After 35 years of farming, Joachim Joseph thought he knew what was eating his maize. Mr. Joseph manages Tumaini Farm, a 150-acre commercial maize and vegetable farm in Madira, just outside of Arusha in northern Tanzania.
Thinking the pest was maize stalk borers, he sprayed the usual pesticides. But the caterpillars didn’t die. It rained, and still the caterpillars didn’t die. Finally, an agriculture officer visited the farm and told him it wasn’t maize stalk borer, it was Fall armyworm.
Mr. Joseph says, “This pest is not a joke…. When there is no maize, there is no food, and there will be a problem.”
Fall armyworm is spreading rapidly, and maize is its favourite food. The pest has devastated maize and other crops in at least 26 African countries over the past two years. Now Tanzania’s agriculture ministry is rushing to tell farmers how to identify and manage the new pest, ahead of the coming maize season.
Once he knew that he was dealing with Fall armyworm, Mr. Joseph sprayed his fields twice, a week apart, with a pesticide called Karate. He caught the culprit in time, and had a good harvest.
A few months later, he planted maize on two three-acre plots during the off-season, as part of his crop rotation plan. That maize is ripening now, and, as he steps between rows to inspect a whitened leaf, the plants reach higher than his head. One of the signs of Fall armyworm is windowing, when parts of leaves become whitish or semi-transparent because they’ve been largely eaten by the caterpillars.
Maize is a staple crop in Tanzania, where it is used in popular dishes such as ugali. But experts worry that there won’t be enough to feed everyone if Fall armyworm goes unchecked.
Juma Mwinyimkuu is the Northern Zone coordinator with Plant Health Services, a branch of Tanzania’s agriculture ministry. He says that since Fall armyworm was officially reported in Tanzania in March 2017, it has spread to 16 of the country’s 30 regions. Some farmers have lost more than half of their crops.
Mr. Mwinyimkuu explains: “Most people are not aware; not only farmers, even extension officers at the district level. It is a new pest, so most of them do not yet know what it is.”
Some farmers have confused Fall armyworm with African armyworm or American bollworm, or, like Mr. Joseph, thought it was maize stalk borer.
Unlike those other pests, Fall armyworm has four evenly-spaced spots that form a square on the second-last segment of its body. It also has an inverted Y-shaped mark on its head.
Mr. Mwinyimkuu says there are three ways to fight Fall armyworm: cultural or manual practices such as collecting and crushing the worms and eggs, often found on the underside of maize leaves; biological methods such as neem-based pesticides or spreading a virus that kills the caterpillars; and chemical methods such as commercial pesticides. He says, “All the methods, you should use. Whatever works.”
He says the key to managing Fall armyworm is to check regularly and intervene early. He explains: “We invite farmers to do what we call ‘scouting’ one week after germination—to move around randomly in the rows of plants to see those damage symptoms first.”
Mr. Mwinyimkuu recommends planting early, weeding often to remove potential host plants, and using proper spacing and fertilizer because healthy plants are less likely to succumb to the pest than weakened ones.
If the caterpillars are small and are found on the leaves, and if the holes in the leaves are small and elongated, it is still possible to control the pest. But if the caterpillars are more mature, the holes are bigger, and there is feces on the plant, it may mean the worm has burrowed into the stem. At that stage, it is very difficult to kill it with pesticides.
It is important to note that spraying fields is not without dangers. Pesticides can kill natural enemies like ants, small wasps, or bacteria that might be controlling Fall armyworm. Also, some pesticides are toxic to humans and contaminate the environment, including bodies of water.
Angela Gerald Mkindi is a PhD student researching pesticides at the Nelson Mandela African Institution of Science and Technology, in Arusha. She says there are many risks when farmers use chemical pesticides against Fall armyworm.
She explains: “For Fall armyworm, some experiments done in Malawi show that some pesticides are ineffective…. In addition, farmers opt to mix up different [types] of pesticides to look for an effective combination. All these efforts result in massive pesticide residues in the soil and the entire ecosystem, and a high risk to the farmer him or herself.”
Ms. Mkindi adds that some pesticides on the market are fake or expired products, which increases the risk to people’s health and the environment. The best way to control Fall armyworm may be to unleash another insect to destroy it. Researchers are busy trying to develop biological methods to control Fall armyworm. One such method is to introduce insect parasitoids that inject their eggs into the Fall armyworm larvae. When the eggs develop, they kill the pest.
While researchers and academics explore those options, Mr. Mwinyimkuu says many farmers don’t want to wait. He says: “The problem with biological methods is they are a bit slow. For example, you may spread the virus, but it may take three to four days [for the Fall armyworm] to be infested and die. And it may reduce the [caterpillars’] appetite, but for those three days, still the destruction continues. Most farmers want instant control measures…. If you spray, within 20 minutes you see the caterpillar die.”
Mr. Mwinyimkuu says the agriculture ministry recommends several pesticides that are effective against Fall armyworm, when applied at the right time.
However, Mr. Mwinyimkuu cautions that in some areas outside of Tanzania, Fall armyworm has become resistant to certain pesticides. He advises farmers who use pesticides to switch products frequently, to reduce the chance that the worms will develop resistance.
While larger-scale commercial farms such as Tumaini Farm may choose to spray, some farmers cannot afford to buy chemical pesticides, or to properly protect themselves while applying them.
Alternatives to chemical pesticides include using neem, ashes, and physically removing and crushing the caterpillars.
Secilia Mrosso is a field officer with the Tropical Pesticides Research Institute, in Arusha. Returning to her office after a field visit, she swipes through her phone to show photo after photo of damaged maize plants covered with Fall armyworm feces. She says the key to managing this pest is to catch it early.
Pointing to a photo of damaged plants, she says: “At that time, the farmer cannot do anything. We just advise them to replant…. We depend on rain-fed agriculture, and when you find that the infestation is so high … that they must uproot all their crops, then you can think … socially, it is a very big threat.”
Ms. Mrosso gently opens a plastic container holding bits of dry grass and what looks like a sprinkling of black pepper. She’s experimenting with these tiny parasitoids, hoping they can be used to attack and kill Fall armyworm during the larval stage.
Every time she travels, she tells farmers to get ready for a fight.
Ms. Mrosso adds: “We suspect that in the coming growing season, [Fall armyworm] will spread all over the country. And if farmers are not be able to recognize them early and control them early, then we shall have a very big mess.”
Photo: Joachim Joseph in his field
Story by Clara Moita, Jaime Little, and Joachim Laizer