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Old disease continues assault on Georgia melons

FUSARIUM WILT isnrsquot a new watermelon disease but this old soilborne enemy is starting to take its toll on seedless watermelon production in Georgia like this melon in early May The disease so far is out zigging the zag of ways to control it
<p> FUSARIUM WILT isn&rsquo;t a new watermelon disease, but this old soilborne enemy is starting to take its toll on seedless watermelon production in Georgia, like this melon in early May. The disease so far is out zigging the zag of ways to control it.</p>
&bull; Fusarium thrives in cool spring conditions, which persisted in much of Georgia&rsquo;s watermelon growing region this spring. &bull; Though not labeled yet for melons, some fungicides used now for agronomic crops, like peanuts, can be used to control Fusarium in melons. &nbsp;

Fusarium wilt has hammered Georgia watermelons for years, and it’s getting worse not better. Farmers could be planting themselves into a yield-crippling corner in the coming years.

It’s a fungal disease that lives in the soil and attacks watermelons roots and kills the plants. Fusarium thrives in cool spring conditions, which persisted in much of Georgia’s watermelon growing region this spring.

The first documented case of Fusarium wilt ever in melons was in Georgia around the turn of the 20th century. In response, the industry developed varieties resistant to the disease. All those resistant varieties have seeds, though.

Watermelon eaters now demand melons without seeds, which are by far the most widely grown varieties in Georgia and Florida. Breeders are trying, but there are no seedless varieties resistant to Fusarium at this time. But even in seedless production, growers have to plant some seeded ‘pollinizers’ in the fields to make melons. Every watermelon-growing county in Georgia has had reports of the disease in seedless melons.

And here’s the thing. The seeded varieties that are supposed to be resistant to the disease are starting to show signs of Fusarium damage, too. This has started just in the last few years in Georgia. “I know some fields this year that are 100 percent seeded and are dying from Fusaruim,” said David Langston, a plant pathologist with the University of Georgia Cooperative Extension.

“This tells me we’ve had a shift in pathogenicity of the Fusaruim wilt from Race 1 to Race 2 to possibly Race 3. Race 1 and 2 are known. Race 3 has been documented but not yet in Georgia, but I suspect that we will probably document that this year,” he said.

Planting more and more seedless varieties has allowed the inoculum to build up in Georgia fields, he said. The seeded pollinizers are exposed to more and more of the disease and natural selection pressure has resulted in the disease now economically hurting both seeded and seedless. It’s hard to pinpoint, but he figures the disease is knocking out 20 percent to 30 percent of yields in infected fields each year; this from a disease that wasn’t on the melon farmer’s radar just a decade ago because the seeded varieties they grew for market then were Fusarium resistant.

There are some techniques being looked at to help, he said. But the most important one is finding and testing watermelon varieties that are resistant to the disease, something plant breeders have had trouble developing into seedless varieties.

Growers could lower their risk for the disease by planting a field in watermelons only every seven years. Only ever 10 years would be better. But growers, due to limited land, usually plant watermelons back to back each year in the same fields. At best some can rotate three or four years. The disease simply builds up in fields that are planted in watermelons each year, killing even more plants the following year.

Rotation not working

But something else is now happening. That rotation management doesn’t seem to be working as well as it once did. Langston has seen fields that have been out of melons for 10 years show signs of economic damage due to Fusaruim wilt. “So the rotational component of our control recommendations is being bypassed somehow by the pathogen, and we’re not real sure how that is happening,” he said.

Fusarium wilt, he said, is now the primary threat disease-wise to Georgia melons. Simply because there are no adequate control methods for it, especially considering that even the rotation management is now compromised.

Grafting watermelons to gourd rootstock, which isn’t hurt by the disease, is doable but very expensive and not widely practiced. And there are some fungicides used now for agronomic crops, like peanuts, that can be used preplant to effectively control Fusarium, he said, but none is labeled for watermelons. “Hopefully we’ll get something labeled for watermelons in the next couple of years.”

Controlling root-knot nematodes with a preplant fumigation can combat Fusaruim damage in melons “because root-knot nematode feeding predisposes watermelons plants to Fusarium wilt,” he said. “Some of the worst damage we see from this is in fields where we knew or could tell were infested with root-knot nematodes.”

Mother Nature can help. Fusarium is a cool season disease. When daytime temperatures reach mid-80s to low 90s for a few days, the disease shuts down. Unfortunately, most damage is done to young melons by this time in Georgia, especially this year when cool spring weather lasted well into May.

Watermelons are big business in Georgia, worth about $100 million annually. Georgia is usually second or third in production each year. Sometimes No. 1. Georgia farmers plant 25,000 to 30,000 acres of melons each year, shooting to sell them around the Fourth of July, the mother of all melon-consuming holidays. Right now, there should be plenty of Georgia melons available for the holiday. The crop, overall, looks good.

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