Speckled Leaf Blotch

Mycosphaerella graminicola

Speckled leaf blotch (also known as septoria tritici and septoria leaf blotch) has recently become a common disease of wheat which can result in significant yield loss if not controlled. The main source of infection is spores from infected crop debris with first infections taking place from March to May. Following infection the fungus develops within the leaf until sporulating lesions appear. The key identification feature during winter is the presence of black pycnidia. Later in the year the lesions also tend to become stripe like. The disease undergoes multiple cycles within a crop.

Speckled leaf blotch (SLB) is a common wheat disease occurring throughout NZ. SLB can be found from late winter but the main infection period is October onwards and this is when disease symptoms become obvious.

Look out for:

Black surface spore cases
Lesions with yellow edges
Long narrow lesions in the early stages/li>

Risk factors:

Crops emerged by mid-late May are at higher risk
High rainfall

Look for black pycnidia (spore cases) on the surface of disease lesions. Also, look for long, narrow lesions constrained by leaf veins (once lesions coalesce this can be harder to see).

SLB infection is always a risk in New Zealand but three factors increase that risk. Firstly, cultivar choice: some varieties are more susceptible to SLB infection (often though, they are higher yielding). Second, planting date: wheat crops emerged before late May are at higher risk. Finally, high rainfall increases the risk from SLB, especially rainfall in Oct/Nov.

Yield losses can be high, often in the order of 30% but up to 80% in extreme cases.

Controlling speckled leaf blotch:

While speckled leaf blotch can be a devastating disease it can be very effectively controlled with the use of appropriate fungicides as illustrated below. The images, taken in December, compare a crop that was not treated with fungicide (Left) to a crop treated with a 3 spray fungicide programme consisting of Prosaro + Phoenix® GS31 | VIMOY iblon + Prosaro at GS39 | CALEY iblon GS65.

The trial was situated at Aorangi, Lower North Island, during spring 2020, with the main disease present being speckled leaf blotch. Some leaf rust was also noted. The very effective disease control is clearly visible and this resulted in a significant and very profitable yield increase.

Crop not treated with a fungicide and which is now effectively dead — A wheat crop which was not treated with any fungicide. Speckled leaf blotch, with also some leaf rust, has killed all green leaf. By mid-December the only green tissue remaining was the stem and ear meaning the crop’s yield potential was severely reduced.

Crop treated with a comprehensive Bayer fungicide progamme and still very healthy — An image of the same crop, taken on the same day, but this time treated with a 3 spray fungicide programme consisting of Prosaro + Phoenix® GS31 | VIMOY iblon + Prosaro at GS39 | CALEY iblon GS65. The very effective control of both diseases resulted in a great looking, healthy crop with excellent yield potential.

Related Pests

Stripe Rust - Wheat

Puccinia striiformis

Stripe rust (Puccinia striiformis) also known as yellow rust, is a common disease of wheat which can result in significant yield loss if not controlled. Stripe rust is favoured by cooler, moist conditions with the initial source of inoculum being infected volunteer cereals. Under favourable conditions stripe rust can develop very quickly forming disease foci surrounding the initial infection source. At first spores tend to be scattered on the leaf but on more mature leaves they show the typical stripe arrangement which gives the fungus its common name. Occasionally stripe rust can infect the ear.

Powdery Mildew - Wheat

Blumeria graminis

Powdery mildew is a common parasitic fungus of wheat. Powdery mildew produces white, fluffy mycelial growth, usually on the leaves but also on the stems and ears and as the disease only infects the outer plant layers it can be scraped off quite easily. Powdery mildew needs to infect living plant material to survive and so wind borne spores from volunteer plants are the likely source of inoculum. Serious disease infections can lead to significant yield losses.

Ear Disease Complex

Ear disease complex is a term used to describe a range of weak pathogens that attack the ear, predominately of wheat, causing the ear to turn black. Due to the black colouration these fungi are often referred to as sooty moulds. While overall these fungi do not lead to high yield losses they do produce an unsightly crop and they can reduce grain quality. The problem tends to be worse in wet summers and when harvest is delayed.

Glume Blotch

Parastgonospora nodorum

Previously referred to as Septoria nodorum and typically referred to as glume blotch (Parastgonospora nodorum) because it is normally seen on wheat ears, the disease can infect wheat foliage when it is called leaf blotch Leaf blotch can be identified from Zymoseptoria tritici by the lack of black pycnidia and the more oval appearance of the lesions. Glume blotch can be a problem in wet seasons and tends to give the ears a purple-brown appearance.

Leaf Rust - Wheat

Puccinia triticina

Leaf rust (also known as brown rust) is a common disease of wheat which can result in significant yield loss if not controlled. Leaf rust is favoured by warmer, drier conditions with the initial source of inoculum being infected volunteer cereals. Under favourable conditions leaf rust can develop very quickly. Spores are scattered at random on the leaf and are often surrounded by a pale chlorotic halo.