Totsiens Giraffes!
On Wednesday we hit the road again to the Vaalharts area where the ARC Grain Crops Institute has a farm in the irrigated area between the Vaal and Orange Rivers. Brad Flett, our maize pathologist host, guided us to his maize field plots where we observed and learned more about the devastating Maize Streak Virus. Depending on the time of infection, symptoms range from mild leaf streaking to overall mottling, severe stunting, and infertility. In Brad’s field trials, which were designed to monitor the pattern and time course of disease spread within the field, we were able to observe the range of symptoms even though distribution of the disease was limited this year due to the drought. Apparently activity of the leafhopper vector was reduced this year due to high heat. Brad explained that although South African cultivars with resistance to MSV have been developed, there is generally a 15% yield drag with resistant cultivars; thus, most commercial farmers find that use of a seed-treatment insecticide is more economical than purchasing resistant cultivars. Subsistence farmers generally do not use either insecticide treatment or resistant cultivars and, in many years, suffer total yield loss due to this disease. These farmers have to rely on using a late planting date to avoid catastrophic losses.
We also discussed the likelihood of this disease entering the United States. Brad described some of his own studies, which have shown zero percent seed-transmission of the disease. Thus, introduction through seed is unlikely; however, movement of the leafhopper vector is still a possibility.
After viewing irrigation systems used in this area and stopping to pick up some boerwors and sosaties for a braai, we drove the 80 km to the Sandveld Game Reserve to spend the night. Those of us with a heartier constitution arose at 6:30 AM to go for a game drive and bird watching with Brad. David reluctantly bid farewell to the giraffes and South Africa…
Posted by on 03/15 at 03:14 AM
