The killer fungus arrives in cotton fields about this time every year. Don't worry: Neozygites fresenii doesn't grow on humans, crops, or beneficial insects. In fact, it's completely harmless to everything but the one substrate it will grow on. But for that one substrate — aphids — the fungus is a real-life, gory horror film shown perpetually during summer months.
Don Steinkraus knows this fungus. And because he does, you might be saving some big money.
Over the course of the last dozen years or so, Steinkraus — a University of Arkansas professor of entomology — has come up with a program based on natural biological controls in cotton fields. He has a “fairly complete” body of research on the aforementioned aphid fungus.
“It's sort of like biological warfare — a lesser version of what we're worried about with terrorist groups,” he says. “This is a deadly disease of aphids that spreads very rapidly and kills fantastic numbers throughout the entire Delta and Southeast.”
Depending on latitude, the fungus usually shows up from the end of June to mid-July.
A killing machine
Although harmless even to the predators and parasitoids that eat aphids, the fungus attacks aphids with zeal. How does it work?
The fungus has several spore types. The first type — produced in the thousands — is shot into the air like a cannon. The spores float around and land on leaves.
The dispersed spores germinate and produce a second type of spore found at the end of a thin stalk. Those spores are very sticky.
“I use the analogy of cockleburs — the spores act very similarly. When aphids walk across a leaf, spores stick to the aphids. The fungus then bores through an aphid's skin and begins to grow within its body.”
The fungus is fast-acting — it kills an aphid in about three days.
“When those three days are up, the aphid explodes and spores are shot into the air again. Those spores hit other aphids in the colony (aphids generally live in colonies), and the process starts all over again. It's impressive how rapidly this stuff spreads.
“I tell you,” says Steinkraus with a laugh, “if there were an equivalent fungus that attacked humans, we'd be in real trouble.”
Steinkraus and colleagues have developed methods for diagnosing the percentage of fungus in the population of cotton aphids within a given field or fields. Those methods are utilized in a program sponsored by Cotton Incorporated and free to all.
“What we're trying to do is similar to what's being done with the SARS virus. We want to tell cotton growers what percentage of their fields' aphids are going to die in the near future,” says Steinkraus.
With such information, farmers can know if they need to use an insecticide or simply wait for nature to have its way.
“In the spring, we work with cotton entomologists in many cotton-growing states: Mississippi, Georgia, Alabama, Louisiana, Arkansas, and South Carolina. Those entomologists provide us with lists of consultants, growers and Extension personnel they think would be good participants in our sampling service.”
Steinkraus then buys a bunch of supplies.
“We buy vials, mailing tubes, Fed Ex envelopes, whatever — and send them free to each of our cooperators. The program is free to those who participate, and we welcome new participants (a signup form is available at the program's Web site and free kits will be sent to those who join). We try to get at least 20 to 30 cooperators per state.”
When participants find aphids in fields, they collect some and send them by Federal Express them to Steinkraus. Once in the laboratory, a random sub-sample of the aphids sent in (usually 50 per field) is gathered. Each of the 50 insects is put on a microscope slide and examined under high-powered magnification.
“This is much like a medical laboratory. When a doctor sends a biopsy sample or a culture, a medical technician diagnoses the sample. What we do is similar. In looking at individual aphids, we're able to tell if they were going to die of fungus-causing disease.”
From each field Steinkraus extrapolates percentages of terminal aphids. Generally, if the fungus is in 15 percent of the aphids or higher, the field they came out of doesn't need to be treated. At that level, the fungus will eliminate aphids as well as an insecticide.
Farmers save money using the service. “Aphid chemicals cost, on average, $10 per acre per treatment. So if you've got 1,000 acres of cotton, the service could save you $10,000. That's why Cotton Incorporated funds us — it's trying to find ways to help farmers save cash.”
Cotton Incorporated deserves enormous credit for taking a chance with the program, says Steinkraus. “Years ago, I gave a talk at the Beltwide (Cotton Conference) on my research. Cotton Incorporated approached me about supporting further research. So I kept at it. A while later, we realized we'd gotten to the point where we could accurately predict what was going to happen within a field. We started the program in Arkansas and expanded it to other states.”
Until aphid populations begin booming, growers aren't terribly concerned with them. So the service's sampling work begins very slowly and then builds to a peak around the first week of July. Then, as the fungus begins killing aphids, the samples peter out.
“During the busy season, I have three people who work full-time diagnosing aphids,” says Steinkraus. “It takes us a full hour to diagnose aphids from one field. Three people working full-time can do about 24 fields per day. It's problematic when we get 50 samples in one day. Our normal turnaround of a day or two is tested when we're deluged with samples. But that's okay.”
The impact of the service goes far beyond just the fields that are sampled. “We fax the results to the person who sent in the sample and put the sampling results on our Web site. The results are also put into various newsletters and the like.”
Some farmers who aren't even sending in samples search the Web site to find out if the fungus has been found in their county or in a field close by. If fungus has been found close by, the farmer can stop being concerned about aphids. Why? Because if the fungus has been found close by, chances are it's already — or soon will be — in his fields.
“I think the program is a very good value for the cotton growers. If we save just a few farmers from having to spray their cotton, the cost of the service is taken care of. Yearly, though, we probably help save farmers far more that that. Savings must be in the range of hundreds of thousands — if not millions — of dollars.”