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Gardening Answers Knowledgebase

Plant Answer Line Question

Keywords: Plant diseases--Control, Prunus, Fruit--Diseases and pests

Have you any advice about how to combat peachtree leaf curl using natural methods at this stage in the season? I've just read about the use of thyme or oregano oil, but no advice on amount used. I would be glad of any help!

Answer:

The information I was able to find about thyme oil as a treatment for Taphrina came from an application to the U.S. Patents Office, so I cannot speak for its efficacy. I did find information from Connecticut Agricultural Experiment Station which mentions thyme oil as an organic-acceptable insecticide.

The U.S. Department of Agriculture's Agricultural Research Service offers research on the use of plant essential oils in postharvest disease control,too.My impression is that the efficacy of these plant-based oils is still being studied and evaluated.

I also found information on managing peach leaf curl (Taphrina deformans)[formerly available online] from the National Sustainable Agriculture Information Service which suggests using lime sulfur, acceptable by U.S. organic standards, though European standards may differ. Below is a more substantial excerpt:

The life-cycle diagram above in Figure 2 shows that the infection period for leaf curl is when new leaves start emerging from buds in the spring. Spraying after the buds have opened is ineffective, because infection takes place as the young leaves emerge, and the fungus develops inside the leaf.

Accordingly, sprays must be applied during the trees' dormant period after the leaves have fallen and before the first budswell in the spring. Many orchardists spray just prior to budswell during the months of February and March. Orchards with a history of severe peach leaf curl benefit from a double application: in the autumn at leaf fall and again in late winter or early spring just before budswell.

Fortunately for the organic grower, lime sulfur is one of the most effective fungicides for control of peach leaf curl and is allowed in certified organic production . Bordeaux and copper fungicides are also approved for certified organic programs and are effective as well, but not as effective as lime-sulfur.

Pscheidt and Wittig (6), performed trials comparing Kocide, lime-sulfur, several synthetic fungicides, and Maxi-Crop seaweed for leaf curl control. Lime-sulfur and one of the synthetics (ziram) were best, roughly twice as effective as Kocide. Seaweed sprays, despite positive anecdotal reports, were completely ineffective.

Severe leaf curl infection can cause the tree to shed many of its leaves and to replace them with a second flush of growth. At this time the tree will benefit from a light feeding with a quickly-available soluble fertilizer such as compost tea or fish emulsion to help it recover.

There are various levels of resistance to leaf curl among varieties; however, because of the relative ease of controlling the disease, breeding for resistance has not been a priority. Redhaven, Candor, Clayton, and Frost are some of the cultivars with resistance to leaf curl, though none is immune. In contrast, Redskin and cultivars derived from it are susceptible.

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The City of Seattle's Integrated Pest Management Solutions pages for landscaping professionals also suggests methods of prevention and control. Damage may be reduced by sheltering the tree from winter and early spring wet. If only a few leaves are affected, they may be removed by hand. Peach leaf curl does not usually kill the tree, though fruit yield will be reduced. This resource also mentions using copper fungicides and lime sulfur when the tree is dormant.

Date 2018-04-11
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May 16 2018 11:15:37