Japanese Hollies are the most widely used plants in all of our landscapes. These include very widely known varieties such as Helleri, Compacta, Hoogandorn & others. This year we have seen a dramatic increase in the death of these Japanese Hollies within the landscape. After many plants were sent to the lab for testing, most of the results have come back the same. The plants are testing positive for a fungus pathogen Thielaviopsis basicola or Black Root Rot. The first symptoms include yellowing of the leaves and a marginal scorch of the foliage. Secondary decline will show patches of brown, desiccated foliage appearing throughout the plant and later total death. The roots of the affected plant will show dark black decaying roots. This is a very devastating disease and one we should all be aware of.
Many factors can contribute to how the disease gets into and spreads throughout the landscape. The first of which is to plant healthy, locally grown stock that has not been shipped in from deep southern climates. Keep plants healthy with regular slow release fertilizers and avoid extremes in watering such as stress from lack of water or over-watering. Contamination of soil from a nearby garden hosts such as tomatoes, eggplants and string beans can also be the culprits. The fungus can be spread easily in the ground water from one plant to another. This fungus can persist indefinitely in the soil or it can survive as a saprophyte on plant debris that remains in the soil.
There are only a few things that you might try to keep your Japanese Hollies healthy. Provide even and adequate water during their times of stress. Fertilize on a regular basis with a slow release fertilizer such as Holly-tone. If symptoms are present you may try a chemical soil drench with a fungicide called Garden Phos. This drench is only effective is used properly and accordingly to all directions. The chemical needs to be mixed then applied slowly as a drench to penetrate through the soil and around the entire root system. The only other choice here is too switch to a resistant plant variety like a Chinese Holly or Boxwood. Enjoy the Garden! -Mark (Head Guru)