M. Grabowski, UMN Extension Educator
First spots of daylily leaf streak can be found in the garden now. M. Grabowski |
In the flower garden and in the vegetable garden, the first
leaf spot diseases have appeared. At this stage, garden plants still look good and it is easy
to overlook a few small spots on lower leaves.
Where did these spots come from? Many are caused by fungal
or bacterial plant pathogens that survive in the soil in last years infected plant debris.
Splashing rain or irrigation carries fungal spores or bacteria from the soil onto new leaves. These start new infections that become leaf spots. Each leaf spot eventually produce fungal spores or bacteria that can
be spread to neighboring plants or within the plant canopy.
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Severe daylily leaf streak at the end of the summer. M. Grabowski, UMN Extension |
Leaf spot pathogens spread
in splashing rain or irrigation or by sticking to hands and tools. Some can
move on wind or moist air currents. With time and the right weather conditions,
a few small leaf spots in June can grow into a devastating disease that causes leaves
to turn brown, wilt or fall off.
Although there is no way to cure existing leaf spots, there
are several things gardeners can do to slow the spread of the pathogen and
reduce the damage caused by the disease.
- Avoid splashing the leaves with irrigation. Use drip irrigation, soaker hose or direct the garden hose at the soil, not the leaves. If sprinklers are the only option, water deeply but infrequently, at the start of a sunny day.
- Space plants to allow air movement between plants and
through the plant canopy. Stake vining Removing diseased leaves to reduceseverity and spread of leaf streak.M. Grabowski, UMN Extension
- Mulch the soil with wood chips, straw or other organic material. This will keep moisture in the soil where the roots can use it and reduce humidity in the plant canopy.
- Scout for leaf spot infections in early summer when disease is just getting started.
- Pinch off infected leaves and compost them. Each leaf spot produces hundreds of fungal
spores or bacteria that can start new leaf spot infections. Soaker hose provides water withoutwetting leaves. M. Grabowski
- Tolerate some leaf spots. A few leaf spots will not hurt your plant’s overall health. Use the cultural control practices above to keep leaf spot diseases in check and reduce their overall impact on your garden.
Fungicide sprays are not necessary to protect the health of
the plant unless the majority of the leaves are killed or dropped as a result
of the disease for several years in a row. These sprays will only be effective
if applied before disease becomes severe. Fungicide sprays protect healthy
green leaves but will not cure existing leaf spots. Because leaf spot diseases
spread throughout the season, fungicide sprays need to be reapplied at
regular intervals throughout the season to be effective. As a result they are
often impractical for a home garden.
When leaf spot disease has been very severe on a particular
plant for several years in a row and cultural control practices have not been
effective in improving the health of the plant. Consider replacing the plant
with a resistant variety or a plant with similar properties (low growing,
yellow flowers) from a different plant family.
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