Maize gets a number of diseases and they can all affect the final yield. One of the most damaging is northern leaf blight (NLB) caused by the fungus Exserohilium turcicum.

Northern leaf blight overwinters in infected maize leaves, husks and trash from the previous crop. The NLB fungal spores are produced when environmental conditions are favourable in the spring and early summer, then with the aid of rain splash and wind, infects the new plant growing in the same or neighbouring paddock.

Developing leaves exposed to periods exceeding 12 hours of wet or damp conditions and temperatures between 18 to 27 degrees Celsius are susceptible to infection from NLB if fungal spores are present. Heavy dews and warm humid conditions spread the disease rapidly and move the infection to the lower leaves and cob. The most common and damaging time for infection is December to January.

Yield loss from NLB is driven by the loss of leaf area, which in turn, reduces the photosynthesis area and yield.

With weather conditions favouring infection up to the early tassel stage in the crop, yield can be impacted by as much as 30 percent. If there is an infection later than this stage, the impact is less, though there is an increased risk of lodging.

To manage NLB risk, try:

1. Crop rotation – growing maize crops back-to-back in the same paddock increases the amount of inoculum passed from one crop to the next.

2. Maize grain – crops of maize grown after a maize grain crop are more susceptible than after silage maize as more stova is left after harvest.

3. Cultivation – if you fully cultivate after harvesting, the maize burying all the residue leaves less plant material to infect. Direct drilling, minimal cultivation and strip tilling leave trash on the surface increasing the risk of infection to the next crop.

4. Hybrid selection – all major seed breeders publish the susceptibility of each hybrid to NLB, so take this into account when choosing your hybrid.

5. Planting date – late planted crops are at higher risk of developing NLB as there is more inoculum in the environment from earlier planted and infected crops and the later planted crops are more likely to be at an earlier growth stage when infected.

6. Fungicides – there are products with activity on NLB, but they have to be sprayed either before or at early infection, protecting the plant from further infection rather than trying to cure it. The best time to prevent the worst impact of the disease is just before or at the early tassel stage.

7. Monitor the crop through its high-risk infection period and growth stage and make a decision on whether to spray.

Talk to your local PGG Wrightson Technical Field Representative on how to manage northern leaf blight in your maize crops.