Another round of rain is on the way. The soil is still a bit warm due to 75-85F days. It's time to watch out for root rot.
Many western and Mediterranean plants, especially those from certain desert and chaparral communities, are quite sensitive to overwatering or even to a single irrigation in an otherwise normally dry summer. A primary cause of death for such drought-resistant plants is crown- or root rots caused by Phytothphora spp. and other species of fungi in moist, warm soils.
In the wet winter the soils are to cold for the Phytothphora to survive. In the warmth of summer there isn't enough moisture neat the surface to encourage Phytothphora. Add water during the summer and you have a recipe for disaster.
Rosemary, as pictured above, is a good indicator plant for Phytothphora problems. The plant doesn't always die, but shoots are killed off by a partial girdling of the crown of the roots. These yellow-browns "strikes" are the first signs of Phytothphora in the soil or a soil too heavy with clay to allow enough drainage. That why I always recommend planting on a mound (as seen above), especially Mediterranean and California natives from dry parts of the state.
Let me know what you think.
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