Tag Archives: disease

More Sugar from Michigan Thanks to Fungicides

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Fungicides: Used (left); Not Used (right)

Fungicides: Used (left); Not Used (right) (Rhizoctonia Control)

Rhizoctonia root rot is a serious disease problem in several sugarbeet-growing regions, with the result sometimes being dramatic—and expensive—reductions in tonnage and quality. Low levels of infections can easily cause yield losses in excess of a ton per acre while high infection levels can cut yields by more than 10 tons per acre. The quality of surviving beets can also be impacted, sometimes resulting in significant losses in recoverable sugar.

“During 2009 and 2010, the Michigan Sugarbeet Advancement Initiative established a study to determine the efficacy and economic impact of various application strategies for the use of Quadris flowable fungicide to control Rhizoctonia root rot.

On average (four trials in each of two years), even with low to moderate levels of Rhizoctonia infection, the per-acre net return of Quadris over the check trials ranged from $94 to $209, depending on the rate, timing and method used. The best treatment in these trials improved recoverable sugar per ton by 14 pounds and percent sugar by 0.7%. Even the “worst” treatment increased RST by 8 pounds and sugar content by 0.3%.”

Authors: Poindexter, S., and Wenzel, T.
Affiliation: Michigan Sugarbeet Advancement, Michigan State University
Title: Rhizoctonia control with quadris—update on Michigan research.
Source: The Sugarbeet Grower. April/May 2011. Pgs. 16-17.

Organic Cherry Growers Spray Fungicides More Often

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Defoliated Cherry Trees

Leaf spot is the most important fungal disease of cherry.  The disease is caused by a fungus known as Coccomyces hiemalis which lives over the winter in the old leaves on the ground.  The first infection of new foliage in the early summer is caused by spores which are discharged from these old leaves.  After the fungus develops on the new leaves, more spores are produced and they may cause further spread of the disease.  Defoliation from leaf spot reduces the number of flower buds and subsequent fruit set for the following year.  Defoliated trees are less cold hardy and may be killed by low temperatures in winter.  Conventional and organic growers who spray regularly and thoroughly every year seldom suffer any serious loss from leaf spot. However, since the spray materials available for organic growers are not as effective as the synthetic chemicals used by conventional growers, the organic growers have to spray more often.

“Cherry leaf spot (CLS)… occurs worldwide and is the most prevalent disease of sour cherry in temperate zones. Epidemics caused by ascospore followed by repeated conidial cycles cause defoliation by midsummer, resulting in low fruit quality. Early defoliation delays acclimation of fruit buds and wood to cold temperatures in the fall, and reduces fruit bud survival during severe winters and fruit set the following spring.

In integrated sour cherry orchards, CLS management typically involves four to eight fungicide treatments per year, starting at petal fall and continuing until late summer. In organic orchards, only a few approved fungicides are available for CLS control, such as sulfur and copper compounds. These compounds are often less effective and more phytotoxic than synthetic fungicides used in integrated fruit growing. Therefore, in Hungarian organic sour cherry orchards, 7 to 12 sprays are applied against CLS in each season.”

Author: Holb, I. M.
Affiliation: University of Debrecen, Hungary.
Title: Effect of sanitation treatments on leaf litter density and leaf spot incidence in integrated and organic sour cherry orchards.
Source: Plant Disease. 2013. 97[7]:891-896.

A floating Fungus Would Destroy Much of the World’s Rice Crop Without Fungicide Sprays

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Rice Field With Sheath Blight

Rice Field With Sheath Blight

Sheath blight is a disease of rice plants which is caused by a fungus that lives in the soil. When rice fields are flooded, the fungus floats to the top of the water and contacts rice plants; the fungus grows out and moves into the rice leaf. The fungus spreads across the water to adjacent plants. The fungus grows across touching plant parts. The flow of water and nutrients in the rice plant is interrupted and the leaf dies, reducing rice yield. Development of resistant cultivars has been slow, because resistance is linked to undesirable traits such as tall plant stature, late maturity, and poor milling quality. Research has shown that a single application of a fungicide provides almost season-long control of sheath blight.

“Sheath blight of rice, caused by the fungus Rhizoctonia solani, is an economically important rice disease that is occurring throughout the rice-producing areas in the world, including the southern United States. Significant losses in grain quality and yield may occur in severely infected rice fields. Despite its economic importance, there are no completely resistant rice cultivars against this fungal rice disease and control methods for sheath blight are limited to heavy usage of fungicides.”

Authors: Shrestha, B. K., et al.
Affiliation: Louisiana State University Agricultural Center, Baton Rouge
Title: Suppression of sheath blight development in rice and sclerotia germination of Rhizoctonia solani by rice-associated strains of Bacillus spp.
Source: Phytopathology. 2013. 103(Supplement 1)(5):S1.9

Downy mildew of Basil is here to Stay

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Downy Mildew Close-up

Downy Mildew Close-up

Downy Mildew Spore Growth on Basil Leaves

Downy Mildew Spore Growth on Basil Leaves

Downy mildew of basil is a new destructive disease that appears to be here to stay. In the first years of its appearance in the U.S., complete crop losses occurred for some growers because basil leaves with any mildew are unmarketable. Applying fungicides frequently and starting before first symptoms are considered necessary to control basil downy mildew effectively.

“Sweet basil (Ocimum basilicum L., Fam. Lamaiaceae) is the most commercially important annual culinary herb crop grown in the United States. Sweet basil is grown for culinary use for both fresh and dry consumption and as a source of essential oil and oleoresin for manufacturing perfumes, food flavors, and aromatherapy products.

Basil downy mildew… is a new disease of basil in the United States. …In the United States, the pathogen was first discovered in Florida in the fall of 2007. Since that time, basil downy mildew has been found throughout the eastern United States and in regions of commercial basil production in the Midwest and California.

Once basil plants become infected and develop symptoms, they are no longer marketable as a fresh product. …Currently, there is no known resistance or tolerance to basil downy mildew leaving 100% of the sweet basil acreage in the eastern United States vulnerable to the pathogen. Without adequate chemical control options and genetic resistance, basil downy mildew has the potential to destroy basil production in the eastern United States and in all other areas where basil is being produced.

Selection criteria such as foliar morphology, plant architecture as well as the presence of secondary metabolites and other factors that provide a less favorable microenvironment to the pathogen need to be examined as potential avenues for developing downy mildew-resistant sweet basil cultivars. Until this can be achieved, basil growers will have to rely on multiple applications of the few commercial fungicides currently registered to produce a marketable crop. Additionally, for organic basil growers, control of basil downy mildew will be even more challenging because there are fewer approved products labeled for organic use.”

Authors: Wyenandt, C. A., et al.
Affiliation: Department of Plant Biology and Pathology, Rutgers University
Title: Susceptibility of basil cultivars and breeding lines to downy mildew (Peronospora belbahrii)
Source: HortScience. 2010. 45(9):1416-1419.

Canadian Onions for Long-Term Storage Depend on Fungicide Sprays

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Late Blight Caused By Botrytis

Late Blight Caused By Botrytis

In eastern Canada, Botrytis Leaf Blight (BLB) of onions caused by the fungus Botrytis squamosa is the key disease for scheduling fungicide applications. BLB is characterized by silver halos on green leaves, followed by leaf tip dieback and leaf blighting, which reduces photosynthesis and consequently bulb size. Although there are some onion cultivars that are tolerant to the disease, they are not widely-planted in Canada because they are not suitable for long-term storage.

“There are no commercially available onion cultivars that are resistant to B. squamosa. However, a few of the early cultivars are known to be tolerant. These cultivars can produce a marketable yield under wet weather conditions and are grown on both conventional farms and organic certified farms for which there are no registered fungicides that are effective against BLB. However, these cultivars are not suitable for long-term storage; hence, they represent only a small part of the total onion acreage in northern climates. Consequently, in most onion production areas where BLB is a problem, the disease is managed through repeated applications of fungicides on a regular calendar-based schedule or following a leaf blight predictive system. Typical fungicide spray programs involve applying fungicides every seven to ten days from the four-leaf growth stage until sprout inhibitor application or 50% soft neck stage.”

Author: Herve Van der Heyden, et al
Affiliation: Compagnie de recherché Phytodata Inc. Quebec, Canada
Title: Comparison of monitoring based indicators for initiating fungicide spray programs to control Botrytis leaf blight of onion
Source: Crop Protection. March 2012. 33:21-28.

30 million Insects per Acre in Chinese Rice Fields Means Growers Must Spray

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Rice Stripe on Leaf

Rice Stripe on Leaf

Insects often transmit diseases when they fed on a crop plant. Rice is fed on by planthoppers which transmit viruses. In one outbreak in China, 30 million planthoppers were estimated to infest each of 50 million acres. Major losses were prevented thanks to insecticide sprays.

“Laodelphax striatellus Fallén (Hemoptera: Delphacidae) is an economically important sap-sucking pest in rice. The leaves infested by L. striatellus turn yellow, wilt, and even die, resulting in yield loss and quality reduction. In addition, L. striatellus transmits rice viral diseases such as Rice black-streaked dwarf virus and Rice stripe virus, which are two of the most serious diseases and often cause major yield losses. In recent years, the damage caused by L. striatellus feeding injury and the diseases transmitted by this planthopper has been increasing in China. When the outbreak occurred in Jiangsu and Anhui provinces in 2004 and 2005, the density of L. striatellus reached 30 million per acre, and 50 million acres of rice was infested, causing 30% of yield reduction in areas without pesticide treatment.”

Authors: C-X Duan1, J-M Wan1, H-Q Zhai2, Q Chen1, J-K Wang1, N Su1 and C-L Lei1
Affiliation:
1Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing, China; 2Chinese Academy of Agricultural Sciences, Beijing, China
Title: Quantitative trait loci mapping of resistance to Laodelphax striatellus (Hemoptera: Delphacidae) in rice using recombinant inbred lines.
Publication: Journal of Economic Entomology. 2007. 100(4):1450-1455.

Fungal Growth on Sugarbeet Leaves Would Lower U.S. Sugar Production

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Fungicide Treatment (Left: Treated - Right: Untreated)

Fungicide Treatment (Left: Treated – Right: Untreated)

The Red River Valley in North Dakota and Minnesota is a major sugarbeet production area. About ½ of U.S. sugar comes from sugarbeets. A disease on the leaves damages the plant’s ability to produce extractable sucrose in the roots. Fungicides kill the fungus before the damage is done to the plants.

“Cercospora leaf spot is the most economically damaging foliar disease of sugarbeet in Minnesota and North Dakota. The disease reduces root yield and sucrose concentration, and increases impurity concentrations resulting in reduced extractable sucrose and higher processing losses.”

“It is difficult to combine high levels of Cercospora leaf spot resistance with high recoverable sucrose in sugarbeet. Consequently, commercial varieties generally have only moderate levels of resistance and require fungicide applications to obtain acceptable levels of protection against Cercospora leaf spot under moderate and high disease severity.”

Authors: M.F.R. Khan1 and A.L. Carlson2
Affiliation:
1North Dakota State University & University of Minnesota; 2Plant Pathology Department, North Dakota State University
Title: Efficacy of fungicides for controlling Cercospora leaf spot on sugarbeet.
Publication: Sugarbeet Research & Education Board of Minnesota and North Dakota. 2011 Research report available at: http://www.sbreb.org/Research/research.htm.

European Consumers Demand Perfect Oranges Making Fungicide Use Necessary

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Alternaria Brown Spot

Alternaria Brown Spot

Spain is a major producer of fresh oranges which are consumed throughout Europe. Disease infections in the citrus orchards can result in spots on the orange peel with no damage to the fruit inside. However, consumers will not pay top price for spotted oranges making fungicide use necessary.

“Alternaria brown spot (ABS) is a severe fungal disease of some mandarins and their hybrids in rainy and semiarid citrus-growing areas. … The presence of ABS in Spain has become a serious problem for ‘Fortune’ mandarin production.”

“Defoliation due to spring infections weakens trees and has an important impact on yield. However, fruit damage causes the most important economic losses. Fruit symptoms include light brown, slightly depressed spots to circular and dark brown areas on the external surface.”

“Although cultural practices that improve ventilation and prevent the growth of lush foliage can greatly reduce disease severity in the orchard, fungicide applications are essential to produce quality fruit for the fresh market. One or two sprays generally are needed to protect spring flush foliage to reduce defoliation and prevent inoculum build-up.”

Authors: A. Vicent, J. Armengol and J. García-Jiménez
Affiliation: Instituto Agroforestal Mediterráneo, Universidad Politécnica de Valencia, Valencia, Spain
Title: Rain fastness and persistence of fungicides for control of Alternaria brown spot of citrus.
Publication: Plant Disease. 2007. 91(4):393-399.

Fungicides Result in Mangoes Suitable for Export

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Mango - Anthracnose

Mango – Anthracnose

Commonly known as the “King of Fruits,” the mango is the most important fruit of Asia. It is grown throughout the tropics and subtropics. Until recently, mango fruit was considered an exotic, specialty item in import markets such as the U.S. and Europe. Today a million tons of mangoes are exported. Among the diseases of mango, anthracnose is the most prevalent in humid growing regions. The incidence of this disease can reach almost 100% in fruit produced under wet or very humid conditions.

“Diseases are primary constraints to production in virtually all areas where mango is grown. … In humid regions, anthracnose is most destructive. … Pesticides are used in most commercial production situations, especially where anthracnose [is] important.”

“…irregular, dark brown to black lesions develop that are somewhat depressed and can crack the fruit surface. Under humid conditions, large areas may be involved and orange to pinkish masses of conidia are formed on the decaying surface. … Lesions on fruit are initially superficial, and penetrate deeper than 5 mm into the flesh only late in development. Anthracnose is caused by three closely related fungi. … Although some mango cultivars are moderately tolerant, none are sufficiently resistant to be produced without fungicides in humid areas.”

“In general, mango production currently has a heavy dependence on chemical disease control measures, especially where disease-conducive environments exist and when export quality fruit are desired.”

Author: R.C. Ploetz
Affiliation:
University of Florida Tropical Research and Education Center, Homestead, FL
Title: The major diseases of mango: strategies and potential for sustainable management.
Publication: Proceedings of the VIIth International Symposium on Mango. 2004. 137-150.

Climate Change Increases Need for Fungicides in Egypt

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The earlier seasonal onset of warm temperatures in parts of the world is resulting in a threat of earlier disease development. With an increase in the potential for more severe epidemics, the number of fungicide applications needed for control also increases. Researchers have determined that 1-3 more fungicide sprays will be needed in Egypt to control tomato diseases as a result of climate change…

“The ranges of several important tomato disease[s] in Egypt; including tomato late blight (the most destructive tomato disease causing fruit yield losses) have expanded since the early 1990s, possibly in response, in part, to climate trends. … Based on analysis of plant/disease/climate relations, an epidemic of late blight onset on tomatoes that is 1-2 weeks earlier means 2-3 additional sprays to achieve sufficient control of late blight. Accordingly, 1-3 more sprays will be applied at the incoming decades of the 2025-2100.”

Authors: M.A. Fahim¹, M.K. Hassanein¹, A.F. Abou Hadid² and M.S. Kadah²
Affiliation: ¹Central Laboratory for Agricultural Climate, Giza, Egypt; ²Climate Change Information Center, Giza, Egypt
Title: Impacts of climate change on the widespread and epidemics of some tomato diseases during the last decade in Egypt
Publication: Acta Horticulturae. 2011. 914.