Managing anthracnose and apical end rot (soft nose) in olives

04 Jul Managing anthracnose and apical end rot (soft nose) in olives

Posted at 07:47h in OliveCare by

July 2021

AOA has received several reports this season of harvested olive fruit being rejected at processing due to high levels of Anthracnose and apical end rot (soft nose).

Anthracnose:

These reports may indicate that some growers were caught out by the wetter and more humid conditions experienced in the groves this year, having failed to undertake strategic application of fungicides throughout the year – discussed below.

The following information is sourced from:

Essentially, to get Anthracnose under control, olive growers need to be spraying at 4 critical times during the year – applying 2 applications each period depending on the rainfall / humidity events experienced.

If this is your situation, you need to start applying fungicides immediately post harvest to your grove:

An example Anthracnose control program:

Note: Always use chemical control options in accordance with permit / label conditions:

Ref: https://australianolives.com.au/chemical-permits/

Always regularly monitor weather conditions and groves for fungal disease symptoms.

If a fungal disease is present or if high risk weather conditions exist:

  • Immediately after harvest apply Mancozeb (Group M3 fungicide) and again 2 weeks later:

View the Mancozeb permit details here: http://permits.apvma.gov.au/PER88358.PDF

  • After pruning apply 1 application of Copper Tri-base Blue-190 (Group M1 fungicide) or approved alternative:

View the copper permit details here: http://permits.apvma.gov.au/PER11360.PDF

View the copper oxychloride Label details here: http://websvr.infopest.com.au/LabelRouter?LabelType=L&Mode=1&ProductCode=81027

  • At flowering – apply AERO Metiram + Pyraclostrobin (Group 11 and M3 dual action fungicide) followed by a second spray in 2 weeks. (An alternative is to use Azoxystrobin (Amistar) Group 11 fungicide, or if in Victoria you can use Cabrio® Pyraclostrobin (Group 11) fungicide):

View the Aero Permit details here: http://permits.apvma.gov.au/PER87332.PDF

View the Amistar Label details here: http://websvr.infopest.com.au/LabelRouter?LabelType=L&Mode=1&ProductCode=58340

View the Cabrio® Fungicide label details here (only for Victoria): http://websvr.infopest.com.au/LabelRouter?LabelType=L&Mode=1&ProductCode=58340

  • At fruit set apply one of the Bayer Luna Range – if approved* and again 2 weeks later.

*The Bayer Luna Range is not yet approved for use on olives (other than in Victoria) but is believed to be effective: ‘Sensation’ – Fluopyram + Trifloxystrobin(Group 7+11) for the control of anthracnose in olives – trial work contracted by Hort innovation Feb 2017, due for completion June 2021.

Note: It is best not to use Group M3 fungicides post flowering to avoid the risk of residues in fruit.

  • Closely monitor the grove for any signs of fungal infection throughout each year.

Note: Always rotate available chemical control options as part of a resistance management strategy, noting that if the same or similar fungicides are regularly used on a crop there is a risk that the fungal pathogens will become resistant to these chemicals, as a consequence their efficacy declines.

Apical end rot (Soft Nose)

The following information is sourced from:

  • Field Guide to Olive Pests, Diseases and Disorders in Australia by Robert Spooner-Hart, Len Tesoriero, Barbara Hall, Stewart Learmonth (2020) pg 58, this guide can be downloaded from the OliveBiz website at:

https://olivebiz.com.au/wp-content/uploads/2020/09/Field-Guide-2nd-edn-revised_2.pdf

  • Haifa Crop Guide – Olive Tree Nutrition:

https://www.haifa-group.com/olives-fertilizer/crop-guide-olive-trees-nutrition

It is possible that the unusual seasonal conditions experienced across the country this year after an extended period of drought may have triggered this soft nose condition.

As mentioned the above article there is possibly a Calcium / Boron issue – so it would be a good idea to take a soil pH test and regular soil and leaf analysis to monitor nutrient availability.

Ref: https://www.haifa-group.com/olives-fertilizer/crop-guide-olive-trees-nutrition

This article also discusses the foliar nutrition option.

Calcium (Ca) functions & deficiency symptoms:

Calcium is also one of the secondary plant nutrients, absorbed by plant roots as Ca2+. Calcium is a constituent of the middle lamella of cell walls as Ca-pectate. Calcium is required as a cofactor by some enzymes involved in the hydrolysis of ATP and phospholipids. It is an important element for root development and functioning, a constituent of cell walls and is required for chromosome flexibility and cell division.

Calcium deficiencies take place only in soils lacking this element, e.g., washed soils in tropical regions. The main symptom of calcium deficiency is the chlorosis starting at the tips of the leaves, like in boron deficiency, but in this case the veins in the chlorotic area of older leaves become white.

Calcium deficiency symptoms

Calcium deficiency is corrected rather easily by adding 5 – 10 kg of calcium oxide per tree. To avoid calcium deficiency, soil pH must be determined before planting a new orchard. The amount of calcium added must be determined after soil analysis. Calcium nitrate e.g., Multi-Cal, is an optional calcium fertilizer that, due to its excellent solubility can be used in fertigation systems.

Boron (B) functions and deficiency symptoms:

Ref: http://www.summerlandolives.com.au/ ; http://www.oliveoilsource.com/

Boron plays a role in cell wall development and is important in pollination, fruit development and the translocation of sugars. An adequate supply of boron is important for flowering. The quality of olive fruit is affected if boron is deficient.

Within plants, boron is relatively immobile. It is not readily relocated from old to young plant tissue. Plants are therefore dependent on a continuous uptake of boron during the growing season. In this respect, its behaviour in plants is very similar to calcium (both are immobile) and deficiency symptoms can be confused.

Boron deficiency occurs more commonly in dry weather. Microbial activity in the soil is reduced, and the movement of boron in the soil solution to plant roots is restricted. Boron is not very mobile, so deficiency appears in the young leaves.

The main symptoms are:

  • Leaves with deficiency contain less than 20 ppm boron, while those from healthy trees have more than 20 ppm (on a dry basis).
  • Leaves around the terminal bud turn light green at their tip and eventually fall off.
  • Gradually, the same symptom appears on leaves near the base of the shoots, which appear dry at their edges.
  • Later growth shows small and distorted leaves that are stunted, fragile and finally drop off. If a small piece of the stem is cut off with a sharp knife, a brown discoloration shows due to necrosis of the cambium.
  • Chlorosis (yellowing) and death of the growing points.
  • Trees suffering from boron deficiency appear chlorotic from a distance and delay entering the vegetative stage.
  • Distortion, thickening and cracking of stems. The stems may be hollow or brittle.
  • Formation of rosettes, growth of auxiliary buds (side shooting), bushy growth and multiple branching. Shortened internodes and secondary shoot production at the tree base.
  • Thickening, twisting and failure of roots to spread out or develop properly. In some cases the roots may show excessive branching.
  • Dropping of buds or blossom. Poor fruit-set.
  • Fruits and seeds may also be affected. Brown sunken areas may develop in fruit, in a symptom called “Monkey-face”.

Correcting boron deficiency

Boron is taken up by plants as undissociated boric acid H3BO3.

Boron deficiency is corrected by broadcasting 113 – 225 g of a 14% – 20% boron fertilizer per tree, or 28 – 56 kg / ha on the soil surface within the drip line during winter. One treatment will last for several years, but because of its mobility in the soil and susceptibility to leaching, annual applications of boron are recommended in most situations. Frequent applications at low rates also minimize the risk of toxicity.

BE VERY CAREFUL not to apply too much since boron toxicity may occur.

A fast correction of boron deficiency in a specific season can be achieved by a foliar spray of 0.05% – 0.1%, of Borax. Spray should be applied until runoff is achieved. Such applications prior to flower bud initiation or immediately prior to flowering significantly improve fruit-set, even in trees with no visible symptoms and low, but not deficient leaf boron levels.

Boron fertilizers

  • Borax, (11% B) is a fine crystalline product for dry soil application, or by application in solution to the soil or foliage.
  • Granubor, (15 % B) and Borate Granular, (14.3 % B) are granulated fertilizers, which makes them more suitable for dry application by machine to the soil. They can be used on their own or in blends with other fertilizers. Granubor and Borate Granular do not dissolve, hence are unsuitable for foliar application.
  • Solubor, (20.5 % B) is a fine, soluble powder for application in solution through a boom-spray to the soil or foliage. Application rate is 1 – 1.5 g / L. Solubor is more soluble than Borax, especially in cold water, and is the recommended choice for foliar applications or ground applications in solution.

The marketplace for boron products also offers high analysis Boron solutions, designed to rapidly correct boron deficiencies in all crops in both soil and foliar applications. Some of them allow enhanced foliar and root uptake due to formulation with organic acids, which assist with assimilating the boron in the plant. They can be applied as a foliar spray, or by fertigation, .e.g., AgroDex Boron, (10%). Application rate: 1 – 2 L / ha.

Boron toxicity symptoms

Olives are classified as “somewhat tolerant” of boron in irrigation water, accepting water levels of boron of 1 to 2 mg / L (roughly equivalent to 1 – 2 ppm). Water with 12 ppm will cause problems for olives that are not tolerant to high levels of boron.

A soil analysis would be the only way to determine if there is a soil problem. One of the most common causes is over-fertilization with or poor placement of boron fertilizer.

In the early stages, the symptoms of boron toxicity are normally expressed as marginal and tip chlorosis of the older leaves. Moderate to severe toxicity produces progressive leaf necrosis, beginning at the tip or margins and gradually covering the whole leaf, resulting in premature leaf drop.