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.

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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.

Fungicides Essential to Carrot Production Worldwide

Organisms that cause diseases on carrot foliage are present wherever carrots are grown. Research has demonstrated that using fungicides to control these foliar pathogens increases carrot yields by 4-8 tons/acre.

“Alternaria leaf blight (ALB) of carrot and cercospora leaf spot (CLS) contribute to significant and recurrent losses for the production of carrots worldwide. … Foliar pathogens defoliate carrots by infecting and blighting leaflets and petioles, which in turn limits photosynthesis and energy storage in roots. Several field studies have shown 20%-80% yield loss for unsprayed carrots compared with carrots subjected to a standard calendar fungicide program.”

“In addition to yield loss, deterioration of petiole and leaf health may reduce the commercial harvestability of roots since strong, healthy petioles are required to properly lift and remove carrots from the soil. When foliage is weakened by disease, additional crop losses ensue as unharvested roots are left behind in the field. … Repeated fungicide applications are expensive but necessary on susceptible carrot cultivars to maintain crop yield and value.” 

Authors: P.M. Rogers and W.R. Stevenson
Affiliation: Department of Plant Pathology, University of Wisconsin-Madison
Title: Integration of host resistance, disease monitoring, and reduced funigicide practices for the management of two foliar diseases of carrot.
Publication: Canadian Journal of Plant Pathology. 2006. 28:401-410.