A couple of weeks ago a friend mentioned that her peach tree looked as though it were about to bloom — much too early! She asked whether, when, and how to treat it for a persistent problem with peach leaf curl fungus.
The combination of severe drought with a shortfall of below freezing temperatures or “chill hours” has caused bloom and germination times to get off the normal schedule. Lack of sufficient soil moisture induces drought-stressed fruit and nut trees to conserve energy by entering into a months-long state of semi-dormancy or slow growth and insufficient chill hours also impedes full dormancy.
Peach leaf curl fungus causes new leaves and shoots to thicken, pucker and turn red. In severe cases, the fruit is also affected. Left untreated, peach leaf curl fungus will lead to severe decline and the eventual death of peach and nectarine trees.
Treatment for the fungus begins with a spraying of copper-based fungicides right after leaf fall in late November or December. New recommendations (March 2014) from UC Davis IPM advise a second spraying for affected trees just before bud swell, usually in February, especially during wet winters.
The timing of the second early spring spraying is going to be tricky this season. You’ll need to monitor the buds regularly for the first signs of bud swell (which precedes bud break, when the buds have slightly split open, showing a bit of petal color).
Copper soap or fixed copper fungicides are the safest. Apply them with a 1% spray oil to increase effectiveness and spray during dry spells; rain will wash off or dilute the sprays.
Bordeaux mixtures are also effective, but must be pre-mixed just before application. Spray to drench all branches and the bark. Copper ions in copper-based fungicides build up in the soil over the years and the synthetic fungicide chlorothalinol, which is also used to treat for peach leaf curl, is a known carcinogenic. Always follow label directions carefully, especially with regard to potential runoff or drift.
Weed seed germination will also be off schedule unless we have sufficient below freezing hours these next two or three weeks. The seeds of poa annua or annual bluegrass and crabgrass seed lie dormant on the soil surface during the winter months and sprout as soon as soil temperatures warm to around 55 degrees, usually about the last week of January in our climate. During mild winters, as this winter has been so far, the seeds will have already germinated and set seed heads.
The first application of a pre-emergent to prevent poa annua and crabgrass seeds from germinating is usually done in mid-January.
But if you’re seeing early spring weeds in your lawn now, applying a pre-emergent to control for them won’t be much help. Set mower blades low and mow the weeds to keep them from setting seed heads. Hand pull or dig out immature weeds as soon as they appear.
Postemergent herbicides, including glyphosate (the active ingredient in Roundup), are less effective during the cold winter, slow-growth months and chemical runoff into our water supply during rainy periods is a concern.