Septoria tritici blotch is present in wheat crops in the Victoria Wimmera and across the medium and high rainfalls regions of SA. Agronomists and growers are encouraged to monitor their wheat for symptoms, with a view to fungicide control if necessary.
This disease was common at low levels in the Wimmera and SA during 2016. The carry-over of inoculum on wheat stubbles combined with recent wet conditions has increased the potential for disease development in early sown crops this year. Given favourable conditions (frequent rain) this disease can cause losses greater than 50%.
Scouting of crops for septoria tritici blotch (STB) symptoms should focus on the older leaves. Look for pale grey to dark brown blotches on the leaves which contain black fruiting bodies (pycnidia), which are visible to the naked eye, within the blotches (Figure 1). If the black fruiting bodies are not observed it may be yellow leaf spot or nutritional disorders such as aluminium toxicity or zinc deficiency.
If septoria is found on the lower leaves, a fungicide management strategy should be considered. Because septoria will not blow in from neighbouring paddocks at this stage of the season an early spray during tillering should be very effective in preventing development of the disease. If control of eyespot is also required then a spray should be timed for growth stage Z30-31. If the disease continues to develop and conditions remain favourable (wet) for disease development a second spray should be applied at full flag leaf (Z39) to protect the upper canopy.
Because of increasing levels of resistance to fungicides in the STB population it is important that the same active ingredient is not used more than once in any season. Where possible apply fungicides that contain a mix of actives. Growers are reminded to always read the chemical label and only use as directed.
Wheat varieties differ in their reaction to STB. Consult a current disease guide or variety sowing guide for current disease ratings. Early sown crops are at greatest risk from STB and should therefore be the initial target for scouting.
Growers and agronomists are encouraged to submit samples for fungicide resistance screening to NSW DPI, as the more samples of STB received the better informed growers will be about the status of fungicide resistance.
To collect and submit samples for fungicide resistance screening please follow these instructions;
- Sample collection; Collect up to 20 leaves in total by walking in two parallel transects 10m apart collecting leaves which have STB lesions every 10m.
- Place the leaves in a paper bag (not plastic) and label with the following;
- Name, contact details, any fungicides applied to the crop and location
- Then post to:
Dr. Andrew Milgate
WWAI, Pine Gully Rd, Wagga Wagga, NSW, 2650