It just seems like one thing after another with conifers. For years we have dealt with stressed conifers due to excessive soil moisture. Iowa has been in a weather pattern of increased spring rainfall for several years. Large amounts of rain that saturate the soil for long periods are problematic for some trees. Conifers especially need well drained soils. If they are planted in a clay soil or any areas where soil can remain saturated for even short time periods conifers will experience root damage. Root damage prevents the tree from uptaking water when they need it. As a result, we often see browning of needles and needle drop (Figure 1), which also occurs with some needle cast diseases that affect spruce.
This spring we have received a lot of samples with Rhizosphaera needle cast (Figure 2). The wet weather is a bit of a double whammy to the spruce as it harms the tree and benefits fungal diseases. We have continued to get lots of samples of spruce, concolor firs, white pine with browning needles that is likely due to root damage.
In the past couple of weeks we are also getting samples with the new growth brown and dead (Figure 3). There have been reports of herbicides causing problems for coniters, particularly spruce and white pine. Please see these articles for more information:
Imprelis damage on trees - Iowa
There have also been many samples from areas where no herbicides were used and so it is most likely environmental. We think that possibly the very hot weather and winds we had earlier this spring combined with damaged roots made it very hard for trees to keep up with the water needs of the new growth.