Diseases of Taxus Cuspidata With Yellow Needles

Phytophthora Root Rot

• Phytophthora root rot is a fungal root disease that can infect a variety of different plants, including Japanese yew. The spores overwinter in the soil, waiting for the right combination of temperature and available water to spring to life. Once active, they enter through damaged or weakened root tissues, slowly destroying the entire root system of highly susceptible plants. Spores spread through water droplets, infected soil, fungus gnats and shore flies. They can also remain in the soil in root or plant debris after you remove a root rot-infested plant.

Root Rot Symptoms

• Phytophthora root rot symptoms begin during the growing season, once enough of the root system is damaged to interfere with plant processes. A loss of root mass means lower water and nutrient intake, so it may take some time before you really notice a problem. Early symptoms are vague, with wilting and yellowing being common, but sometimes in yews no signs are present until the plant collapses suddenly. Digging around the troubled yew will reveal roots that are brown, black, squishy or smell bad; the white growing tips of many of the roots may be missing as well.

Dealing with Root Rot

• Once your Japanese yew is infected with root rot, it can be difficult to get under control. The chemicals available to homeowners are not especially effective, but if your yew is small enough to dig, replanting is an excellent option. Once the plant is out of the ground, examine the root system carefully and remove all damaged roots to eliminate the source of disease before replanting.

  Because phytophthora root rot occurs where standing water or overwatering are constant problems, moving your yews to a raised bed or improving the drainage in their current bed by removing them, amending the bed heavily and replanting are crucial to managing root rot. Don't fertilize right away, but do continue to water regularly. Check the moisture level of the yew's soil with your fingers -- if it feels dry 2 inches below the surface, it's time to water.

Other Causes of Yellowing Needles

• Yellow needles are far from exclusive to phytophthora root rot, so if your yew is yellowing, but the bed drains well and you're not keeping the soil constantly moist, it may be an environmental problem at work. Normal aging causes needle drop in all evergreens, including Japanese yews, but usually the yellow needles appear in the spring before the plant sheds them. By checking the soil pH and nutrient levels, protecting your plant from herbicide runoff from lawns and other beds, and continuing to water your yews through the winter, you can avoid the most common environmental causes of yellowing needles in yews.