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.

French Apple Production Requires Dozens of Pesticide Sprays every Year

Codling Moth

Codling Moth

Apple Scab

Apple Scab

French apple production totals about 1.9 million tons worth approximately $750 million annually. French apple orchards are plagued with the same major pests that infest orchards worldwide: the fungal disease, apple scab, and the insect, codling moth. Both pests would seriously damage most of the apple crop in France without the dozens of pesticide sprays that are made.

“In Southern France, over 35 pesticide treatments are applied yearly in apple orchards, among which 8-15 are targeted against the codling moth.”

“Codling moth is a major pest of pome fruit orchards throughout their area of cultivation…. Two or three larval generations are present in southern France and insecticide applications are needed from the beginning of the first larval generation in May until fruit harvest.”

”Chemical control of apple scab represents a considerable part of the pest control measures necessary to protect an apple orchard when it is planted with one or several cultivars susceptible to the disease. In France, as many as 15-20 fungicide treatments per year may be necessary to control the disease.”

Authors: Monteiro, L. B., Lavigne, C., Ricci, B., Franck; P., Toubon, J-F
Affiliation: UFPR, Parana Federal University; INRA Plantes et Systemes de Culture Horticoles
Title: Predation of codling moth eggs is affected by pest management practices at orchard and landscape levels.
Source: Agriculture, Ecosystems and Environment. 2013. 166:86-93.

Authors: Simon, S., et al.
Affiliation: Unite Experimentale Gotheron, Institut National de la Recherche Agronomique.
Title: Effect of codling moth management on orchard arthropods.
Source: Agriculture, Ecosystems and Environment. 2007. 122:340-348.

Authors: Brun, L., et al.
Affiliation: INRA, UMR Pathologie Vegetale.
Title: Effects of apple cultivar susceptibility to Venturia inaequalis on scab epidemics in apple orchards.
Source: Crop Protection. 2008. 27:1009-1019.

Organic Apple Growing Not Popular in Sweden

Apple Scab

Apple Scab

The Swedish government set a goal of having 20% of the total crop area grown organically by 2010. Organic fruit acreage did not make the goal and is still less than 5%. Growers fear low yields and poor quality by not using chemical pesticides in organic systems. Apple production would decline significantly in Sweden if the majority of growers gave up the use of pesticides and used organic methods. A major problem for apple growers in Sweden is apple scab.

 “There is a large demand for domestically grown apples in Sweden. However, approximately 85% of the apples consumed in Sweden are imported, and the percentage of imported organic apples is even higher. Organic fruit is produced on 4% of the orchard area.

The estimated cost price of producing organic apples in a 5 ha orchard is €1.14 per kg, which is twice as high as for conventionally produced apples, mainly due to lower yields in organic production. Modern apple orchards have average yields of 40 ton/ha in conventional production and around 20 ton/ha in organic production.

The high cost price of organic apples was mainly due to lower yields in organic production, but also higher costs for weed control. Although it is possible to generate similar economic returns from organic production, few conventional growers in Sweden are converting to organic production. Another obstacle is that growers fear low yields and poor quality in organic production due to pests, diseases and weeds.”

Authors: Ascard, J., et al.
Affiliation: Swedish Board of Agriculture.
Title: Cost price calculations for organically and conventionally grown apples in Sweden.
Source: Ecofruit Proceedings. 2010.

Apples Can be grown in New Zealand Thanks to Fungicide Sprays

Apple Scab

Apple Scab

Apple scab is the most economically important disease of apples in the world. Fungal scab infections cause cracks in apples. Infected leaves fall off the tree which can result in reduced tree growth for one to three years. Apple growers worldwide have been spraying fungicides for over 100 years to control scab. And in New Zealand…..

“New Zealand apple industry spray programmes for control of black spot (scab), caused by Venturia inaequalis, typically use 16-20 fungicide applications each season, including dodine and fungicides in the demethylation inhibitor (DMI) group. These fungicides are particularly important to orchardists because their systemic activity prevents black spot development when they are applied after infection has occurred.”

Authors: R.M. Beresford1, P.J. Wright2, P.N. Wood3 and N.M. Park3
Affiliation: 1The New Zealand Institute for Plant & Food Research, Auckland, New Zealand; 2The New Zealand Institute for Plant & Food Research, Pukekohe, New Zealand; 3The New Zealand Institute for Plant & Food Research, Hawke’s Bay Centre, Hastings, New Zealand.
Title: Sensitivity of Venturia inaequalis to myclobutanil, penconazole and dodine in relation to fungicide use in Hawke’s Bay apple orchard.
Publication: New Zealand Plant Protection. 2012. 65:106-113.

“Organic Farming Just Didn’t Work: Trees Became a Source of Pestilence”

Organic apple production in the Eastern US is very difficult because of the presence of insects and disease pests. The moist climate is perfect for mold, rots and other fungi. Recently, a couple in New Hampshire felled their organic apple trees. They explained their reasons in an article for the Concord Monitor.

“In 10 years of organic apple production we had yet to turn a profit. Additionally, the trees in our organic block were the least healthy on the farm and were a source of pestilence for our other apple trees. After harvest, the trees were cut down and will serve their last purpose: keeping us warm next winter.”

“Apple scab – which appears with the springtime rain in New England – was the toughest problem. In an organic orchard sulfur and copper are the pesticides used to combat scab. Trouble is, they wash off and are at best poor fungicides. At a recommended rate of 12 pounds per acre and their propensity to was off, I was spraying this block every time it rained, over and over again.”

“Last June we came to the realization that the organic block was not only a net financial drain on the farm but, more important, an environmental drain. I was spraying it more, using more fuel, more pounds of pesticides, more precious time, and it was serving as the source of pestilence for the rest of the farm.”

Author: Chuck Souther
Headline: Organic apple farming just didn’t work: Trees became a source of pestilence
Publication: New Hampshire Concord Monitor. 10 January 2010.