Diseases
Leaf or Woody stem disease?
Most diseases we have here in Colorado are fungal diseases that either infect the leaf or woody material, twig or trunk. Whether the disease is Fungal or Bacterial they are usually very difficult to control requiring multiple treatments. In addition to anti-fungal or antibacterial treatments there are a few things we can do to help prevent and fight disease.
Adequate watering - drought stress greatly increases the severity in which a disease will take hold.
Pruning - removing diseased wood and thinning will help reduce the spread of diseases.
Cleaning up fallen leaves - for leaf fungal diseases, removing and disposing of infected leaves can reduce the return of a disease the following year.
Leaf Diseases
Leaf diseases are common years with long wet springs. Branch thinning will increase air flow through the tree helping to prevent the spread of the disease. During Fall removing infected leaves reduces the chance of reinfection the following spring.
Treatments can be applied via Basal (trunk) sprays - where the chemical is adsorbed through the bark, soil drench - treatments are applied into the soil around the trunk allowing for root adsorption, or trunk injection - where chemicals are injected directly into the woody trunk using special equipment.
Treatments are usually done in spring and fall.
Growth regulators can be used in conjunction with all of these treatments to greatly increase efficacy while helping to protect the tree from drought stress.
Trunk and Twig Diseases
Diseases infecting woody material are much more damaging than those infecting leaves. Diseases that infect the woody material usually exhibit signs on the tree as bark discoloration, bark deformation, or resin exuding from the wood, (as shown above.) These cause twig die back leading to branch die back or even tree mortality. Root infections will also show a combination of these signs and symptoms.
Treatments are generally the same as those for Leaf Diseases and performed at the same times. If a tree is diagnosed in the summer with a disease It can be beneficial to immediately treat the disease as opposed to waiting for fall.
Trees that appear to be healthy may in fact have small infections that do not require treatments as the tree is capable of fighting the infection. However, it is shown in studies that drought stress can weaken a tree to the point where a small infection can spread through out a tree causing severe damage.