It has now been a full ten years since a mysterious illness affecting 10,000 containerized boxwood (Buxus spp. and cvs., Zones 5–9) shrubs in North Carolina and over 100,000 boxwoods in Connecticut was found. Since then, the illness has unfold to all areas of the US the place boxwood is grown. Alongside the best way, we now have realized quite a bit in regards to the notorious illness now generally known as boxwood blight. Nonetheless, regardless of nice progress in administration and schooling, I continuously encounter confusion and misidentification of the illness. Taking a more in-depth have a look at this bane of many landscapes will enable you correctly acknowledge the illness and perceive your administration choices.
The place did it come from?
Boxwood blight is assumed to have originated in japanese Asia and was by chance launched by means of the decorative nursery commerce to the UK, the place the illness was first present in 1994. Over the following fifteen years, the illness unfold throughout Europe and into western Asia, even making its strategy to New Zealand. As a result of boxwood is used so continuously in decorative gardening, it was solely a matter of time till it made its strategy to the US (in 2011).
Two different host vegetation are inclined to the illness: candy field (Sarcococca spp. and cvs., Zones 6–9) and pachysandra (Pachysandra spp. and cvs., Zones 4–9). Together with boxwood itself, these vegetation are within the boxwood household, Buxaceae. Boxwood blight illness is brought on by two sister fungal species, Calonectria pseudonaviculata and C. henricotiae. The previous is discovered worldwide and is answerable for all boxwood blight in the US, whereas the latter additionally causes boxwood blight within the UK and a few components of Europe.
The place is it now?
Boxwood blight is now nicely established in North America and normally arrives in new landscapes by chance on contaminated nursery inventory. The spores produced by the fungal illness on contaminated leaves and stems could be unfold by way of wind or rain splash. They’re additionally continuously unfold throughout upkeep. The spores keep on with clothes, sneakers, and particularly instruments. Outbreaks usually happen following shrub shearing in summer time. American boxwood (B. sempervirens, Zones 6–8) and English boxwood (B. sempervirens ‘Suffruticosa’, Zones 6–8) are among the many most generally planted shrubs in lots of landscapes, and each are extremely inclined. Climate additionally performs a big function within the severity every season, because the formation of spores happens finest in excessive humidity and when temperatures are between 60 and 80 F, so illness spreads quickest throughout moist, heat durations in summer time.
What can we do about it?
Boxwood blight was as soon as thought-about a deadly illness, with full-plant elimination and abandonment the only real choices. The excellent news is that we now have tolerant sorts of boxwood and know that though boxwood blight does kill inclined shrubs if left unaddressed, it’s manageable in some conditions. Nonetheless, administration requires a multifaceted method, and every scenario should be thought-about independently to weigh the expense, obtainable choices, and probability of success.
Take all measures doable to cut back leaf wetness, which is able to drastically cut back spore germination and an infection. We can not forestall rain, in fact, however we will take different measures. Plant boxwood in full solar, not below timber or towards partitions that block mild for half the day. Keep away from overhead irrigation, and encourage airflow across the vegetation. Lastly, think about hand-pruning fairly than shearing. If shearing should be accomplished, do it early within the season. It’s doubtless that over-shearing performs a detrimental function in boxwood well being.
All the time begin with clear, uninfected vegetation. Examine usually, destroy contaminated leaf litter, and prune out contaminated branches. Remember that garments and instruments could unfold spores, so you will have to sterilize any gear after use.
Chemical administration could be efficient for boxwood blight, however solely when mixed with an intensive cultural administration program. A very good program is intensive and could also be costly, requiring foliar functions as soon as each one to 2 weeks throughout peak blight season in summer time and early fall. This may increasingly solely be advisable for high-value plantings.
If replanting is your purpose, discuss with skilled boxwood growers about your choices for more-resistant boxwood species and cultivars appropriate on your hardiness zone. A few of these embrace Asiatic cultivars of B. microphylla (Zones 6–9) and B. harlandii (Zones 6–9), and NewGen™ Independence® (B. ‘SB 108’) and Freedom® (B. ‘SB 300’) from the NewGen™ boxwood collection (Zones 5–8). Lastly, think about avoiding the illness altogether by planting nonhost shrubs. Dwarf cultivars of Japanese holly (Ilex crenata and cvs., Zones 5–7), native yaupon holly (I. vomitoria and cvs., Zones 7–11), viburnum (Viburnum spp. and cvs., Zones 2–9), leucothoe (Leucothoe spp. and cvs., Zones 5–9), and arborvitae (Thuja spp. and cvs., Zones 2–9) could provide engaging choices for diversification.
Matthew Borden, DPM, is a plant well being marketing consultant specializing in diagnostics and built-in administration of panorama plant pests and illnesses.