Category: Onion

The 2021 Vidalia Onion Crop and Disease Update will be held on Wednesday, Feb. 17. It will be held virtually this year from 10 a.m. to 11:30 a.m.

University of Georgia (UGA) Extension scientists will provide an update on disease management recommendations to onion producers and industry experts.

The speakers include Chris Tyson, area onion agent, and Bhabesh Dutta, UGA Extension plant pathologist.

Click here to register.

Abnormally dry weather conditions for Southeast Georgia have benefited Vidalia onion farmers who are trying to plant this year’s crop, says Chris Tyson, University of Georgia Extension Area Onion Agent at the Vidalia Onion & Vegetable Research Center in Lyons, Georgia.

“Most growers are completely finished or they’re finishing up within this week or shortly thereafter. That’s a good thing that we’re not dragging on into January like we do some years when we have weather delays,” Tyson said.

“We’re not always done by this time every year. Some years if it’s wet or we’re getting rains, it just delays us and goes on into Christmas or past Christmas and even into January on some years.”

Benefit to Planting Being Done

Since producers did not experience weather delays during planting and able to finish on time or earlier in some instances, they now can focus on applying fertilizer and fungicide sprays.

This also benefits them with regards to their H-2A labor.

“If they use H-2A labor, they have a contract with them to finish by a certain time, so they have all of that arranged before they ever come as far as their dates of when they’re going to work. If they have to work them longer, they have to do some renegotiation there with H-2A contract. They want them to get finished by that time so everything will work out with their H-2A labor,” Tyson said.

Drought Monitor

According to the U.S. Drought Monitor, much of central and southeast Georgia are classified as ‘D0’ or abnormally dry. While the dry conditions were favorable for planting, they are not ideal for production. Much of the state received rainfall on Wednesday. But more is needed to produce a substantial crop.

“For the most part we’ve had pretty good weather as far as planting onions. Now that we’re getting a little bit of rain, most people need it and want it at this point,” Tyson said.

Vidalia onions are famous for their mild-sweet flavor and are a favorite of consumers and chefs across the U.S. Due to this popularity, there is also significant demand for organically-grown Vidalia onions. 

Soil-borne bacterial diseases like sour skin and slippery skin caused by Burkholderia sp. impact quality and yield of organic onions in Georgia. The pathogens are soil-borne. Current organic management practices do not eliminate or eradicate them from the soil.

This makes management extremely challenging, according to Bhabesh Dutta, University of Georgia (UGA) Cooperative Extension plant pathologist.

“Conventional onion production is itself challenging, and organic onion production is more challenging,” Dutta said. “We do have some grasps on managing those issues in conventional ag, whereas in organic ag, we don’t have those options. The No. 1 issue we’ve been facing in any onion industry, especially in organic onions, is sour skin and slippery skin diseases.”

Conditions Favorable for Disease Development

Warm temperatures and intermittent rainfall during the spring can predispose organic onions to infection with these bacterial pathogens. Vidalia onion growers experienced similar weather conditions (warm and wet) this past spring. This led to considerable yield losses both in the field and in storage.

Sour skin was also worse last year for producers. It is usually more of a problem during harvest in the latter part of the growing season. As it thrives in warm conditions, symptoms can manifest earlier in the season depending on temperature. The disease can progress from the upper foliage to the leaves in the lower part of the plant and then to the bulb’s outer scales.

Bulbs that are infected with sour skin usually have an acrid, sour odor and other foul odors that are associated with secondary organisms. Bulbs will turn reddish-brown to brown in color over time, as the tissues rot and copious amounts of fluids are produced.

Appropriate Management Strategies

Organic onion growers need management strategies that are not just effective but also economically and environmentally sustainable. The UGA Vidalia Onion Research and Extension Group is researching organic and physical soil-amendments that can reduce soil-borne pathogens including Burkholderia sp.

The amendments like soil solarization, soil-biofumigation (wild mustard), soil-applied biological controls and cover crops will be evaluated in certified organic fields at UGA.

“With respect to sour skin, which is one of the worst diseases you can ever have on onion; on organic onion, this disease is particularly bad. The pathogen survives in the soil and stays in the soil. Any management options, like the use of copper or use of any chemicals, which you cannot use; you can use some kind of copper in organic (production), but it doesn’t have much efficacy on management of sour skin,” Dutta said.

“What we are thinking, unless we do some kind of soil amendments – physical, cultural, biological soil amendments – we may not be able to reduce the pathogen in populations of this sour skin pathogen.”

UGA scientists also plan to evaluate the impact of these amendments on reducing weeds, plant-parasitic nematodes and other soil-borne fungal and oomycetes organisms. Researchers will also focus on studying the impact of these amendments on soil-microbiome and prevalence of insect natural predators and enemies. The aim is to foster the “systems approach” without negatively altering the diversity and prevalence of both beneficial microbes and natural enemies.

“We have to think outside of the box, but we also respect the stewardship of organic certification. Whatever we do, it should be within the limits of that organic certification or organically approved methods,” Dutta said. “This method with which I talked about is within that limit.”

Abnormally dry conditions in Southeast Georgia are only helping Vidalia onion farmers who are transplanting this year’s crop.

Chris Tyson, University of Georgia Extension Area Onion Agent at the Vidalia Onion & Vegetable Research Center in Lyons, Georgia, said onion producers don’t need a lot of water right now anyway. The lack of rainfall is not a detriment at this stage in the growing season.

“During the planting season we need the dry weather. We don’t need rain, because every time we have a rain event it causes delays. You have a week or two of rainy weather, and even though that’s good for putting water back in the sub-soil and the aquifer and replenishing all of that; for us, two weeks of bad delays and we might want to be finished planting by the week of Christmas or week before Christmas and we’re having to plant into January,” Tyson said.

US Drought Monitor

According to the US Drought Monitor, more than 25 counties in the southeast part of the state, are classified as “D0” or abnormally dry. These include Georgia’s top two onion-producing counties Tattnall and Toombs.  

“Obviously we need water for our onions and most onions are under a pivot anyway to give them what they need, but the same thing is true for harvest,” Tyson said. “Rain is sort of the enemy during harvest time because it creates delays and causes disease. At planting, it’s not so much disease as it’s more the delays it causes.

“Onions can get by with relatively low amount of water up until the spring time when they start bulbing and getting closer to harvest when they really have a high water demand. For the first half of the season, they have relatively low requirements for water. Usually we can give them what they need with our irrigation systems if we have to give them any water during the winter time.”

What a difference a year makes for Georgia’s Vidalia onion producers. Last year’s weather conditions consisted of hot temperatures when growers were planting their seedbeds. That’s not been the case this year, however.

“It’s been a real quiet year. Everything’s been going very well. This time last year we were dealing with really hot temperatures, some extreme. We think the plants have suffered some, but we’ve had really great conditions this year,” said Chris Tyson, University of Georgia Cooperative Extension Area Onion Agent at the Vidalia Onion and Vegetable Research Center in Lyons, Georgia.

“Until (last Thursday) when we had some rain from the hurricane (Zeta) that came through; we actually got over an inch of rain in some places which was actually much needed; but we haven’t had a lot of rain to promote disease in the last several weeks.

“We haven’t had much rain. We’ve had mild temperatures, everything has been going really good.”

All Seedbeds Planted

Tyson said all of the seedbeds have been planted. Some were planted as early as the first week in September, and it continued all the way to the end of September. The first seeds that were planted are likely to be transplanted this week on a limited scale. However, during the second or third week in November, transplantings will pick up and continue in December.

Vidalia onion seeds are planted in a separate field from where they’ll be transplanted. Tyson said growers want the diameter of the plants to be as big around as a pencil. When they get to that size, farmers will pull them out of the ground off the seedbed and transplant them into the fields.

High Population Density of Plants

They grow seedbeds at a high population density with about two million seeds per acre. They’ll transplant between 85,000 and 100,000 plants per acre. An acre of seedlings leads to between 18 and 20 acres of transplanted fields. Vidalia onion producers utilize this planting strategy to protect against weed pressure.

 “When those plants are very small, we have a lot of weed pressure. We don’t have a lot of good herbicide options for those really small plants. What we do on our seedbeds, we use a type of fumigant to fumigate the soil and sterilize the soil to help kill off a lot of weeds and a lot of weed seeds,” Tyson said.

“That’s expensive. That’s the biggest obstacle to just planting the seed in the field one time and being done with it is weed control. The costs and the labor to grow them that way, it’s a lot more intensive.”

It’s never too early for Vidalia onion growers to start thinking about bacterial diseases that are problematic this time of year; especially Center Rot.

While Southeast Georgia is the perfect environment for onion production, it also presents different challenges for onion producers. There are many plant diseases that can impact production. According to a UGA Extension publication, during this time of year of seedling and transplant growth, the warmer temperatures favor diseases like Xanthomonas blight and center rot.

Symptoms

Water-soaked lesions that expand and span the length of the leaf blade are foliar symptoms of Center Rot. This leads the leaf to become bleached and blighted. As the disease worsens, there is severe wilting and blighting of the foliage. This can result in death of the plant tissues above ground.

Bacteria move from the foliar tissue into the bulb, causing decay. This has been demonstrated experimentally with Pantoea ananatis, one of four Pantoea species associated with center rot. UGA Extension emphasize the importance of protecting onion leaves, which can reduce bulb rot incidence.

Management

For producers to control Center Rot, they’ll need to apply an integrated approach that targets reducing potential sources of inoculum. This counters the spread of the bacteria, according to a UGA Extension publication. UGA Extension strongly advises onion producers to use certified onion seed to avoid introducing inoculum into the field.

UGA Extension also recommends early-maturing and mid-maturing cultivars. Epidemics are favored by high thrips pressure and hot and humid conditions, which are encountered more with late-maturing cultivars. Early-maturing cultivars are better equipped to avoid conditions that are suitable for bacterial disease development.

Thrips control is also effective in reducing center rot incidence. Disease management options are limited once in season. Weed control can potentially reduce initial inoculum.