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!
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.
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.