By Erica Faber – Technical Manager
As we progress into Winter, newly planted trees may be showing some signs of stress with the colder, wetter weather as well as the development of flower buds. Nutrient uptake through the roots slows down as the soil temperatures become colder and the rate of transpiration decreases. Nutrient deficiencies may start becoming apparent due to this as well as the higher demand for certain nutrients at key phenological stages eg. flower development.
Yellowing and distortion of leaves may be notable. Blotchy or mottled interveinal yellowing and smaller, rounder cup shaped leaves are typical symptom of Zinc deficiency which may be noticed this time of year. Other trace elements that are in higher demand at this time of year are also Boron and Magnesium. Ensure that these trace elements are part of your foliar fertiliser program. Bud-Wiser is an example of a foliar product that delivers Zinc, Boron and Magnesium and can be incorporated into your program depending on compatibility with the other products you are spraying.
Leaf showing sign of Zinc deficiency.
Leaf showing sign of Magnesium deficiency.
Leaf showing sign of Boron deficiency.
Root health may also be affected due to the increase in soil moisture and with it the increase in pressure of Phytophthora Root Rot. A preventative programme throughout the winter months is advisable alongside a program to increase soil fertility and microbe diversity which also act to reduce the incidence of Phytophthora cinnamomi. Aliette can be added to your foliar sprays which is a product more suited to the sensitive young trees than Phosphoric acid. This of course will only be effective if there is enough leaf to take up the chemical. Should your young trees be a bit sparse with regard to leaf cover, then soil drenches can be applied. Ridomil or Terracin (a natural biocide) can be used. Remember to follow up either of these products with Mycorrcin to help stimulate beneficial soil microbes. A good layer of coarse mulch also helps to encourage healthier root growth and supports a wider diversity of microbes. Symptoms of Phytophthora are pale, narrow leaves and necrotic roots.
Young tree showing sign of Phytophthora Root Root.
Stressed trees may also experience leaf drop or tip dieback. If you are concerned about any secondary fungal infection then a dual contact and systemic fungicide can be included with your foliar spray programme.
For any further concerns, feel free to post photos and questions onto our Grower Facebook page as the answers may be helpful to other growers or contact John or Kyra.