Yellow, brown, blotchy leaves on boxwood can be harmless and grow out after a few corrections, but they can also indicate a bad fungus. There is one thing you definitely have to do, the most important thing is to first identify or rule out a fungal infestation. Depending on the result, the box tree is then treated.
Natural causes
Various natural causes cause the boxwood to produce yellow leaves as it grows (without disease):
1. Cold
boxwoods often get yellow-brownish leaves when exposed to sunlight in winter. A completely natural reaction, with the dye the plant increases its frost protection. You don’t have to do anything here, just wait until the leaves turn green again.
2. Incorrect location and care errors
If a box tree in a sunny position has yellow leaves but the box trees are not in the shade, the box tree is probably a little too sunny. If a dry and hot summer causes unusually strong evaporation of the leaves, a lack of water quickly sets in, which leads to leaf discoloration. If the boxwood is too dry, this also causes an acute nutrient deficiency, which also plays a role in the leaf discoloration. If the boxwood stands in wet earth after every long period of continuous rain, the location is also not very favorable and the boxwood can react to the waterlogging with yellow leaves.
In an actually suitable location, you can cause the deficiencies just described by incorrect maintenance, by insufficient irrigation and nutrition or by too well-intentioned irrigation. In any case, the care errors should be corrected promptly because they promote disease.
After that, it is first of all to wait and see whether the box tree “can get itself back into place” at the given location. If so, the discoloration will disappear again in the following year (s); if not, it has to be transplanted.
3. Plant protection products
A box tree can show similar symptoms if weed killers have been applied in its vicinity. Avoid using agents with aggressive active ingredients in the vicinity of box trees, if possible, and rely on manual labor; after weeding (harvesting) you may even be able to use the chemically non-polluted wild herbs for salads and teas.
Otherwise only an earth exchange would help here quickly; usually you will rather rely on the fact that the discoloration grows out.
The mushrooms on the boxwood
The most common boxwood diseases are caused by fungi, with four main fungal pathogens causing problems for boxwood:
1. Boxwood shoot deaths Boxwood shoot
deaths are caused by a tube fungus called Cylindrocladium buxicola, which has only been on the rise in Germany for some time. The unpleasant fungus is blown with the wind on the shoots and leaves, penetrates the plant through the leaves and spreads from there. This happens particularly quickly in warm, humid summers: If the fungus is allowed to frolic on a sufficiently moist leaf surface for five hours or more at temperatures of 25 ° C or more, it makes its way through the wax layer of the leaves.
You can recognize the infestation with boxwood shoot death by orange to brown spots on the leaves. They enlarge and grow together to form an area, at some point white spore beds form on the underside of the leaves and black longitudinal stripes on the shoots. Characteristic is the intense leaf fall in a short time and that the shoots gradually die off.
2.
Boxwood cancer Boxwood cancer is caused by the tubular fungus Volutella buxi, which is often limited to a single plant and does not necessarily infect the entire population (depends of course on how far apart the boxwoods are).
Here a pink to orange colored fungus coating first appears on the underside of the leaf, then the bark tears open and flakes off. The diseased leaves, which are now mostly discolored, remain hanging much longer, and there are no stripes on the branches.
Boxwood cancer occurs mainly in too cool summers and does not look particularly bad at first. But the fungal spores overwinter like when shoots die in fallen leaves, if the boxwood shrimp is not discovered at some point and fought by pruning, it can also kill the boxwood.
3. Boxwood
wilt Boxwood wilt is caused by the tubular fungus Fusarium buxicola, symptoms are similar to the above, but the bark of the boxwood is largely dark in color.
The leaves become withered, not simply dry, but leathery soft, the shoots appear almost unchanged for a long time, but you will always find more dark brown spore beds as small dots on the leaves.
Box wilt occurs in all weathers, it mainly affects weakened box trees, but it can be cured through consistent pruning.
4.
Boxwood rust Boxwood rust is caused by the rust fungus Puccinia buxi and creates the typical red-brown, arched rust bosses on the leaves. At some point, white fungal lawns will appear on the undersides of the leaves, which will spread.
This fungus also primarily affects older and weakened plants, regardless of the general weather conditions.
Acute fungal attack – what to do?
As soon as you notice boxwood shoots dying or other fungi, you should intervene, even with the slightest infestation:
- Prune infested book trees immediately and vigorously
- Always cut into healthy tissue
- Dispose of cut shoots with household waste or burn them
- Disinfect secateurs
- Rake together all fallen leaves and dispose of them
- If other, valuable plants are threatened, this also applies to the top soil layer …
- Because the spores of the fungus remain contagious for years
- Do not plant a new box tree in this location for years
The use of chemical pesticides against fungi may be possible, but should be planned with specialists in order to avoid the development of resistance.
Prevent and prevent fungal infestation on boxwood
Excessive fungal infestation is one of the biggest annoyances in the home garden, and not just on boxwood, and the preventive measures are basically always the same:
1. Buy resistant plants
If the boxwood is to be planted first, you can best prevent any disease and pest infestation with a little care when choosing the boxwood and purchasing it from a specialist dealer. In a forum dealing with the topic, it is recommended not to buy a DIY box tree because it is usually already infected with diseases and pests. You drive safer with plants from local culture, the company Gartenbau Taraborrelli from Remseck is often recommended (www.gartenbau-taraborrelli.de).
The whole trouble with fungi like boxwood dieback only began when the cemetery gardeners were often “replaced by easy-care box trees” in the first bloom of neoliberalism. The high demand led to heavy young plant production; Plants raised quickly with too much nitrogen, not fully matured and not growing a fungus.
The susceptibility of the various types of boxwood available to boxwood shoot death was already researched in 2008, here is the list from “less susceptible” to “very susceptible”:
- Buxus balearica, Balearic boxwood, the second of the species native to Europe
- Buxus riparia, a variety of Japanese boxwood
- Sarcococca sp. (Shade flowers, meat berries, also box trees)
- Buxus microphylla ‘Faulkner’, a well-known cultivar of a variety of Japanese boxwood
- Buxus bodinieri, Chinese boxwood
- Buxus microphylla var. Japonica, the “Japanese variety of the Japanese boxwood”
- Buxus glomerata ‘Green Gem’, a variety of the Cuban boxwood
- Buxus sempervirens, our native common box tree in its original form
- Buxus harlandii, Chinese boxwood
- Buxus macowanii, a box tree from eastern South Africa
- Buxus sempervirens ‘Suffruticosa’, a well-known cultivar of the common boxwood
- Buxus sinica var. Insularis, Korean boxwood
Regardless of this, other sources state various cultivars of the common boxwood as particularly susceptible to shoot death:
- Buxus sempervirens ‘Blauer Heinz’
- Buxus sempervirens ‚Raket‘
- Buxus sempervirens ‚Rotundifolia‘
- Buxus sempervirens ‘Suffruticosa’ (see above, is also sold as “edging box”)
The following species and varieties are classified as having good resistance to boxwood shoot death:
- Buxus microphylla ‘Schopes’
- Buxus microphylla ‚Herrenhausen‘
- Buxus sempervirens ‚Arborescens‘
- Buxus sempervirens “Elegant”
- Buxus sempervirens var. arborescens
2. Check the location, correct care errors
Fungi always attack the weakened plants first – after all, it is their job to dispose of dying plants, and the hard-working waste disposal company starts work early. So the best way to prevent disease is to grow a strong, healthy box tree; the correct location and the possible maintenance errors have already been discussed.
There are authors who are of the opinion that nowadays it is less a matter of maintenance errors and more simply of inattentiveness / neglect. With a little better information, most of the care errors could easily be avoided or the professional hobby gardener would recognize for himself that he can only be happy with a garden that is very easy to care for …
3. Moisture management
If you have repeated problems with fungi, you should (have) examined the moisture levels and moisture currents on your property.
Perhaps a few drainages only need to be installed in certain directions, perhaps you also live in a region in which the well-known critical combination of increasing sealing + seepage of rainwater into busy municipal sewage systems caused the groundwater level to rise – which could make a completely new garden design necessary .
4. Plant strengthening
is always good: through strengthening potash fertilization in late summer, plant strengtheners and “more nature in the garden”, so that evolution eventually creates natural enemies against shoot deaths and boxwood moths.
Plant strengthening also includes preventive treatment with fungicides (fungicides), which should, however, be discussed with a specialist mushroom for mushroom.
Conclusion
By misbreeding and importing new harmful fungi, the boxwood has developed into a very sensitive plant. Leaf discoloration is therefore always a reason for increased attention and, if necessary, targeted fungus control. If the evergreen deciduous wood is / has to be replanted, only robust new varieties from specialist shops should be selected; In regions with a lot of fungal infestation on boxwood, you can also use boxwood substitutes such as Lonicera nitida (shiny honeysuckle), Ilex crenata (Japanese pod) or the new small-leaved rhododendron variety ‘Bloombux’.
