29 November 2023
Farmers in the eastern summer rainfall areas are once again experiencing problems with cutworms.
Dr Gerhard Verdoorn, operations and stewardship manager at CropLife South Africa, says agents, companies and farmers are struggling to control cutworms this year.
“The problem is that cultivation practices have changed but the chemicals have not changed,” he says.
According to Corné Louw, head of applied economics and membership services at Grain SA, it is difficult to determine the extent of the damage but the problem is growing. There was a significant outbreak last year and he has received more complaints in the past two seasons than before.
So far, the problem is more prevalent in the eastern production areas of Mpumalanga and the eastern Free State. There have been few complaints from western production areas.
However, Jako Benadie, an agriculturalist associated with Bayer who works mainly in the eastern production region, believes the number of cutworms is not much higher than the previous two seasons, when intervention was necessary to combat damage and prevent crop losses.
Since the summer planting season in the eastern summer rainfall areas has begun, it is natural that diseases and pests will occur there first, says Benadie. Most cutworm infestations so far have been reported in the Free State, KwaZulu-Natal and Mpumalanga.
“Where the damage is severe, farmers have to replant parts of their lands, but it is usually not necessary to replant everything. We find that practices like minimum tillage, where a burn-down spray programme was not applied in time, have created a very good overwintering habitat for cutworms.
“A good way to make cutworms feel unwelcome is to work or spray plant residues and winter weeds about three to four weeks before planting with a weedkiller along with a registered cutworm pesticide. Another spraying against cutworms should be done at planting time.”
Complex problem
Prof Johnnie van den Berg, head of the integrated pest control programme at North West University, says this year’s cutworm problems are the worst in a long time. Research has shown that outbreaks are related to the interaction between cutworms and the weeds they eat.
He explains that cutworm moths prefer to lay their eggs on weeds above maize and that their larvae prefer to eat weeds rather than maize seedlings.
Therefore, there can be thousands of cutworms on fields that had weeds until shortly before planting time. “What happens is that we breed the larvae on the weeds during the winter months and then remove the weeds shortly before planting.”
After this, the larvae begin to eat the maize. By then, they are large and therefore more difficult to control.
In the short term, says Van den Berg, insecticides are the only solution. “Miracles are expected from the sprays we use, while in a way we create the problem ourselves with new cultivation practices.”
He believes the long-term solution lies in weed control and cleaning fields of weeds for 30 to 35 days before planting.
Residual weeds problematic
Verdoorn says residual weeds during the off-season provide food to cutworms. Because the ground is wetter, the cutworms are deeper in the ground where chemicals do not reach them. “It’s not like in normal dry conditions where they come out at night and work above the ground.”
A factor that exacerbates the problem is that farmers mix herbicides and insecticides that are incompatible, making them less effective.
Due to conservation tillage, there is more dry material on the fields. When farmers spray chemicals on dry land, the dry material absorbs them and they do not reach their target.
“Or farmers apply the chemicals to totally dry land and the dry land absorbs the toxin before reaching the target. The pyrethroids must be washed into the ground, or the ground must have at least a good wet layer so that the chemicals can move into the ground.”
Verdoorn says a SWOT analysis should be done to investigate the problem more thoroughly. “I want to know what the farmers’ cultivation practices are, what chemicals they use and what their soil moisture is so that we can to some extent find out what the problem is.”
Farmers with cutworm problems should WhatsApp Verdoorn at 082 446 8946 with their name, district and farm name so he can contact them to learn more about their situation.
