Date posted: 08 November 2013
If you have visited our barley crop lately, you will notice it is not quite 100%. Unfortunately, our plants have two different fungal diseases - Net Form of Net Blotch (NFNB) and leaf rust. These diseases are specific to barley crops and are quite common in barley crops around the world. Luckily treatment is relatively easy... To help manage the situation we called in our resident “Crop Doctor”, Dr Hugh Wallwork, who works as a Cereal Crop Pathologist with SARDI.
Dr Wallwork explained that the diseases spread easily via airborne spores which travel in wind currents, and when they land on healthy, susceptible barley plants they penetrate into the leaves causing infection. These spores must have travelled a long way to reach our little plot!
Have a look at the photos in the art gallery on the right hand side of this page and you will see what these diseases look like.
NFNB causes brown markings (lesions) on the leaf which progress into streaks along and across the leaf blade (usually running along with the veins). These markings can create a net like pattern (hence the name NFNB). The leaves also become yellow. This ‘chlorosis’ indicates the plant tissue is dying from the stress of the disease.
Leaf rust, on the other hand, appears as brown spotted pustules (which release the spores), which then turn into black spots on older plants.
Fungicide sprays are most widely used management option. They kill off the disease spores and prevent further infection. If left untreated, these diseases damage the green leaf area so much so that yields are greatly reduced. In fact, NFNB can reduce barley yields by up to 70 per cent due to the fungus penetrating the plant stem, blocking nutrient transfer and causing collapse of the plants. Plant breeders are also working to breed resistant varieties which can withstand attack from such disease, however our crop is unfortunately not resistant.
One more thing...
If you have a look at the photo gallery, you will notice another photo of plant disease. Along with the fungal diseases, our plants also have a virus - barley yellow dwarf virus (BYDV). BYDV is transmitted by aphids, which, after feeding on the plants, transfers the virus into the leaves where it multiplies and blocks the plumbing of the plant (the phloem), resulting in yellow damaged leaves. Unfortunately there is no treatment for this disease except to kill the aphids and prevent further spread to other plants. This season has been bad for aphids with a cool summer last year allowing them to survive in large numbers during the hot months and early rains allowing the surviving aphids to find fresh green plants after their autumn flights from perennial pastures.
So... after a few hard knocks and a bit of treatment, our plants appear to be doing well. Let’s hope we get back on track now for a good finish to our season!