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Stone fruit (almond) rust in almonds

Tranzschelia discolor
Stone fruit rust (SFR) is a wet weather fungal disease of almonds (and related stone fruit) and if left uncontrolled can cause severe premature leaf drop, causing yield and fruit quality reductions. There are several strains of stone fruit rust, each attacking a specific species of stone (or related) fruit; consequently, rust from plums won’t infect a neighbouring almond orchard, for example. The disease is sporadic in most regions of Australia because it requires both warm and wet conditions for long enough periods for it to develop. The premature loss of leaves can result in more impact than the initial loss in crop as trees must survive on stored food reserves for the remainder of the season.  This can often lead to weak bud development the following year and subsequently lower yields. Hosts include almonds (same genus as stone fruit, and genetically compatible), apricots, nectarines, peaches and plums. In almonds, SFR is more commonly known as almond rust or rust.
 
Bayer default disease

Description

Almond rust initially appears as many small, pale-bright yellow spots on the upper leaf, which often merge into clusters of three or more spots. The underside of the leaf develops orange-brown rusty spots which are made up of masses of spores and make the leaf seem like it’s covered with brown dust. Shoots can also be infected in almonds when the leaf disease severity is high.  In severe infections premature defoliation of the tree occurs.

Rust spots can be confused with herbicide damage or shot hole. Herbicide damage can appear a few days after application, whereas rust and shot hole appear more than 10 days after favourable wet conditions but only rust produces the rusty brown spores on the underside of the leaf.

Almond rust survives as spores which are released and spread by wind or rain splash from infected leaves from the previous season which have remained attached to the tree over winter. It also only infects green tissue. For infection to be successful, leaves must remain moist for at least four hours, and ideal temperatures (15 -24 °C) are required. Spores will not germinate when temperatures are above 30 °C or if there is no moisture present.

Control

Whilst all varieties of stone fruit can become infected, some are more susceptible than others, so avoid growing susceptible varieties in areas prone to rust infections. Most of the commonly grown almond varieties are susceptible to rust, although the expression of symptoms can vary between varieties. The severity of rust infections is often highly dependent on environmental conditions.  

The main control tactics for almond rust involves reducing inoculum carryover from one season to the next by removing all infected leaves and destroying them and by using a well-designed spray program, focusing on early-mid season when foliage is most susceptible to the disease. 

Orchard design is also important to avoid favouring disease development. Humid conditions, which can be common in valleys, favour disease development, therefore if possible, avoid planting in valleys. Plant trees in a design that enables maximum air flow through the orchard which will allow rapid drying of foliage. Prune trees thoroughly to form open canopies which will allow better spray coverage and increased air flow, both which help reduce infection risk. Younger trees are more resistant to rust, so if rust is a persistent problem in older orchards consider replacing trees.

Monitor trees closely, as spores are readily spread by wind and rain and an outbreak can occur quickly. In orchards where rust has been present and conditions are conducive for the disease to proliferate, a full fungicide program should be used.  

Luna® Sensation and is registered for the control of rust in almonds and should be applied at the first sign of rust.
 
 

Related Product

Luna Sensation
Luna Experience brand tag


References 

Herbiguide (Viewed Nov 2019), ‘Rust of Stone Fruit’, http://www.herbiguide.com.au/Descriptions/hg_Rust_of_Stone_Fruit.htm

Hetherington, S (2005), ‘Rust of stone fruit’, NSW DPI, Primefact 78, https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0014/42260/Rust_of_stone_fruit_-_Primefact_78.pdf

Magarey, P (2018), ‘All About Almonds Fact Sheet: Managing Rust of Almonds’, Australian Almonds, https://industry.australianalmonds.com.au/wp-content/uploads/2018/07/Pest-Disease-Disease-1-Managing-Rust-in-Almonds-HR.pdf

Munroe, N (2005), ‘Rust’, Integrated Pest and Disease Management for Australian Summer Fruit, Pest and Disease fact sheets, NSW DPI,  pg 70 - 73, https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0008/184526/summerfruit-fulla.pdf

Plantix, (Viewed Nov 2019), ‘Plum rust’, https://plantix.net/plant-disease/en/100017/plum-rust

Ullio, L (2009), ‘Common Diseases of nectarines’, Primefacts 890, Industry and Investment, NSW Government, https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0011/1185698/Common-diseases-of-nectarines.pdf