Great weather for making hay but soil moisture levels in some fields and landscapes are getting low. The popular trend towards installing drip irrigation in field production nurseries and well maintained landscapes is sure paying off in 2016.
A recent visit to a Christmas tree plantation revealed a few Colorado spruce exhibiting wilting. These were being grown on a silt loam which had poor water holding capacity – and that is a lot of tender new growth to support in the canopy.
Sugar maples, birch and beech are trees with relatively shallow roots systems. And so it goes that these are the sentinel species that are first to indicate when they are stressed by high temperatures and moisture levels.
River birch (Betula nigra) will often be the first to show symptoms, especially where they are growing on high parts of the field or landscape. Leaves will turn generally yellow, may be undersized and some older leaves on the stem drop prematurely. In my experience, they exhibit foliar yellowing mid to late summer most years. We don’t usually see it this early.
We are also seeing a bit more interveinal chlorosis (and necrosis) on many species this year, usually caused from nutrient deficiency such as iron and manganese on our high pH soils. The dryer soil conditions result in lower transport of soil nutrients up into the canopy, sometimes leading to exacerbated nutrient deficiency symptoms.
What can we do to help right now? Supplement with low volume irrigation. Focus on your dryer sites with more shallow-rooted or vulnerable species. Anything you can do to get low volumes of water over the root zone during long periods of time. On a small scale, Gator bags can be very effective. Micro-irrigation systems are the best.
Mulching soils in the spring, when moisture levels are adequate, can help delay soil evaporation in the summer months. Adding mulch now will only serve to keep moisture away from the soil root zone. Wait to mulch once soil moisture levels have returned. Adding plant residue and compost to improve organic matter % on an ongoing basis will help delay soil moisture losses in the future.
Oh, and hindsight is 20:20.