700,000 Germans Died Due to Fungicide Shortage

Potato blight

Potato blight

The fungus p. infestans was first found in Europe causing the late blight rot of potatoes in the 1840s. In 1845/1846 the fungus destroyed all the potatoes in Ireland and 1.5 million people died. The fungus spread throughout Europe and caused potato crop failures until the late 1800s when the use of copper was found to be an effective fungicide for protecting potatoes from infection by p. infestans. The use of copper as a fungicide spray on potatoes became widespread throughout Europe in the early 1900s. However, in Germany during World War I, all the copper was requisitioned for making bullets. The German civilian population had become dependent on potatoes due to shortages of other foods. A late blight epidemic destroyed Germany’s potato crop in 1916 due to the lack of protection with a fungicide.

“…the last major famine caused by P. infestans occurred in 1916 during World War I. It resulted in the deaths of 700,000 German civilians, who were unable to protect their potato crop because copper was needed to produce bullets, rather than fungicides. Even today, more than 170 years after the Irish epidemic, frequent applications of fungicides are necessary to grow potatoes in moist climates, and losses occur even in dry areas, such as Israel and the western United States. Potatoes remain a fungicide-intensive crop, despite more than 150 years of study of P. infestans and the disease it causes.”

Authors: Schumann, G. L., and C. J. D’Arcy.
Affiliation: Marquette University, and University of Illinois.
Title: Hungry Planet: Stories of Plant Diseases.
Source: The American Phytopathological Society. 2012.

Potato Farmers in Ecuador Depend on Fungicides

Potato leaves with late blight; Fungicide treatment on right

Potato leaves with late blight (L); Fungicide treatment (R)

Carchi is the most important potato-growing zone in Ecuador. Smallholder households dominate production and they sell the vast majority of output. The biggest biological constraint to potato production in Ecuador is the disease late blight caused by the fungus p. infestans. The fungus can infect all the potato plants in a field in three days and losses can be as high as 100%. A survey of smallholder potato farmers in Carchi showed how dependent they are on fungicides.

“Even though potatoes have been one of the main crops in the Andes for thousands of years, under present production and market conditions the farmers in Carchi cannot produce potatoes without pesticides, particularly fungicides against late blight (caused by Phytophthora infestans) and insecticides to control the Andean weevil (Premnotrypes vorax). Every one of the farmers in the area covered by our project in the province of Carchi used fungicides. On average, they treated 6.7 times with 2.6 products at each treatment. They generally applied fungicides up to eight times during each production cycle, making fungicides the most frequently applied type of product.”

Authors: Sherwood, S. G., et al.
Affiliation: Integrated Pest Management Project, International Potato Center (CIP),
Title: Reduction of risks associated with fungicides: technically easy, socially complex.
Source: 2002. Reduction of Risks Associated with Fungicides: Technically Easy, Socially Complex. pp. 93–109. In: Fernández-Northcote E.N. (ed), Memorias del taller internacional Complementando la resistencia al tizón (Phytophthora infestans) en los Andes, Febrero 13–16, 2001, Cochabamba, Bolivia, GILB, Taller Latinoamérica 1. Centro Internacional de la Papa, Lima, Perú. Available online: http://www.share4dev.info/kb/output_view.asp?outputID=3480

Fungicides Keep Lettuce from Turning Slimy


Lettuce Drop

The fungus causing lettuce drop causes a rot that usually begins on the stem near the soil surface and a water-soaked area appears; it can spread downward until roots decay and can spread upward.  The pathogen rapidly ascends the stalk, killing the leaves in succession until it reaches the heart of the lettuce plant. Layers of collapsed leaves lie flat on the soil surface after infection. Inner leaves are invaded completely by the fungus, which reduces the head to a wet, slimy mass. The entire plant may collapse in less than two days.

“Lettuce drop is one of the most destructive diseases of lettuce and has been reported in all lettuce-growing regions of the world. In the USA, the disease regularly occurs in the two primary lettuce-producing states of Arizona and California. Yield losses vary from 1% to nearly 75% depending on conditions, but under ideal disease conditions an entire field may be lost. The disease is caused by two closely related soilborne fungi, Sclerotinia sclerotiorum (Lib.) de Bary and S. minor Jagger.

Sclerotia of S. sclerotiorum can survive up to seven years and their longevity is affected by location of sclerotia within the soil profile, duration of burial and soil temperature and moisture.

Commercially acceptable cultivars with adequate levels of resistance are not currently available. Thus, current management strategies for lettuce drop rely primarily on fungicides such as iprodione and boscalid.”

Authors: Chitrampalam, P., and B. M. Pryor.
Affiliation: Department of Plant Sciences, University of Arizona, Tucson
Title: Population density and spatial pattern of sclerotia of Sclerotinia sclerotiorum in desert lettuce production fields.
Source: Canadian Journal of Plant Pathology. 2013. 35[4]:494-502 Available: http://www.tandfonline.com/doi/abs/10.1080/07060661.2013.841758#.U35Ck_ldV1Y

Give Peas a Chance

Pea Powdery Mildew

Pea Powdery Mildew

Pea powdery mildew caused by the obligate biotrophic fungus Erysiphe pisi DC is an air-borne disease of worldwide distribution, being particularly important in climates with warm dry days and cool nights. The disease can cause 25-50% yield losses, reducing total yield biomass, number of pods per plant, number of seeds per pod, plant height and number of nodes. The disease can also hasten crop maturity, rapidly raising tenderometer values beyond optimal green pea harvesting levels. Severe pod infectation leads to seed discolouration and downgrading of seed quality. It can also damage quality of processing pea giving tainted and bitter characteristics. Conidas and fungal debris from heavily infected crops can cause breathing and allergy problems for machinery operators.

“Crop rotation is of limited usefulness in managing powdery mildew. Powdery mildew epidemics sweep large areas with ease, and the separation of crops in time and space can delay epidemics but not prevent them.

Fungicide must be applied when the number of plants infected is still low and infection level on each plant is minimal (<5% infection).

Generally, only one application is required, unless infection comes in very early and/or conditions conducive to infection persist. In this case, follow-up applications may be required.

Extensive research throughout the agrochemical industry expanded options for powdery mildew control in the 1980s through introduction of several triazoles (sterol demethylation inhibitors) and two additional members of the morpholine group, fenpropimorph and fenpropidin. These have proven very effective in controlling pea powdery mildew.

More control options are recently available with the broad-spectrum fungicides strobirulins and anilinopyrimidines and the powdery mildew specifics spiroxamine and quinoxyfen. New mixtures are continuously being tested and approved for powdery mildew control in pea, such as the formulation mixture of the strobirulin pyraclostrobin plus the carboxamide boscalid.”  

Authors: Fondevilla, S., and D. Rubiales.
Affiliation: University of Cordoba, Spain.
Title: Powdery mildew control in pea. A review.
Source: Agron. Sustain. Dev. 2012. 32:401-409.

Michigan Tart Cherry Orchards Rely On Fungicide Protection Every Year

Cherry Leaf Spot Infection

Cherry Leaf Spot Infection

Michigan is the leading producer of tart cherries in the United States, with annual yields of 90.9-127.3 million kg, which represents approximately 75% of the total US production.

Leaf spot is the most important fungal disease of cherry trees in Michigan. The appearance of numerous spots on the leaf is usually followed by rapid yellowing and dropping. In experiments, it has been demonstrated that poor control of leaf spot can result in 72% of the tree branches dying during the winter months.

“Cherry leaf spot (CLS) is the most damaging pathogen of tart (sour) cherry trees. All commercial tart cherry cultivars grown in the Great Lakes region of the United States are susceptible to CLS, including the widely grown cultivar Montmorency, which accounts for more than 90% of the tart cherry acreage in Michigan. Left unmanaged, CLS infection causes significant defoliation by mid-summer, resulting in fruit that is unevenly ripened, soft, poorly colored and low in soluble solids. Early defoliation also delays acclimation of fruit buds and wood to cold temperatures in the fall, increases tree mortality during severe winters and reduces fruit bud survival and fruit set the following year.

The almost complete reliance of the tart cherry industry on the cultivar Montmorency has driven a strict dependence on fungicides for disease management. Typically, 6-8 fungicide applications per year are required, beginning at petal fall and continuing through to late summer after harvest.”

Author: Proffer, T. J., et al.
Affiliation: Michigan State University
Title: Evaluation of dodine, fluopyram and penthiopyrad for the management of leaf spot and powdery mildew of tart cherry, and fungicide sensitivity screening of Michigan populations of Blumeriella jaapii.
Source: Pest Management Science. 2013. 69:747-754.

Apple Scab Would Almost Completely Destroy Dutch Apple Orchards Without Fungicide Sprays

Apple Scab

Apple Scab

Apple scab is caused by a fungus Venturia inaqualis, which overwinters in infected leaves on the orchard floor.  Mating among different strains of the fungus occurs shortly after leaf fall and spores develop in the fallen leaves during the winter.  Spring rains cause spores to be forcibly discharged. Spores continue to mature and are discharged over a period of 5-9 weeks. If the surface of apple tissue is wet and temperatures are suitable, the spores germinate and penetrate the cuticle and outer layers of the plant, causing an infection.  The fungus grows beneath the cuticle and eventually ruptures it and forms dark green lesions.  Masses of spores are produced asexually within the lesions and become detached during rain.  Water splashes and redistributes these spores, causing secondary infections. Each leaf scab lesion is capable of producing 50,000-100,000 spores. Assuming 50,000 leaves per tree have 2% scab infection, about 50 million spores would be present on a single tree.  One spore can cause an infection. Infections early in the season can kill tissues near the fruit surface and the fruit develops unevenly as uninfected portions continue to grow.  Cracks appear in the skin and flesh and the fruit may become deformed.  Heavily infected fruit fall from the tree resulting in yield losses.  Scab lesions on harvested apples result in a lower price for growers since the commercial tolerance for scab damage approaches zero.

“Apple scab [Venturia inaequalis (CKE.) Winter] is one of the most important diseases of apple, causing considerable losses every year in many countries. Crop losses in the Netherlands caused by apple scab would be about 80% if no control measures were taken; therefore, 15-22 conventional spray applications per season are used to prevent apple yield loss under Dutch weather conditions.”

Authors: Holb, I. J., et al.
Affiliation: Department of Plant Protection, Centre of Agricultural Sciences, Debrecen University.
Title: Summer epidemics of apple scab: the relationship between measurements and their implications for the development of predictive models and threshold levels under different disease control regimes.
Source: Journal of Phytopathology. 2003. 151:335-343.

New Fungicides Take the Worry out of Controlling Mildew on Lettuce


Lettuce Downy Mildew

Downy mildew is a common fungus in most lettuce growing regions, especially during cool, moist weather.  Spores can be blown long distances.  Under favorable conditions, downy mildew is a very explosive disease, capable of appearing at high incidence in a field overnight.  When spores land on lettuce foliage, they germinate and can penetrate the lettuce leaf within three hours.  Lettuce is susceptible at all growth stages to the downy mildew pathogen.  Following penetration and establishment in the leaf, fruiting stalks grow through the leaves and branch repeatedly producing several spores on each tip, resulting in a whitish mat of millions of spores on each plant.  Affected tissues turn brown.  The fungus can penetrate to leaves internal to the wrapper leaves.  Relatively low levels of infection can downgrade a crop, cause significant trimming losses at harvest and promote decay by bacterial organisms during postharvest transport and storage.  During transit, lesions become soft and slimy as secondary decay organisms gain entrance through the tissues infected with the downy mildew fungus. High levels of disease can render a crop unmarketable.

“Incited by the obligate parasite Bremia lactucae, downy mildew is one of the most devastating diseases of lettuce worldwide. Attempts to manage this fungal disease using host-plant resistance have frequently failed due to the development of new races of the pathogen. Therefore, chemical control is of the utmost importance in humid areas where environmental conditions are very favorable for disease development.

Since the year 2000, a number of new fungicides targeting the Oomycetes, the class of fungi to which downy mildew belongs, have come to the market or are being considered for registration. It was the objective of these studies to investigate a select number of these for potential use in Florida for lettuce downy mildew control.

Of those investigated, mandipropamid and fenamidone consistently provided for high levels of control. Fluopicolide, dimethomorph, dimethomorph plus ametoctradin, cyazofamid, and propamocarb also provided significant control. With the majority of these fungicides already being labeled or close to being labeled on lettuce, it would appear that lettuce growers now have a wide array of efficacious downy mildew fungicides with differing modes of action from which to choose. This is a far cry from the situation that existed during 1989, when the EBDC fungicides were being threatened with cancellation and metalaxyl insensitivity was becoming widespread.”

Authors: Raid, R. N., and D. D. Sui.
Affiliation: University of Florida, IFAS, Everglades Research and Education Center.
Title: Management of lettuce downy mildew with fungicides.
Source: Proc. Fla. State Hort. Soc. 2012. 125:218-221.

Moldy Oranges Not Acceptable in Europe

Green mold and blue mold

Green mold and blue mold

Green mold is caused by a fungus which is ubiquitous to all citrus growing regions. Spores of this organism are airborne and large numbers are produced by the fungus on the surface of infected fruit. These spores will contaminate the packinghouse and its equipment, storage rooms, transit containers, and even the retail marketplace. Spores accumulate in water used in drenches and soak tanks. The fungus survives in the field on soil debris and produces spores that infect split and injured fruit in the tree and on the ground.

“Satsuma mandarin, one of the most economically important citrus crops in Izmir (Turkey). The most widely grown cultivar is primarily exported to European markets. Postharvest green mould caused by Penicillium digitatum and blue mould P. italicum are the most significant postharvest diseases of Satsuma mandarins. Control of the postharvest decay of mandarin is most commonly achieved by applications of synthetic fungicides.”

Authors: Yildiz, F., et al.
Affiliation: Department of Plant Protection and Horticulture, Ege University, Turkey.
Title: Effects of preharvest applications of CaCl2, 2,4-D and benomyl and postharvest hot water, yeast and fungicide treatments on development of decay on Satsuma mandarins.
Source: Phytopathology. 2005. 153:94-98.

Organic Cherry Growers Spray Fungicides More Often

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.

Powdery Mildew of Grapes Must be Controlled for Wine Quality

Powdery Mildew On Grapes

Powdery Mildew On Grapes

Powdery mildew exists wherever grapes are grown for wine. The fungus that causes grape powdery mildew is an obligate parasite, which means it must grow on grape tissue and will not parasitize any other species of plants. The fungus penetrates only the epidermal cells sending tubular suckers into them to absorb nutrients. The mass of fungal growth on grape skin give the impression that the grapes are sprinkled with flour. This impression is enhanced by the smell of moldy flour released by the diseased grapes. Fungicide sprays effectively control the incidence of powdery mildew of grapes from 99% to < 1% which is very important for the quality of wine.

“Analysis of wines made from powdery mildew-affected grapes has revealed that even slight infection leads to compositional changes, an oily mouthfeel and undesirable fungal/earthy flavours when compared with wines made from disease-free grapes.

The strongest link to the effect of powdery mildew was elevated ratings of ‘oily’ and ‘viscosity’ attributes in wines made from grapes with as little as 1-5% powdery mildew compared to wines made from disease free grapes.

…wines made from diseased grapes were rated as having more pronounced fungal, earthy and cooked tomato aroma attributes than wines made from uninfected grapes.

Juice from the most severely diseased grapes had a dusty and mushroom aroma and acid taste compared to the others.

When subjected to the heat test, wines made from grapes with severe powdery mildew showed greatest haziness, so there is the potential for spoilage of wine during storage due to haze.”

Authors: CRCV Update
Title: Powdery mildew impacting on wine quality
Source: Wine Industry Journal. 2004. 19[6]:71-75.