTPA on clay, ferric citrate, ferrous ammonium sulfate, ferrous sulfate, ferrous sulfate+sulfur, or iron glucoheptonate at a rate of 0.2 g Fe/container. Similar plants were treated initially and 2 and 4 months later with foliar sprays of FeDTPA, FeEDDHA, ferric citrate, ferrous sulfate, or iron glucoheptonate at a rate of 0.8 g Fe/L. After 6 months, palms receiving soil applications of FeEDDHA, FeEDTA+FeHEDTA on vermiculite, FeDTPA, or FeEDTA+FeDTPA on clay had significantly less chlorosis than plants receiving other soil-applied Fe fertilizers or untreated control plants. Palms treated with foliar Fe fertilizers had chlorosis ratings similar to untreated control plants. Palms with the most severe Fe chlorosis also had the highest levels of leaf spot disease caused by Exserohilum rostratum (Drechs.) K.J. Leonard & E.G. Suggs. Neither chlorosis severity nor leaf spot severity was correlated with total leaf Fe concentration.
Container-grown mexican fan palm (Washingtonia robusta) and queen palm (Syagrus romanzoffiana) transplanted into a field nursery having phosphorus (P)-sufficient and P-deficient soils were treated at the time of planting with four commercial microbial inoculants (each containing arbuscular mycorrhizal fungi, alone or with other microbial components or fertilizers), two fertilizers, or nothing (control). All but the control palms received applications of an 8N–0.9P–10K palm fertilizer every 3 months for 2 years. None of the treatments improved growth over the control in the P-deficient soil. In the P-sufficient soil, none of the microbial inoculants improved growth over that of similarly fertilized noninoculated palms. Discrepancies were observed regarding nonmycorrhizal fungi and bacteria present in the microbial inoculant products. The type and quantity of these microbes listed on the labels of the microbial inoculant products did not necessarily match the type and quantity actually detected in the products.
A commercially available microbial inoculant (Plant Growth Activator Plus) that contains 50 microorganisms, primarily bacteria, was evaluated in a soilless container substrate to determine its effects on root bacterial populations and growth response of container-grown plants at three fertilizer rates. The tropical ornamental plants included hibiscus (Hibiscus rosa-sinensis `Double Red'), spathiphyllum (Spathiphyllum `Green Velvet') and areca palm (Dypsis lutescens). The bacterial groups enumerated were fluorescent pseudomonads, actinomycetes, heat-tolerant bacteria, and total aerobic bacteria. Analysis of the inoculant before its use determined that fluorescent pseudomonads claimed to be in the inoculant were not viable. The plant variables measured were plant color rating, shoot dry weight and root dry weight. Only hibiscus shoot dry weight and color rating increased in response to the addition of the inoculant to the substrate. Hibiscus roots also had a significant increase in the populations of fluores-cent pseudomonads and heat-tolerant bacteria. From a commercial production point of view, increasing fertilizer rates in the substrate provided a stronger response in hibiscus than did addition of the microbial inoculant. Furthermore, use of the inoculant in this substrate did not compensate for reduced fertilizer inputs.
Type 1 (necrotic) fairy rings in turfgrass result in dead or badly damaged grass. This type of fairy ring is a severe problem on golf course greens as they interfere with the aesthetics and playability of the putting surface. In Florida, Lycoperdon spp., basidiomycetes that produce puffball mushrooms, have been implicated as a common cause of Type 1 fairy rings on hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) putting greens. The fungicide flutolanil has basidiomycetes as the sole fungal target. It is also the only carboxin-related fungicide registered for use on turfgrass. Two experiments were conducted to examine the effect of flutolanil as a curative and preventive treatment for fairy ring caused by Lycoperdon. One experiment, established after the rings were present, determined that flutolanil significantly reduced mushroom production. The second experiment was conducted on a golf course that had experienced Type 1 fairy rings previously. One-half of each of nine putting greens was treated with flutolanil on a preventive basis. The other half of each green served as an untreated control. Type 1 fairy rings, due to Lycoperdon, developed only on the untreated control half of each green. These experiments confirm that flutolanil does have curative and preventive activity against Lycoperdon spp. that cause Type 1 fairy rings.
Palms are an important component of landscapes in tropical, subtropical, and Mediterranean climates, but are anatomically very different from broadleaf trees. Very little is known about the movement and persistence of systemic fungicides into various parts of the palm canopy. This information is critical in selecting fungicides that may be effective against diseases that infect specific parts of the palm. In this study, potassium phosphite was injected into mature coconut palms (Cocos nucifera) at rates of 0, 30, 60, or 90 mL per tree. Various leaf tissue samples were collected periodically thereafter up through 60 weeks and were analyzed for phosphite concentrations. Phosphite moved quickly into leaflet tissue, but concentrations dropped off sharply between 1 and 5 weeks after injection. This drop in leaflet concentrations was balanced by a concomitant increase in spear leaf concentrations. Phosphite persisted at high concentrations in basal rachis tissue of both old and new leaves throughout the experiment. This suggests that this material may be useful for controlling diseases that infect spear leaves and petiole or rachis tissue, but not leaflets.
Palms (Arecaceae) are affected by a variety of pathogens, most of which are fungi. We detail pathogens, host ranges, disease description, diagnosis and epidemiology as well as management for the significant, usually fatal, diseases affecting palms grown in the continental United States and Hawaii. These include fusarium wilt (Fusarium oxysporum f.sp. canariensis) of canary island date palm (Phoenix canariensis), diamond scale (Phaeochoropsis neowashingtoniae), ganoderma butt rot (Ganoderma zonatum), lethal yellowing (Candidatus Phytoplasma palmae subgroup 16SrIV-A), and diseases caused by Nalanthamala (Gliocladium), Phytophthora, and Thielaviopsis. We have omitted the leaf spot and minor blight diseases that often affect palms but pose no long-term consequence to their health and survival. Visual symptoms of lethal palm diseases are often similar, necessitating the isolation or detection of the pathogen with cultural, microscopic, or molecular methods. Management of palm diseases is varied, often requiring in-depth knowledge of the biology of the pathogen and its' infection process. Quarantine, eradication, sanitation, and proper species selection and culture are necessary practices to limit the spread of new and existing diseases of palms in landscapes and nurseries.
Taxonomic diversity of bacteria associated with golf course putting greens is a topic that has not been widely explored. The purpose of this project was to isolate and identify culturable bacteria from the rhizosphere of creeping bentgrass (Agrostris palustris Huds.) at two sites (Alabama and North Carolina) and hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] at two sites (Florida and South Carolina) for a minimum of 3 years with sampling initiated after the construction process. Randomly selected colonies were identified using gas chromatography for analysis of fatty acid methyl ester profiles. Over 9000 isolates were successfully analyzed. When a similarity index of 0.300 or higher was used, the average number of unidentifiable isolates was 38.6%. The two dominant genera in both bentgrass and bermudagrass rhizospheres were Bacillus and Pseudomonas with Bacillus dominant in bermudagrass and Pseudomonas dominant or equal to Bacillus in bentgrass. Other genera that comprised at least 1% of the isolates at all four sites were Clavibacter, Flavobacterium, and Microbacterium. Arthrobacter also comprised a significant portion of the bacterial isolates in the bentgrass rhizosphere, but not the bermudagrass rhizosphere. Overall, there were 40 genera common to all four sites. At the species level, there were five that comprised at least 1% of the isolates at each location: B. cereus, B. megaterium, C. michiganensis, F. johnsoniae, and P. putida. As has been reported for many grasses, we found considerable taxonomic diversity among the culturable bacterial populations from the rhizospheres of bentgrass and bermudagrass grown in sand-based putting greens.