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Examining what’s causing fungal disease on your plants and seedlings

January 13, 2024

Q. Last spring my peach tree had peach leaf curl. What can I do to prevent it from reappearing this year?

Peach leaf curl is a fungal disease that causes red, warty disfiguration of peach leaves. Mild cases, in which only a few leaves are affected, will not harm the tree. Sometimes the discoloration will appear on tender new growth and flowers. It also can cause corky spots on the fruit. Moderate or severe cases can impair the tree’s ability to photosynthesize, which can lead to decreased fruit production and quality. Very severe cases can weaken the tree to the point where removal is necessary.

There are several options for treating/preventing peach leaf curl, but they involve spraying the tree during its dormant period. Once bud break occurs (you can see pink or red peeking out of the buds), it is too late to spray. In our area, Valentine’s Day is our cutoff date. This is nice because I can remind my husband that it’s time to spray the peach trees and that Valentine’s Day is coming up. I think this sounds less like nagging.

The fungicides that are commercially available to homeowners include copper-based sprays (Kop-R Spray Concentrate and Liqui-Cop). Chlorothalonil is a synthetic fungicide that is also available. Lime-sulfur, which smells terrible, is no longer available for homeowner use.

When treating, aim to thoroughly douse the tree – it should be dripping wet. This process should be repeated once a year to keep your peach trees happy. If you would rather not spray, or the spray is not effective, you can plant a resistant variety such as Indian Free, Frost, or Muir.

Q. Every time I try to start seedlings indoors, they will germinate, grow about an inch, then fall over and die. What is causing this?

This phenomenon is called “damping off” and it’s caused by fungus. There are some things you can do to lessen the chance of this happening, but even experienced seed-starters have this problem.

If you are using a seed starting tray that has been used before, it should be sterilized with a bleach solution (2-3 tablespoons bleach in a gallon of water). Let the tray dry in the sun. New trays don’t have to be sterilized. Use seed starting mix (not regular planting mix). Seed-starting mix is fast draining and contains no fertilizer. The presence of fertilizer encourages bacterial and fungus growth, which can overwhelm tender little sprouts quickly.

The sprouts should get lots of light, either from sunlight or a grow light. If using a grow light, try to get the tray as close as possible to the light source – more light means faster growth.

If feasible, direct a fan on a low setting to circulate air above the soil surface. This keeps the very top layer of planting mix dry and encourages stouter growth in the seedlings.

Once the seedlings produce their first set of true leaves, start applying very dilute fertilizer with every other watering.

Los Angeles County

[email protected]; 626-586-1988; http://celosangeles.ucanr.edu/UC_Master_Gardener_Program/

Orange County

[email protected]; http://mgorange.ucanr.edu/

Riverside County

[email protected]; https://ucanr.edu/sites/RiversideMG/

San Bernardino County

[email protected]; 909-387-2182; http://mgsb.ucanr.edu

Orange County Register

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