What to Do When Sand Juniper Leaves Turn Yellow? Detailed Causes and Solutions
Sand juniper (Juniperus sabina) is evergreen year-round, with a low-growing habit, a distinctive crown shape, and dense branches. It is an excellent evergreen groundcover plant for northern regions, but yellowing leaves can occur during cultivation. So what are the causes of yellowing leaves in sand juniper and what are the solutions?
1. Dry soil causing yellowing leaves
Although sand juniper is suited to growing in dry sandy soil, if it remains in dry soil and dry air for a long time, the lower leaves on the branches tend to turn whitish and yellow. If it is not a grafted seedling, especially a grafted seedling not using Chinese arborvitae (Platycladus orientalis) as rootstock, this condition is even more likely to appear.
Control measures:
Water moderately until thoroughly soaked. At the same time, sand juniper requires a loose, well-aerated ecological environment. If the soil remains overly wet for a long time, the plant will suffer root rot due to lack of oxygen, and the leaves will turn yellow, especially the new leaves. Therefore, the amount of watering should be controlled, and the soil should be loosened appropriately for aeration. Sometimes excessive fertilization can also cause yellow leaves, so the amount of fertilizer applied should be controlled.
2. Disease causing yellowing leaves
The mycelium of sand juniper rust overwinters on junipers; in February to March of the following year the teliospores mature, the galls absorb water, swell and crack, and when conditions are suitable large numbers of basidiospores are produced, beginning infection of the alternate hosts, which include Rosaceae plants such as crabapple, hawthorn, pear, and apple. In early May aeciospores are produced, June is the peak period of the disease, and from August to September the aeciospores mature and are spread by wind to conifers such as sand juniper.
This disease mainly damages the needles and young shoots of sand juniper. In the early stage of the disease, the leaves show small orange-yellow, glossy lesions, which then gradually expand; on the lesions appear small yellow dots the size of pinheads, and when the weather is humid they secrete mucus, and after drying the yellow dots turn black, which are the pycnidia of the pathogen. The following year, when rain occurs, they germinate and produce basidiospores, which are spread by wind and rain. In warm, rainy years in spring, the disease is severe. If scattered yellow dots appear on young twigs and leaves, it is generally this disease.
Control measures:
Prune out diseased branches in winter. From October to November, spray sand juniper with a mixed solution of 0.3% sodium pentachlorophenate and 1 degree Baume lime sulfur, which can prevent infection by rust spores. From mid-to-late March, before the teliospores germinate, spray 1 to 2 degrees Baume lime sulfur or an equivalent-formulation 160 to 200 degrees Baume Bordeaux mixture 2 to 3 times, once every 7 to 10 days, with good results.
3. Pests causing yellowing leaves
If sand juniper shows small patches of yellowing in a row, after eliminating disease, it may be damage by trunk-boring pests (such as longhorn beetles). Carefully check the branch and trunk areas to see whether there are frass holes, or break off a withered yellow branch to see whether there are insect tunnels from longhorn beetle damage.
Control measures:
Strengthen the maintenance and management of sand juniper, improve tree vigor, and reduce opportunities for pest invasion. Use a syringe to inject 30 to 50 times diluted 80% dichlorvos emulsifiable concentrate into the borer holes in the branches and trunk of sand juniper to kill the larvae. Before injection, remove wood shavings and insect frass from the tunnels, and after injection seal the tunnel openings with clay. If the pest damage is severe, they can be removed and destroyed in a concentrated manner.
4. Physiological chlorosis
If spreading sand juniper shows large-area yellowing, with no pests or diseases found and the soil moisture moderate, it may be physiological chlorosis of sand juniper. In the early stage of chlorosis the leaves turn yellow, then appear yellow-white, most obviously in the new leaves. In severe cases the leaf tissue dies, affecting normal photosynthesis, and then the whole plant gradually withers and dies. This is usually because the soil and water in northern regions contain more alkaline salts, which affects the plant's absorption of iron ions, causing physiological iron deficiency in the plant and leading to chlorosis.
Control measures:
Ferrous sulfate can be mixed into fertilizer and applied. Mix 2.5 kg to 3 kg of ferrous sulfate, 5 kg to 7.5 kg of oil cake, 10 kg to 15 kg of manure, and 200 kg to 250 kg of water, and after decomposing to a black color it is ready for use; spray a 0.2‰ ferrous sulfate solution, covering both the front and back of the leaves, once every 3 days, for several consecutive times, which can improve the yellowing of young leaves.